RU2684655C1 - Extra high strength multiphase steel and method for production of cold-rolled steel strip from it - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: to provide homogeneous mechanical properties and minimum tensile strength of 980 MPa, obtaining multiphase steel containing the following, wt. %: C from 0.075 to 0.115, Si from 0.400 to 0.500, Mn from 1.900 to 2.350, Cr from 0.250 to 0.400, Al from 0.005 to 0.060, N from 0.0020 to 0.0120, S is less than or equal to 0.0020, Nb from 0.005 to 0.060, Ti from 0.005 to 0.060, B from 0.0005 to 0.0010, Mo from 0.200 to 0.300, Ca from 0.0010 to 0.0060, Cu is less than or equal to 0.050, Ni is less than or equal to 0.050, the rest is iron and unavoidable impurities, wherein total content of Mn + Si + Cr ranges from 2.500 to 3.250 wt. %. To produce steel strip from multiphase steel, hot-rolled strip is made, which is subjected to cold rolling to thickness of 0.50 to 3.00 mm, then continuous annealing is performed, wherein cold-rolled steel strip is heated to 700–950 °C and cooled from annealing temperature at cooling rate of about 15–100 °C/s first to first intermediate temperature of about 300–500 °C, then at cooling rate of about 15–100°C to second intermediate temperature of about 160–250°C, and then with air at cooling rate of about 2–30 °C/s. Coating is applied at annealing temperature.EFFECT: invention relates to metallurgy, particularly to multiphase steel used for light-duty vehicles.35 cl, 13 dwg, 5 ex

Description

The invention relates to a high-strength multiphase steel with a two-phase microstructure or a complex-phase microstructure and with small proportions of residual austenite having improved properties for production and processing, in particular, for lightweight vehicles according to the restrictive part of claim 1.

The invention also relates to a method for producing cold-rolled steel strips from such steel in accordance with claim 18 and steel strips produced therefrom in accordance with clause 34 of the claims.

In particular, the invention relates to steels with a tensile strength in the region of at least 980 MPa for producing components that have improved deformability, for example, increased hole distribution (xpand®) and increased bending angles and improved welding properties.

The tough competition in the automotive market forces manufacturers to constantly look for solutions to reduce fuel consumption by cars while maintaining the highest comfort and maximum passenger safety. In this case, decisive importance are, on the one hand, the reduction in the weight of all components of the vehicle and, on the other hand, the best possible properties of individual components with a large static and dynamic load during operation, as well as in the event of an accident. The suppliers of semifinished products try to take this into account in such a way that with the help of high-strength steels with a lower sheet thickness, it becomes possible to reduce the weight of vehicle components, while the properties of the components will remain the same or perhaps even improve.

These newly developed steels must meet not only the requirements for weight reduction, but also the high requirements for materials in terms of elasticity, tensile strength and elongation at fracture, as well as in relation to the heat-hardening index, as well as the requirements for components in respect of crack insensitivity edges, energy absorption and specified hardening with respect to the effect of mechanical hardening and the effect of heat hardening. In addition, it is necessary to ensure good machinability. This applies to both processes performed by the automaker, for example, deformation, welding or varnishing, as well as manufacturing processes performed by suppliers of semi-finished products, such as surface coating with a metal or organic coating.

The combination of properties required for a steel material ultimately represents a compromise between the specific properties of the individual components. Therefore, in the construction of vehicles, biphasic steels are increasingly used, and these steels consist of a ferritic basic microstructure, which includes the martensitic second phase and, possibly, an additional phase containing bainite and residual austenite. The characteristic technological properties of two-phase steels are well known, such as a very low ratio of yield strength and very high tensile strength, with strong cold hardening and good cold deformability.

In addition, multiphase steels, such as complex-phase steels, ferritic-bainitic steels, bainitic steels and martensitic steels, which have different microstructural compositions, are used to a greater extent in the construction of vehicles.

Difficult-phase steels in hot-rolled or cold-rolled form are steels that contain small proportions of martensite, residual austenite and / or perlite in the ferritic / bainitic basic microstructure, where the ultimate grinding of the grain is obtained by delayed recrystallization or by precipitating micro-alloying elements.

These steels are currently used in structural components, chassis components and corresponding crash components, as well as flexible cold rolled strips. Such a construction facilitation technology, called Tailor Rolled Blank (TRB®), can significantly reduce weight as a result of the selection of sheet thickness depending on the load along the length of the component.

However, with currently known alloys and existing continuous annealing installations for widely differing sheet thicknesses, production using TRB® technology, in the presence of a multiphase microstructure, is impossible without limitations, such as, for example, heat treatment before cold rolling. In areas with different sheet thicknesses, a homogeneous multiphase microstructure cannot be specified in cold-rolled and hot-rolled steel strips due to the temperature gradient that occurs in the specified process windows.

If thin sheets are to be manufactured, economic reasons dictate that cold-rolled steel strips are usually annealed by continuous annealing with recrystallization to produce a thin sheet that can be deformed as desired. Depending on the composition of the alloy and the cross section of the strip, the technological parameters, such as pulling speed, annealing temperature and cooling rate, are set in accordance with the required microstructure, as well as mechanical and technological properties.

The degree of thinning by rolling during cold rolling describes the percentage difference in the thickness of the hot strip at the beginning relative to the thickness of the cold strip at the end, based on the initial thickness of the hot strip. The degree of refinement by rolling is related to the thickness of the strip and, therefore, this should be interpreted as part of a reduction in thickness.

Typically, the degree of refinement by rolling during cold rolling is relatively constant, reaching about 40% in the case of thicker strips over 2 mm and about 60% in strips up to 1 mm thick. To achieve the values of technological characteristics in accordance with the standards, a moderate degree of cold rolling of 50% is required, as is required in the case of continuous annealing treatment, to ensure normal recrystallization. In the case of classical steels, deviations towards higher or lower quantities lead to fluctuations in the values of technological characteristics, as described in the case of TRB®.

It is known that to achieve a fine-grained microstructure after the continuous annealing procedure, a minimum degree of cold rolling is set depending on the recrystallization temperature in order to set the appropriate dislocation density for the annealing recrystallization.

If the degree of refinement by rolling is too low (even in local areas), the critical recrystallization threshold cannot be exceeded and the microstructure cannot be improved. After recrystallization, grains of different sizes in the cold strip also set the growth of grains of different sizes in the final microstructure, which leads to fluctuations in the values of the characteristics. When cooled from a furnace temperature, grains of various sizes can turn into components of a different phase and provide additional non-uniformity.

To obtain the required microstructure, the cold strip is heated in a continuous annealing furnace to a temperature at which, upon cooling, the formation of the required microstructure (for example, a two-phase or complex-phase microstructure) is achieved.

If, due to stringent corrosion protection requirements, the surface of the cold strip must be hot-dip galvanized, then the annealing treatment is usually carried out in a continuous hot-dip galvanizing plant, while heat treatment or annealing with galvanizing downstream is carried out as part of a continuous process.

In the case of continuous annealing of hot-rolled or cold-rolled steel strips using the concepts of alloys, which are known, for example, from documents EP 2 028 282 A1 and EP 2 031 081 A1, there is a problem for super-strength two-phase steels with a minimum tensile strength of about 980 MPa the fact that there is only a small technological window with suitable annealing parameters. Therefore, even in the case of minimal changes in cross section (thickness, width), adaptation of technological parameters is required to achieve uniform mechanical properties.

With the expansion of technological windows, with constant technological parameters, the desired properties of the strip are possible even in the case of large changes in the cross section of the bands to be annealed.

This applies not only to flexible rolling strips with different sheet thicknesses over the strip length, but also primarily to strips with different thickness and / or different widths that require consistent annealing.

Uniform temperature distribution is difficult to achieve just at different thicknesses in the transition region from one band to another. In the case of alloy compositions with too small technological windows, with continuous annealing, this can lead, for example, to the fact that a thinner strip will pull too slowly through the furnace, which reduces productivity, or a thicker strip will pull too fast through the furnace, and the temperature required for annealing to obtain the desired microstructure will not be reached. The consequence of this is an increase in the number of defects.

Thus, an appropriate process parameter for a material with a relatively constant degree of thinning by cold rolling rolling is a speed reference during continuous annealing, because the conversion phase depends on temperature and time. Therefore, the more insensitive the steel with respect to the uniformity of mechanical properties with the profiles of changes in temperature and time with continuous annealing, the greater will be the technological window.

Particularly acute is the problem of too narrow a process window when processing annealing of cold strips with too low or too high degrees of refinement by rolling during cold rolling, as well as when processing annealing of strips with a sheet thickness varying along the length of the strip when producing components with load optimization from hot or cold. cold streaks.

A method for producing a steel strip with different thickness along the length of the strip is described, for example, in DE 100 37 867 A1.

In the case of application of the known concepts of alloys for a group of multiphase steels, due to the narrow technological window, it is difficult to ensure, with continuous annealing of strips of various thickness, uniform mechanical properties along the entire length of the strip.

Difficult-phase steels also have an even narrower process window than biphasic steels.

The task of relatively homogeneous mechanic-technological properties of various cold strips with varying degrees of refinement by rolling during cold rolling is practically unattainable with the known concepts of the alloy during continuous annealing. The degree of refinement by rolling during cold rolling, necessary for recrystallization annealing, sets a very clear limit on the flexibility of material production throughout the entire process chain. The final thickness of the cold strip determines the thickness of the hot strip and, thus, the parameters for the production of hot strip.

With a flexible method of cold rolling strips of multiphase steels of known compositions, very small technological windows mean that either areas with a lower sheet thickness due to conversion processes during cooling have too high levels of strength, due to the increased martensite content, or areas with a greater sheet thickness reach too low levels of strength due to too low a martensite content. Homogeneous mechanical and technological properties along the entire length or width of the strip are practically unattainable within the framework of the well-known concept of the alloy with continuous annealing.

The known concepts of alloys for multiphase steels are characterized by a too narrow technological window and therefore are practically inapplicable for the production of cold strip with varying degrees of rolling during cold rolling, and for a flexible method of rolling strip.

Published document DE 10 2012 002 079 A1, revealing heavy-duty multiphase steel with a minimum tensile strength of 950 MPa, which already has a very wide technological window for continuous annealing of hot or cold strips, and it was shown that even with this steel it is impossible to obtain variable degrees of refinement rolling with a uniform thickness of the hot strip (the main thickness of the hot strip) and at the same time have uniform material properties.

Therefore, the known concepts of alloys now allow only the production of steels of the same strength class with given cross-sectional areas for cold strip and hot strip (sheet thickness and strip width), and thus changing the concepts of alloys for different strength classes and / or cross-sectional areas.

It is also known from the prior art that the increase in strength is achieved by increasing the amount of carbon and / or silicon and / or manganese, and the increase in strength is achieved by structural conditions and mixed crystalline hardening (mixed crystalline hardening).

However, with an increase in the number of the above-mentioned elements, the properties of the material during processing deteriorate progressively, for example, during welding, deformation and coating by hot dip.

However, steel production is experiencing a tendency to reduce the carbon and / or manganese content in order to improve cold working and obtain better consumer properties.

One example is a test for dispensing a hole to describe and quantify the behavior of cracks at an edge. In suitably optimized grades, the steel consumer expects greater values than standard materials. However, weldability, characterized by carbon equivalent, also attracts attention.

The automotive industry increasingly requires steel grades that meet the requirements for yield strength (Re) / elasticity limit (Rp0.2) with significant differences depending on the application. This leads to the development of steel with a relatively large yield stress interval at a typical tensile strength range.

The low yield strength ratio (Re / Rm) is typical for two-phase steel and is primarily useful for the ability to deform during stretching and deep-drawing procedures.

A higher yield strength ratio (Re / Rm) is typical for difficult-phase steels and is characterized by resistance to cracks at the edge. This can be attributed to the smaller differences in the strengths of individual microstructural components, which has a positive effect on uniform deformation in the region of the cutting edge.

The analytical landscape to achieve a minimum tensile strength of multiphase steels of 980 MPa is very diverse and contains very large ranges of alloys for carbon, manganese, phosphorus, aluminum and chromium and / or molybdenum, which increase the strength, as well as the addition of micro alloys individually or in combination, and on the characteristics of the material properties.

The measurement spectrum is wide, and the thickness is in the range from 0.50 to 3.00 mm, while the range between 0.80 and 2.10 mm is relevant in quality.

Thus, the purpose of the present invention is to present a new concept of an alloy for ultrastrong multiphase steel, a method for producing a steel strip from such ultrastrong multiphase steel, and to present a steel strip that is obtained in accordance with this method, and for which the process window during continuous annealing of cold stripes can be expanded so that from the specified thickness of the hot strip (the main thickness of the hot strip) it is possible to obtain different thicknesses of the cold strip, or from different thicknesses of grief whose strip could be the thickness of the cold strip (the main thickness of the cold strip), that is, various degrees of refinement by rolling could be used instead of relatively constant degrees of refinement by rolling during cold rolling. In this case, the most homogeneous material properties of the possible should be achieved regardless of the specified degree of refinement by rolling.

In addition, the process window for annealing, in particular, continuous annealing of steel strips that have been rolled to final thickness, must be expanded so that, in addition to strips with different cross sections, it is also possible to produce steel strips with a thickness that varies the length of the strip, and, if possible, the width of the strip, with the most uniform mechanical and technological properties of the possible.

According to the present invention, this goal is achieved with the aid of ultrastrong multiphase steel with a minimum tensile strength of 980 MPa, containing, by weight. %:

C from 0.075 inclusive to 0.115 inclusive

Si from 0.400 inclusive to 0.500 inclusive

Mn from 1,900 inclusive to 2,350 inclusive

Cr from 0.250 inclusive to 0.400 inclusive

Al 0.005 inclusive up to 0.060 inclusive

N from 0,0020 inclusive to 0,0120 inclusive

S less than or equal to 0.0020

Nb from 0.005 inclusive to 0.060 inclusive

Ti from 0.005 inclusive to 0.060 inclusive

B from 0.0005 to 0.0010 inclusive

Mo from 0.200 to 0.300 inclusive

Ca from 0.0010 inclusive to 0.0060 inclusive

Cu less than or equal to 0.050

Ni less than or equal to 0.050

The rest is iron, including the inherent steel associated with smelting impurities, while the total content of Mn + Si + Cr ranges from 2.500% inclusive to 3.250% inclusive with the process window, which is as wide as possible during annealing, in particular, with continuous annealing of cold strips of this steel.

Through the alloy concept of the present invention, the mechanic-technological properties are reliably achieved in a narrow range for cold strips with varying degrees of refinement by rolling during cold rolling. The degree of refinement by rolling is related to the thickness of the strip and therefore must be understood in terms of reducing the thickness. For this, the chosen and carefully observed alloy composition is very important, with an emphasis on limited and very limited boron content, which has proven to be very effective in achieving uniform material properties with varying degrees of cold rolling.

In addition, the mechanical and technological properties that can be obtained are achieved in a narrow range over the strip width and strip length by setting the volume proportions of the microstructural phases in a controlled manner.

In addition, the previous production philosophy, where the final thickness of the cold strip (final thickness) determines the required thickness of the hot strip, can be discarded to the extent that only one selected main thickness of the hot strip is important for different thicknesses of the cold strip. However, also as an advantage, it is possible to obtain the thickness of the cold strip, which is to be achieved, in the same way, but from a hot strip with different thicknesses. This greatly increases production flexibility and also reduces production costs.

In addition, the steel according to the present invention has the advantage of a significantly increased processing window compared to known steels. As a result, this ensures an increased level of reliability of the process of continuous annealing of a cold strip with a multiphase microstructure. Therefore, with continuous annealing of cold strips, it is possible to ensure more uniform mechanical and technological properties of strips with varying degrees of refinement by rolling during cold rolling, and even in different cross sections and other usually identical technological parameters in the strip or in the transition region of two strips.

In accordance with the present invention, it is possible to use the invented steel to produce a steel strip in which multi-phase steel is used to produce a hot strip, the steel strip is hot rolled from a hot strip with a final thickness to be obtained, and then the steel strip is annealed, particular, continuous annealing.

The properties of multiphase steel assume that with a selected main hot strip with a specific thickness or selected hot strips with different thicknesses in a wide range of thinning degrees by rolling from 10% to 70%, the steel strips are cold rolled with the required final thickness.

In this case, according to the present invention, the chemical composition of the multi-phase steel is selected depending on the desired final thickness of the steel strip. Thus, within the selected graduations of the cold strip thickness to be obtained, it can be produced from the main hot strip with a thickness corresponding to cold strips with one or several finite thicknesses, or alternatively, the main cold strip can be produced from hot strips with different thicknesses. consistent thickness.

To achieve uniform mechanical properties, the advantage of cold rolling a steel strip to a final thickness of 0.50 mm - 3.00 mm has been proven, and the chemical composition of multiphase steel is chosen in advance, depending on the desired final thickness, as follows:

final thickness 0.50 mm to 1.00 mm inclusive: the sum of Mn + Si + Cr ranges from 2.500% inclusive to 3.100% inclusive,

final thickness over 1.00 mm to 2.00 mm inclusive: the sum of Mn + Si + Cr ranges from 2.650% inclusive to 3.150% inclusive,

final thickness over 2.00 mm to 3.00 mm inclusive: the sum of Mn + Si + Cr ranges from 2.700% inclusive to 3.250% inclusive. Thus, the required final thickness of the steel strip is bound to the composition of the hot strip alloy produced from multi-phase steel.

It has been proven to have the advantage that the chemical composition of multi-phase steel is selected depending on the desired final thickness, as follows:

final thickness 0.50 mm to 1.00 mm inclusive: the C content is less than or equal to 0.100% and the carbon equivalent CEV (IIW) is less than or equal to 0.62%,

final thickness over 1.00 mm to 2.00 mm inclusive: the C content is less than or equal to 0.105% and the carbon equivalent CEV (IIW) is less than or equal to 0.64%,

final thickness over 2.00 mm to 3.00 mm inclusive: the C content is less than or equal to 0.115% and the carbon equivalent CEV (IIW) is less than or equal to 0.66%.

In this case, the carbon equivalent (CEV) (IIW) is calculated according to the expression

CEV (IIW) =% C +% Mn / 6 + (% Cu +% Ni) / 15 + (% Cr +% Mo +% V) / 5.

It was also shown the advantage that the chemical composition of multi-phase steel is selected depending on the desired final thickness, as follows:

final thickness 0.50 mm to 1.00 mm inclusive: the content of Mn is from 1.900% inclusive to 2.200% inclusive,

final thickness over 1.00 mm to 2.00 mm inclusive: the content of Mn is from 2.050% inclusive to 2.250% inclusive,

final thickness over 2.00 mm to 3.00 mm inclusive: the content of Mn is from 2.100% inclusive to 2.350% inclusive.

This applies to continuous annealing of successive strips with different cross-sections of the strip, and also to strips with a variable sheet thickness along the strip length or strip width. For example, it is possible to produce cold stripes with varying degrees of refinement by rolling during cold rolling.

In accordance with the present invention, increased strength and ultrastrong cold strips, which are produced using the continuous annealing method, are made from multiphase steel with a variable sheet thickness, and, as an advantage, it is possible to produce components with load optimization from this material using deformation technology .

The material produced can be produced using a hot-dip galvanizing line, or in an installation only for continuous annealing in the form of a cold strip in a trained or untrained state, and even in a state after heat treatment (aging), and in a state of bending by stretching or without bending by stretching (stretching flexion-straightening).

At the same time, it is possible to change the technological parameters in a special way, to set microstructural proportions in such a way that it can produce steel in various strength classes, for example, with yield strengths between 550 MPa and 950 MPa, and tensile strength between 980 MPa and 1140 MPa.

The composition of the alloy, in accordance with the present invention, can be used to produce steel strips by intercritical annealing between Ac1 and Ac3, or by austenitizing annealing above Ac3 with final controlled cooling, to obtain a two-phase or multiphase microstructure.

It has been proven that annealing temperatures of about 700 to 950 ° C are advantageous. According to the present invention, depending on the whole process (only continuous annealing or with an additional coating by hot dip), there are different approaches to heat treatment.

In the case of the installation of continuous annealing without subsequent coating by hot dip, the steel strip after cold rolling to the final thickness is cooled, starting from the annealing temperature, with a cooling rate of about 15 to 100 ° C / s to an intermediate temperature of about 160 - 250 ° C. Additionally, cooling can be carried out in advance, at a cooling rate of about 15 to 100 ° C / s to the previous intermediate temperature of 300-500 ° C. Cooling to room temperature eventually occurs at a cooling rate of about 2 to 30 ° C / s (see method 1, figure 7). Alternatively, cooling can be performed at a cooling rate between about 15 and 100 ° C / s from an intermediate temperature of 300-500 ° C to room temperature.

In the case of heat treatment, as part of the hot dip coating procedure, there are two temperature control options. The cooling stops, as described earlier, before entering the melting bath, and lasts only after leaving the bath until the intermediate temperature reaches about 200 - 250 ° C. Depending on the temperature of the melting bath, the temperature in the melting bath is about 400 to 470 ° C. Cooling to room temperature is carried out at a rate of about 2 to 30 ° C / s (see method 2, figure 8).

The second variant of temperature control during the hot dip coating procedure involves maintaining the temperature for about 1 to 20 seconds at an intermediate temperature of about 200 to 350 ° C, followed by reheating to a temperature of about 400 to 470 ° C required for the hot dip coating procedure. . At the end of this procedure, the strip is cooled to approximately 200 - 250 ° C. Then cooling to room temperature is carried out at a cooling rate of approximately 2 to 30 ° C (see method 3, figure 7c).

In the case of the known two-phase steels, not only carbon, but also manganese, chromium and silicon are responsible for the transformation of austenite to martensite. Only the invented combination of elements that add carbon, silicon, manganese, nitrogen, molybdenum and chromium, as well as niobium, titanium and, above all, boron within the limits shown, provides on the one hand the required mechanical properties, such as a minimum tensile strength of 980 MPa, and at the same time, a significantly expanded process window during the continuous annealing procedure.

It is also characteristic of the material that, due to the addition of manganese with an increase in the percentage by weight, the ferritic region shifts to longer periods of time at lower temperatures during cooling. The percentage of ferrite decreases to a greater or lesser degree as the proportion of bainite increases, depending on the technological parameters.

With a low carbon content of less than or equal to 0.115%, the carbon equivalent may be reduced, the weldability will be improved, excessively hard spots during welding can be avoided. In addition, with resistance spot welding, the life of the electrode increases significantly.

The effect of the elements in the alloy according to the present invention will be described in more detail later. Related elements are inevitable, and, if necessary, are taken into account in the framework of the concept of analysis in terms of their effect.

Associated elements are elements that are already present in iron ore or fall into steel as a result of the production process. Usually they are undesirable mainly because of their negative impact. Everything possible is being done to remove them to an acceptable level or turn them into less destructive forms.

Hydrogen (H) can diffuse as one element along the iron lattice, without creating stresses in the lattice. As a result, hydrogen in the iron lattice is relatively mobile and can be absorbed relatively easily when processing steel. Hydrogen can be absorbed into the iron lattice only in atomic (ionic) form.

Hydrogen significantly adds brittleness and diffuses mainly into places that are convenient in terms of energy (defects, grain boundaries, etc.). Defects in this work as traps for hydrogen, and can significantly increase the residence time of hydrogen in the material.

Cold cracks can be created by recombination into molecular hydrogen. This behavior occurs in the case of hydrogen embrittlement or in the case of corrosion of a fracture crack caused by hydrogen. Even in the case of deferred cracking, the so-called late destruction, which occurs without external stresses, hydrogen is often mentioned as the reason for this. Thus, the hydrogen content in the steel should remain as low as possible.

A more uniform microstructure, which, in the case of steel in accordance with the present invention, is achieved, including through an extended process window, also reduces the susceptibility to increased brittleness due to hydrogen.

Oxygen (O): In the molten state, steel absorbs gases relatively well. However, at room temperature, oxygen is soluble only in very small quantities. Like hydrogen, oxygen can diffuse into the material only in atomic form. Due to the pronounced effect of embrittlement, and the negative impact on the resistance to aging, everything possible is being done to reduce the oxygen content during production.

On the one hand, procedural approaches are used, such as vacuum processing and, on the other hand, analytical approaches are used to reduce the oxygen content. By adding specific alloying elements, oxygen can be transferred to less destructive states. For example, it is common to remove oxygen in the process of steel deoxidation with manganese, silicon, and / or aluminum. However, the resulting oxides can impart negative properties, like defects, to the material.

For the above reasons, the oxygen content in the steel should be as low as possible.

Phosphorus (P) is a trace element of iron ore, with dissolution in the iron lattice, as a substituting atom. Phosphorus increases rigidity and improves the ability to harden through mixed crystalline solidification. However, everything is being done to reduce the phosphorus content to as small values as possible, for example, because, among other things, its low solubility in the solidification medium means that it has a strong tendency to segregate and greatly reduces the level of hardness. The attachment of phosphorus to the grain boundaries causes destruction at the grain boundaries. In addition, phosphorus increases the transition temperature from hard to brittle behavior to 300 ° C. During hot rolling, phosphorus oxides near the surface at the grain boundaries can lead to the formation of damage.

However, in some steels, due to low cost and a significant increase in strength, phosphorus is used in small quantities (less than 0.1%) as an element of microalloying, for example, in steels with increased strength without implanting atoms, steels with thermal hardening or even concepts of alloys for two-phase steels. The steel according to the present invention differs from the well-known analytical concepts that use phosphorus as an agent for the formation of a mixed crystal, among other things, in that phosphorus is not added to it, but, on the contrary, its content is kept as low as possible.

For the above reasons, the phosphorus content in steel according to the present invention is limited to the quantities that are unavoidable in steel production. Preferably, the P content should be less than or equal to 0.020%.

Sulfur (S), like phosphorus, is bound as a trace element in iron ore. Sulfur is undesirable in steel (with the exception of steel for machine tools), since it exhibits a strong tendency towards segregation and greatly increases brittleness. Therefore, everything is being done to achieve a low sulfur content in the melt, for example, by vacuum processing. In addition, the sulfur present is added by adding manganese to a relatively harmless manganese sulfide compound (MnS). Manganese sulphides are often drawn in-line during the rolling process and work as nucleation sites for conversion. Usually, in the case of diffusion-controlled conversion, this creates a microstructure of pronounced lines and, in the case of the formation of strongly pronounced lines, there may be a deterioration of mechanical properties, such as, for example, pronounced martensite lines instead of scattered martensite islands, reduced elongation at fracture.

For the reasons described above, the sulfur content in steel in accordance with the present invention is limited to less than or equal to 0.0020%, or preferably to less than or equal to 0.0015%, optimally to less than or equal to 0.0010%.

Alloy elements are usually added to steel to affect specific properties as desired. The alloying element can therefore affect different properties in different steels. The effect is usually largely dependent on the amount and condition of the solution in the material. Accordingly, the ratios can vary greatly and be very complex.

The effect of alloying elements will be described in more detail below.

Carbon (C) is considered the most important alloying element in steel. Its target use in the amount of up to 2.06% turns iron into steel. The proportion of carbon is often greatly reduced in the production of steel. In the case of two-phase steel with continuous hot dip coating, its proportion in accordance with EN 10346 or VDA 239-100 is a maximum of 0.230%, with no minimum value specified.

Carbon is embedded in the iron lattice due to its relatively small atomic radius. The solubility is a maximum of 0.02% in the α-gland and a maximum of 2.06% in the gamma-iron. Carbon, in dissolved form, greatly enhances the hardenability of steel, and is thus important for the formation of a sufficient amount of martensite. However, an excessively high carbon content increases the stiffness difference between ferrite and martensite, limiting weldability.

To meet the requirements, for example, in relation to the maximum distribution of the hole and bend angles, as well as for improved weldability, the steel according to the present invention contains carbon in an amount less than or equal to 0.115%.

The differing solubility of carbon in the phases necessitates the need for explicit diffusion procedures during phase conversion, and the procedures can lead to different kinetic conditions. In addition, carbon increases the thermodynamic stability of austenite, as demonstrated in the phase diagram in the expansion of the austenite region at lower temperatures. As the content of forcibly dissolved carbon in martensite increases, the lattice distortions, and the associated phase strength, with an increase in production without diffusion, increase.

Carbon also forms carbides. The microstructural phase that occurs in almost every steel is cementite (Fe ₃ C). However, much more rigid special carbides can form with other metals, such as, for example, chromium, titanium, niobium, and also vanadium. Therefore, not only the type, but also the distribution and degree of deposition are critical to the resulting increase in strength. Therefore, to ensure, on the one hand, sufficient strength and, on the other hand, effective weldability, improved hole distribution, improved bending angle and sufficient resistance to the formation of cracks caused by hydrogen (without delayed fracture), the minimum C content is fixed to 0.075%, and the maximum the C content is fixed at 0.115%, despite the fact that the content has a differentiation with dependence on the cross section, such as:

final thickness 0.50 mm to 1.00 mm inclusive (C less than or equal to 0.100%),

final thickness over 1.00 mm to 2.00 mm inclusive: (C less than or equal to 0.105%)

final thickness over 2.00 mm to 3.00 mm inclusive: (C less than or equal to 0.115 wt.%).

When casting, silicon (Si) binds oxygen and therefore is used for sedation purposes when deoxidizing steel. For the subsequent properties of the steel, it is important that the segregation coefficient be significantly lower than, for example, that of manganese (0.16 compared to 0.87). Segregation usually results in a linear arrangement of the microstructural components, which adversely affects the properties during deformation, such as the distribution of the hole and the ability to bend.

In a manner characteristic of the material, the addition of silicon gives a strong mixed crystalline solidification. At a rough estimate, the addition of 0.1% silicon increases the tensile strength by about 10 MPa, while in the case of adding up to 2.2% silicon, the elongation decreases only slightly. This was tested on sheets of different thickness and at different annealing temperatures. The increase in silicon from 0.2% to 0.5% gave an increase in strength of about 20 MPa in the yield strength and about 70 MPa in tensile strength. Elongation at fracture decreases by about 2%. The latter situation is attributed, inter alia, to the fact that silicon lowers the solubility of carbon in ferrite and increases the activity of carbon in ferrite, thereby preventing the formation of carbides, which, like brittle phases, reduce ductility, which in turn improves deformability. The effect of a slight increase in strength from silicon in steel, in accordance with the present invention, provides the basis for a wide process window.

An additional important effect is that silicon shifts the formation of ferrite in the direction of less time and temperature, and therefore allows to obtain enough ferrite before hardening by quenching. During hot rolling, this provides the basis for better cold rolling. When hot dip coating is applied, the accelerated formation of ferrite causes austenite to enrich with carbon and thereby stabilize. As silicon slows down carbide formation, austenite is additionally stabilized. Thus, with accelerated cooling, the formation of bainite can be suppressed in favor of martensite.

The addition of silicon according to the present invention has led to additional unexpected effects, which will be described later. The aforementioned delay in carbide formation can also be effected, for example, with the help of aluminum. However, aluminum forms stable nitrides, and there will not be enough nitrogen to form carbonitrides with micro-alloying elements. Fusion with silicon eliminates this problem, since silicon does not form carbides or nitrides. Therefore, silicon indirectly has a positive effect on the formation of precipitation of micro-alloys, which, in turn, has a positive effect on the strength of the material. Since the increase in the conversion temperature caused by silicon tends to promote coarsening of the grains, the micro-alloy with niobium, titanium and boron is particularly convenient, as are the given characteristics of the nitrogen content in steel in accordance with the present invention.

It is known that during hot rolling of steel, a high content of silicon leads to the formation of strongly adhering red scale and an increased risk of rolled-in scale, which can affect the results of subsequent acid cleaning and acid cleaning performance. This effect is not observed in the steel according to the present invention, with a silicon content of 0.400% to 0.500%, when acid cleaning is preferably carried out using hydrochloric acid instead of sulfuric acid.

Regarding the galvanizing ability of steels containing silicon, it is stated, in particular, in DE 196 10 675 C1, that steels containing up to 0.800% silicon or up to 2,000% silicon cannot be hot-dip galvanized due to the very poor wettability of the steel surface with liquid zinc.

In addition to recrystallization of cold rolled strip, atmospheric conditions during annealing treatment in a continuous hot dip coating installation lowers iron oxide, which can form on the surface, for example, during cold rolling, or as a result of storage at room temperature. However, for oxygen-affinity alloying elements, such as, for example, silicon, manganese, chromium, boron, atmospheric gas is an oxidizing agent, and as a result, segregation and selective oxidation of these elements can occur. Selective oxidation can occur outside, that is, on the surface of the substrate, and inside, within the metal matrix.

It is known that silicon, in particular, diffuses into the surface during annealing, and forms, by itself or with manganese, oxides on the surface of steel. These oxides can inhibit the contact between the substrate and the melt and can interfere, or severely degrade, the wetting reaction. As a result, non-galvanized spots, so-called “bald spots” or even large areas without any coating may appear. In addition, the adhesion of the zinc or zinc alloy layer on the steel substrate may decrease due to an impaired wetting reaction due to insufficient formation of the inhibitor layer.

In contrast to conventional knowledge in the art, it was unexpectedly discovered by testing that an effective hot dip plating of a steel strip, and effective adhesion of the coating can be achieved solely by the appropriate use of the furnace during recrystallization annealing and during the passage of a hot dip bath.

For this purpose, it is initially necessary to ensure that the surface of the strip is free from residues of scale, acid cleaning emulsion or rolling emulsion, or other contaminating particles through a chemical-mechanical or thermo-hydrodynamic pre-cleaning procedure. In addition, to prevent silicon oxides from reaching the surface of the strip, it is necessary to resort to methods that promote the internal oxidation of the alloying elements below the surface of the material. In this case, different measures are applied, depending on the installation configuration.

In the case of one plant configuration, in which the annealing step is carried out in a radial tube furnace (RTF): (see method 3 in FIG. 9), the internal oxidation of the oxygen of the furnace atmosphere can influence the internal oxidation of the alloying elements (in the protective atmosphere of the gas N ₂ -H ₂ ). The specified partial pressure of oxygen must satisfy the following equation, with the furnace temperature between 700 and 950 ° C.

-12> Log pO ₂ ≥ -5 * Si ^-0.25 - 3 * Mn ^-0.5 -0.1 * Cr ^-0.5 -7 * (- ln B) ^0.5

In this case, Si, Mn, Cr, B set the appropriate proportions of the alloy in steel in wt.%, And pO2 sets the partial pressure of oxygen in minibars.

In the case of a plant configuration in which the furnace area consists of a combination of a direct fire furnace (DFF) and a non-oxidizing furnace (NOF), and downstream of a radial tube furnace (see method 2 in figure 8), the selective oxidation of the alloying elements may likewise be influence the gas atmosphere areas of the furnace.

The partial pressure of oxygen, and thus the oxidation potential of iron and alloying elements, can be given by the combustion reaction in NOF. This should be set in such a way that oxidation of the alloying elements takes place inside, under the surface of the steel, and a thin iron oxide layer is formed on the surface of the steel after passing through the NOF area. This is achieved, for example, by lowering the CO value below 4 vol.%.

With a protective atmosphere of gas N ₂ -H ₂ downstream in a radial tube furnace, a possible layer of iron oxide is reduced, and in this way, the alloying elements are further oxidized inside. The specified partial pressure of oxygen in this area of the furnace must satisfy the following equation, while the furnace temperature must be between 700 and 950 ° C.

-18> Log pO ₂ ≥ -5 * Si ^-0.3 - 2.2 * Mn ^-0.45 -0.1 * Cr ^-0.4 -12.5 * (- ln B) ^0.25

In this case, Si, Mn, Cr, B set the appropriate proportions of the alloy in steel in wt.%, And pO2 sets the partial pressure of oxygen in minibars.

In the transition region between the furnace → zinc bath (nozzle), the dew point of the gas atmosphere (in the protective atmosphere of the gas N ₂ -H ₂ ) and thus the partial pressure of oxygen must be set in such a way as to avoid oxidation of the strip before immersion into the melting bath. It is proved that it is preferable to have dew points in the range from -30˚С to -40˚С.

The above measures in the area of the furnace of the continuous hot-dip coating installation prevent the formation of oxides on the surface, and ensure uniform, effective wettability of the strip surface by the liquid melt.

If instead of the hot dip coating procedure (in this case, for example, hot dip galvanizing), a path is chosen with a method that includes continuous annealing followed by electrolytic galvanizing (see method 1 in figure 6a), then there is no need to take any or specific measures to ensure the ability to galvanize. It is known that the galvanization of more alloyed steels can be carried out much simpler by means of electro-deposition, rather than by means of using continuous hot dipping. In electrolytic galvanizing, pure zinc is deposited directly on the strip surface. In order to avoid suppressing the flow of electrons between the steel strip and zinc ions, which causes galvanization, it is necessary to make sure that there is no oxide layer covering the surface of the steel strip. This condition is usually accomplished by reducing the atmosphere during annealing and by pre-cleaning before electrolysis.

To provide the widest technological window possible during annealing and the possibility of subsequent galvanizing, the minimum silicon content is fixed at 0.400 wt.%, And the maximum silicon content is fixed at 0.500 wt.%.

Manganese (Mn) is added to almost all steels for the purpose of converting harmful sulfur to manganese sulphides. In addition, through mixed crystallization, manganese increases the strength of ferrite and shifts the α- / γ-conversion towards lower temperatures.

The main reason for adding manganese to multiphase steels, for example, in the case of biphasic steels, is a significant improvement in enhancing potential hardening. Due to the inhibition of diffusion, the conversion of perlite and bainite shifts in the direction of greater time and the initial temperature of martensite decreases.

However, at the same time, the addition of manganese makes it possible to increase the hardness ratio between martensite and ferrite. In addition, the formation of microstructure lines is improved. The large difference in hardness between the phases and the formation of martensite lines provides a lower distribution of the hole, which is the equivalent of increased sensitivity to cracks at the edge.

Manganese, like silicon, tends to form oxides on the surface of steel during annealing. Depending on the annealing parameters and the content of other alloying elements (in particular, silicon and aluminum), manganese oxides (for example, MnO) and / or mixed manganese oxides (for example, Mn ₂ SiO ₄ ) can be formed. However, manganese is considered less critical with a small Si / Mn or Al / Mn ratio, since the formation of granular oxides instead of oxide films is more likely. However, high manganese content can adversely affect the appearance of the zinc layer and the adhesion of zinc. The above measures for setting furnace areas with continuous hot dip coating contribute to reducing the formation of oxides and mixed manganese oxides on the steel surface after annealing.

For these reasons, the manganese content is fixed in the range from 1.900% to 2.350%.

To achieve the required minimum strength, it is preferable to maintain the differentiation of the manganese content depending on the strip thickness.

In the case of a final thickness from 0.50 mm to 1.00 mm inclusive, the manganese content is preferably in the range from 1.900% inclusive to 2.350% inclusive, in the case of a final thickness from 1.00 mm to 2.00 mm inclusive, the manganese content is in the range from 2.050% inclusive to 2.250% inclusive, in the case of a final thickness from 2.00 mm to 3.00 mm inclusive, the manganese content is in the range from 2.100% inclusive to 2.350% inclusive.

Another feature of the present invention is that the manganese content can be compensated for by simultaneously changing the silicon content. Increased strength (in this case, yield strength, YS) due to manganese and silicon is usually described in a convenient way by the Pickering equation:

YS (MPa) = 53.9 + 32.34 [wt.% Mn] + 83.16 [wt.% Si] + 354.2 [wt.% N] + 17.402 d ^(-1/2)

However, this is primarily based on the effect of mixed crystalline hardening, which, according to this equation, is weaker for manganese than for silicon. However, as mentioned earlier, manganese at the same time significantly increases the hardenability, as a result, the proportion that increases the strength of the second phase increases significantly in the case of multiphase steels. Therefore, the addition of 0.1% silicon should be balanced in the first approximation by the addition of 0.1% manganese to increase strength. For steel with a composition in accordance with the present invention and an annealing procedure including time / temperature parameters according to the present invention, the following relationship was obtained on an empirical basis for yield strength and tensile strength (TS):

YS (MPa) = 185 + 147.9 [wt.% Si] + 161.1 [wt.% Mn]

TS (MPa) = 574 + 189.4 [wt.% Si] + 174.1 [wt.% Mn]

In comparison with the Pickering equation, the manganese and silicon coefficients are approximately equal for the yield strength and for tensile strength, and thus the possibility of replacing manganese with silicon is proved.

On the one hand, chromium (Cr) in dissolved form and even in small quantities can significantly increase the ability of steel to harden. On the other hand, with appropriate temperature control, chromium in the form of chromium carbides affects the solidification of the particles. The associated increase in the number of crystallization centers with a simultaneous decrease in carbon content leads to a decrease in the hardenability.

In biphasic steels, the addition of chromium mainly improves the potential for enhanced hardening. Chromium in a dissolved state shifts the conversion of perlite and bainite by a longer time, at the same time lowering the initial temperature of martensite.

An additional important effect is that chromium significantly increases the heat resistance, so that the hot-dip bath almost does not reduce the strength.

In addition, chromium is a carbide forming agent. If mixed chromium and iron carbides are present, it is necessary to choose the austenization temperature before hardening, which is high enough to dissolve the chromium carbides. Otherwise, an increased number of nuclei can lead to degradation of the hardening potential.

Similarly, chromium tends to form oxides on the surface of the steel during annealing, as a result, the quality of hot dip coating may suffer. The above measures for setting furnace areas with continuous hot dip coating contribute to reducing the formation of chromium oxides or mixed chromium oxides on the steel surface after annealing.

Thus, the chromium content is fixed in the range from 0.250% to 0.400%.

Molybdenum (Mo): The addition of molybdenum leads, as well as the addition of chromium and manganese, to improved hardenability. The conversion of perlite and bainite shifts to longer times, and the initial temperature of martensite decreases. At the same time, molybdenum is a strong agent for carbide formation, which provides finely scattered mixed carbides, including with titanium. In addition, molybdenum significantly increases heat resistance, therefore no decrease in strength in the hot dip bath is expected. Molybdenum also promotes mixed crystalline solidification, but is less effective than manganese or silicon.

Therefore, the molybdenum content is set between more than 0.200% and up to 0.300%. For cost reasons, the molybdenum content is preferably set in the range between greater than 0.200% and 0.250%.

As a compromise between the required mechanical properties and the possibility of hot dipping, it is preferable that the alloy concept in accordance with the present invention has a total Mo + Cr content of less than or equal to 0.650%.

Copper (Cu): Adding copper can increase tensile strength and improve hardening potential. In combination with nickel, chromium and phosphorus, copper can form a protective oxide layer on the surface, which significantly reduces the corrosion rate.

In combination with oxygen, copper can form, at the grain boundaries, harmful oxides, which can adversely affect, in particular, hot deformation processes. Therefore, the copper content is fixed at less than or equal to 0.050%, and is thus limited to the quantities that are inevitable in the production of steel.

Nickel (Ni): In combination with oxygen, nickel can form, at the grain boundaries, harmful oxides, which can adversely affect, in particular, hot deformation processes. Therefore, the nickel content is fixed at less than or equal to 0.050%, and is thus limited to the quantities that are unavoidable in the production of steel.

Vanadium (V): Since, in the present alloy concept, the addition of vanadium is not necessary, the content of vanadium is limited to the quantities that are unavoidable in steel production.

Aluminum (Al) is usually added to steel to bind oxygen and nitrogen dissolved in iron. Oxygen and nitrogen are thus converted into aluminum oxides and aluminum nitrides. These depositions can affect the grinding of grains through an increase in crystallization centers and can thus improve the properties of stiffness and strength value.

Aluminum nitride does not precipitate in the presence of titanium in sufficient quantity. Titanium nitrides have a lower formation enthalpy and are formed at higher temperatures.

In the dissolved state, aluminum, like silicon, shifts the formation of ferrite to a shorter time, and thus allows a sufficient amount of ferrite to form in two-phase steel. It also inhibits the formation of carbide and thereby provides a delayed conversion of austenite. For this reason, aluminum is also used as an alloying element in steels with residual austenite (TRIP-steel) to replace part of silicon. The reason for this approach is based on the fact that aluminum is somewhat less critical in the reaction of galvanization than silicon.

Therefore, the aluminum content is limited to 0.005% to a maximum of 0.060%, and the addition is carried out for the purpose of calming down the steel.

Niobium (Nb): Niobium in steel behaves differently. During hot rolling on the production line, it retards recrystallization through the formation of very finely scattered depositions, while the density of the crystallization centers increases, and after the conversion a finer grain is formed. The proportion of dissolved niobium also suppresses recrystallization. Deposition contribute to the strength of the final product. These may be carbides or carbonitrides. Often these are mixed carbides in which titanium is also embedded. This effect starts at 0.005%, most pronounced starting at 0.010% niobium. In addition, precipitation prevents grain growth during (partial) austenization during hot galvanizing. Above 0.060% niobium additional effects are not expected. Proved that the content is preferably from 0.025% to 0.045%.

Titanium (Ti): Because of its high chemical affinity for nitrogen, titanium usually precipitates during solidification, like TiN. In addition, it appears along with niobium as a mixed carbide. TiN is very important for the stability of the grain size in the continuous furnace. Deposits have a very high level of temperature stability, in contrast to mixed carbides, they are present at 1200 ° C primarily as particles that inhibit the growth of grains. Titanium also retards recrystallization during hot rolling, but is less effective for this than niobium. Titanium promotes dispersion hardening. Larger TiN particles are less effective than finer scattered mixed carbides. The highest efficiency is achieved in the range from 0.005% to 0.060% titanium; thus, it is characteristic of the alloy according to the present invention. It is proved that for this purpose the content is preferably from 0025% to 0.045%.

Boron (B): Boron is an extremely effective alloying element for achieving varying degrees of refinement by rolling. Unexpectedly, tests have shown that the range for adding boron, which is very narrow in accordance with the present invention, has a pronounced effect in terms of the homogeneity of the mechanical properties of the produced cold strips at varying degrees of refinement by rolling and subsequent processing. This pronounced effect initially makes it possible to set, instead of a relatively constant degree of refinement by rolling during cold rolling, specific ranges of the characteristic value after the process steps (figures 7, 8 or 9) also for a material with varying degrees of refinement by rolling, based on the main thickness of the hot strip. or on the main thickness of the cold strip.

In addition, boron is an effective element for enhancing hardenability, effective even in very small quantities. The initial temperature of martensite remains unchanged. In order to become effective, boron must be present in the solid solution. Since it has a high chemical affinity for nitrogen, nitrogen must first be removed, preferably using the desired stoichiometric amount of titanium. Due to the low solubility in iron, the dissolved boron will preferably join the edges of austenitic grains. In this position, it partially forms Fe-B carbides, which adhere and lower the energy of the grain boundaries. Both effects help to delay the formation of ferrite and perlite, thereby increasing the hardenability of the steel. However, an excessively high boron content is dangerous, since iron boride can have a negative effect on the hardenability, deformation and rigidity of the material. Boron also tends to form oxides or mixed oxides when annealing is carried out in a continuous hot dip coating procedure, and this lowers the quality of galvanizing. The aforementioned measures for setting the furnace areas with continuous hot dip coating are needed to reduce the formation of oxides on the steel surface.

For the above reasons, the boron content in the alloy concept, in accordance with the present invention, is fixed at values greater than 0.0005% to 0.0010%, preferably at values less than or equal to 0.0009% or optimally from 0.0006% to 0.0009% inclusive.

Nitrogen (N) can be both an alloying element and a concomitant steel production element. Excessive nitrogen content increases strength, coupled with rapid loss of rigidity, as well as the effects of aging. On the other hand, by targeting the addition of nitrogen, in combination with titanium and niobium micro-alloying elements, fine-grained hardening can be obtained with titanium nitrides and (niobium (carbo)) nitrides. Moreover, the formation of coarse grain is suppressed when reheated before hot rolling.

In accordance with the present invention, the nitrogen content for this reason is fixed at values from 0.0020% inclusively to 0.0120% inclusively.

It has been proven that it is preferable to maintain the required properties of the steel so that nitrogen is added depending on the sum of Ti + Nb + B.

In the case of the total content of Ti + Nb + B from 0.010% inclusive to 0.070% inclusive, the nitrogen content should be maintained at a level of 0.0020% inclusive to 0.0090% inclusive. When the total content of Ti + Nb + B is more than 0.070%, the nitrogen content from 0.0040% inclusive to 0.0120% inclusive was preferred.

For the total content of niobium and titanium, a content of less than or equal to 0.100% was preferred, and due to the basic interchangeability of niobium and titanium to a minimum niobium content of 0.0010%, and because of the cost, a content of less or equal to 0.090% was particularly preferable.

When interacting with the elements of microalloying with niobium and titanium with boron, the total content is less than or equal to 0.102% was preferred, and the total content is less than or equal to 0.092% was especially preferred. A higher content no longer has an improvement effect within the scope of the present invention.

In addition, the maximum content of ≤ 0.365 wt.% Was successful, as the total content of Ti + Nb + V + Mo + B for the reasons described above.

Calcium (Ca): The addition of calcium in the form of calcium-silicon mixed compounds causes the deoxidation and desulfurization of the molten phase during the production of steel. For example, the reaction products are converted to slag, and the steel is cleaned. In accordance with the present invention, an increased level of purity improves the properties of the final product.

For these reasons, the Ca content is set from 0.0010% inclusive to 0.0060% inclusive. A content of less than or equal to 0.0030% was preferred.

Tests conducted using steel according to the present invention have shown that with intercritical annealing between Ac1 and Ac3, or upon annealing with austenization above Ac3, with completion of controlled cooling, two-phase steel with a minimum tensile strength of 980 MPa and thickness from 0.50 can be produced mm to 3.00 mm, which is characterized by adequate tolerance to fluctuations in the process.

Therefore, in accordance with the present invention, a significantly expanded process window is provided for the alloy composition, in comparison with the known alloy concepts.

The annealing temperatures required for a two-phase microstructure are approximately in the range between 700 and 950 ° C for the steel according to the present invention, thus, depending on the temperature range, a partially austenitic (two-phase region) or a fully austenitic (austenite region) microstructure is obtained.

The tests also showed that the specified proportions of the microstructure remain after intercritical annealing between Ac1 and Ac3 or austenitic annealing above Ac3, followed by controlled cooling even after a further process step with hot dip coating at temperatures between 400 and 470 ° C, for example, zinc or zinc magnesium.

The material after continuous annealing and periodic hot-dip coating can be performed in a trained or untrained state, and / or a stretch-bend-straighten state or in a non-stretch-bend straightening state, and also in a post-heat treated condition (aging).

Moreover, the steel strips consisting of the alloy composition in accordance with the present invention, are characterized by further processing with a high degree of insensitivity to cracks at the edge and a high bending angle.

A very small difference in the characteristic value of the steel strip in the longitudinal and transverse directions relative to the direction of its rolling is preferable during subsequent use of the material. For example, cutting blanks from a strip can be done independently of the direction of rolling (that is, across, along or diagonally or at an angle relative to the direction of rolling), and thus minimizes waste.

To enable cold rolling of a hot strip to produce steel, in accordance with the present invention, a hot strip is produced according to the present invention with final rolling temperatures in the austenitic region above Ar3 and at coiling temperatures above the initial bainite temperature.

As part of the further processing of the steel strip, in accordance with the present invention, it is possible to manufacture a hardened component, for example, for the automotive industry.

In this case, the workpiece is cut from a steel strip, in accordance with the present invention, said workpiece is then heated to a temperature above Ac3, and a component is created from the heated workpiece, and then strengthened in a deformation tool or in air.

As an advantage, the steel according to the present invention has the property that hardening occurs even when cooled in stationary air, therefore, a separate cooling of the deformation tool can be omitted.

When hardening, the microstructure of the steel is transferred to the austenitic range by heating, preferably to temperatures above 950 ° C in a protective atmosphere of gas. During subsequent cooling in air or protective gas, the martensitic microstructure of the high-strength component is formed.

Subsequent tempering helps reduce the intrinsic stresses in the hardened component. At the same time, the stiffness of the component decreases so that the required values of impact strength are achieved.

Other distinctive features and advantages of the present invention will be more apparent from the following description of exemplary embodiments illustrated in the drawings, in which:

Figure 1 shows (schematically) a technological chain for the production of a strip consisting of steel according to the present invention,

Figure 2 shows the chemical composition (examples 1 to 5) of steel according to the present invention,

Figure 3 shows (schematically) a time / temperature graph of the steps of the hot rolling and cold rolling process and continuous annealing (additionally hot dip coating) using the steel of the present invention as an example,

Figure 4a shows the ratio of the thickness of the hot strip to the thickness (final thickness) of the cold strip on the example of the prior art,

Figure 4b shows the degree of refinement by rolling relative to the thickness (final thickness) of a cold strip using the example of the prior art,

Figure 5a shows the ratio of the thickness of the hot strip to the thickness (final thickness) of the cold strip by the example of steel according to the present invention for the case of the main thickness of the hot strip,

Figure 5b shows the degree of thinning by rolling relative to the thickness (final thickness) of a cold strip by the example of steel according to the present invention for the case of the main thickness of a hot strip,

Figure 6a shows the ratio of the thickness of the hot strip to the thickness (final thickness) of the cold strip using the example for steel according to the present invention for the case of the main thickness of the cold strip (the specific final thickness of the cold-rolled steel strip to be obtained),

Figure 6b shows the degree of thinning by rolling relative to the thickness of the cold strip (final thickness) using the example of steel according to the present invention for the case of the main thickness of the cold strip (the specific final thickness of the cold-rolled steel strip to be obtained),

Figure 7 shows method 1, temperature / time curves (options with annealing are shown schematically),

Figure 8 shows method 2, temperature / time curves (options with annealing are shown schematically),

Figure 9 shows method 3, temperature / time curves (annealing options are shown schematically)

Figure 10 shows the characteristic values of the material by the example of steel according to the present invention for the case of the main hot strip thickness of 2.30 mm with a variable degree of refinement by rolling after cold rolling, transversely and longitudinally with respect to the rolling direction (in tabular form),

Figure 11 shows the characteristic values of the material on the example of steel according to the present invention for the case of the main thickness of the hot strip 2.30 mm with a variable degree of refinement, transversely relative to the direction of rolling (graphically),

Figure 12 shows the characteristic values of the material by example for steel according to the present invention for the case of a main hot strip thickness of 2.30 mm with a variable degree of refinement by rolling after cold rolling, longitudinally relative to the direction of rolling (graphically) and

Figure 13 shows a schematic diagram of a sub-peritectic grade (base alloy HCT500XD, increasing the added amounts and additional substances cause changes in other grades or the corresponding ranges of sheet thickness).

Figure 1 schematically illustrates a processing chain for the production of a strip of steel according to the present invention. Various process paths related to the present invention are shown. Before hot rolling (the final rolling temperature), the process path is the same for all the steels according to the present invention, after which the process paths diverge depending on the desired results. For example, the hot strip after acid cleaning can be galvanized or can be cold-rolled with varying degrees of refinement by rolling. A soft-annealed hot strip or a soft-annealed cold strip can also be cold-rolled and galvanized.

The material can also be processed without a hot dip coating procedure, that is, only within continuous annealing and without subsequent electrolytic galvanizing. From a material with an optional coating can be produced a complex component. After this, a hardening process with air cooling in accordance with the present invention may take place. Additionally, there may be a tempering step at the end of the heat treatment of the component.

Figure 2 illustrates, by way of examples 1 to 5, the compositions of the alloys of the tested steels, depending on the required thickness of the cold strip (final thickness). From the main thickness of the 2.30 mm hot strip, cold strips of various thicknesses are obtained. Depending on the required strip thickness, example 1 shows the composition of the alloy for a cold strip with a thickness of 2.0 mm, example 2 - a cold strip with a thickness of 1.80 mm, example 3 - a cold strip with a thickness of 1.50 mm, example 4 - a cold strips with a thickness of 1.20 mm, and example 5 - cold strips with a thickness of 1.00 mm.

Figure 3 schematically illustrates the temperature / time curve for the process steps and the continuous annealing of the strips made from the alloy with the composition according to the present invention. Time and temperature dependent conversion for hot rolling process and also for heat treatment after cold rolling, component manufacturing, quenching and additional tempering.

Figure 4 illustrates the ratio of the thickness of the hot strip and the thickness of the cold strip (final thickness) (figure 4a) and the degree of thinning by rolling relative to the thickness of the cold strip (final thickness) (figure 4b) using the example of the prior art.

Figure 5 illustrates the ratio of the thickness of the hot strip and the thickness of the cold strip (final thickness) (figure 5a) and the degree of thinning by rolling relative to the thickness of the cold strip (final thickness) (figure 5b) on the example of steel, in accordance with the present invention, for the case of the main thickness of hot stripes.

Figure 6 illustrates the ratio of the thickness of the hot strip and the thickness of the cold strip (figure 6a) and the degree of thinning by rolling relative to the thickness of the cold strip (final thickness) (figure 6b) on the example of steel, in accordance with the present invention, for the case of the main thickness of the cold strip (with the required the specific final thickness of the cold rolled steel strip).

Figures 7, 8, 9 schematically illustrate three variants of temperature / time curves in accordance with the present invention for the case of annealing and cooling processing and austenization conditions, which are different in each case.

By varying the temperature control of the present invention, in the indicated range, mutually different characteristic values and / or also different distribution results for the hole and bending angles are obtained. Differences in principle relate to temperature / time parameters during heat treatment followed by cooling.

Method 1 (FIG. 7) represents annealing and cooling of the produced cold rolled steel strip to the final thickness in a continuous annealing unit. First, the strip is heated to a temperature in the range from about 700 to 950 ° C (Ac1 to Ac3). The annealed steel strip is then cooled from the annealing temperature with a cooling rate of about 15 - 100 ° C / s to an intermediate temperature (ZT) of about 200 - 250 ° C. This schematic illustration does not show the second intermediate temperature (approximately 300 - 500 ° C).

Then the steel strip is cooled with air at a cooling rate of about 2 - 30 ˚C / s to room temperature (RT), or cooling at a cooling rate of about 15 - 100 ˚ C / s is maintained until it reaches room temperature.

Method 2 (figure 8) shows the process in accordance with method 1, but the cooling of the steel strip is briefly interrupted when passing through a hot dip vessel for the purpose of hot dip coating application, in order to continue cooling with a cooling rate of about 15 - 100 ° C / s to an intermediate temperature of about 200 - 250˚С. The steel strip is then cooled with air at a cooling rate of about 2 to 30 ° C / s until it reaches room temperature. Method 2 corresponds to annealing, i.e. hot dip galvanizing in combination with a direct fire furnace and a radial tube furnace, as shown in figure 8.

Method 3 (FIG. 9) similarly shows the process in accordance with method 1 with the hot dip coating procedure, but the cooling of the steel strip is briefly interrupted (about 1 to 20 s) at an intermediate temperature in the range of about 200 to 400 ° C and heated to the temperature (ST) required for the hot-dip coating procedure (approximately 400 - 470 ° C). Then the steel strip is cooled to an intermediate temperature of about 200 to 250 ° C. Subsequent cooling of the steel strip with air is carried out at a cooling rate of about 2–30 ° C / s until it reaches room temperature.

Method 3 corresponds, for example, to the process carried out in a continuous annealing plant, as shown in figure 9. In addition, in this case, by means of an induction furnace, the steel is optionally heated directly in front of the zinc bath.

Figures 10, 11, 12 show in tabular form (figure 10) and graphically characteristic values of the material on the example of steel, in accordance with the present invention, for the case of the main hot strip thickness of 2.30 mm with a variable degree of refinement by rolling after cold rolling, transversely (figure 11 ) and longitudinally (figure 12) relative to the direction of rolling as an example of processing in accordance with method 3 (figure 9).

The degree of refinement by rolling thus varies from 13% to 35% for the cold rolling stage, and 55% (30% + 25%) or 68% (35% + 33%) if cold rolling is carried out twice. It is impressively shown that for very small degrees of deformation, and also for very different degrees of deformation, relatively homogeneous values are achieved with a traditional range of vibrations for tensile strength, and for yield strength, transversely and longitudinally with respect to the direction of rolling.

For industrial production with hot dip galvanized in accordance with method 3, as shown in figure 9, the following examples are illustrative in the framework of the so-called applicability tests:

Example 1 (cold strip 2.00 mm of the main hot strip 2.30 mm) alloy composition in wt.%.

Steel according to the present invention with a content of 0.104% C; 0.487% Si; 2.248% Mn; 0.016% P; 0.0009% S; 0.0052% N; 0.043 Al; 0.321% Cr; 0.214% Mo; 0.0278% Ti; 0.0374% Nb; 0.0007% B; 0.0016% Ca according to method 3 according to figure 9, coated with hot dip, the material had previously undergone hot rolling at the required final rolling temperature of 910 ° C and was wound at the required winding temperature of 650 ° C with the main thickness of the hot strip 2.30 mm and passed cold rolling after acid cleaning without additional heat treatment (such as, for example, batch type annealing) to 2.00 mm in one pass (thinning rate by rolling 13%).

The ratio of yield strength Re / Rm in the transverse direction was 65%.

- elasticity limit (Rp0.2) 689 MPa - tensile strength (Rm) 1061 MPa - elongation at break (A80) 11.4% - heat strengthening index (ВН2) 52 MPa - hole spreading factor in accordance with ISO 16630 38% - bending angle in accordance with VDA 238-100 (longitudinal, transverse) 112˚ / 102˚

The characteristic values of the material in the transverse direction relative to rolling correspond, for example, to HC660XD.

The ratio of yield strength Re / Rm in the longitudinal direction was 63%.

- elasticity limit (Rp0.2) 661 MPa - tensile strength (Rm) 1044 MPa - elongation at break (A80) 12.0% - heat strengthening index (ВН2) 52 MPa - hole spreading factor in accordance with ISO 16630 38% - bending angle in accordance with VDA 238-100 (longitudinal, transverse) 112˚ / 102˚

The characteristic values of the material in the longitudinal direction with respect to rolling correspond, for example, to CR590Y980T-DP.

Example 2 (cold strip 1.80 mm of the main hot strip 2.30 mm) alloy composition in wt.%.

Steel according to the present invention with a content of 0.104% C; 0.495% Si; 2.226% Mn; 0.011% P; 0.0008% S; 0.0048% N; 0.052 Al; 0.317% Cr; 0.212% Mo; 0.0381% Ti; 0.0361% Nb; 0.0008% B; 0.0019% Ca in accordance with method 3 according to figure 9, coated with hot dip, the material previously passed hot rolling at the required final rolling temperature of 910 ° C and was wound at the required winding temperature of 650 ° C with the main thickness of the hot strip 2.30 mm and passed cold rolling after acid cleaning without additional heat treatment (such as, for example, batch type annealing) to 1.80 mm in one pass (thinning rate by rolling 22%).

The ratio of yield strength Re / Rm in the transverse direction was 66%.

- elasticity limit (Rp0.2) 717 MPa - tensile strength (Rm) 1089 MPa - elongation at break (A80) 10.6% - heat strengthening index (ВН2) 48 MPa - hole spreading factor in accordance with ISO 16630 31% - bending angle in accordance with VDA 238-100 (longitudinal, transverse) 102˚ / 96˚

The characteristic values of the material in the transverse direction relative to rolling correspond, for example, to HC660XD.

The ratio of yield strength Re / Rm in the longitudinal direction was 64%.

- elasticity limit (Rp0.2) 682 MPa - tensile strength (Rm) 1067 MPa - elongation at break (A80) 11.5% - heat strengthening index (ВН2) 48 MPa - hole spreading factor in accordance with ISO 16630 31% - bending angle in accordance with VDA 238-100 (longitudinal, transverse) 102˚ / 96˚

The characteristic values of the material in the longitudinal direction with respect to rolling correspond, for example, to CR590Y980T-DP.

Example 3 (cold strip 1.50 mm main hot strip 2.30 mm) alloy composition in wt.%.

Steel according to the present invention with a content of 0.102% C; 0.488% Si; 2.170% Mn; 0.012% P; 0.0008% S; 0.0048% N; 0.041 Al; 0.333% Cr; 0.218% Mo; 0.0351% Ti; 0.0345% Nb; 0.0009% B; 0.0018% Ca according to method 3 according to figure 9, coated with hot dip, the material was previously hot rolled at the required final rolling temperature of 910 ° C and was wound at the required winding temperature of 650 ° C at the main thickness of the hot strip 2.30 mm and passed cold rolling after acid cleaning without additional heat treatment (such as, for example, batch type annealing) to 1.50 mm in a single pass (degree of refinement by rolling 35%).

The ratio of yield strength Re / Rm in the transverse direction was 68%.

- elasticity limit (Rp0.2) 727 MPa - tensile strength (Rm) 1060 MPa - elongation at break (A80) 11.2% - heat strengthening index (ВН2) 58 MPa - hole spreading factor in accordance with ISO 16630 28% - bending angle in accordance with VDA 238-100 (longitudinal, transverse) 98˚ / 92˚

The characteristic values of the material in the transverse direction relative to rolling correspond, for example, to HC660XD.

The yield strength ratio Re / Rm in the longitudinal direction was 67%.

- elasticity limit (Rp0.2) 697 MPa - tensile strength (Rm) 1047 MPa - elongation at break (A80) 12.6% - heat strengthening index (ВН2) 58 MPa - hole spreading factor in accordance with ISO 16630 28% - bending angle in accordance with VDA 238-100 (longitudinal, transverse) 98˚ / 92˚

The characteristic values of the material in the longitudinal direction with respect to rolling correspond, for example, to CR590Y980T-DP.

Example 4 (cold strip 1.20 mm main hot strip 2.30 mm) alloy composition in wt.%.

Steel according to the present invention with a content of 0.103% C; 0.493% Si; 2.244% Mn; 0.013% P; 0.0009% S; 0.0049% N; 0.042 Al; 0.332% Cr; 0.226% Mo; 0.0315% Ti; 0.0346% Nb; 0.0007% B; 0.0013% Ca in accordance with method 3 according to figure 9, coated with hot dip, the material previously passed hot rolling at the required final rolling temperature of 910 ° C and was wound at the required winding temperature of 650 ° C with the main thickness of the hot strip 2.30 mm and passed cold rolling after acid cleaning without additional heat treatment (such as, for example, batch type annealing) to 1.20 mm in two passes (degree of refinement by rolling 30% and 25%).

The ratio of yield strength Re / Rm in the transverse direction was 60%.

- elasticity limit (Rp0.2) 673 MPa - tensile strength (Rm) 1119 MPa - elongation at break (A80) 10.2% - heat strengthening index (ВН2) 78 MPa - hole spreading factor in accordance with ISO 16630 27% - bending angle in accordance with VDA 238-100 (longitudinal, transverse) 102˚ / 94˚

The characteristic values of the material in the transverse direction relative to rolling correspond, for example, to HC660XD.

The ratio of yield strength Re / Rm in the longitudinal direction was 60%.

- elasticity limit (Rp0.2) 659 MPa - tensile strength (Rm) 1098 MPa - elongation at break (A80) 10.9% - heat strengthening index (ВН2) 78 MPa - hole spreading factor in accordance with ISO 16630 27% - bending angle in accordance with VDA 238-100 (longitudinal, transverse) 102˚ / 94˚

The characteristic values of the material in the longitudinal direction with respect to rolling correspond, for example, to CR590Y980T-DP.

Example 5 (cold strip 1.00 mm main hot strip 2.30 mm) alloy composition in wt.%.

Steel according to the present invention with a content of 0.100% C; 0.467% Si; 2.169% Mn; 0.011% P; 0.0008% S; 0.0050% N; 0.043 Al; 0.340% Cr; 0.223% Mo; 0.0293% Ti; 0.0387% Nb; 0.0009% B; 0.0019% Ca in accordance with method 3 according to figure 9, coated with hot dip, the material previously passed hot rolling at the required final rolling temperature of 910 ° C and was wound at the required winding temperature of 650 ° C with the main thickness of the hot strip 2.30 mm and passed cold rolling after acid cleaning without additional heat treatment (such as, for example, batch type annealing) to 1.00 mm in two passes (degree of refinement by rolling 35% and 33%).

The ratio of yield strength Re / Rm in the transverse direction was 67%.

- elasticity limit (Rp0.2) 701 MPa - tensile strength (Rm) 1042 MPa - elongation at break (A80) 11.1% - heat strengthening index (ВН2) 58 MPa - hole spreading factor in accordance with ISO 16630 34% - bending angle in accordance with VDA 238-100 (longitudinal, transverse) 117˚ / 109˚

The characteristic values of the material in the transverse direction relative to rolling correspond, for example, to HC660XD.

The yield strength ratio Re / Rm in the longitudinal direction was 68%.

- elasticity limit (Rp0.2) 695 MPa - tensile strength (Rm) 1016 MPa - elongation at break (A80) 12.1% - heat strengthening index (ВН2) 58 MPa - hole spreading factor in accordance with ISO 16630 34% - bending angle in accordance with VDA 238-100 (longitudinal, transverse) 117˚ / 109˚

The characteristic values of the material in the longitudinal direction with respect to rolling correspond, for example, to CR590Y980T-DP.

Figure 13 shows a schematic diagram of a chain of a sub-peritectic variety with a basic analysis of HCT500XD, based on the fact that increasing additional quantities and additional substances can give a change to other varieties according to their minimum tensile strength (classes) or the corresponding sheet width ranges.

The invention has been described above using steel sheets with a final thickness of 0.50 mm to 3.00 mm. If necessary, it is also possible to obtain a final thickness in the range from 0.10 mm to 4.00 mm.

Claims (65)

1. Heavy-duty multi-phase steel with a minimum tensile strength of 980 MPa, containing, wt.%: From 0.075 to 0.115 Si from 0.400 to 0.500 Mn from 1,900 to 2,350 Cr from 0.250 to 0.400 Al 0.005 to 0.060 N from 0,0020 to 0,0120 S less than or equal to 0.0020 Nb from 0.005 to 0.060 Ti 0.005 to 0.060 B from 0.0005 to 0.0010 Mo from 0.200 to 0.300 Ca 0.0010 to 0.0060 Cu less than or equal to 0.050 Ni less than or equal to 0.050 iron and inherent steel associated with smelting impurities, while the total content of Mn + Si + Cr is from 2,500 to 3,250 wt.%. 2. Steel under item 1, characterized in that the amount of Mn + Si + Cr is from 2,500 to 3,100 wt.%, Or from 2,650% to 3,150 wt.%, Or from 2,700 to 3,250 wt.%. 3. Steel according to Claim. 1, characterized in that the B content is less than or equal to 0.0009% by weight, in particular, from 0.0006 to 0.0009% by weight. 4. Steel according to claim 1, characterized in that when the content of C is less than or equal to 0.100 wt.% The carbon equivalent of CEV (IIW) is less than or equal to 0.62%, or when the content of C is less than or equal to 0.105 wt.% Of carbon equivalent of CEV (IIW) less than or equal to 0.64%, or when the C content is less than or equal to 0.115 wt.%, The carbon equivalent of CEV (IIW) is less than or equal to 0.66%. 5. Steel under item 1, characterized in that the content of Mn is from 1,900 to 2,350 wt.%. 6. The steel according to claim 1, characterized in that the content of Mn is from 1,900 to 2,200 wt.%, Or from 2,050 to 2,250 wt.%, Or from 2,100 to 2,350 wt.%. 7. Steel under item 1, characterized in that when the content of Ti + Nb + B is from 0.010 to 0.070 wt.% The nitrogen content N is from 0.0020 to 0.0090 wt.%, And when the content is Ti + Nb + B more than 0.070% by weight, the N content is from 0.0040 to 0.0120% by weight. 8. The steel according to claim 1, characterized in that the content of S is less than or equal to 0.0015 wt.%, In particular the content of S is less than or equal to 0.0010 wt.%. 9. Steel under item 1, characterized in that the Mo content is less than or equal to 0.250 wt.%. 10. The steel according to claim 1, characterized in that the content of Ti is from 0.025 to 0.045 wt.%. 11. The steel according to claim 1, characterized in that the Nb content is from 0.025 to 0.045 wt.%. 12. The steel according to claim 1, characterized in that the sum of Nb + Ti is less than or equal to 0.100 wt.%, In particular, the sum of Nb + Ti is less than or equal to 0.090 wt.%. 13. Steel under item 1, characterized in that the sum of Cr + Mo is less than or equal to 0.650 wt.%. 14. The steel according to claim 1, characterized in that the sum of Ti + Nb + B is less than or equal to 0.102 mass%, in particular the sum of Ti + Nb + B is less than or equal to 0.092 mass%. 15. Steel according to claim 1, characterized in that the content of Ca is less than or equal to 0.0030% by weight. 16. Steel under item 1, characterized in that the yield strength YS and tensile strength TS are determined depending on the content of Si and Mn in accordance with the following ratios: YS (MPa) = 185 + 147.9 [% Si] +161.1 [% Mn] TS (MPa) = 574 + 189.4 [% Si] +174.1 [% Mn]. 17. Method for the production of steel strip of multi-phase steel according to any one of paragraphs. 1-16, characterized in that it produces hot rolled strip from multiphase steel, hot rolled steel strip passes cold rolling to the required final thickness from 0.50 to 3.00 mm, after which the steel strip passes annealing, in particular continuous annealing, in which cold rolled the steel strip is heated with continuous annealing to a temperature in the range of about 700-950 ° C and then cooled from the annealing temperature at a cooling rate of about 15-100 ° C / s first to the first intermediate temperature of about 300-500 ° C, then at a speed of and cooling about 15-100 ° C to a second intermediate temperature of about 160-250 ° C, then the steel strip is cooled with air at a cooling rate of about 2-30 ° C / s to room temperature, or at a cooling rate of about 15-100 ° C / c from the first intermediate temperature to room temperature. 18. Method for the production of steel strip from multi-phase steel according to any one of paragraphs. 1-16, characterized in that it produces hot rolled strip from multiphase steel, hot rolled steel strip passes cold rolling to the required final thickness from 0.50 to 3.00 mm, after which the steel strip passes annealing, in particular continuous annealing, in which cold rolled The steel strip is heated with continuous annealing to a temperature in the range of about 700-950 ° C and during the hot dip coating procedure after heating and subsequent cooling to a temperature of about 400-470 ° C, cooling is stopped before by stepping into the melting bath, after the hot dip coating procedure, cooling is continued at a cooling rate between about 15-100 ° C / s to an intermediate temperature of about 200-250 ° C, and then the steel strip is cooled with air at a cooling rate of about 2-30 ° C / s to reach room temperature. 19. Method for the production of steel strip from multi-phase steel according to any one of paragraphs. 1-16, characterized in that hot rolled strip is produced from multiphase steel, hot rolled steel strip passes cold rolling to the required final thickness from 0.50 mm to 3.00 mm, after which the steel strip passes annealing, in particular continuous annealing, at which cold rolled steel strip is heated with continuous annealing to a temperature in the range of about 700-950 ° C and, during the hot dip coating procedure after heating and subsequent cooling to an intermediate temperature of about 200-250 ° C before entering In a melting bath, the temperature is maintained for about 1–20 s, then the steel strip is heated to a temperature of about 400–470 ° C and, after the hot-dip coating procedure, cooling is performed at a cooling rate between about 15 and 100 ° C / s to an intermediate temperatures of about 200-250 ° C, followed by cooling with air at a cooling rate of about 2-30 ° C / s to room temperature. 20. A method according to any one of claims. 17-19, characterized in that with a selected main hot rolled strip with a specific thickness or selected hot rolled strips with differing thicknesses in a wide range of thinning degrees by rolling from 10% to 70%, hot rolled steel strips are cold rolled to the desired final thickness. 21. A method according to any one of claims. 17-19, characterized in that the chemical composition of multi-phase steel is chosen depending on the desired final thickness of the steel strip. 22. The method according to p. 21, characterized in that the chemical composition of multi-phase steel is selected depending on the desired final thickness as follows: the final thickness from 0.50 to 1.00 mm - the sum of Mn + Si + Cr is from 2,500 to 3,100 wt.%, the final thickness in excess of 1.00 to 2.00 mm - the amount of Mn + Si + Cr is from 2.650 to 3.150 wt.%, the final thickness in excess of 2.00 to 3.00 mm - the amount of Mn + Si + Cr is from 2.700 to 3.250 wt.%. 23. The method according to p. 22, characterized in that the chemical composition of multi-phase steel is chosen depending on the desired final thickness as follows: the final thickness is from 0.50 to 1.00 mm — the C content is less than or equal to 0.100 wt.% and the carbon equivalent of CEV (IIW) is less than or equal to 0.62%, the final thickness is from 1.00 to 2.00 mm — the C content is less than or equal to 0.105 mass% and the carbon equivalent of CEV (IIW) is less than or equal to 0.64%, the final thickness is from 2.00 to 3.00 mm — the C content is less than or equal to 0.115 wt.% and the carbon equivalent of CEV (IIW) is less than or equal to 0.66%. 24. The method according to p. 22 or 23, characterized in that the chemical composition of multi-phase steel is chosen depending on the desired final thickness, as follows: the final thickness is from 0.50 to 1.00 mm - the content of Mn is from 1,900 to 2,200 wt.%, the final thickness is from 1.00 to 2.00 mm inclusive: the content of Mn is from 2.050 to 2.250 wt.%, the final thickness is from 2.00 to 3.00 mm inclusive: the content of Mn is from 2,100 to 2,350 wt.%. 25. The method according to any one of paragraphs. 17-19, characterized in that with continuous annealing, the oxidation potential during annealing with the configuration of the installation consisting of the area of direct fire (NOF) and radial tube furnace (RTF), increases when the CO content of NOF is less than 4% by volume, This RTF partial pressure of oxygen in the furnace atmosphere with a decrease for iron set in accordance with the following equation: -18> Log pO ₂ ≥ -5 * Si ^-0.3 - 2.2 * Mn ^-0.45 -0.1 * Cr ^-0.4 -12.5 * (- ln B) ^0.25 , Si, Mn, Cr and B mean the corresponding alloying proportions in steel in wt.%, and pO ₂ means oxygen partial pressure in mbar, and to avoid oxidation of the strip, immediately before immersion in the melting bath, the dew point of the gas atmosphere is set to -30 ° C or lower. 26. A method according to any one of claims. 17-19, characterized in that when annealing only with a radial tube furnace, the partial pressure of oxygen in the furnace atmosphere satisfies the following equation: -12> Log pO ₂ ≥ -5 * Si ^-0.25 - 3 * Mn ^-0.5 -0.1 * Cr ^-0.5 -7 * (- ln V) ^0.5 , Si, Mn, Cr and B mean the corresponding alloying proportions in steel in wt.%, and pO ₂ means oxygen partial pressure in mbar, and to avoid oxidation of the strip, immediately before immersion in the melting bath, the dew point of the gas atmosphere is set to -30 ° C or lower. 27. The method according to p. 25 or 26, characterized in that in the case of strips of different thickness with continuous annealing, comparable conditions of the microstructure and the characteristic mechanical values of the bands are set by adapting the speed of the installation during heat treatment. 28. The method according to p. 25 or 26, characterized in that the steel strip is subjected to training after annealing or hot dip coating procedure. 29. A method according to any one of claims. 17-19, characterized in that the steel strip is subjected to stretching-bending-straightening after annealing or hot dip coating procedure. 30. A method according to any one of claims. 17-19, characterized in that the workpiece is cut out from the steel strip and then heated to a temperature above Ac ₃ , the heated workpiece is deformed to create a component, and then strengthened in the tool or in air. 31. The method according to any one of paragraphs. 17-19, characterized in that the steel strip is part of a sub-peritectic chain of grades, while vanadium is lowered as an alloying element. 32. Steel strip produced by the method according to any one of paragraphs. 17-19, having a minimum distribution of the hole in accordance with ISO 16630 20%, in particular 25%. 33. The steel strip in accordance with claim 32, having a minimum bend angle in accordance with VDA 238-100 in 70 ° in the longitudinal direction or in the transverse direction, in particular 85 °. 34. The steel strip according to claim 32, having a minimum value of Rm x α (tensile strength x bending angle in accordance with VDA 238-100) is 100000 MPa, in particular 120000 MPa. 35. The steel strip of claim 32, having a crack-free, pending state for at least 6 months, satisfying the requirements of SEP 1970 for tensile and compression test specimens.

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