RU2417273C2 - Steel material of high corrosion resistance produced by hot-dip galvanising - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: steel material produced by hot-dip galvanising has layer of alloyed coating containing Zn at amount of 35 wt % or more and Mg at amount from 1 to 60 wt %. Also, the layer of alloyed coating contains a non-equilibrium phase, thermal capacity of which measured by differential scanning calorimetry at rate of temperature growth 0,5°C/sec is equal to 1 J/g or more. Additionally, 5 vol % or more, mainly 50 vol % or more, of the said layer correspond to an amorphous phase. The layer of alloyed coating also can contain, in wt %, Al from 0.07 to 59% and one or more elements, chosen from Cr, Mn, Fe, Co, Ni and Cu in summary amount from 0.1 to 10% and one or more elements out of La from 0.1 to 10%, Ce from 0.1 to 10%, Ca from 0.1 to 10%, Sn from 0.1 to 10%, P from 0.005 to 2% and Si from 0.02 to 7%.

EFFECT: production of steel material of high corrosion resistance of both proper layer of coating and metal iron protected with applied layer and of high processability not associated with fracture caused by formation of inter-metallic compounds of added elements.

23 cl, 2 dwg, 5 tbl, 2 ex

Description

FIELD OF THE INVENTION

The present invention relates to a surface-treated steel sheet with high corrosion resistance, and more particularly, to a steel material obtained by hot dip galvanizing.

State of the art

Galvanized steel is used in a wide range of areas, such as automobiles, household electrical appliances, building materials, etc., but in order to ensure long-term anticorrosive effect, electroplating is usually used at high applied weight. The reason for this is that galvanization (galvanization) by itself slows down the corrosion in the steel material. At the same time, zinc, whose corrosion potential is low, protects the steel material in those places where metallic iron is bare, the anticorrosion effect due to this is achieved due to the consumption of zinc and, therefore, the greater the amount of zinc per unit surface, the longer it takes the effect will persist. It has recently been discovered that zinc corrosion products themselves also have the effect of inhibiting the corrosion of the coating layer and metallic iron. This effect is also associated with the absolute amount of zinc, which is why it is also desirable in this case to have a greater amount of zinc. On the other hand, if the amount of zinc deposited becomes large, there is a tendency to deteriorate workability, weldability and other characteristics that are required of the steel material. In cases where it is possible, to obtain a high resistance to corrosion, it is desirable to use a smaller amount of the applied coating.

In order to impart sufficient corrosion resistance with less coating, many attempts have been made to increase the corrosion resistance by galvanizing by adding alloying elements. In practice, Zn-Ni-doped coatings, Zn-Fe-doped coatings and the like are widely used mainly for automotive steel sheets, while Zn-Al-doped coatings are widely used mainly for building materials. In particular, to further increase the corrosion resistance, coating layers with Mg or Si additives have been developed.

However, if the addition of alloying components is used to increase the corrosion resistance of the coating layer, then, depending on the combination of the type of alloying components and the corrosion environment, the coating layer is sometimes finally passivated. As mentioned above, for the corrosion resistance of a galvanized steel material, both the low corrosion rate of the coating layer itself and the tread protection function due to the dissolution of the coating layer protecting uncoated metallic iron are important. If the coating layer is passivated, while the corrosion rate of the coating layer itself becomes extremely small, the tread protection function is finally lost and even, on the contrary, a phenomenon arises when the corrosion of uncoated metallic iron is, in the end, intensified.

To date, there are few documents in the patent literature on a method for obtaining opposite functions of increasing the corrosion resistance of the coating layer itself and providing tread protection of metallic iron without coating.

For example, Japanese Patent Publication (A) No. 6-248424 discloses an idea related to a Zn-Mg doped coating, which consists in creating a gradient in the distribution of the concentration of alloying components over the thickness of the coating layer in order to ensure high corrosion resistance in the surface layer and tread protection near metallic iron. Such an idea could be excellent if it could be implemented in an inexpensive way, but it requires the creation of a gradient of components along the thickness of the coating layer, vapor deposition coating, or other relatively expensive and difficult to reproduce methods. The use of higher-performance hot dip coating to create a gradient of components across the thickness of the alloyed coating layer is very difficult. Coating with gradient components by alloying with metallic iron, for example hot dip plating, is possible, but by alloying with metallic iron, it is mainly possible to adjust the ratio of the Fe element and other coating components, resulting in corrosion resistance that can be achieved , consists in a set of coating components, mainly containing Fe, and in this case it is impossible to hope for a sufficiently high resistance to corrosion.

Further, Japanese Patent Publication (A) No. 6-346254 discloses a method for using a multilayer coating structure consisting of a base metal coated with Zn by vapor deposition and additionally coated with Cr vapor deposition to reduce the corrosion rate of Zn and maintain the tread protection for a long time. In this case, we are also talking about a method of coating by vapor deposition.

Japanese Patent Publication (A) No. 2001-234361 discloses a non-galvanizing method for depositing a multi-layer Ni-Au coating that reduces corrosion of the underlying Ni layer due to the highly corrosion-resistant Au, by providing the underlying Ni layer of Ni with a precious metal layer below and a base Ni layer above and using the tread protection function of the upper base Ni layer to improve overall corrosion resistance. The application of this idea for hot dip galvanizing will again require a multilayer structure, due to which a large increase in production costs cannot be avoided.

Both technologies disclosed in Japanese Patent Publication (A) No. 6-346254 and Japanese Patent Publication (A) No. 2001-234361 represent ideas for separating the functions of corrosion resistance and tread protection by using multilayer coatings having layered structures. About the technology disclosed in Japanese Patent Publication (A) No. 6-248424, it can be said that it represents a similar idea consisting in separating two opposite functions between the upper part of the layer and the lower part of the layer. In other words, to date, the only idea is to separate two opposing functions between several layers.

Along with this, one of the problems that occurs when increasing the corrosion resistance of the coating layer by adding alloying components is the disadvantage that the alloyed coating, as a rule, is characterized by poor machinability. In particular, the greater the number of types of added elements, for example, the third or fourth elements, the easier it will form intermetallic compounds causing poor plasticity or supersaturated solutions, etc. and the greater the likelihood of poor machinability.

Further, the elements of the components added to improve corrosion resistance also form intermetallic compounds of different compositions or cause precipitation from the matrix of intermetallic compounds of different compositions into the matrix. Under these conditions, a pair of intermetallic compounds of different compositions or a pair consisting of a matrix and an intermetallic compound form electrochemical elements of corrosion, which ultimately in some cases intensify corrosion.

Considering the negative effect of the formation of these intermetallic compounds, it can be assumed that if it were possible to make the metal structure of the doped coating amorphous, then no intermetallic compounds would form. In this way, it would be possible to eliminate the negative effects and it would be possible to obtain a steel sheet with an alloyed coating having high corrosion resistance and excellent machinability.

However, usually upon receipt of an amorphous metal, a big problem arises, namely, that the cooling rate, which is required for the formation of an amorphous structure, is extremely high.

For example, Japanese Patent Publication (A) No. 2005-126795 discloses a method for forming an amorphous coating comprising flame spraying a metal powder with Mg and Zn onto a base material at a cooling rate of 100,000 ° C./sec or higher.

To obtain a conventional amorphous alloy during its solidification from a melt state, a high cooling rate is required. In conventional hot dip coating, when the cooling rate during cure from the molten state is 100 ° C / sec or lower, formation of an amorphous structure during coating is not possible. For the method of production by flame spraying, mass production of a homogeneous material at a low cost is difficult.

Japanese Patent Publication (A) No. 2005-60805 discloses a film-shaped alloy containing an amorphous phase formed by manufacturing alloy particles containing a system of Fe, Co and an Ni-based alloy, which may include zinc up to 20% as a selectively added element , and having an amorphous phase in an amount of 50 vol.% or more. This method of producing amorphous alloy particles and forming a film on a substrate has drawbacks similar to the disadvantages of flame spraying, and therefore there can be no question that this method is suitable for low-cost mass production.

As for the cooling rate, in recent years, alloy compositions that can be obtained in an amorphous state even at a low cooling rate have been discovered and energetically investigated. An alloy of this kind, if cured at a low cooling rate, can be made amorphous even if the alloy has a relatively large volume due to the low cooling rate. Therefore, such an alloy is called "bulk amorphous." If the cooling rate required for the formation of an amorphous structure becomes sufficiently low and that the amorphous alloy can be formed at a cooling rate that could be obtained using the traditional hot dip coating method or lower, then the possibility of applying an amorphous coating by hot dipping.

However, to date, the only published examples of alloy systems forming bulk amorphous structures are based on Zr, Mg, Fe, Pd, Co, Ca, and other limited elements. There are no examples of Zn-based alloys.

There are several examples with Zn as an element selectively added to some bulk amorphous structure based on other elements. In particular, Japanese Patent Publication (A) No. 2006-2252 discloses a bulk amorphous Mg-based alloy containing Zn as a selective element in an amount of up to 30 atomic%, and Japanese Patent Publication (A) No. 2004-149914 discloses a bulk amorphous Zr / Hf-based alloy containing Zn as a selective element in an amount of up to 30 atomic%.

However, there is not a single example of a bulk amorphous alloy containing, as its main component, Zn, which is necessary for corrosion resistance of a steel sheet coated by hot dip. In addition, there are no examples of a combination of elements essential to achieve the required technical characteristics and the possibility of producing a steel sheet with a hot dip coating. Thus, there are no published examples of patents devoted to a steel sheet with an amorphous coating based on Zn, deposited by hot dip.

Disclosure of invention

The objective of the present invention is to provide a steel material with high corrosion resistance, obtained by hot dip galvanizing by immersion, which results in both higher corrosion resistance of the coating layer and the protection property of metallic iron by the applied layer, as well as machinability, which is not accompanied by destruction due to the formation of intermetallic compounds of added elements.

The inventors of the present invention investigated the increased corrosion resistance of a steel material produced by hot dip galvanizing by immersion, and studied methods for achieving increased corrosion resistance of both the coating layer by elements added to the coating layer and the protection property by which metallic iron is protected. and found that in a specific component system, when the cooling rate during curing is to a certain extent high, coating should be achieved with both of the above properties achieved. In addition, the authors conducted experiments, changing the chemical components and cooling for curing, and investigated the physical properties of the coatings related to solving the problem, as a result, they established that it is possible to realize both increased corrosion resistance of the coating layer itself and the property of protection of metal iron, supporting part of the nonequilibrium phase in the coating.

Further, the inventors of the present invention conducted various studies regarding a method for suppressing deterioration in machinability and corrosion resistance, caused by intermetallic compounds due to elements added to a coated steel material obtained by hot dip galvanizing by immersion, and found a solution to the problem by making amorphous coating layer. In addition, the authors studied systems of chemical components that improve the ability to form an amorphous structure, which contains mainly Zn and does not contain elements that have a negative effect on corrosion resistance and workability, only by adding elements effective in terms of corrosion resistance, or elements not exhibiting negative effects, and it was found that it is possible to obtain steel material with high corrosion resistance by hot dip galvanizing I, having made only a few improvements in the traditional hot dip coating method.

The present invention was made on the basis of the above studies, and its essence is as follows:

(1) Steel material with high corrosion resistance, obtained by hot dip galvanizing by immersion method, characterized in that it has a doped coating layer containing Zn in an amount of 35 wt.% Or more, and that said alloyed coating layer contains a nonequilibrium phase whose heat capacity, measured using differential scanning calorimetry, is 1 J / g or more.

(2) Steel material with high corrosion resistance, obtained by hot dip galvanizing by immersion method, characterized in that it has a doped coating layer containing Zn in an amount of 35 wt.% Or more, and that said alloyed coating layer contains a nonequilibrium phase whose heat capacity, measured using differential scanning calorimetry with a temperature rise rate of 0.5 ° C / sec, is 1 J / g or more.

(3) A steel material with high corrosion resistance obtained by hot dip galvanizing according to any one of (1) or (2), in which the Zn content is 40 wt.% Or more.

(4) A steel material with high corrosion resistance obtained by hot dip galvanizing according to any one of (1) to (3), wherein said alloyed coating layer contains, in wt.%: Mg: 1 to 60% and Al: from 0.07 to 59%.

(5) A steel material with high corrosion resistance obtained by hot dip galvanizing according to (4), wherein said alloyed coating layer contains, in wt.%: Zn: 40% or more, Mg: from 1 to 45% and Al: from 0.07 to 59%.

(6) A steel material with high corrosion resistance obtained by hot dip galvanizing according to any one of (4) or (5), in which the Mg and Al contents in said alloyed coating layer satisfy the ratios expressed by formulas 1-5 below :

,

,

where the name of the element% denotes the content of the element in wt.%.

(7) Steel material with high corrosion resistance, obtained by hot dip galvanizing according to any one of (1) to (6), further comprising, as components in said alloyed coating layer, one or more elements selected from Cr, Mn , Fe, Co, Ni and Cu in a total amount of from 0.1 to 10 wt.%.

(8) A steel material with high corrosion resistance obtained by hot dip galvanizing according to any one of (1) to (7), further comprising one or more elements selected from Bi, Mo, W, and said alloyed coating layer Y in a total amount of from 0.1 to 10 wt.%.

(9) Steel material with high corrosion resistance, obtained by hot dip galvanizing according to any one of (1) to (8), additionally containing in the specified alloyed coating layer, in wt.%, One or more of La: from 0 , 1 to 10%, Ce: from 0.1 to 10%, Ca: from 0.1 to 10%, Sn: from 0.1 to 10%, P: from 0.005 to 2% and Si: from 0.02 up to 7%.

(10) A steel material with high corrosion resistance obtained by hot dip galvanizing by immersion according to (1) or (2), wherein said alloyed coating layer contains an amorphous phase in an amount of 5 vol.% Or more.

(11) A steel material with high corrosion resistance obtained by hot dip galvanizing according to (10), wherein said alloyed coating layer contains Al and Mg, and the contents of Zn, Al and Mg satisfy the ratios expressed by the following formulas 6- 8:

,

,

where the name of the element% denotes the content in wt.% of this element.

(12) A steel material with high corrosion resistance obtained by hot dip galvanizing according to (10) or (11), wherein said alloyed coating layer contains, in wt.%, One or more of Ca, Y and La in a total amount of from 0.1 to 10 wt.%.

(13) A steel material with high corrosion resistance obtained by hot dip galvanizing according to any one of (10) to (12), wherein the Al content in said alloyed coating layer is 14 wt.% Or less.

(14) A steel material with high corrosion resistance obtained by hot dip galvanizing according to (1) or (2), characterized in that 50 vol.% Or more of said alloyed coating layer is an amorphous phase.

(15) Steel material with high corrosion resistance obtained by hot dip galvanizing according to (14), wherein said alloyed coating layer contains, in wt.%, Zn: from 35 to 60%, Mg: from 25 to 60 %, Ca: from 1 to 10% and Al: from 0.07 to 25%, the rest are inevitable impurities.

(16) Steel material with high corrosion resistance, obtained by hot dip galvanizing by immersion method, characterized in that it has a doped coating layer containing Zn in an amount of 40 wt.% Or more, and in that 50 vol.% Or more of said the doped coating layer is an amorphous phase.

(17) Steel material with high corrosion resistance obtained by hot dip galvanizing according to (16), wherein said alloyed coating layer contains, in wt.%, Mg: from 1 to 55%, Ca: from 1 to 45 % and Al: from 0.07 to 45% with a total Mg and Ca content of at least 5%, and the rest are inevitable impurities.

(18) A steel material with high corrosion resistance obtained by hot dip galvanizing by immersion according to (16), wherein said alloyed coating layer contains, in wt.%, Mg: from 1 to 25%, Ca: from 1 to 10 % and Al: from 0.07 to 25% with a total Mg and Ca content of 5% or more, and the rest are inevitable impurities.

(19) A steel material with high corrosion resistance obtained by hot dip galvanizing according to (16), wherein said alloyed coating layer contains, in wt.%, Zn: from 40 to 60%, Mg: from 34 to 55 %, Ca: from 1 to 10% and Al: from 0.07 to 25%, and the rest are inevitable impurities.

(20) A steel material with high corrosion resistance obtained by hot dip galvanizing according to any one of (14) to (19), further comprising, as components in said alloyed coating layer, one or more elements selected from Cr, Mn, Fe, Co, Ni and Cu in a total amount of from 0.1 to 10 wt.%.

(21) Steel material with high corrosion resistance, obtained by hot dip galvanizing according to any one of (14) to (20), further comprising, as components in said alloyed coating layer, one or more elements selected from Bi, Mo, W, Si, Ti, V, Ag and Y in a total amount of from 0.1 to 10 wt.%.

(22) A steel material with high corrosion resistance obtained by hot dip galvanizing according to any one of (14) to (21), further comprising, as components in said alloyed coating layer, in wt.% One or more elements selected from La: from 0.1 to 10%, Sn: from 0.1 to 10% and P: from 0.005 to 2% ..

(23) A steel material with high corrosion resistance obtained by hot dip galvanizing according to any one of (1) to (22), comprising said alloyed coating layer on a part of the surface of the steel material.

Brief Description of the Drawings

Figure 1 is a view showing the area for calculating the peak of differential scanning calorimetry and heat capacity due to the nonequilibrium phase.

Figure 2 is a view illustrating the compositional limits of paragraph 5 for the case of a three-component Zn-Mg-Al system.

The implementation of the invention

Further, the present invention is described in detail.

The inventors of the present invention have found that both the increased corrosion resistance of the coating layer itself and the protection property protecting metal iron in the coating are determined by the nonequilibrium phase in the coating. In particular, it was found that the higher the degree of nonequilibrium and the greater the proportion of the nonequilibrium phase, the better the property of the tread protection that protects metallic iron, while maintaining high corrosion resistance of the coating layer due to alloying components. In addition, it was found that the contribution of the nonequilibrium phase to the property of tread protection can be analyzed by the total heat capacity of the exothermic peak, which is correlated with the nonequilibrium phase of the deposited alloy that appears in the spectrum of differential scanning calorimetry (DSC) with increasing coating temperature.

The presence of a nonequilibrium phase is determined by measuring the exothermic reaction when the temperature is measured by the DSC method to a melting point or lower. The nonequilibrium phase is a metastable phase; therefore, it is in a state with a higher energy compared to a more stable equilibrium phase. During the transition to the equilibrium phase, the difference in energy between the equilibrium phase and the nonequilibrium phase disappears as heat is released. On the other hand, the transformation phase from the low-temperature equilibrium phase to the high-temperature equilibrium phase, melting, or other phenomena are defined in DSC as endothermic reactions. However, the oxidation reaction, like the conversion from the nonequilibrium phase to the equilibrium phase, becomes a heat-generating reaction, and therefore, in order to prevent the oxidation reaction during measurement, it is necessary to raise the temperature of the inert gas atmosphere. Further, if thermographic analysis (TGA) is carried out simultaneously or in parallel with DSC and it turns out that the mass does not change at the temperature at which the exothermic reaction of DSC proceeds, the latter can be identified as heat generation due to the nonequilibrium phase, and if there is an increase in mass, the exothermic the reaction can be identified as heat generation due to the oxidation reaction. If there is a decrease in mass and there is the possibility of oxidative decomposition, then in the presence of an alloy in the framework of the present invention, no oxidative decomposition reaction occurs.

With the same amount of nonequilibrium phase, the higher the degree of nonequilibrium, the higher the heat capacity. With the same nonequilibrium phase, the higher the volume% of the nonequilibrium phase in the entire material, the higher the heat capacity. For this reason, both heat capacity are expressed as heat capacity according to the DSC method when the temperature rises.

The exothermic reaction is measured by DSC measurement on an exothermic peak. By integrating the peak area, the heat capacity can be quantified.

Let us explain in more detail the calculation method. We denote the amount of heat measured by DSC per unit mass per unit time as WO (t) (in units of W / g). t stands for time (in seconds). Having only a graph for temperature T (in ° C) and WO (t), it is possible to convert t = T / V using the rate of temperature rise V during the measurement (in ° C / s). Estimating the amount of heat WBG (t), which forms the background from the rectilinear part before and after the exothermic peak, and integrating WO (t) -WBG (t) in the region including the exothermic peak, the heat capacity ΔН (in J / g) can be calculated from the exothermic peak . The specified calculation is expressed by the numerical formula (formula 9):

However, the DSC peak in the method for determining the nonequilibrium phase according to the present invention, as the only peak, is a peak for half the value from 30 ° C. or lower in temperature units and the half measurement value of 60 seconds or less in time units when measured with DSC at 0, 5 ° C / sec or less for 60 sec or less. Depending on the measuring equipment and the state of the sample, sometimes the DSC value changes with a very small roughness of the background level. If you use this as a peak and integrate it for a long time or in a wide temperature range, sometimes a large heat capacity is obtained as a result of the calculation. In this case, the apparent heat capacity, calculated over a wide range of integration, differs from the heat generated by the nonequilibrium phase, which is the essence of the present invention. Therefore, such heat capacity is excluded.

Further, when there are several exothermic peaks with half values from 30 ° C or lower, the sum of the integrated values is used as the heat capacity. When an amorphous layer, etc., is formed during crystallization, sometimes peaks corresponding to the structural relaxation of the amorphous phase, crystal nucleation, crystal grain growth, etc. are separated. As for the compositional peak, the total compositional peak is integrated. In the composite peak, the total half-value sometimes exceeds 30 ° C in units of temperature, but in the case when the composite peak becomes larger in width when the peaks are combined with the initial small half-values, the centers of the individual peaks separate to a certain extent from each other, as a result of which in the composite At the peak there is a series of inflection points, and at the edges there is a series of peaks in the form of tubercles. In quantitative terms, on the curve of the graph of the dependence of the magnitude of the change in the value of the DSC for 60 seconds per time or temperature, i.e. on the curve, the DSC values differentiated by time, changes in the DSC by two or more time points in the compositional peak at the noise level are recognizable. In contrast, with changes in the background level having a slight unevenness, only curve changes are observed within the noise level.

Further, when the exothermic peak is determined once by melting or, as a rule, by the phase transformation between the equilibrium phases, the exothermic peak, determined in the overlying temperature range, is a signal related to a phenomenon that is clearly not related to the nonequilibrium phase according to the present invention, and therefore it was not used for calculation according to the present invention.

Figure 1 schematically shows a graph of DSC data and part for calculating heat capacity. In this figure, 1 indicates the exothermic peak due to the nonequilibrium phase, 2 indicates the area for determining the specific heat from the exothermic peak due to the nonequilibrium phase, and 3 indicates the endothermic peak of the melting point.

This calculation can be done automatically using DSC instruments recently available on the market and supplied with computers, for example EXTAR 6000 series, manufactured by SII NanoTechnology Inc. etc., only by defining the boundaries around the data region, including the calculated peak.

More specifically, the inventors have found in a coating containing a nonequilibrium phase with a heat capacity of 1 J / g or more, as determined by DSC at a temperature rise rate of 0.5 ° C / sec, that a satisfactory property of tread corrosion prevention can be obtained while maintaining increased corrosion resistance the coating layer itself, i.e. both properties can be achieved simultaneously. The corrosion resistance of the coating layer itself is almost completely independent of heat capacity (heat capacity by the DSC method), the reason for which is the nonequilibrium phase, but the tread protection property is enhanced due to the heat capacity by the DSC method, as a result of which a coating with a heat capacity of 2 J / g or more is preferred.

Even in a commercially available coated steel sheet in which the alloy coating includes two or more types of components, the coating includes a small amount of nonequilibrium phase. For example, a steel sheet with a coating containing 55 wt.% Al-Zn-1.5 wt.% Si includes immediately dissolved components in a state of supersaturation, after which it is possible to talk about the type of coating with a nonequilibrium phase, but the degree of nonequilibrium in terms of heat capacity by the DSC method, the level is 0.1 J / g or less. In addition, among the commercial hot dip galvanized steel sheets that the inventors were able to acquire, even with a coating comprising a certain amount of nonequilibrium phase, the degree of nonequilibrium in terms of heat capacity by the DSC method was at most about 0.1 J / g. There was not a single coating obtained by hot dipping with a degree of nonequilibrium close to 1 J / g.

In the absence of the possibility of increasing the disequilibrium, to increase the cooling rate, it is necessary to increase the production rate, improve the quality of the grains of the coating layer, heat treatment to improve the properties of the base of the steel sheet, etc. The required cooling rate is increased at the most to about 10 ² ° C / sec. With a set of components of a conventional hot dip coating, it is apparently not possible to produce a coating with a sufficiently high nonequilibrium.

The reason why the coating, including the nonequilibrium phase, has the property of tread protection, has not yet been clarified, but this property is thermally unstable in the nonequilibrium phase compared to the equilibrium phase. Similarly, this applies to electrochemical dissolution, which is also facilitated in comparison with dissolution in the equilibrium phase. For this reason, even if the alloy components exhibit passive high corrosion resistance, a slight dissolution partially occurs in the nonequilibrium phase. There is the possibility that a sufficiently low corrosion potential for tread protection can be maintained without significantly increasing the overall corrosion rate. However, in order to find out the exact mechanism of the phenomenon, further detailed investigation is needed.

Note that for the DSC measurement, the coating layer deposited on the steel material is mechanically removed, resulting in a sample. In the process, pieces of metallic iron removed from the steel material can be removed using a magnet. It should be taken into account that during processing it is possible to release heat in the sample, this heat can cause a change from the nonequilibrium phase to the equilibrium phase, and therefore caution must be exercised. More specifically, with continuous grinding and when using a face mill, etc. it is preferable to simultaneously cool the sample with kerosene or some other non-aqueous solvent that does not chemically interact with the coating metal. In the event that the coating layer is manually removed with a knife, chisel, etc., the heat generated does not affect the state of the alloy, and cooling is not required in this case.

In the case of a coating layer, which includes a large amount of nonequilibrium phase, if the Zn concentration is lower than 35 wt.%, The effect of suppressing the corrosion of the coating layer or metallic iron by zinc corrosion products becomes extremely small, as a result of which, from the point of view of overall corrosion resistance, it is necessary that the concentration of Zn was 35 wt.% or higher. Moreover, if the concentration of Zn is lower than 40 wt.%, In order to provide a sufficient property of tread protection, Zn alone becomes insufficient, and therefore it is more preferable that the concentration of Zn is 40 wt.% Or higher.

Further, Mg and Al are preferred as alloy elements added to obtain a coating layer with high corrosion resistance. Both Mg and Al increase the corrosion resistance of the Zn-based alloy coating layer itself and stabilize the Zn-based corrosion product, which has a high ability to protect underlying steel sheet even after corrosion of the coating layer, i.e. basic zinc chloride, which contributes to an additional increase in corrosion resistance. The addition of Mg also has an effect on the formation of a nonequilibrium phase.

When the Mg content is less than 1 wt.%, Its effect on the formation of a nonequilibrium phase is insufficient. If it exceeds 60 wt.%, Mg becomes too active and the corrosion resistance of the coating layer itself, on the contrary, deteriorates. In addition, when the magnesium content is less than 60 wt.%, If the amount of Mg exceeds 45 wt.%, The effect of increasing the corrosion resistance does not correspond to the increase in the added amount. Magnesium-related dross tends to increase. From the point of view of maintenance of the electrolytic bath and the like, 45 wt.% Or less are more preferable.

Al is added for reasons of adhesion of the coating layer. If its content is less than 0.07 wt.%, The effect is small and therefore it is preferable to add it in an amount of 0.07 wt.% Or more. Corrosion resistance of the coating layer itself increases with increasing Al content, but a content of more than 59 wt.% Leads to an imbalance between Zn and Mg, and therefore it is undesirable. 45 wt.% Or less are more preferred, which provides a tread protection property even with a small nonequilibrium phase, whereby such a concentration is preferable.

In order to produce a coating with a sufficiently high content of nonequilibrium phase, the necessary cooling rate should be changed depending on the alloy components. On the contrary, if it were possible to use an extremely high cooling rate, it would be possible to obtain a layer of an alloyed coating of the steel material of the present invention, without paying much attention to the selection of alloy components.

From the point of view of the hot dip coating manufacturing process, a coating composition is preferred that forms a nonequilibrium phase with as slow cooling as possible. Even in the case of immersion in water or the installation of a gas cooling device using supercooled gas, it is preferable that a nonequilibrium phase can form at a cooling rate below 10 ⁴ ° C / sec. From the point of view of device stability and economy, it would be more preferable if the formation of this phase would be possible at a cooling rate of 10 ³ ° C / s or lower and, most preferably, at a cooling rate of 10 ² ° C / s or lower. In the latter case, production would be possible without a significant change in the production process.

On the other hand, an increase in the choice of coating components would be facilitated by an increase in the cooling rate of the process. It would be desirable for the process to provide a cooling rate of 10 ² ° C./sec or higher. More desirable is a process providing a cooling rate of 10 ³ ° C / s or higher. It would be even more desirable if it were possible to obtain a cooling rate of 10 ⁴ ° C / sec or higher.

However, in reality, the cooling rate to which the coating layer is exposed during curing varies not only depending on the cooling method, but also on the thickness of the cooled steel material or the thickness of the coating.

In other words, in general, the cooling of the coating removes heat from the outer surface, resulting in the closer to the surface, the higher the cooling rate. It follows that the cooling rate of the coating layer differs from the average cooling rate of the steel material. For this reason, even if the doped coating layers having the same ability to form a nonequilibrium phase are cooled using the same cooling method, the proportion of the nonequilibrium phase in the doped coating layer varies depending on the thickness of the coating. In other words, the closer to the surface layer, the higher the cooling rate and, accordingly, the easier the formation of a nonequilibrium phase. Even in the case of a thick coating, the fraction of the surface layer is relatively small and, accordingly, the fraction of the nonequilibrium phase is also small.

In the coated steel material of the present invention, in which the formation of a nonequilibrium phase in the composition of the coating alloy is somewhat difficult, in order to obtain a nonequilibrium phase with a specific heat of 1 J / g or more using DSC, it is necessary to make the coating thickness extremely small with a conventional cooling method. On the other hand, with such a coating with an alloy composition in which the formation of a nonequilibrium phase occurs, it is somewhat difficult if, for example, cooling is carried out using an ultra-low temperature (-150 ° C) gas, using gas immediately after evaporation of liquid nitrogen, sometimes it is possible to obtain a nonequilibrium phase with a heat capacity of 1 J / g or more (according to the DSC method), even if the coating thickness is increased.

In the manufacture of the coated steel material of the present invention by hot dip coating to obtain an increased coating thickness, at least water cooling is required. Depending on the ingredients, special cooling may be required, such as immersion in liquid nitrogen, for example.

Given the above cooling rate and coating thickness for the production of coated steel material of the present invention using a cheaper method and a sufficient coating thickness, it is necessary to select an alloy with a special set of chemical components with which a nonequilibrium phase is easily formed. In particular, the authors of the present invention studied the Zn-Al-Mg system, which they defined as a highly corrosion-resistant coating, and as a result, it was found that with the following set of components it is possible to produce a steel sheet with a coating having a sufficient nonequilibrium phase using a relatively inexpensive method.

Alloy components must satisfy five ratios:

,

,

where the name of the element% denotes the content of the element in wt.%. A simple ternary Zn-Al-Mg component system is illustrated in FIG. The interior of the hatched polygon in FIG. 2 represents the applicable composition of the components. In Fig.2: 4 denotes the Zn line 94.3 wt.%, 5 Al line 0.08 wt.%, 6 Al line wt.% = 2 × Mg wt.%, 7 Al line wt.% = 1.24 × Mg wt.% - 12.32 and 8 denotes the region of the composition of claim 5 (in the case of the ternary system Zn-Al-Mg). The reason why the nonequilibrium phase is easily formed in the Zn-Al-Mg ternary system is not clear, but it is possible that the nonequilibrium phase is easily formed as a result of competition in the formation of a stable phase of a stable composition of intermetallic compounds and a eutectic composition in the intermediate region of the composition.

The alloyed coating layer of the coated steel material of the present invention may contain, as added elements, one or more elements selected from Cr, Mg, Fe, Co, Ni, and Cu, and in total amount from 0.1 to 10 wt.%. The addition of these elements mainly improves the adhesion of the coating to the steel material. If their content is less than 0.1 wt.%, The named effect is small, and if more than 10 wt.%, Then there is a tendency to increase the melting temperature of the electrolytic bath, which complicates the production.

Further, the layer may contain as added elements one or more elements selected from Bi, Mo, W, and Y, and in total components from 0.1 to 10 wt.%. The addition of these elements mainly improves the adhesion of the coating to the steel material, but also has the effect of easily forming a nonequilibrium phase. If their content is less than 0.1 wt.%, The effect is small, while if it is more than 10 wt.%, The melting temperature of the electrolytic bath rises too high, or too much scale is formed, which may make production difficult. In particular, Y additionally has the effect of improving corrosion resistance.

Further, the layer may also contain, as added elements, one or more of (mass%): La: from 0.1 to 10%, Ce: from 0.1 to 10%, Ca: from 0.1 to 10%, Sn: from 0.1 to 10%, P: from 0.005 to 2% and Si: from 0.02 to 7%. The addition of these elements allows to improve the ductility of the coating containing the nonequilibrium phase, and to improve workability, and also has the effect of the easy formation of the nonequilibrium phase. If the content of these documents is below the limits of added quantities, then the effect is small, while if it exceeds the upper limits, corrosion resistance tends to deteriorate.

The authors of the present invention carried out studies of coating samples comprising a nonequilibrium phase, and in the course of these studies found that even in the presence of nonequilibrium phases, there are coating samples that enhance the effect of the nonequilibrium phase depending on the content of a typical nonequilibrium phase, i.e. amorphous phase. In other words, the inventors have found that even in the case of a coating containing a nonequilibrium phase of the present invention, an exceptional effect of improving the tread protection in the coating samples with a proportion of amorphous volume of 5% or more compared with the tread protection with a fraction of amorphous volume of less than 5% is exhibited. . Typically, if the tread protection property is improved, the corrosion rate of the irreversibly dissolving coating is increased compared to the case in which the tread protection is absent. The non-equilibrium phase steel material of the present invention is characterized by an improved tread protection property, which is maintained while improving the corrosion resistance of the coating, however, if the metallic iron is not closed and irreversibly corrodes, there is a slight increase in the corrosion rate compared to the corrosion state of one coating in the absence metallic iron without coating. Such an increase in the corrosion rate due to tread protection is additionally inhibited if the amorphous phase is 5% or more compared with the case when the amorphous phase is only less than 5%.

Even in coatings with a 5% amorphous phase or more, in particular, if the contents of Zn, Al and Mg are within the limits satisfying the ratios below (formulas 6-8), the effect of suppressing an increase in the corrosion rate of the coating with tread protection is large:

,

,

where the name of the element% denotes the content in wt.% of this element.

Creating an Al concentration of 14 wt.% Or lower leads to better tread protection and is therefore preferred.

Further, in coating samples having an amorphous volume fraction of 5% or more, as a result of the inclusion of one or more elements of Ca, Y and La in the total amount of 0.1 to 10 wt.%, An effect of improving the tread protection effect itself occurs . With the addition of 0.1 wt.% Or less, this effect is not clear, while when it exceeds 10 wt.%, Scale forms, the melting point rises, etc. and therefore, production efficiency is deteriorating.

The authors of the present invention, in addition, undertook a separate study, studying the improvement of the corrosion resistance of galvanized steel materials, and in the process found that when adding alloy components to the deposited layer in order to improve the corrosion resistance of Zn, the added alloy components form intermetallic compounds that cause deterioration machinability and corrosion resistance of the applied layer. Even if there are no intermetallic compounds and if the crystalline phase dopes the coating, the formation of a solute in a state of supersaturation leads to a deterioration in workability. As a result, the authors of the present invention came to the conclusion that it is necessary to make the coating layer amorphous in order to eliminate all the harmful effects caused by intermetallic compounds or dissolved substances in a state of supersaturation. The inventors have found that if you include Zn in an amount of 35 wt.% Or more and form a coating with an amorphous structure in a volume fraction of 50% or more, corrosion resistance and workability are significantly improved compared to a traditional coating with intermetallic compounds and dissolved substances in oversaturation state. An amorphous structure is one of the types of a typical nonequilibrium phase and, as a result, an amorphous coating is one of the types of coating with a nonequilibrium phase.

It should be noted that, usually, the heat capacity by the DSC method is proportional to the volume fraction of the amorphous structure, but depending on the combination of elements, some change occurs even with the same volume fractions of amorphous phases. However, in a series of experiments conducted by the inventors of the present invention, a coating containing an amorphous phase in a volume fraction of 5% or more always has a DSC heat capacity of 1 J / g or more.

If the Zn content is less than 35 wt.%, The effect of suppressing the corrosion of steel material by zinc corrosion products cannot be obtained. If the Zn content is less than 40 wt.%, The tread protection required for the coated steel material in some cases becomes insufficient or the corrosion resistance of the coating itself becomes insufficient, and therefore Zn is contained in an amount of 40 wt.% Or more. More preferably, the concentration of Zn is 50 wt.% Or higher. If the volume fraction of the amorphous structure is less than 50%, deterioration of machinability due to the crystalline phase or a negative effect on corrosion resistance due to the electrochemical conjugation of crystalline phases can hardly be eliminated. The larger the volume fraction of the amorphous structure, the better. If it is equal to 90% or more, the negative effect of the crystalline phase is almost absent, which is thus particularly preferred.

An amorphous alloyed coating containing from 0.07 to 45 wt.% Al as an alloy component forms an Al-Fe alloy or an Al-Fe-X-based alloy at the interface with metallic iron, thereby providing a minimum degree of adhesion of the coating, such as a hot dip coating, and forms a relatively stable oxide film on the surface layer of the electrolytic bath, providing a formation of scale, whereby such a coating is preferred. If the Al content is less than 0.07 wt.%, The appearance of the effect is too unlikely. Al tends to a certain extent to inhibit the ability to form an amorphous structure in a Zn-based alloy. If it is included in an amount of more than 45 wt.%, Then the ability to form an amorphous structure, which could be realized in the process of coating by hot immersion, cannot be obtained, as a result of which the upper limit is set to 45 wt.%. More preferred 25 wt.% Or less.

Mg improves the ability to form an amorphous structure of a Zn-based alloy and contributes to corrosion resistance, so inclusion of 1 to 55 wt.% Mg is preferred. If the Mg content is less than 1 wt.%, This effect is unlikely, but if it exceeds 55 wt.%, The coating becomes too active and the corrosion resistance tends to deteriorate. When it comes to corrosion resistance, it is preferable to choose 25 wt.% Or less. At 25 wt.% Or less, the formation of scale is better suppressed, and performance is also improved.

On the other hand, when it comes to improving the ability to form an amorphous structure, the Mg content is preferably chosen from 25 to 60 wt.%. In particular, at this Mg content, when the Zn content is selected from 35 to 60 wt.%, And Ca from 1 to 10 wt.%, The ability to form an amorphous structure is high, production is possible even at a low cooling rate, and sufficient volumetric Amorphous content even with a large amount of coating applied. With this set of components and the choice of Mg content from 34 to 55 wt.%, Zn from 40 to 60 wt.% And Ca from 1 to 10 wt.%, The ability to form an amorphous structure is high and the production ability improves, which makes these conditions preferable.

Ca also improves the ability to form an amorphous structure of the Zn-based alloy and contributes to corrosion resistance, therefore it is preferable to include it in an amount of from 1 to 45 wt.%. If its content is less than 1 wt.%, The indicated effect is unlikely. When exceeding 45 wt.% The coating becomes too active and there is a tendency to decrease the resistance to corrosion. From the point of view of corrosion resistance, a choice of 10 wt.% Or less is preferred.

Further, it is preferable to ensure the inclusion of Mg and Ca in a total amount of 5 wt.% Or more in order to ensure a minimum ability to form an amorphous structure in the manufacture of coatings by hot dipping. The total amount of Mg and Ca added is, from the point of view of the ability to form an amorphous structure, mainly to a certain extent large, but both of these elements are active, which is why, from the point of view of resistance to corrosion, their total amount is 60 wt.% Or less. Even more preferably, the total amount of 35 wt.% Or less.

It is possible to include as added elements one or more elements selected from Cr, Mn, Fe, Co, Ni and Cu in a total amount of from 0.1 to 10 wt.%. The addition of these elements mainly improves the adhesion of the coating to the steel material. If their amount is less than 0.1 wt.%, This effect is unlikely, while if it exceeds 10 wt.%, The melting temperature of the electrolytic bath rises too high, and production can become difficult.

It is possible to include as added elements one or more elements selected from Bi, Mo, W, Si, Ti, V and Ag in a total amount of from 0.1 to 10 wt.%. These elements have combined effects of improving the ability to form an amorphous structure and improving the adhesion of the coating to the steel material. If their amount is less than 0.1 wt.%, The effect is unlikely, while if it exceeds 10 wt.%, The melting temperature of the electrolytic bath rises too high and production can become difficult.

It is also possible to include as added elements one or more of La: from 0.1 to 10 wt.%, Sn: from 0.1 to 10 wt.% And P: from 0.005 to 2 wt.%. The addition of these elements can improve the ductility of the amorphous phase and further improve workability and, in addition, have an effect on improving the ability to form an amorphous structure. If the number of elements is less than the lower limits of the quantities of added elements, the effect is unlikely, while if it exceeds the upper limits, there is a tendency to deteriorate corrosion resistance.

It should be noted that a highly corrosion-resistant steel material produced by hot dip galvanizing by immersion may have the above alloyed coating layer on the surface of steel material sections that require high corrosion resistance. However, it is not necessary to apply a layer over the entire surface of the steel material.

Steel material with high corrosion resistance obtained by hot dip galvanizing can be used as a base steel material with a surface treated using paint. In this case, it is possible to suppress the development of corrosion bubbles in the event of damage to metallic iron after staining. Due to this property of small cracks in the coating layer even after machining, the corrosion resistance after painting the machined part is improved.

The steel material used as the substrate is not particularly limited. Aluminum deoxidized steel, ultra low carbon steel, high carbon steel, various high strength steels, Ni-Cr-containing steels, etc. may be used. Steelmaking methods, steel strength, hot rolling method, etching method, cold rolling method and other preliminary methods for processing steel material are not particularly limited.

As for the coating production method, the present technology can be applied to all types of hot dip coating methods, regardless of whether it is a Sendzimir method, an in-line method, a preliminary coating method, or some other manufacturing method. However, even within the steel material of the present invention and depending on the ingredients, in some cases there is a need to choose a cooling method or coating thickness according to the cooling rate required during the solidification process of the coating alloy.

In the steel material of the present invention, in order to obtain an amorphous structure with a volume fraction of 50% or more in a coating with an alloy composition having a rather low ability to form an amorphous structure, the coating thickness should be made small. The reason for this is that with the conventional cooling method closer to the surface, the cooling rate is higher, as a result of which a smaller thickness means a greater proportion of amorphousness. On the other hand, even in the case of an alloy with a composition having a rather low ability to form an amorphous structure, for example, when using gas with an extremely low temperature, -150 ° C, using gas directly after evaporation of liquid nitrogen for cooling, or using cooling by fog, even if the coating is thicker, an amorphous structure with a volume fraction of 50% or more is obtained.

In the production of the steel material of the present invention by hot dip coating, with an increase in coating thickness, in some cases, special cooling is required such as immersion in liquid nitrogen. In an alternative case, when the workability is not significant, using an alloy containing a large amount of Hf or Zr in order to improve the ability to form an amorphous structure, it is possible to apply a hot dip coating with a volume fraction of amorphousness not exceeding the scope of the present invention, at a cooling rate of the order of the speed of conventional water cooling or even air cooling depending on the combination of components. Hf and Zr typically include in the range of 2 to 35 wt.% In total. If their amount is less than 2 wt.%, The effect of improving the ability to form an amorphous structure is negligible, while when you turn on more than 35 wt.%, In the same way as in the case of Ca, the effect of activity in the coating layer becomes too large, and increases the likelihood of deterioration in corrosion resistance in the coating layer.

The volume fraction of the amorphous structure can be measured by making an incision along the cross section of the coated steel material, polishing it and etching it, after which the surface coating layer is observed using an optical microscope (hereinafter abbreviated as “optical microscope”). In the part that has become amorphous, no texture is observed during etching, but in the rest of the crystalline phase a texture is observed due to grain boundaries, subgrain boundaries, precipitation, etc. For this reason, regions that have become amorphous parts and crystalline parts are clearly distinguishable, so it is possible to translate them into volume fractions using the linear segment method or image analysis. When the texture is too small and the measurement using opt. the microscope becomes difficult, a thin sample is made from the cross section of the coating layer and examined using a transmission electron microscope, making measurements in a similar way. In the case of a transmission electron microscope in an unobserved region of the texture, a halo pattern of the electron diffractogram can be used to confirm the amorphous structure. In the case when, using wholesale. microscope over the entire surface, the texture is not observed or in the case where there are parts on which the texture is not observed and the question arises that they are large unstressed grains, it is preferable to obtain a thin sample for an electron microscope and confirm the amorphous phase by the absence of diffraction spots in diffractogram of the electron beam and from the observation of the halo pattern. When using as wholesale. microscope, and electron microscope, it is preferable to find the ratio of the areas using computer image processing in 10 or more different fields, get the average value of the ratio of the areas and use it as a volume fraction.

Example 1

Each surface-treated steel material shown in Table 1 and Table 2 (continuation of Table 1) is prepared using 0.8 mm thick cold-rolled steel sheet, 10 mm equal-shelf angular steel and 10 cm side length, or hot-rolled steel as the base materials. 10 mm thick sheet.

The cold-rolled steel sheet is cut into 10 cm × 10 cm pieces, then coated using a batch type hot dip coating apparatus Resca Co., Ltd. The temperature of the electrolytic bath is standardized by the melting temperature of the electrolytic composition plus 50 ° C, depending on the composition of the electrolytic bath. The weight of the coating is adjusted by blowing air, after which the material is cooled, using nitrogen gas cooling at 25 ° С, depending on the need, fog cooling at 25 ° С, or, in order to control the cooling rate, it is cooled with low-temperature nitrogen gas at - 150 ° C.

Equal-flanged angular steel is cut longitudinally into pieces 10 cm long, and a hot-rolled steel sheet is cut into 10 cm × 10 cm squares. Each sample is coated by hot dipping using the Euler method using a crucible furnace. The sample is then cooled, using, depending on the need, cooling with water or cooling with liquid nitrogen. A test sample is used for each of the following evaluation tests.

By the ease of formation of a nonequilibrium phase, a coated steel material forming a nonequilibrium phase with a specific heat by the DSC method of 1 J / g or more is estimated as the “necessary cooling rate” by the cooling method and coating, in which the specific heat is achieved by the DSC method.

In the case of a cold-rolled steel sheet, a sample forming a nonequilibrium phase with a DSC heat capacity of 1 to 2 J / g using a combination of a cooling method (for 25 g / m ² or less using nitrogen gas cooling, for 35 g / m ² or less using cooling with fog or 60 g / m ² or less using cooling of ultra-low-temperature gaseous nitrogen using gas generated by the evaporation of liquid nitrogen) and the coating thickness is estimated as “good (X) required cooling rate”, and the sample, the image which has a nonequilibrium phase with a DSC heat capacity greater than 2 J / g under the same conditions or with a DSC heat capacity of 1 J / g or more with a coating thickness of the same conditions or more, is estimated as “very good (OX) required cooling rate” . On the other hand, a sample with a DSC heat capacity of less than 1 J / g is estimated to be “poor (P) required cooling rate”.

Hot-rolled steel sheet and equal-angle angular steel made using hot dip coating are difficult to control the thickness of the coating, therefore, all steel materials with a coating forming a nonequilibrium phase with a specific heat of 1 J / g or more are evaluated as “OX required speed cooling. " On the other hand, a steel material with a coating with a heat capacity by the DSC method of less than 1 J / g is estimated as "P is the required cooling rate."

The thickness of each of the coatings is measured by weight reduction as a result of acid dissolution of the coating layer. The components of the alloy in the coating are determined by analyzing the coating dissolving acid solution using Induced Plasma Spectroscopy (ICP).

To analyze the nonequilibrium phase, the coating layer, including metallic iron, is subjected to machine grinding, the contained metallic iron is removed using a magnet, after which the ground powder is used to measure the DSC curve from normal temperature to melting temperature at a temperature rise rate of 0.5 ° C / sec and calculate the heat capacity by the area of the exothermic peak.

In a corrosion test, the property of tread protection and the corrosion resistance of the coating layer itself are simultaneously evaluated during tread protection by manufacturing a sample with an uncoated part of metallic iron and evaluating both the formation of rust on the uncoated part of metallic iron and the coating loss in a cyclic corrosion test ( CTK) with repeated drying and humidification cycles.

A rectangle of 50 mm × 70 mm is made from the surface of the evaluated sample. The remaining parts are closed with a tape seal. The rectangular part 1 mm × 50 mm in the center of the surface is drilled 0.5 mm deep into the surface using a face mill to open metallic iron. Face drilling is carried out while cooling the workpiece. Particular attention is paid to the fact that the nonequilibrium phase in the coating layer around the treated part does not turn into the equilibrium phase.

The following CCC conditions were used: [salt spraying: 35 ° С, 5 g / l of an aqueous NaCl solution, 2 hours] → [drying: 50 ° С, 20-30% relative humidity, 4 hours] → [moistening: 50 ° С, 95% relative humidity, 2 hours] (the interval between operations is 30 minutes, including processing). 8 hours of treatment in such conditions are 1 cycle. The test included 21 cycles.

After the CTK, the presence of rust is first confirmed on the part of unclosed metallic iron in the center of the evaluated surface. A sample that does not exhibit rust formation on an uncoated portion of metallic iron is rated as having a tread protection property with a rating of “X”, a sample that exhibits rust formation with a rust degree of 5% or less based on the area of the uncoated portion is evaluated at “U” (satisfactory) and a sample in which rust is formed on the surface of more than 5% is evaluated at “P”. Further, the corrosion products from each sample, after evaluating the formation of rust, are removed by etching, and the mass change after testing is used to measure the corrosion loss of the coating layer. A sample with a corrosion loss of less than 2 g / m ^{2 is} evaluated as “OX”, with a loss of 2 to 5 g / m ^{2 it is} evaluated as “X”, and with a loss of 5 g / m ² or more as “P”.

For part of steel materials with a coating and the tread protection property “X” for corrosion testing, a rectangular part of 3 mm × 50 mm is drilled in the center of the estimated area into the depths of 0.5 mm using a face mill to expose metallic iron. The sample is used as a "test sample with activated tread protection." This “test pattern with activated tread protection” is used for the same CTK as above. After the CTK, the formation of rust on the uncovered part of metallic iron in the center of the surface being evaluated is first confirmed. A sample that does not exhibit rust formation on an uncoated portion of metallic iron is rated as having OXOX protective property, while a sample that exhibits rust formation with a rust degree of 5% or less, based on the area of the uncoated portion, rated as "OX". Even a sample in which rust forms in an area of more than 5% is rated “X” because the initial rating is “X”.

Further, for “test specimens with activated tread protection”, the corrosion products from each specimen, after evaluating the formation of rust, are also removed by etching, and the mass change after testing is used to measure the corrosion loss of the coating layer. By designating the corrosion loss of a 1 mm × 50 mm non-coated metallic iron sample as CR1 and the corrosion loss of a “tread-activated test specimen” as CR2, the CR2 value divided by CR1 (CR2 / CR1) is defined as the ability to suppress corrosion acceleration due to tread protection. A CR2 / CR1 value of 1.05 or less is evaluated as “OX”, and a value above 1.15 is evaluated as “Y”. Initially, lower tread protection is outside the scope of the assessment.

Coating adhesion is evaluated for cold-rolled steel sheet when bending a test sample coated 180 ° C with the applied layer to the outside and then conducting the so-called 0T bending adhesion test, after which the coating layer is removed from the bent portion using adhesive tape. A sample in which the coating does not peel off is evaluated as “OX”, a sample in which the coating is removed, but there are no pieces of coating with a maximum length of more than 0.1 mm per 10 mm around the bent part and with five or less removed pieces of coating with a maximum length 0.1 mm or less is rated “X”, and a sample with one or more removed pieces of coating larger than 0.1 mm or more than six removed pieces of coating of 0.1 mm or less is rated “P”.

To evaluate the coating of equal-angle angular steel, the coating layer is subjected to peeling test using adhesive tape without bending and an assessment is carried out in a similar manner. In other words, a sample in which the coating does not peel off is evaluated as “OX”, a sample in which the coating does not peel, but there are no removed pieces of coating with a maximum length of more than 0.1 mm in a square section of 10 mm × 10 mm and with five or less removed pieces of coating with a maximum length of 0.1 mm or less is rated “X”, and a sample with one or more removed pieces of coating larger than 0.1 mm or more with six removed pieces of coating 0.1 mm or less is evaluated like "P". For cases of cold-rolled steel sheet and equal-angle steel or hot-rolled steel sheet, direct comparison is not possible, but a relative comparison of these types of steel is possible.

The workability of the coating layer is evaluated by the diameter of the maximum inscribed circle at the place of the coating where no cracks are observed in the coating layer in the 180 ° bending test. When using the thickness of the sheet T as the unit of diameter of the inscribed circle, the specimen with the diameter of the maximum inscribed circle without cracks is 0T, i.e. without visible cracks, even in the bending adhesion test, it is evaluated as “OX”, a sample with a maximum inscribed circle diameter without cracks 1T-3T is rated as “X” and a sample with 4T or higher is rated as “P”. Equal-flanged angular steel and hot-rolled steel sheet are not materials for which such an assessment is required, and therefore they were not rated and designated as “-”.

Further, part of the types of steel with sufficient tread protection in table 1 and table 2 (continuation of table 1), in particular, samples No. 1-10, 29, 47-51 and 54, were measured for the volume fraction of amorphous content in the coating layer. The volume fraction of the amorphous structure in the coating layer was determined by obtaining two thin samples for a transmission electron microscope for each of the positions, dividing the thickness of the coating layer of the test sample by five equal parts, measuring the ratio of the areas of the amorphous region of each field using computer analysis and obtaining the average value of the ratio of the areas of amorphous regions of all fields as the volume fraction of the amorphous structure.

Table 3 shows the volume fraction of amorphous in the coating layer, the effect of tread protection in harsh conditions using a “test sample with activated tread protection” (property of accelerated tread protection) and the suppression of the acceleration of corrosion during tread protection (CR2 / CR1).

As follows from table 1 and table 2 (continuation of table 1), the steel material of the present invention is the best in corrosion resistance and retains high enough characteristics with respect to coating adhesion, workability, scale formation, etc. In particular, the steel material of the present invention, containing Mg in an amount of from 1 to 55 wt.% And Al in an amount of from 0.07 to 45 wt.%, Is better in terms of corrosion resistance. Of these, the steel material of the present invention with an amount of Zn-Al-Mg within the limits indicated in FIG. 2 requires only a small cooling rate for its production, as a result of which even fog cooling could be used as cooling for its production. In addition, a material containing one or more elements selected from Cr, Mn, Fe, Co, Ni, and Cu proved to be particularly improved in adhesion, while a material containing one or more elements selected from La, Ce, Ca , Sn and P, proved to be particularly improved in machinability. Along with this, with 40 wt.% Or less Zn, in some cases, the tread corrosion prevention property becomes somewhat worse, but with a coating comprising Mg and Al, a sufficiently good tread corrosion prevention property is provided. A material containing Bi, Mo, W, and Y is simultaneously improved both in terms of adhesion and in terms of the required cooling rate.

A material that contains components in amounts that go beyond the steel material coated with the present invention or with a DSC heat capacity less than 1 J / g due to the nonequilibrium phase is not good enough in corrosion resistance or even if it is good in terms of resistance to corrosion of the coating layer itself, it is not good enough with respect to the tread protection property and has as a disadvantage rust 5% or more of the area of the uncovered part of the area of metallic iron.

As follows from table 3, the corrosion acceleration in the steel material of the present invention with a volume fraction of amorphous 5% or more is suppressed with tread protection compared to other types of steel. This effect becomes more pronounced within the content of the components defined in formulas 6-8. In addition, a steel material of the present invention with 14 or less wt.% Al is better in terms of tread protection compared to other steel materials of the present invention.

Example 2

Each surface-treated steel material shown in Table 4 and Table 5 is prepared using cold-rolled steel sheet 0.8 mm thick, equal-angle steel 10 mm thick and 10 cm side length, or 10 mm hot-rolled steel sheet as the base materials.

The cold-rolled steel sheet is cut into 10 cm × 10 cm pieces, then coated using a batch type hot dip coating apparatus Resca Co., Ltd. The temperature of the electrolytic bath is standardized by the melting temperature of the electrolytic composition plus 50 ° C depending on the electrolytic composition. The coating weight is adjusted by blowing air, after which the material is cooled, using nitrogen gas cooling at 25 ° C, depending on the need, fog cooling at 25 ° C, or nitrogen gas is cooled at -150 ° C in order to control the cooling rate .

Equal-flanged angular steel is cut longitudinally into pieces 10 cm long, and a hot-rolled steel sheet is cut into 10 cm × 10 cm squares. Each sample is coated by hot dipping using the Euler method using a crucible furnace. The sample is then cooled, using, depending on the need, cooling with water or cooling with liquid nitrogen. A test sample is used for each of the following evaluation tests.

Regarding the necessary critical cooling rate, indicating the ability to form an amorphous structure, it should be noted that the amorphous structure is formed by a deposited layer of the surface of the steel material, and therefore this speed does not always correspond to the cooling rate in the mass of the steel material. For this reason, to evaluate the quality of take the method of cooling, coating and bulk. the proportion of amorphous at this point in time. The ability to form an amorphous structure depends very little on the composition of the alloy of the electrolytic bath. Depending on the cooling method, materials that require a reduction in application to 25 g / m ² or less when cooling with gaseous nitrogen, to 35 g / m ² or less when cooling by fog and to 60 g / m ² or less in case of ultra-low temperature cooling gaseous nitrogen when using the gas generated by the evaporation of liquid nitrogen to obtain a volume fraction of amorphous content of 50% or more, are evaluated as “X”. Materials for which a volume fraction of amorphous content of 50% is not achieved even under the indicated conditions are evaluated as “P”. Moreover, from materials with a high ability to form an amorphous structure with a grade of "X", materials that can increase the coating to less than 30 g / m ² when cooled by gaseous nitrogen, to less than 45 g / m ² when cooled by fog and up to 80 g / m ² when cooled by ultra-low-temperature gaseous nitrogen when using the gas generated by the evaporation of liquid nitrogen to obtain a volume fraction of amorphous content of not less than 50%, are evaluated as "OX", while materials giving a volume fraction of amorphous content of 50% or more in conditions 30 if more g / m ² under cooling with nitrogen gas, 45 or more g / m ² while cooling with mist and 80 or more g / m ² under cooling ultralow nitrogen gas by using the gas generated by evaporation of liquid nitrogen are reported as "Ohoho"

The state of the scale in the process of coating production is a visual observation. A material with a large scale and difficulty in coating is rated “P”, a material with a relatively large amount of scale and possible coating is rated “Y”, a material with a small amount of scale, ease of coating and relatively good coating surface properties is rated as “OX” ".

Coating is measured by weight loss resulting from acid dissolution of the coating layer. The components of the alloy in the coating are determined by analyzing the coating dissolving acid solution using Induced Plasma Spectroscopy (ICP).

The volume fraction of the amorphous structure of the coating layer is determined by obtaining two thin samples for a transmission electron microscope for each of the positions, dividing the thickness of the coating layer of the test sample into five equal parts, measuring the ratio of the areas of the amorphous region of each field using image analysis using a computer and obtaining the average the value of the ratio of the areas of amorphous regions of all fields as the volume fraction of the amorphous structure.

The corrosion test was carried out based on the salt spray test (SST) described in JIS-Z-2371. For the assessment, corrosion losses were used after testing using salt water with a concentration of 10 g / l for 3000 hours. Material with losses of less than 2 g / m ² is rated as “OX”, with 2-5 g / m ² as “X”, with 5-10 g / m ² as “Y” and with more than 10 g / m ² as “ P".

Coating adhesion is evaluated for cold-rolled steel sheet when bending a test sample coated 180 ° C with the applied layer to the outside and then conducting the so-called 0T bending adhesion test, after which the coating layer is removed from the bent portion using adhesive tape. A sample in which the coating does not peel off is rated “OX”, a sample in which the coating peels off, but there are no pieces of coating with a maximum length of more than 0.1 mm per 10 mm around the bent part and with five or less exfoliated pieces of coating with a maximum length 0.1 mm or less is evaluated as “X”, and, likewise, a sample with 6-10 removed pieces of coating larger than 0.1 mm or less than 10 removed pieces of larger than 0.1 mm or less is rated as “Y ", And a sample with one or more pieces of p removed zmerom more than 0.1 mm, or more than 10 decoating pieces of 0.1 mm or less is evaluated as "P".

To assess the adhesion of the coating of equal-angle angular steel, the coating layer is subjected to peeling test using adhesive tape without bending and the assessment is carried out in a similar manner. In other words, a sample in which the coating does not peel off is evaluated as “OX”, a sample in which the coating does not peel, but there are no pieces with a maximum length of more than 0.1 mm in a square section of 10 mm × 10 mm and with five or less pieces with with a maximum length of 0.1 mm or less, is rated as “X”, and, likewise, a sample with 6-10 removed pieces larger than 0.1 mm or more than six pieces of 0.1 mm or less is rated as “Y” and a sample with one or more pieces larger than 0.1 mm or more than 10 pieces in size om 0.1 mm or less is evaluated as "Y". For cases of cold-rolled steel sheet and equal-angle steel or hot-rolled steel sheet, direct comparison is not possible, but a relative comparison of these types of steel is possible.

The machinability of the coating layer is evaluated by the diameter of the maximum inscribed circle, at that place of the coating where no cracks are observed in the coating layer in the 180 ° bending test. When using the thickness of the sheet T as the unit of diameter of the inscribed circle, the specimen with the diameter of the maximum inscribed circle without cracks is 0T, i.e. without visible cracks, even in the bend adhesion test, it is evaluated as “OX”, a sample with a maximum inscribed circle diameter without cracks IT is evaluated as “X”, a sample with a maximum inscribed circle diameter from 2T to 3R is evaluated as “Y” and a sample with 4T or higher is rated “P”. Equal-flanged angular steel and hot-rolled steel sheet are not materials for which such an assessment is required, and therefore they were not rated and designated as “-”.

As follows from table 4 and table 5 (continuation of table 4), the steel material of the present invention is the best in corrosion resistance and retains high enough characteristics with regard to coating adhesion, workability, scale formation, etc. In particular, the steel material of the present invention, containing Mg in an amount of from 1 to 55 wt.% And Al in an amount of from 0.07 to 45 wt.%, Is better with respect to coating adhesion and workability. Of these materials, containing from 1 to 25 wt.% Mg, from 1 to 10 wt.% Ca and from 0.07 to 25 wt.% Al, it is better in terms of corrosion resistance. Alternatively, a material in which the concentration of Mg is in the range from 25 to 60 wt.%, In particular from 34 to 55 wt.%, And containing Ca in an amount of from 1 to 20 wt.% And Al in an amount of from 0.07 up to 25 wt.%, showed corrosion resistance close to the corrosion resistance of the steel materials of the present invention, but in particular this material proved to be able to form an amorphous structure, which proves the possibility of producing a coated steel material with a high degree of deposition, which has good technical har performance when using an inexpensive cooling device. In addition, a material containing one or more elements selected from Cr, Mn, Fe, Co, Ni, and Cu has been found to be particularly improved in terms of adhesion, while a material containing one or more elements selected from La, Sn and P proved to be particularly improved in terms of machinability. In addition, a material containing one or more elements selected from Bi, Mo, W, Si, Ti, V, Ag, and Y has been improved both in terms of adhesion and in its ability to form an amorphous structure.

A comparative steel material containing components in amounts that went beyond the content of the components of the steel material coated with the coating of the present invention or with a low volume fraction of amorphism was unsatisfactory with respect to corrosion resistance or, if it had good corrosion resistance, was characterized by poor machinability.

Hot galvanized steel material of the present invention obtained by hot dip galvanizing can be obtained using the traditional hot dip coating method. It has both high corrosion resistance and improved tread protection. In addition, a steel material having an amorphous phase of the present invention has excellent corrosion resistance and workability compared to a hot dip crystalline coating. It can be widely used for cars, buildings, residential buildings, etc. and prolongs the service life of parts and contributes to the efficient use of resources, reducing environmental stress and reducing the complexity and costs of maintenance while maintaining production capabilities similar to the existing level of technology.

Claims (23)

1. Steel material with high corrosion resistance, obtained using hot dip galvanizing by immersion, characterized in that it has a doped coating layer containing Zn in an amount of 35 wt.% Or more, and Mg in an amount of from 1 to 60 wt.%, wherein said doped coating layer contains a nonequilibrium phase, the heat capacity of which, measured by differential scanning calorimetry, is 1 J / g or more. 2. Steel material with high corrosion resistance, obtained using hot dip galvanizing by immersion, characterized in that it has a doped coating layer containing Zn in an amount of 35 wt.% Or more, and Mg in an amount of from 1 to 60 wt.%, wherein said doped coating layer contains a nonequilibrium phase, the heat capacity of which, measured using differential scanning calorimetry with a temperature rise rate of 0.5 ° C / s, is 1 J / g or more. 3. The steel material according to any one of claims 1 or 2, wherein said alloyed coating layer contains Zn in an amount of 40 wt.% Or more and Mg in an amount of from 1 to 60 wt.%. 4. The steel material according to claim 1 or 2, in which the specified layer of the alloyed coating contains from 0.07 to 59 wt.% Al. 5. The steel material according to claim 4, in which the specified layer of the alloyed coating contains, wt.%: Zn 40% or more, Mg from 1 to 45% and Al from 0.07 to 59%. 6. The steel material according to claim 4, in which the contents of Mg and Al in the specified alloyed coating layer satisfy the ratios expressed by the following formulas 1-5:

,
where the name of the element in% indicates the content of the element in wt.%. 7. The steel material according to claim 1 or 2, wherein said alloyed coating layer further comprises one or more elements selected from Cr, Mn, Fe, Co, Ni and Cu in a total amount of from 0.1 to 10 wt.%. 8. The steel material according to claim 1 or 2, wherein said alloyed coating layer further comprises one or more elements selected from Bi, Mo, W and Y in a total amount of from 0.1 to 10 wt.%. 9. The steel material according to claim 1 or 2, wherein said alloyed coating layer further comprises, wt.%: One or more of La from 0.1 to 10%, Ce from 0.1 to 10%, Ca from 0, 1 to 10%, Sn from 0.1 to 10%, P from 0.005 to 2% and Si from 0.02 to 7%. 10. The steel material according to claim 1 or 2, in which the specified layer of the alloyed coating contains an amorphous phase in an amount of 5 vol.% Or more. 11. The steel material of claim 10, in which the specified layer of the alloyed coating contains Al and Mg, and the content of Zn, Al and Mg satisfies the ratios expressed by the following formulas 6-8:

,
where the name of the element in% indicates the content in wt.% of this element. 12. The steel material of claim 10, in which the specified layer of the alloyed coating contains one or more of Ca, Y and La in a total amount of from 0.1 to 10 wt.%. 13. The steel material of claim 10, wherein said alloyed coating layer contains Al in an amount of 14 wt.% Or less. 14. The steel material according to claim 1 or 2, characterized in that 50 vol.% Or more of the specified layer of the alloyed coating is an amorphous phase. 15. The steel material according to 14, in which the specified layer of the alloyed coating contains, wt.%: Zn from 35 to 60%, Mg from 25 to 60%, Ca from 1 to 10% and Al from 0.07 to 25% The inevitable impurities are the rest. 16. Steel material with high corrosion resistance, obtained using hot dip galvanizing by immersion, characterized in that it has a doped coating layer containing Zn in an amount of 40 wt.% Or more, and Mg in an amount of from 1 to 55 wt.%, wherein 50 vol.% or more of the specified layer of the alloyed coating is an amorphous phase. 17. The steel material according to clause 16, in which the specified layer of the alloyed coating contains, wt.%: Ca from 1 to 45% and Al from 0.07 to 45% with a total Mg and Ca content of at least 5% and the rest are inevitable impurities . 18. The steel material according to clause 16, in which the specified layer of the alloyed coating contains, wt.%: Mg from 1 to 25%, Ca from 1 to 10% and Al from 0.07 to 25% with a total content of Mg and Ca 5 % or more and the rest are inevitable impurities. 19. The steel material according to clause 16, in which the specified layer of the alloyed coating contains, wt.%: Zn from 40 to 60%, Mg from 34 to 55%, Ca from 1 to 10% and Al from 0.07 to 25% and inevitable impurities are the rest. 20. The steel material according to clause 16, in which the specified layer of the alloyed coating additionally contains one or more elements selected from Cr, Mn, Fe, Co, Ni and Cu in a total amount of from 0.1 to 10 wt.%. 21. The steel material according to clause 16, in which the specified layer of the alloyed coating further comprises one or more elements selected from Bi, Mo, W, Si, Ti, V, Ag and Y in a total amount of from 0.1 to 10 wt. % 22. The steel material according to clause 16, in which the specified alloyed coating layer further comprises one or more elements selected from La from 0.1 to 10 wt.%, Sn from 0.1 to 10 wt.% And P from 0.005 to 2 wt.%. 23. The steel material according to any one of claims 1 and 2 or 16, wherein said alloyed coating layer is at least on a portion of the surface of the steel material.

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