KR20080110674A - Cold-working steel - Google Patents

Abstract

FIELD OF THE INVENTION The present invention relates to cold worked steels, wherein the cold worked steels are, by weight percent, 1.3-2.4 (C + N), at least C of 0.5, 0.1-1.5 Si, 0.1-1.5 Mn, 4.0-5.5 Cr , 1.5-3.6 (Mo + W / 2), W has a chemical composition of up to 0.5, 4.8-6.3 (V + Nb / 2), Nb up to 2, and up to 0.3 S, 10, on the one hand (C + N ) And on the other hand the content of (V + Nb / 2) is balanced against each other so that the content of these components is formed by the coordinates of A, B, C, D, A in the coordinate system of FIG. And the coordinates of [(C + N), (V + Nb / 2)] for this point are: A: [1.38, 4.8] 15 B: [1.78, 4.8] C: [2.32, 6.3] D [1.92, 6.3], characterized in that it substantially contains only iron and impurities in the specified content.

Description

Cold Work Steel {COLD-WORKING STEEL}

The present invention relates to cold worked steels, ie steels used for working under cold conditions of workpieces. Common examples of the use of such steels include tools for cutting and punching, thread cutting such as threading dies and thread taps, cold extrusion, pressing of powders, deep drawing, Cold forging. The present invention also relates to a method of producing steel and a method of pressing a powder or processing a metalworking material by means of a tool comprising the steel.

There is a great demand for high quality cold worked steels with such adequate hardness, good resistance to abrasion and high toughness / ductility in use. Satisfaction of these properties is important for optimal tool performance. VANADIS ^® 4 is a powder metallurgically manufactured cold worked steel that has a combination of toughness / ductility and resistance to wear for high performance tools that are manufactured and sold by the applicant and are recognized to be excellent. The nominal composition of this steel is, by weight percent, 1.5 C, 1.0 Si, 0.4 Mn, 8.0 Cr, 1.5 Mo, 4.0 V, the remaining iron and inevitable impurities. This steel is particularly suitable for applications where adhesive / abrasive wear or chipping is a major problem, i.e. for thick workpieces and for soft / tacky processing such as austenitic stainless steel, simple carbon steel, aluminum, copper, etc. It is appropriate for things like things. General examples of cold working tools in which steel can be used are mentioned in the introduction above. In general, VANADIS ^® 4, the object of Swedish patent 457,356, is characterized by excellent wear resistance, high compressive strength, good hardenability, good toughness, good dimensional stability against heat treatment and good resistance to tempering. It is important for high performance cold work steels.

Applicant manufactures and sells other powder metallurgically manufactured cold-worked steel VANADIS ^® 6, which is characterized by its excellent resistance to abrasion and relatively good toughness, whereby its abrasive wear is a major feature. It is appropriate in the use of phosphorus and in the use in which the manufacture takes place continuously. The nominal composition of this steel in weight percent is 2.1C, 1.0Si, 0.4Mn, 6.8 Cr, 1.5 Mo, 5.4 V, the rest of iron and inevitable impurities. The resistance to chipping, machinability and grinding are not as good as VANADIS ^® 4.

Subsequent to VANADIS ^® 4 mentioned above are marketed under the name VANADIS ^® 4 Extra and are characterized by greater toughness than VANADIS ^® 4, and other performance features in principle have the same field of use and compare with these materials Is maintained or improved. The steel has achieved enormous commercial success with subsequent chemical compositions of 1.38% C, 0.4% Si, 0.4% Mn, 4.7% Cr, 3.5% Mo and 3.7% V.

Many commercial steels are known and fall within the broad composition ranges detailed in US Pat. No. 4,249,945. Steels with a chemical composition of 2.45 C, 0.50 Mn, 0.90 Si, 5.25 Cr, 9.75 V, 1.30 Mo and 0.07 S are available on the market, and also the steels are 1.80 C, 0.50 Mn, 0.90 Si, 5.25 Cr, 1.30 Mo and It contains 9.00 V. The steel is manufactured and marketed in powder metallurgy for applications requiring excellent wear resistance and adequate toughness.

By virtue of their outstanding properties, the above-mentioned VANADIS ^® steels have obtained a leading market position among high performance cold worked steels. In addition, the aforementioned competitive steels have been successful in the same market. VANADIS ^® 4 Extra has proven to be particularly good.

Accordingly, the applicant of the present invention seeks to provide another high performance cold worked steel having a better property profile than the above mentioned steels. According to one aspect of the invention, the steel should have properties for improved use in general, especially in tubes with VANADIS ^® 6. According to another aspect, it is advantageous to provide a steel with good resistance to abrasion at the same level as VANADIS ^® 6 and VANADIS ^® 10 and with significantly improved toughness / ductility in relation to this steel. According to another aspect, the steel is characterized by good machinability and improved resistance to wear. According to another aspect of the present invention, it is an object to be able to provide steel with high hardness, preferably with good hardenability. The field of use of this lecture is in principle the same as for VANADIS ^® 4.

It is an object of the present invention to provide a steel that meets at least some of the above mentioned high demands for high performance cold worked steel. It is obtained by cold-worked steel having a chemical composition of up to% by weight, the composition of which is 1.3-2.4 (C + N), of which C is at least 0.5, 0.1-1.5 Si, 0.1-1.5 Mn, 4.0-5.5 Cr , 1.5-3.6 (Mo + W / 2), W up to 0.5, 4.8-6.3 (V + Nb / 2), Nb up to 2, and up to 0.3 S, on the one hand The content of (C + N) and on the other hand (V + Nb / 2) are balanced against each other. In the coordinate system of 11, it is in the area formed by the coordinates of A, B, C, D, A, and the coordinates of [(C + N), (V + Nb / 2)] for this point are A: [1.38 , 4.8], B: [1.78, 4.8], C: [2.32, 6.3], D: [1.92, 6.3], with the remainder being substantially only iron and containing impurities of normal content. Furthermore, a method for cutting, shearing, punching and / or forming at cold conditions of a metalworking material by means of a tool comprising a steel according to the invention, and a method of pressing metal powder by a tool comprising a steel according to the invention. It is an object of the present invention to provide a method for producing a steel according to the present invention.

The steel according to the invention is produced powder metallurgically, which is a prerequisite for the steel to be a high degree free from oxide inclusions. Preferably powder metallurgical production comprises gas atomization of the steel melt with nitrogen as an atomizing gas, whereby the steel alloy will obtain a minimum content of nitrogen. If desired, the steel powder can be nitrided into the solid phase, thereby further increasing the content of nitrogen in the steel. Consolidation then takes place by hot hydrostatic forming. This steel can be used in this condition or after forging / rolling to final dimensions.

Unless stated otherwise, the description of the present invention always refers to the volume percentage in terms of the structural components of the steel and the weight percentage in terms of the chemical composition of the steel. Unless stated otherwise, by name MX-carbide, M ₇ X ₃ -carbide or simple carbide is always intended to be carbide as well as nitride and / or carbide nitride. By M ₆ C-carbide it always means only carbide.

The following is true for the individual alloy materials and their interrelationships and for the structure and heat treatment of the steel.

Carbon, and suitably an amount of nitrogen, must be present in the steel in an amount, which is generally with vanadium and, where appropriate, with niobium in the hardened and tempered conditions of the steel from the austenitization temperature (TA) of 1050 ° C. Suitable and thereby form 8-13% by weight of MX-carbide, in which M is substantially vanadium and X is carbon and nitrogen, preferably predominantly carbon, of which at least 90% by volume of carbide is at most 2.5 μm, Preferably it has an equivalent diameter of at most 2.0 μm. Such MX-carbide contributes to imparting desirable wear resistance to the steel in a manner known to those of ordinary skill in the art, and this carbide also has a constant effect on providing finer particles and is also secondary Affects a certain amount of curing. By the applied heat treatment, i.e. by the choice of austenitization temperature and tempering temperature, the content of steel in the MX-carbide can vary within this range, thereby obtaining a microstructure suitable for this purpose, which is attached to It is described in more detail in the description of the figures and of the experiments performed. In addition to these MX-carbide, the steel should be essentially free from other primary precipitated carbides such as M ₇ X ₃ -and M ₆ C-carbide.

Preferably, the steel contains no more than about 0.12%, preferably up to about 0.10%, of nitrogen more than what is essentially and naturally formed by uptake from the added pre-processing material and / or from the surroundings. . In conceivable embodiments, the steel may contain more and deliberately added amounts of nitrogen, which nitrogen may be supplied by solid phase nitriding of the steel powder used in the manufacture of the steel. In this case at least half of the major part of (C + N) may be nitrogen, in which case M is predominantly vanadium carbide and wherein nitrogen is the main component together with vanadium or may be pure vanadium nitride Carbon is present only as dissolved in the matrix of the steel under substantially cured and tempered conditions.

Vanadium must be present in the steel with at least 4.8% or more but up to 6.3% content with carbon present and any nitrogen present, thereby increasing the total content of 8% to 13% by vol% under hardened and tempered conditions of use of the steel. To form the mentioned MX-carbide. In principle vanadium can be substituted by niobium but this requires twice the amount of niobium as compared to vanadium, which is therefore a disadvantage. In addition, niobium exhibits a more angular form of MX-carbide and is larger than pure vanadium carbide, whereby breakdown or chipping can be initiated and thus have the disadvantage of degrading the toughness of the material. Thus, niobium should not be present in an amount of greater than 2%, preferably at most 1% and suitably at most 0.1%. Most preferably, the steel does not contain any intentionally added niobium, and content exceeding the impurity content in the form of residual elements resulting from the pre-processing material involved in the manufacture of the steel is not allowed.

According to one aspect of the invention, the content of (C + N) on the one hand and the content of (V + Nb / 2) on the other hand are balanced with respect to each other so that the content of these components is shown in FIG. In the coordinate system, the coordinates of [(C + N), (V + Nb / 2)] in the area formed by the coordinates of A, B, C, D, and A are: A: [1.38, 4.8 ], B: [1.78, 4.8], C: [2.32, 6.3], D: [1.92, 6.3]. Within this range, steels with very advantageous property profiles can be provided. Suitable combinations of hardness, resistance to wear, ductility and machinability can be obtained by suitable heat treatment. Within the widest range of composition, the hardness and resistance to abrasion will increase the highest total content of (C + N) and (V + Nb / 2) in the steel, and the ductility at lower total content of these components Are benefited by

According to a more preferred embodiment, the content of these components is in the region formed by the coordinates of E, F, G, H, E in the coordinate system of FIG. 11 and [(C + N), (V) + Nb / 2)] coordinates are E: [1.48, 4.8], F: [1.68, 4.8], G: [2.22, 6.3] and H: [2.02, 6.3].

According to an even more preferred embodiment, the content of (C + N) on the one hand and the content of (V + Nb / 2) on the other hand are balanced against each other so that the content of these components is K in the coordinate system of FIG. In the region formed by the coordinates of L, M, N, and K, and the coordinates of [(C + N), (V + Nb / 2)] for this point are K: [1.62, 5.2], L: [1.82, 5.2], M: [2.05, 5.8], N: [1.85, 5.8].

According to another aspect of the invention, on the one hand the content of (C + N) and on the other hand the content of (V + Nb / 2) are balanced against each other such that the content of these components is 0.32 ≦ (C + N ) / (V + Nb / 2) ≤0.35 is satisfied.

According to another aspect of the invention, the content of (C + N) on the one hand and the content of (V + Nb / 2) on the other hand are balanced against each other so that the content of these components is determined by the coordinate system of FIG. In the region formed by the coordinates of A ', B', C ', D', A ', the coordinates of [(C + N), (V + Nb / 2)] for this point are A: [ 1.52, 5.2], B: [1.93, 5.2], C: [2.18, 5.9] and D: [1.77, 5.9].

In addition, carbon contributes to hardness by being present in the solid solution of the matrix of the steel in a hardened and tempered condition at an austenitic temperature (T _A ) of 980-1050 ° C. (T _A ).

Silicon is present as residual element from the production of the steel in a content of at least 0.1%, generally at least 0.2%. Silicon increases carbon activity in the steel and thus contributes to providing the appropriate hardness for the steel. Too high a content can lead to brittleness problems by solution hardening so that the maximum content of silicon in the steel is 1.5%, preferably at most 1.2%, suitably at most 0.9%. Advantageous content of Si for steel is 0.2-0.5 Si. This steel has a nominal content of 0.4% Si.

Manganese is added to the steel in a content of at least 0.1%, thereby binding the amount of sulfur that may be present in the steel by forming manganese sulfide. As well as manganese, chromium and molybdenum also contribute to providing adequate hardenability to the steel, which means that 0.1% can be tolerated without manganese content adversely affecting the steel properties. At high contents, manganese can cause undesirable stabilization of residual austenite, which leads to impaired hardness. In addition, residual austenite will make steel less dimensionally stable, which is a major drawback. Thus, the manganese content should not exceed 1.2% Mn and the advantageous manganese content for the steel is in the range of 0.1-0.9% Mn. The steel has a nominal content of 0.4% Mn.

As mentioned above, chromium contributes to the hardenability of the steel and for this reason should be present in a content of at least 4.0%, preferably at least 4.5%. In addition, chromium is a carbide forming component and is used in many steels to contribute to the steel's resistance to wear by the formation of M ₇ X ₃ -carbide. These carbides can be dissolved to varying degrees by selection of the appropriate austenitization temperature upon curing and in this way the chromium and carbon dissolved in the austenite are subsequently precipitated to varying degrees to form very small secondary precipitated carbides, which Precipitated carbides, along with tempering, will effectively contribute to providing the desired hardness to the steel.

The steel according to the invention shows, among other things, a very good resistance to abrasion, which must be able to harden to a relatively high hardness. This can be achieved at the same time that the steel is given superior, i.e. surprisingly good ductility, than other steels of applicants on the market for similar use. By limiting the content of chromium, the formation of M ₇ X ₃ -carbide could be avoided or at least minimized thanks to the formation of major precipitated MX-carbide. In order to obtain this advantageous carbide composition, the chromium content should be limited to a maximum of 5.5% and more preferably to a maximum of 5.1%. Advantageous chromium content in steel is 4.8%.

More than half the major parts of chromium added to the steel will dissolve in the steel thereby contributing to the hardenability of the steel. According to the idea of the present invention, the steel must have the necessary hardenability to change the dimension hardened all the time, and if steel is used in coarse dimensions, the hardenability is a particularly important aspect. Thus, molybdenum must be present in the steel in an amount of at least 1.5%. Without the risk of undesired precipitation of M ₆ C-carbide, the content of molybdenum can be allowed up to 3.6% Mo. Preferably, the steel comprises 1.5 to 2.6% Mo, more preferably 1.6 to 2.0% Mo.

Molybdenum can be replaced by tungsten to a certain degree, but this has the disadvantage of requiring twice the amount of tungsten as compared to molybdenum. It also makes dealing with the scalp more difficult. Therefore, tungsten should not be present in a content of at most 0.5%, preferably at most 0.3%, and more suitably in excess of at most 0.1%. Most preferably, the steel does not contain any deliberately added tungsten and, in the most preferred embodiment, it is not acceptable in content above the impurity level in the form of residual components resulting from the pre-processing materials involved in the production of the steel.

Sulfur is present mainly in steel as impurities at up to 0.03%. According to one embodiment, the steel can be designed to contain intentionally added sulfur in an amount of up to 0.3%, preferably up to 0.15%, in order to improve the machinability of the steel.

The nominal composition of the steel according to the invention is 1.77% C, 0.4% Si, 0.4% Mn, 4.8% Cr, 2.5% Mo, and 5.5% V, and the remainder is substantially iron.

The following compositions are examples of conceivable variants of steel within the scope of the present invention, which are 1.9% C, 0.4% Si, 0.4% Mn, 4.8% Cr, 3.5% Mo, 5.8% V, and the remainder is substantially iron.

The following composition is another example of the conceivable deformation of the steel, which is 1.67% C, 0.4% Si, 0.4% Mn, 4.8% Cr, 2.3% Mo, 5.2% V, and the remainder is substantially iron.

The following composition is another example of the conceivable deformation of the steel, which is 1.80% C, 0.4% Si, 0.4% Mn, 4.8% Cr, 1.8% Mo, 5.8% V, and the remainder is substantially iron.

The deformations have been optimized to obtain somewhat different property profiles, whereby steels with increased content of carbide former molybdenum and vanadium will have excellent resistance to wear at the expense of rather low ductility. Steels with a reduced content of these two components will have high ductility instead of rather low resistance to abrasion.

In the production of steel, the steel melt first consists of carbon, silicon, manganese, chromium, molybdenum, possibly tungsten, vanadium, possibly niobium, if possible sulfur above impurity content, inevitable nitrogen, remaining iron and It is first prepared containing the intended amount of impurities. Powder is made from this melt by nitrogen gas worization. The droplets formed in the gas atomization are quench cooled, whereby the formed vanadium carbide and / or mixed carbide of vanadium and niobium do not have time to grow and are very thin and their thickness is a fraction of micrometers. In the following, the droplets are markedly irregular in shape from the precipitated carbides in the zone of the residual melt in the dendrite network in small droplets which quickly strengthen before the droplets are strengthened to form powder grains. If the steel contains nitrogen in excess of an unavoidable impurity content, this is obtained by nitrification of the powder, as described, for example, in SE 462,837.

After sieving, if the powder to be nitrided is properly performed before nitriding, the powder is filled into a capsule and then air escaped and sealed and exposed to hot hydrostatic molding, HIP: ing, which is known to be hot and high pressure. Occurs in; 950-1200 ° C. and 90-150 MPa; It is generally about 1150 ° C. and 100 MPa, whereby the powder is fortified to form a completely dense body.

By HIP: ing, the carbide will have a more regular shape than it has in the powder. The predominant volume part is up to about 1.5 μm in size and rounded. The occasional particles are elongated and somewhat longer, up to about 2.5 μm. This variant is best suited by a combination of the destruction of very thin particles in powder and coalescence.

Steel can be used in HIP: ed conditions. Generally steel is hot worked after HIP: ing by forging and / or hot rolling. This is done at an initial temperature of 1050 to 1150 ° C., preferably about 1100 ° C. Here, additional coalescence and in particular rotational ellipsoid of the carbide occur. After forging and / or rolling, at least 90 vol% of the carbide has a size of at most 2.5 μm, preferably at most 2.0 μm.

In order to be able to machine the steel by the cutting tool, it must first be soft annealed. This occurs at temperatures below 950 ° C, preferably below about 900 ° C. When the tool is given the final form by cutting, it is cured and tempered. In austenitization, MX-carbide dissolves to some extent and thereby precipitates secondary in annealing. In addition to these MX-carbide steels should not contain any other carbides. In general, hardening can occur from significantly lower austenitization temperatures than typical for steels with a corresponding resistance to abrasion at 980 to 1150 ° C., preferably below 1100 ° C., thereby undesirably reducing MX-carbide. Avoid extensive dissolution. Suitable austenitization temperatures are 1000-1050 ° C. This is a decisive advantage for tool manufacturers because the steel can then be heat treated with major parts of other tool steels on the market. Under the hardened conditions of the steel, T _A 980-1050 ° C., the matrix comprises only the martensite containing 0.4-0.6% carbon in solid solution as an essential configuration.

Subsequent tempering may be carried out at a temperature of 200 to 600 ° C, preferably 500 to 560 ° C. The end result consists of 8-13 vol% of tempered martensite and of tempered martensite of MX-carbide, which is a general microstructure for the present invention, in which M is substantially vanadium and X is preferably the main carbon Carbon and nitrogen, wherein at least 90 vol% of the carbide has an equivalent diameter of up to 2.5 μm, preferably up to 2.0 μm. These carbides have a predominantly rounded or rounded shape but temporarily long carbides may be present. In this description, the equivalent diameter D _ekv is defined as D _ekv = 2√A / π, where A is the zone of carbide particles in the section studied. Generally at least 96 vol% of MX-carbide, _-nitride and / or carbide nitrides have D _ekv <3.0 μm. In general, the carbide also has some form of ellipse and no carbide with an actual length exceeding 3.0 μm in the observed section. After hardening and tempering, the steel has a hardness of 56-66HRC.

Other features and aspects of the present invention are apparent from the following description of the appended claims and the experiments performed.

1 shows the microstructure of a steel according to the invention after hardening and tempering.

2 shows the microstructure of a commercial comparative material after curing and tempering.

3 shows the microstructure of another commercial comparative material after curing and tempering.

4 is a graph showing the hardness of the steel according to the present invention, depending on the austenitization temperature.

5 is a graph showing the hardness of the steel according to the invention according to the tempering temperature and at different austenitization temperatures.

6 is a graph showing the number of comparative materials and the ductility of high temperature tempered steel according to the present invention.

7 is a graph showing the number of comparative materials and the machinability of the steel according to the invention.

8 is another graph showing the machinability of the steel according to the invention as well as the comparative material.

9 shows a combination of wear resistance and unnotched impact energy for the steel according to the invention as well as for the number of comparative materials.

10 shows the number of comparative materials as well as the rate of wear in the wear test of the steel according to the invention.

FIG. 11 shows a graph over the relationship between the content of carbon and any present nitrogen to the content of vanadium and any present niobium.

12 shows a graph over edge wear on top and half knives after a cutting test.

13a, b show the side of the upper knife after the cutting test.

Figures 14a, b show the front side of the upper knife after the cutting test.

Figures 15a, b show the front side of the lower knife after the cutting test.

The chemical compositions of the observed steels are given in Table 1. Sulfur shown for certain steels in this table is an impurity. Other impurities were not considered and do not exceed the standard impurity level. The balance is iron. In Table 1, steel 7 has a chemical composition according to the invention. Steel 1-5 is a reference substance.

Table 1-Chemical composition expressed in weight percent of the observed steel

River C Si Mn Cr Mo W V S One 2.45 0.50 0.90 5.25 1.30 9.75 0.07 2 1.5 1.0 0.4 8.0 1.5 4.0 3 1.38 0.4 0.4 4.7 3.5 3.7 4 2.1 1.0 0.4 6.8 1.5 5.4 5 2.9 1.0 0.5 8.0 1.5 9.8 7 1.9 0.4 0.4 4.8 3.5 5.8 0.02

Steels 1-5 are commercial steels, of which all but the steel no.1 are applicant's steels. Samples of these steel materials were ordered and analyzed according to chemical composition. All these steels were made from powder metallurgy and ordered in soft-annealed conditions. Six tons of melt were produced from steel no. 7 according to conventional molten metallurgical techniques. Metal powders were prepared from the melt by nitrogen gas atomization of the melt jet. Molded small droplets were quench cooled.

Two tons of blanks were produced from a powder of steel no. 7, which has a chemical composition according to Table 1. The steel powder is filled into a capsule of sheet metal, which is then sealed, deaerated, heated to about 1150 ° C., and then hot isostatic pressed (HIP) at a pressure of about 1150 ° C. and 100 MPa. )do. The initial carbide structure of this powder was destroyed in HIP: ing as the carbides coalesced. In the HIP: ed condition of the steel, the carbide obtained a more regular shape and approached the elliptic shape. These are still very small. The predominant portion over 90% by volume has an equivalent diameter of up to 2.5 μm, preferably up to about 2.0 μm.

The blank was then forged at a temperature of 1100 ° C. with round bars of 100 mm dimensions. Steel no. 7 was soft annealed at 900 ° C. and its microstructure was observed and hardness tests were performed. Carbide is essentially an elliptical MX-carbide, which is very small in terms of equivalent diameter and is still present in the material in the form of a size up to about 2.0 μm. After soft annealing, test samples were taken from steel no. 7 for subsequent irradiation. Test samples of the same type were taken from Reference Materials 1-5 which were ordered in soft annealed conditions.

The heat treatments along with the hardening and tempering of the various steels are shown in Table 2. The microstructures of the hardened and annealed conditions were examined for the three steels of reference steels no. 4 and 1 shown in FIGS. 2 and 3 and steel no. 7 according to the invention shown in FIG. 1, respectively. In FIG. 1 the steel according to the invention contains 11.7 vol% of MX-carbide in a matrix of tempered martensite. No carbides other than MX-carbide were detected. Carbide having an equivalent diameter of more than 3.0 μm could sometimes be found in the steel according to the invention under hardened and tempered conditions.

Reference steel no. 4 of FIG. 2 included a total of about 14.4 vol% of carbide under cured and tempered conditions, of which MC-carbide was about 9.2 vol% and M ₇ C ₃ -carbide was about 5.2 vol%. As is apparent from the figure, M ₇ C ₃ -carbide is relatively large and generally larger than MC-carbide, which mainly adversely affects ductility. Reference steel no. 1 in FIG. 3 comprises about 15.7 vol% of MC-carbide under hardened and tempered conditions. No other carbides were detected. The high content of carbide results in a relatively good resistance to wear but low ductility to steel.

The hardness after heat treatment as defined in Table 2 is given in Table 2. After high temperature tempering, steel 7 according to the invention obtained a hardness comparable to a high alloy reference material, which was about 1 HRC unit higher than the observed reference material no.2-4.

In addition, the impact strength of the material was observed and the results are shown in FIG. 6. The impact energy (J) absorbed in both the LC2 and CR2 directions was measured and a dazzling improvement was measured when compared mainly with reference material no. 4, a material for further development for steel no. 7 according to the invention. The best value for steel no. 7 according to the invention is 37J in the cross direction CR2, which is the value measured after high temperature tempering. This corresponds to an improvement of about 60% compared to reference substance no.4.

Even when hardness is taken into account, steel no. 7 according to the invention has a unique combination of high hardness and very good ductility closest in relation to reference material no. 5 having a considerable hardness as shown in FIG. 9. The sample rod is a cut and ground, un-notched sample rod, which is cured to a hardness according to Table 2 and has a dimension of 7x10 mm and a length of 55 mm.

In addition, the hardness of steel no. 7 according to the invention was observed after various austenitization temperatures and tempering temperatures. The results are shown graphically in FIGS. 4 and 5. At a relatively low austenitization temperature of 1030 ° C., steel no. 7 exhibited a maximum hardness value, which should be shown to be very advantageous in terms of heat treatment, and the major part of the tool steel on sale is heat treated at about this temperature. The main part of the reference steel must be heated to about 1060-1070 ° C, thereby obtaining the maximum hardness. For reference steel no. 1, the maximum hardness is not obtained up to a temperature of 1100-1150 ° C.

As is evident from FIG. 5, significant pronounced secondary hardening is obtained by tempering at temperatures between 500 and 550 ° C. In addition, this steel offers the possibility of low temperature tempering of about 200-250 ° C. It is also evident from the figure that residual austenite can be removed by high temperature tempering.

In addition, the resistance to abrasion of the steel according to the invention was compared with a number of reference materials and the results are given in FIG. 10. In the abrasion test, sample rods with dimensions Ø15 mm and length 20 mm were used. This observation was performed as a pin-on-disk test with SiO ₂ as abrasive wear agent. Prior to the abrasion test, reference steel no. 2-5 and steel no. 7 according to the invention were at a high temperature tempered to a hardness of 62.5 HRC. Reference steel no. 1 had a rather high hardness, 62.7 HRC, which was obtained by tempering at 540 ° C./3×2 h and curing at 1120 ° C./30 min. In addition, the wear rate of mg / min is shown in Table 2. Steel no. 7 is shown to have almost the same resistance to wear as reference steel no. 4 and is superior to reference steels no. 2 and 3. Reference steel no. 5 has a rather good resistance to abrasion when compared to reference steel no. Reference steel no.1 has the best resistance to wear among all steels.

In two different experiments, the machinability of steel no. 7 according to the invention was compared with reference steels 2-5 and the results are shown in Table 2 and in FIGS. 7 and 8. FIG. 7 shows the results when testing machinability by turning of soft annealed test samples with cemented carbide cutting edges, and FIG. 8 shows the drilling test for material with an uncoated drill. These test results show that steel no. 7 according to the invention has very good machinability, ie high values of V30 and V1000, which is in fact doubled when compared to reference material 4.

In the utilization test, resistance to edge wear was observed by the cutting test. The cutting knife was made of steel no. 4 and steel no. The knives were cured and tempered to hardness of 60.5 HRC and 60.0 HRC, respectively. The cutting test was performed with an ESSA eccentric press at a cutting speed of 200 cuts per minute and a maximum cutting load capacity of 15 tons. Cutting was performed on high strength steel strips with steel grade Docol 1400M, width 50mm, thickness 1mm. The cutting gap was 0.05 mm.

Edge wear on both the upper and lower knives was measured and the results are shown in FIG. 12. The graph in FIG. 12 shows edge wear after 100,000 cuts and after the end of the test. For knives made from steel no. 5, this test should be stopped after 150,000 cuts by chipping of the edges. Knives made from steel no. 7 showed no tendency for chipping after 315,000 cuts after the end of the test. It is evident that steel no. 7 exhibits better resistance to edge wear than steel no.

In FIGS. 13 a, b the sides of the upper knife of steel no. 7 after 315000 cuts and steel no. 5 after 150000 cuts are shown after the completed test, ie the face of the cutting tool is parallel to the cutting direction. From the figure, steel no. 5 shows greater abrasive wear as compared to steel no. 7 after a double cut after 150000 cuts.

Figures 14a, b show the front face of the upper knife of river no. 5 and the steel no. 7, Figures 15a, b show the front face of the lower knife of river no. 5 and the river no. 7, respectively, 150000 cut and After 315000 cuts, the face of the cutting tool is perpendicular to the cutting direction of the steel plate. This may show that both the upper and lower knives made from steel no. 5 exhibit chipping of the edges while the edge of steel no. 7 does not tend to chip.

This application test shows that the steel of the present invention has better resistance to wear and better toughness than reference steel no. In particular, resistance to chipping is advantageous.

According to the concept of the present invention, such steel must have good hardenability. With the steel according to the invention it has been demonstrated that the hardenability can be varied within a wide range of steel compositions. This can be done by varying the content of molybdenum within a given limit, whereby the steel according to the invention having a content of molybdenum at or near the lower limit of the range is obtained from the upper or lower limit of molybdenum in the range. A relatively low curability will be obtained when compared to the steel according to the invention having a content, but the curability in the entire range of molybdenum content is obtained so as not to exceed the curability of the reference materials nos. On a relative scale of 1-10, where 1 = inferior curability and 10 = highest curability, steel no. 7 according to the invention obtains a grade 10. A deformation of the steel according to the invention with a content of 2.3% molybdenum would yield grade 4. These grades and the grades for certain reference materials are shown in Table 2.

TABLE 2

River Heat treatment T _A // holding time + T _a / holding time Hardness (HRC) Relative Curability 1 = most inferior 10 = highest Unnotched impact energy in the direction of CR2 (J) Wear rate at 62.5 HRC (mg / min) Machinability rotation by cemented carbide V30 (m / min) Machinable drilling with uncoated drill V1000 (m / min) One 1120 ℃ / 30min + 540 ℃ / 3x2h 62.7 2 12 1.6 (62.7 HRC) - - 2 1050 ℃ / 30min + 525 ℃ / 2x2h 61.5 31 5.0 58 - 3 1050 ℃ / 30min + 525 ℃ / 2x2h 61.8 64 7.0 100 - 4 1050 ℃ / 30min + 525 ℃ / 2x2h 61.5 One 22.5 2.6 34 17 5 1050 ℃ / 30min + 525 ℃ / 2x2h 62.7 13 2.2 30 - 7 1050 ℃ / 30min + 525 ℃ / 2x2h 62.6 10 37 2.4 73 30

By means of known theoretical calculations, i.e., calculation by Thermo Calc, the content of molybdenum and carbide content in solid solution of the matrix in equilibrium is represented by steel no. 6 compared with steels no. 4 and 7. Calculations were made for variations of the inventive steel. Steel no. 6 has a composition containing 1.8% C, 0.4% Si, 0.4% Mn, 4.8% Cr, 1.8% Mo and 5.8% V and is designed to further reduce the cost of the alloying components. The results are shown in Table 3 below.

TABLE 3

MC-carbide (volume-%) M ₇ C ₃ -Carbide (volume-%) Mo (weight-%) of solid solution in matrix River No. 4 11.1 6.4 0.75 River No.6 12.8 0 1.0 River No.7 13.9 0 1.9

Compared to steel no. 7, steel no. 6 has a low content of molybdenum in solid solution in the matrix to result in low hardenability. However, the hardenability is sufficient for hardening and tempering of rectangular bars having a degree of steel no. 4 and dimensions up to 400 × 200 mm or round bars having Ø250 mm, which covers the dimensions of the tool for the intended application area. Because of the small amount of MC-carbide in the matrix, steel No. 6 will have higher ductility than steel No. 7 due to its low resistance to abrasive wear. Compared to steel No. 4, both steel Nos. 6 and 7 of the present invention will have high ductility and excellent resistance to abrasive wear.

As a result, the steel according to the invention is obtained so that the material has a very good resistance to wear and high hardness, which is not only in machine knives but also in deep cutting, pressing of powders, cold extrusion, threading dies and thread cutting such as thread taps. It makes steel suitable for use in cold working tools for cutting and punching. Surprisingly good ductility, relatively good machinability by the steel, and by the steel of the most preferred embodiment showing very good hardenability, this makes the steel always hardened and used for very good coarse dimensions. Steel can be provided with an exceptionally good and very suitable property profile. In addition, steel can be provided within the scope of the present invention, which steel does not have very good hardenability, but the rest have equally excellent properties, which is in terms of cost in the case of the thinner dimensions of the tool to be produced. Another advantage is that.

Claims (22)

As cold worked steel, In weight percent, 1.3-2.4 (C + N), of which C is at least 0.5, 0.1-1.5 Si, 0.1-1.5 Mn, 4.0-5.5 Cr, 1.5-3.6 (Mo + W / 2), W max 0.5 4.8-6.3 (V + Nb / 2), Nb is up to 2, and Has a chemical composition of up to 0.3 S, On the one hand the content of (C + N) and on the other hand the content of (V + Nb / 2) are balanced against each other so that the content of these components is A, B, C, D, In the region formed by the coordinates of A, the coordinates of [(C + N), (V + Nb / 2)] for this point A: [1.38, 4.8] B: [1.78, 4.8] C: [2.32, 6.3] D: [1.92, 6.3], The remainder is substantially only iron and is characterized by containing a general content of impurities, Cold work steel. The method of claim 1, On the one hand the content of (C + N) and on the other hand the content of (V + Nb / 2) are balanced against each other so that the content of these components is equal to E, F, G, H, In the region formed by the coordinates of E, the coordinates of [(C + N), (V + Nb / 2)] for this point E: [1.48, 4.8] F: [1.68, 4.8] G: [2.22, 6.3] H: [2.02, 6.3] Characterized by Cold work steel. The method of claim 2, On the one hand the content of (C + N) and on the other hand the content of (V + Nb / 2) are balanced against each other so that the content of these components is determined by K, L, M, N, In the region formed by the coordinates of K, the coordinates of [(C + N), (V + Nb / 2)] for this point K: [1.62, 5.2] L: [1.82, 5.2] M: [2.05, 5.8] N: [1.85, 5.8] Characterized by Cold work steel. The method according to any one of claims 1 to 3, On the one hand the content of (C + N) and on the other hand the content of (V + Nb / 2) are balanced against each other so that the content of these components is 0.32 ≦ (C + N) / (V + Nb / 2). Characterized by satisfying the condition of ≤ 0.35, Cold work steel. The method according to any one of claims 1 to 4, Characterized in that it contains 0.1-1.2% Si, preferably 0.2-0.9% Si, Cold work steel. The method of claim 5, wherein It is characterized by containing 0.4% Si, Cold work steel. The method according to any one of claims 1 to 6, Characterized in that it contains 0.1-1.3% Mn, preferably 0.1-0.9% Mn, Cold work steel. The method of claim 7, wherein Characterized in that it contains 0.4% Mn, Cold work steel. The method according to any one of claims 1 to 8, Characterized in that it contains 4.5-5.1% Cr, Cold work steel. The method of claim 9, It is characterized by containing 4.8% Cr, Cold work steel. The method according to any one of claims 1 to 10, Characterized in that it contains 1.5-2.6% (Mo + W / 2), Cold work steel. The method according to any one of claims 1 to 11, Characterized in that it contains 1.6-2.0% (Mo + W / 2), Cold work steel. The method of claim 12, Characterized in that it contains 1.8% (Mo + W / 2), Cold work steel. The method according to any one of claims 1 to 13, Characterized in that it contains at most 0.3% W, preferably at most 0.1% W, Cold work steel. The method according to any one of claims 1 to 14, Characterized in that it contains at most 0.3% Nb, preferably at most 0.1% Nb, Cold work steel. The method according to any one of claims 1 to 15, Characterized in that it contains a maximum of 0.15% S, Cold work steel. The method according to any one of claims 1 to 16, The steel has a hardness in the range of 58-63 HRC obtained after curing from a temperature of 980 to 1050 ° C., Preferably having a hardness in the range of 59-62 HRC after curing from a temperature of 980 to 1020 ° C. and tempering at a temperature of 500-560 ° C./2×2 h. Cold work steel. The method according to any one of claims 1 to 17, The steel has a microstructure containing 8-13 vol% MX-carbide, -nitride, and / or -carbonitride evenly distributed in the matrix of the steel after curing and tempering from 1050 ° C, where M is substantially Vanadium, X is carbon and / or nitrogen, At least 90 vol% of carbide, nitride, and / or carbide nitrides have an equivalent diameter (D _ekv ) of less than 3.0 μm and are substantially free of M ₇ C _{3 -carbide} , _-nitrides and / or carbides , Cold work steel. The method of claim 18, At least 90 vol% of the MX-carbide has a maximum extension length of 2.0 μm, Cold work steel. 20. A method for cutting, shearing, punching and / or forming a metalworking material under cold conditions by means of a tool comprising the cold worked steel according to any one of claims 1 to 19. 20. A method for pressing metal powder by a tool comprising the steel according to any one of claims 1 to 19. As a method of manufacturing steel, a) making a metal powder from the metal melt; b) hot hydrostatically forming said powder at a pressure of 90-150 MPa and a temperature of 950-1200 ° C. to form a reinforcing body; c) initially hot working said reinforcing body at a temperature of 1050-1150 degrees Celsius; d) soft-annealing at about 900 ° C .; And e) curing from a temperature of 980 to 1050 ° C. and tempering at a temperature of 500 to 560 ° C. for a hardness in the range of 58-66 HRC, preferably 61-63 HRC, The metal powder has a composition according to claim 1, How to make steel.

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