BRPI0709944A2 - cold work steel - Google Patents

Abstract

<B> COLD WORKING STEEL <D> The invention relates to cold working steel having the following chemical composition in% by weight: 1.3-2.4 (C + N), where at least 0, 5 C, 0.1-1.5 Si, 0.1-1.5 Mn, 4.0-5.5 Cr, 1.5-3.6 (Mo + W / 2), but at most 0, 5 w, 4.8- 6.3 (V + Nb / 2), but at most 2 Nb, and at most 0.3 S, in which the content of (C + N), on the one hand, and ( V + Nb / 2), on the other hand, are balanced in relation to each other so that the contents of these elements are within an area that is defined by the coordinates A, B, C, D, A in the coordinate system of Figure 11, where the coordinates of L (C + N), <V + Nb / 2)] for these points are A: [1.38, 4.8], B: [1.78, 4.8], C : [2.32, 6.31, D: [1.92, 6.3], as the balance essentially only Fe and impurities in normal quantities.

Description

"STEEL FOR COLD WORK"

TECHNICAL FIELD

The invention relates to a cold working steel, that is, a steel for use in working materials that are subjected to cold application. Typical examples of the use of steel are cutting and threading tools such as threading screwdrivers and tap taps, for cold extrusion, for powder pressing, for deep drawing, for cold forging. The invention also relates to a method of handling a metalworking material or to pressing the powder by a tool comprising steel as well as to a method of producing it.

STATE OF ART

There are many requirements regarding the high quality of cold work steels, such as suitable hardness for use, and good wear resistance and high hardness / ductility. It is important for optimal tool performance that these properties are met.

VANADIS® 4 is a metallurgically manufactured cold working steel powder produced by this Applicant and which has an excellent wear resistance and hardness / ductility combination for high performance tools. The nominal composition of the steel is in% by weight. weight: 1.5 C, 1.0 Si, 0.4 Mn, 8.0 Cr, 1.5 Mo, 4.0 V, as iron balance and inevitable impurities. Steel is particularly suitable for uses where adhesive / abrasive wear or breakage are the dominant problems, ie for soft / sticky working materials such as stainless steel, austenite, plain carbon steel, aluminum, copper, etc., as well as for materials. thick work Examples of cold working tools in which the steel can be used are mentioned in the introduction above. It can generally be said that VANADIS® 4, which is the object of SE 457356, is characterized by good wear resistance, high compressive strength. , boatability, excellent hardness, excellent dimensional stability in relation to heat treatment and good tempera resistance; all the properties that are important for a high performance cold work steel.

The Applicant produces and sells another powder metallurgically manufactured cold working steel (VANADIS® 6), which is characterized by excellent wear resistance and relatively good hardness, and is suitable for use in which abrasive wear is the dominant feature and where production occurs over long production runs. Nominal composition of steel is, in% by weight: 2.1 C, 1.0 Si, 0.4 Mn, 6.8 Cr, 1.5 Mo, 5.4 V, as iron balance and inevitable impurities. The breaking, machinability and grinding resistance are not good for VANADIS® 4.

A continuation of VANADIS® 4, mentioned above, is sold under the name VANADIS® 4 Extra and is characterized by a hardness that is even better than that of VANADIS® 4, its other performance characteristics being maintained or improved compared to this material and having, in principle the same field of application. Steel has been very commercially successful and has the following chemical composition by weight: 1.38% C, 0.4% Si, 0.4% Mn, 4.7% Cr, 3.5% Mo, 3, 7% V.

Several commercial steels are known which have the wide range of composition specified in US 4,249,945. Steel having the chemical composition 2.45 C, 0.90 Si, 5.25 Cr, 9.75 V, 1.30 Mo and 0.07 S is commercially available, as is a steel containing 1.80 C, 0 , 50 Mn, 0.90 Si, 5.25 Cr, 1.30 Mo and 9.00 V. The steels are after metallurgically produced and sold for use and applications requiring good wear resistance and adequate hardness.

Due to their excellent properties, the VANADIS® steels mentioned above have gained the market leading position among high performance cold work steels. The competing steels mentioned above are also marketed success. VANADIS® 4 Extra, in particular, has proven to have excellent properties.

Therefore, the present Applicant has the ambition to provide yet another high performance cold working steel having a property profile that is considerably better than those of the steels mentioned above. According to one aspect of the invention, steel should have properties for general use which are improved, particularly with respect to VANADIS® 6. According to another aspect, it is desired to provide a steel having good wear resistance at the same level as VANADIS. ® 6 and VANADIS® 10, but with considerably improved hardness / ductility compared to these steels. According to another aspect, the steel is characterized by good machinability and improved wear resistance. In yet another aspect of the invention, it is also an object of the invention to be able to provide a steel having high hardness, preferably in combination with good machinability. The steel application fields are in principle the same as for VANADIS®4.

DESCRIPTION OF THE INVENTION

It is an object of the invention to provide a steel that meets at least some of the high needs mentioned above of a high performance cold work steel. This is achieved by a cold working steel of the following chemical composition by weight%: 1.3-2.4 (C + Ν), where at least 0.5 C, 0.1-1.5 Si, 0 , 1-1.5 Mn, 4.0-5.5 Cr, 1.5-3.6 (Mo + W / 2), but at most 0.5 W, 4.8-6.3 (V + Nb / 2), but at most 2 Nb, and at most 0.3 S, where the content of (C + Ν) on the one hand and (V + Nb / 2) on the other hand are balanced. in relation to the other mode that the contents of these elements are within an area that is defined by the coordinates A, B, C, D, A in the coordinate system of Figure 11, where the coordinates of [(C + Ν), (V + Nb / 2)] for these points are A: [1.38, 4.8], B: [1.78, 4.8], C: [2.32, 6.3], D: [1.92 , 6,3], with essentially only Fe balance and impurities in normal quantities. It is also an object to provide a method for cold cutting, shearing, punching and / or shaping of a metal working material by a tool comprising a steel according to the invention, a method for pressing a metal powder by a tool comprising a steel according to the invention, and a method for manufacturing a steel according to the invention.

The steel according to the invention is a metallurgically produced powder, which is a prerequisite for the sugar to be highly free of oxide inclusions. Preferably, the metallurgically produced powder comprises gas atomization of a steel melt using nitrogen as gas. atomization, thus the mild steel will reach a minimum nitrogen content. If desired, steel powder can be solid phase nitrided to increase the nitrogen content of steel. Then consolidation is performed by hot isostatic pressing. The steel may be used in this condition or after biasing / rolling to the desired final dimension.

When nothing is stated, the present description always refers to% by weight relative to the chemical composition of the steel and% by volume to the structural components of the same. By denoting MX carbides, M7X3 carbides or only carbides, it is always understood that carbides such as nitrites and / or carbonitrides, if nothing else is said. Porcarbetos of M6C is always implied nothing but decarbetes.

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

Carbon, and where appropriate also a certain amount of nitrogen, should be present in the steel in a concentration such that, under the hardening condition of the steel, typically from a 1050 ° C degusting temperature Ta, is suitable together with vanadium where appropriate, niobium, to form 8-13% by weight of MX carbides, where M is essentially vanadium and X is carbon and nitrogen, preferably predominantly carbon, of which at least 90% by volume carbides have an equivalent diameter of at most 2.5 μm , preferably at most 2.0 μπκ Such MX carbides contribute in a manner that is known per se to a person skilled in the art for steel to achieve desirable wear resistance and they also have a certain effect of providing finer grains, and also a certain amount of secondary hardening. Through tailored heat treatment, i.e. choosing austenizing and quenching temperatures, the carbide content of MX may be varied within the above range so that a microstructure that is suitable for the purpose is obtained, which is described in greater detail in the description. of the experiments performed and the description of the attached figures. In addition to these MX carbides, steel should be essentially free of other precipitated main carbides, such as M7X3 and M6C carbides.

Preferably, the steel does not contain more nitrogen than is inevitably and naturally understood due to absorption from the surrounding area and / or added raw materials, ie about 0.12%, preferably about 0%. , 10%. However, in one possible embodiment steel may contain a larger amount of nitrogen, deliberately added, which may be provided by the solid phase nitriding of the steel powder that is used in the production of steel. In this case, most of (C + N) may be nitrogen, which means that in this case said M is mainly vanadium carbonitides in which onitrogen is the main ingredient, along with vanadium, that is, even nitrides. of pure vanadium, whereas carbon essentially exists only as dissolved in the steel matrix in its hardening and quenching condition.

Vanadium should be present in steel at a concentration of at least 4.8%, but a maximum of 6.3% so that, together with carbon and any nitrogen present, form the above-mentioned MX carbides in a total content of 8-13%. by volume under the hardening conditions and tempering of the use of steel. Vanadium may in principle be substituted for niobium, but this requires twice the amount of niobium as compared to vanadium, which is a disadvantage. Niobium also results in a broader shape of the carbides of MX and they become wider than pure vanadium carbides, so that fractures or breaks can be initiated, thus decreasing material strength, which is a disadvantage. Therefore, niobium should not be present at a concentration above 2%, preferably at most 1% and suitably at most 0.1%.

It is more preferred that steel does not contain any deliberately added and would not be tolerated at concentrations above the amounts of impurity in the form of residual elements from raw materials included in the production of steel. According to one aspect of the invention, the quantities in steel of (C + Ν), on the one hand, and (V + Nb / 2), on the other hand, should be balanced against each other so that the contents of these elements are within an area that is defined by the coordinates A, B, C, D, A in the coordinate system of Figure 11, where the coordinates of [(C + Ν), (V + Nb / 2)] for these points are A: [1,38, 4,8], B: [ 1.78, 4.8], C: [2.32, 6.3], D: [1.92, 6.3]. Within these ranges it is possible to obtain a steel with a very useful property profile. A suitable combination of hardness, wear resistance, ductility and machinability can be obtained by means of adapted heat treatment. Within this wider composition range it is generally true that the hardness and wear resistance will increase the higher the total amount of (C + N) and (V + Nb / 2) in steel, while the ductility is favored the lower the amount of these elements. .

According to a more preferred embodiment, the amount of these elements should be within an area defined by the coordinates E, F, G, Η, E in the decoordinate system of Figure 11, where the coordinates of [(C + Ν), (V + Nb / 2)] for these points are: E: [1.48, 4.8], F: [1.68, 4.8], G: [2.22, 6.3], H: [2, 02, 6.3].

According to an even more preferred embodiment, the contents of (C + Ν) on the one hand and (V + Nb / 2) on the other hand should be balanced against each other so that the contents of these elements are within each other. an area that is defined by the coordinates K, L, Μ, Ν, K in the coordinate system of Figure 11, where the coordinates of [(C + Ν), (V + Nb / 2)] for these points are: K: [1 , 62.5.2], L: [1.82, 5.2], M: [2.05, 5.8], N: [1.85, 5.8].

In yet another aspect of the invention, the amounts of (C + Ν), on the one hand, and of (V + Nb / 2), on the other hand, should be balanced against each other so that the contents of these elements fill. condition 0.32 <(C + Ν) / (V + Nb / 2) <0.35.

In yet another aspect of the invention, the amounts of (C + Ν), on the one hand, and of (V + Nb / 2), on the other hand, should be balanced against each other so that the contents of these elements are within an area that is defined by the coordinates A ', B', C ', D', A 'in the coordinate system of Figure 11, where the coordinates of [(C + Ν), (V + Nb / 2)] for these points are: A ': [1.52, 5.2], B': [1.93, 5.2], C ': [2.18, 5.9], D': [1.77, 5.9].

Carbon also contributes to the hardness present in solid solution in the steel matrix in its hardened or tempered condition at a concentration of 0.4-0.6% by weight at a Ta austenization temperature of 980-1050 ° C.

Silicon is present as a residual element of steel production at a concentration of at least 0.1%, usually at least 0.2%. Silicon increases the carbon activity in steel and therefore contributes to its having a suitable hardness. Very high contents may result in brittleness problems due to solution hardening and therefore the maximum concentration of silicon in steel is 1.5%, preferably at most 1.2%, suitably at most 0.9%. A Si concentration which is advantageous for steel is 0.2-0.5 Si. The steel has a nominal content of 0.4 Si.

Manganese is added to steel at a concentration of at least 0.1% in order to react with the amount of sulfur that may be present in the steel to form manganese sulfides. Manganese, as well as the chromium and molybdenum elements, also contributes to the steel having adequate temperability, which means that a 0.1% manganese content can be tolerated without any negative effects on steel properties. At high concentrations, manganese may cause undesirable stabilization of residual austenite, which results in poor hardness. Residual austenite will also result in a steel with less dimensional stability, which is a major drawback. Therefore, the amount of manganese should not exceed 1.2%, and an advantageous content of the same grade is in the range 0.1-0.9% Mn. Steel has a nominal concentration of 0.4% Mn.

As mentioned above, chromium contributes to the weatherability of steel and for this reason it should be present in a concentration of at least 4.0%, preferably at least 4.5%. Chromium is also a carbide forming element and, in many steels, is used to aid the wear resistance of steel by forming M7X3 carbides. Such carbides can be dissolved in various extensions by choosing an appropriate hardening temperature in the hardening, and the chromium and carbon that have been dissolved in the austenite of this manner can then be precipitated to varying lengths to form secondary carbide precipitates which will efficiently contribute to produce the steel. maximum hardness desired relative to tempering.

Steel according to the invention should, among other things, exhibit very good wear resistance and should be temperable to a comparatively high hardness. It has now been shown that this can be achieved while giving the steel a surprisingly good ductility, superior to some of the Applicant's own steels that are sold for similar applications. By limiting the chromium content, it has been possible to prevent, or at least minimize, the formation of M7X3 carbides in favor of the formation of major precipitated MX carbides. To achieve such a favorable carbide concentration, the chromium content should therefore be limited to a maximum of 5.5% and even more preferably a maximum of 5.1%. A chromium content that is beneficial to steel is 4.8%.

Most of the chromium that is added to the steel will be dissolved in it so that it contributes to its durability. According to the concept of the invention, steel should have a temperability requirement for varying dimensions to be completely hardened, and if steel should be used in thicker dimensions, weatherability is a particularly important aspect. Therefore, molybdenum should be present in steel at a concentration of at least 1.5%. Without the risk of undesirable M6C carbide deprecipitation, the demolbdenum content can be tolerated up to 3.6% Mo. Preferably, the steel contains between 1.5 and 2.6% Mo and even more preferably between 1.6 and 2.0% Mo. Mo. To some extent, molybdenum may be substituted for tungsten, but this requires doubling the amount of tungsten as compared to molybdenum, which is an inconvenience. This also makes handling the escarpment more difficult. Therefore, tungsten should not be present in an amount of more than 0.5%, preferably 0.3%, and most appropriately 0.1%. It is more preferred that steel does not contain any deliberately added tungsten and the most preferred embodiment should not be tolerated in quantities above the level of impurity in the form of residual elements from the raw materials included in the manufacture of steel.

Sulfur is present in steel mainly as a impurity in an amount of at most 0.03%. However, it is possible, according to one embodiment, for steel to contain sulfur deliberately added to a content of up to a maximum of 0.3%, preferably a maximum of 0.15%, in order to improve its machinability.

A nominal steel composition according to the invention is 1.77% C, 0.4% Si, 0.4% Mn, 4.8% Cr, 2.5% Mo and 5.5% V, as essentially iron balance.

The following composition is an example of a possible variation of steel within the scope of the invention: 1.9% C, 0.4% Si, 0.4% Mn, 4.8% Cr, 3.5% Mo, 5, 8% V, as essentially iron balance.

The following composition is yet another example of a possible variation of steel: 1.67% C, 0.4% Si, 0.4% Mn, 4.8% Cr, 2.3% Mo, 5.2% V, as an essentially iron balance. The following composition is yet another example of a possible variation of steel: 1.80% C, 0.4% Si, 0.4% Mn, 4.8% Cr, 1.8% Mo, 5 , 8% V, as essentially iron balance.

The above variants have been optimized to achieve somewhat different property profiles so that steel with a higher content of carbetomolybdenum and vanadium formers will exhibit better wear resistance over slightly lower ductility. Steel that has a smaller amount of these two elements will present greater ductility at the expense of slightly less wear resistance.

In steelmaking, a melt is first prepared containing the necessary quantities of carbon, silicon, manganese, chromium, molybdenum, possibly tungsten, vanadium, possibly niobium, possibly sulfur beyond the amount of impurity, nitrogen in an inevitable amount, iron and impurities as balance. A powder is produced from this melt by atomizing with nitrogen gas. The droplets formed in the gas atomization are rapidly cooled, so that the vanadium and / or mixed vanadium and carbide carbides formed have no time to grow, become extremely thin, having a thickness of no more than a fraction of a micrometer - and acquire a pronounced irregular shape from carbides that are precipitated in residual molten areas in the dendrite structure in rapidly solidifying small debris before the drops solidify to powdered grains. Where steel contains nitrogen in addition to the inevitable impurity content, this is achieved by nitrifying the powder, for example as described in SE 462.837.

After sieving, which, if the powder is to be nitrided, is carried out properly prior to nitriding, the powder is introduced into capsules which are then vacuum sealed and exposed to hot isostatic pressing, HIP, as is known, at high temperature and high pressure, 950-1200 ° C and 90-150 MPa; typically at about 1150 ° C and 100MPa, so that the powder is consolidated to form a completely dense body.

Through the HIP process the carbides will get a much more regular format than they have in the powder. Predominant part of the volume has a maximum size of about 1.5 pm and a rounded shape. Actual particles are still elongated and slightly longer, at most about 2.5 μm. The transformation is most likely due to the combination of very fine powder dissolution and coalescence.

Steel can be used in HIP process condition. However, steel is usually hot worked after HIP processing by forging and / or hot rolling. This is carried out at an initial temperature between 1050 and 1150 ° C, preferably about 1100 ° C. In this way there is additional coalescence and, in particular, a spheroidization of the carbides. After forging and / or rolling, at least 90% by volume of the carbides have a maximum size of 2.5 μm, preferably a maximum of 2.0 μπι.

In order to be able to work the steel cutting tools, it must first go through the soft annealing process. This occurs at a temperature below 950 ° C, preferably about 900 ° C. When the cutting tool has its final shape, it is hardened and tempered. In austenization, the carbides of MX are dissolved to some extent so that they can then precipitate on heating. Apart from these MX carbides, steel should not contain any other carbides. Hardening may occur from a considerably lower austenization temperature than that which is common for steels with corresponding wear resistance, typically between 980 and 1150 ° C, preferably below 1100 ° C, thereby avoiding a large dissolution of MX carbon. undesirable. A suitable self-cleaning temperature is in the range 1000-1050 ° C. This is a decisive advantage for the toolmaker as steel can then be heat treated along with most other steel tools on the market. In the hardened steel condition, Ta is in the range of 980-1050 ° C, the matrix consists essentially only of martensite which contains 0.4-0.6% carbon in the solid solution.

Subsequent quenching may be performed at a temperature between 200 and 60 ° C, preferably at a temperature between 500-560 ° C. The end result is the microstructure which is typical for the invention and which consists of 8-13% by volume tempered martensite of carbides of MX, where M is essentially vanadium and X is carbon of nitrogen, preferably in the main carbon, of which at least 90 carbides. % by volume have an equivalent diameter of at most 2.5 μm, preferably at most 2.0 μm. Carbides have a predominantly round or round shape, but occasionally longer carbides may be present. In this description, the equivalent diameter Dekv is defined as Dekv = 2va / 7c, where A is the area of the carbide particle in the section studied. Typically, at least 96% by volume of MX carbides, nitrides and / or carbonitrides have a Dekv <3.0 μπι. Normally, the carbides are also spheroidized to the point that none of the carbides had an exact length above 3.0 pm in the considered section. After hardening and hardening, the steel has a hardness of 58-66 HRC.

Other features and aspects of the invention will become clearer from the appended claims, and from the following description of the experiments that have been performed.

BRIEF DESCRIPTION OF DRAWINGS

In the following description of the experiments performed, reference will be made to the accompanying drawings, of which

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

Figure 2 shows the microstructure of a comparative commercial material after hardening and tempering,

Figure 3 further shows the microstructure of a comparative commercial material after hardening and tempering, Figure 4 is a graph showing the hardness of a steel according to the invention as a function of austenization temperature,

Figure 5 is a graph showing the hardness of a steel according to the invention at different austenization temperatures and as a function of tempering temperature,

Figure 6 is a graph showing the ductility of a high temperature hardened steel according to the invention, as well as various comparative materials,

Figure 7 is a graph showing the machinability of steel according to the invention, as well as various comparative materials,

Figure 8 is still a graph showing the machinability of a steel according to the invention as well as a comparative material,

Figure 9 shows the combination of non-notched impact energy and wear resistance for a steel according to the invention as well as for a variety of comparative materials,

Figure 10 shows the wear rate of wear tests of the steel according to the invention as well as a number of comparative materials,

Figure 11 shows a graph about the relationship between carbon content and any existing nitrogen relative to vanadium content and any existing niobium,

Figure 12 shows a graph about the upper and lower wear of a knife after cutting,

Figure 13a, b shows the lateral side of the upper knife after cutting tests,

Figure 14a, b shows the front face of the upper knife after cutting tests, and

Figure 15a, b shows the lateral face of the lower knife after cutting tests.

DESCRIPTION OF CONDUCT EXPERIMENTS

The chemical composition of the steels examined is shown in Table 1. In the Table, the sulfur in some steels is an impurity. Other impurities have not been determined, but do not exceed normal impurity levels. The balance is iron. In Table 1, steel 7 has a chemical composition according to the invention. Steels 1-5 are reference materials.

Table 1 - Chemical composition of the steels analyzed, in% by weight.

<table> table see original document page 19 </column> </row> <table> Steels 1-5 are all commercial steels, but steel # 1 is the Applicant's steels. Material samples of these steels were sorted and analyzed for chemical composition. All of these steels are metallurgically manufactured and were ordered under the condition of soft annealing. A 6 ton melt was produced from steel No. 7 according to a conventional melting technique. Metal powder was manufactured from the nitrogen gas atomization melt of a melt sprayer. The small drops formed cooled quickly.

Molds of 2 tons each were made from No. 7 steel powder, having the chemical composition according to Table 1. The steel powder was disposed into sheet metal capsules, which were then vacuum-sealed, heated to about 1150 ° C and then subjected to hot isostatic pressing (HIP) at about 1150 ° C and at a pressure of 100 MPa. The originally obtained carbide structure of the powder was broken during the HIP process, while the carbides coalesced. In the steel submitted to the HIP process, the carbides obtained a more regular shape, close to the spheroidal shape. They are still very small. The predominant portion, more than 90% by volume, has an equivalent diameter of at most 2.5 μπι, preferably at most about 2.0 μπι.

The molds were then forged at a temperature of 100 ° C to the size of a 100 mm round bar. Steel No. 7 underwent the soft annealing process at 900 ° C and its microstructure was examined and hardness tests were performed. Carbides are present in the material in the form of essentially multi-spheroidal MX carbides, at most about 2.0 μm in length, terms of equivalent diameter. After soft annealing, the test samples were taken from steel # 7 for analysis. The same type of test samples were taken from reference materials 1-5 which had been ordered in the soft annealing condition.

The heat treatment with regard to hardening and quenching of the various steels is presented in Table 2. The microstructure in the hardening and quenching condition has been for three of the steels, more specifically steel No. 7 according to the invention, shown in Figure 1, and with reference to steels No. 4 and 1, shown in Figures 2 and 3, respectively. The steel according to the invention, Figure 1, contained 11.7% by volume of carbides of MX in the matrix, which was toughened martensite. No carbides other than MX carbides can be detected. Occasional carbides having an equivalent diameter of more than 3.0 μm could be found in the steel according to the invention in the hardening and quenching condition.

Reference steel No. 4, Figure 2, contained in the hardening and quenching condition a total of about 14.4% by volume of carbides, of which about 9.2% by volume were MC carbides and about 5.2% by volume were M7C3 carbides. It is clear from the Figure that M7C3 carbides are relatively large, generally larger than MC carbides, which results in a negative effect, especially on ductility. The reference steel No. 1, Figure 3, contained, in the condition of hardening and quenching, about 15.7% by volume of MC decarbs. No other carbides were detected. The high carbide concentration resulted in a steel with a relatively good wear resistance but less ductility.

The hardness after heat treatment as defined in Table 2 is also shown in Table 2. After tempering at high temperature, steel No. 7 according to the invention obtained a hardness comparable to the reference material No. 5 at high temperature. alloy, and the hardness was about 1 unit HRC higher than that of the reference materials in the 2-4 analyzes.

The impact strength of the above materials was also examined and the results are shown in Figure 6. Impact energy (J) absorbed in both directions LC2 and CR2 was measured and for steel No. 7 according to the invention a dramatic improvement. was measured when compared mainly to reference material No. 4, which is the desired material for further development. The best value for steel No. 7 according to the invention was 37 J in the transverse direction (CR2), which was measured after tempering at high temperature. This corresponds to an improvement of approximately 60% compared to reference material No. 4.

Even when hardness is considered, it is clear that steel No. 7 according to the invention has a unique combination of high hardness and very good ductility, the closest to reference material No. 5 which has comparable hardness as shown. Figure 9. Sample sticks were cut and ground, 7 χ 10 mm non-notched sample sticks and 55 mm long, hardened to the hardness according to Table 2.

The hardness of steel No. 7 according to the invention was also examined after various tempering and tempering temperatures. The results are shown in the graphs of Figures 4 and 5. At a relatively low temperature of 1030 ° C, steel no. 7 exhibited a maximum hardness, which should be interpreted as very advantageous from a thermal degradation point of view, Since most of the steel-making tools on the market are heat treated around this temperature. Most reference steels should be heated to about 1060-1070 ° C to reach maximum hardness. For reference steel No 1, a maximum hardness is not reached up to a temperature of 1100-115 O0C.

As can be seen from Figure 5, pronounced secondary hardening is obtained by tempering at the maximum temperature between 500 and 550 ° C. The steel also allows for the possibility of a low tempering temperature, about 200-250 ° C. It is also noted from the figure that residual austenite can be eliminated by tempering at high temperature.

The wear resistance of the steel according to the invention was also compared with various reference materials and the results are shown in Figure 10. In the wear test, swab samples having a diameter of 15 mm and a length of 20 mm were used. The analysis was conducted in the pin-on-disc test with SiO2 as abrasive wear agent. Prior to wear tests, reference steels 2-5 and steel No. 7 according to the invention had been hardened to a high temperature to a hardness of 62.5 HRC. Reference steel # 1 had a slightly higher hardness, 62.7 HRC, obtained by hardening from 1120 ° C / 30 min and quenching at 540 ° C / 3x2h. The wear rate at mg / min is also shown in Table 2. Steel # 7 had approximately the same good wear resistance as reference steel # 4, and was higher than reference steels # 2 and # 3. 5 showed slightly better wear resistance when compared to steel No. 7. Among all steels tested, reference steel No. 1 showed the best wear resistance.

In two separate experiments, machinability of No. 7 according to the invention was compared with reference steels 2-5 and the result is shown in Table 2 and also in Figures 7 and 8. Figure 7 shows the result of the Machinability of soft-annealed test samples with a carbide cutting edge, and Figure 8 shows bore tests for uncoated materials. The results of these tests show that steel No. 7 according to the invention has very good machinability, that is, high values of V30 and V1000, almost double when compared to reference material 4.

In the utilization tests, the wear resistance of the thread was examined by cutting tests. Cutting knives were produced from steels 4 and 7. The knives were hardened and tempered to a hardness of 60.5 and 60.0 HRC, respectively. The cutting tests were performed on an ESSA eccentric press with a maximum cutting load capacity of 15 tons and a cutting speed of 200 cuts per minute. The cut was made with high strength steel strips on Docol1400M brand steel, width 50 mm, thickness 1 mm. The cutting clearance was 0.05 mm.

Thread wear on the top and bottom of the knives has been measured and the result is shown in Figure 12. In Figure 12 a graph shows the wire wear after 100000 cuts and after the end of the test. For the knife produced from No. 5 steel, the test had to be interrupted after 150000 cuts due to wire breakage. The blade produced from steel No. 7 showed no tendency to break after 315000 cuts when it determined it. It is evident that steel No. 7 showed better resistance to wire wear than steel No. 5.

In Figures 13a, b, the side face of the upper knife produced from steel No. 5 after 150000 cuts and steel No. 7 after 315000 cuts is shown after the end of these, that is, the face of the cutting tool that is parallel to the direction of cut. It can be seen from the figures that steel No. 5 exhibits significantly more abrasive wear after 150000 cuts when compared to steel No. 7 after more than twice that of cuts.

Figures 14a, b show the front face of the superhide knife produced from steels 5 and 7, and Figures 15a, b show the front lower face of the knife produced from steels 5 and 7, i.e. the face of the cutting tool that is perpendicular to the cutting direction of the steel plate after 150000 and 315000 cuts, respectively. Note that both the top and bottom of the knife produced from steel No. 5 show a breakage of the wire, while steel wire No. 7 shows no tendency to breakage.

Usage tests indicate that inventive steel has a higher hardness and wear resistance than reference steel No. 5. In particular, the breaking strength is advantageous.

According to the concept of the invention, steel should be of good temperability. With the steel of the invention, it has been proved possible to let the tempera- bility vary within wide ranges of the steel composition. This can be done by varying the molybdenum content within the limits provided, so that a steel according to the invention having a molybdenum content equal to or near the lower dolimite of the range will have a tempera- ture that is relatively low compared to a steel according to invention having a molybdenum content equal to or near the upper limit of the range, but throughout the molybdenum concentration range a tempera- bility is obtained that of the reference materials in paragraphs 1 and 4. In a scale of 1 to 10, where 1 = a worst temperability and 10 = the best temperability, steel No. 7 according to the invention achieves a value of 10. A variation of the steel according to the invention having a content of 2.3% demolibdenum will reach a value of 4. The values obtained for some reference materials are shown in Table 2. Table 2

<table> table see original document page 27 </column> </row> <table> Through known theoretical calculations, for example, Term Cale, the carbide content and the amount of solid solution in the matrix at equilibrium were calculated for a variation of the inventive steel denoted action 6, and compared to steels 4 and 7. Steel 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 made to be able to reduce the cost of the alloy with other elements, even afterwards. The result is shown below in Table 3.

Table 3

<table> table see original document page 28 </column> </row> <table>

Compared to No. 7 steel, No. 6 steel has a lower amount of molybdenum in the solid solution in the matrix, which results in lower temperability. However, the weatherability is of the order of steel No. 4 and is sufficient for the hardening and tempering of 250 mm diameter round bars or square bars up to 400 χ200 mm, which covers the dimensions of the tools for the intended use area. Due to the low amount of MC carbides in the matrix, steel No. 6 will have a higher sensitivity than steel No. 7, to the detriment of less abrasive wear resistance. Compared to steel No. 4, both steel No. 6 and No. 7 of the invention will have greater flexibility and better resistance to abrasive wear. As a conclusion it can be stated that with a steel according to the invention a material is obtained. It has a high hardness and very good wear resistance, which makes it suitable for use in cold working tools for cutting and punching, tapping, such as threading tapping and tapping, cold extrusion, for powder pressing , for deep pulling, as well as for machine knives. The steel also exhibits surprisingly good ductility, relatively good machinability and in its most preferred embodiment also exhibits very good temperability, allowing it to become completely hardened even with very thick dimensions and can be produced with a property profile. which is very suitable and rarely good for the intended use.

A steel within the scope of the invention may also be provided, which does not necessarily have very good toughness, but which, for the rest, had the same good properties, which is still an advantage, as can be seen from a business perspective. In the case of tools of thinner dimensions should be manufactured.

Claims (22)

1.A cold-working steel, characterized in that it has the following chemical composition, in% by weight: -1,3-2,4 (C + Ν), where at least 0,5 C, -0,1 -1.5 Si, -0.1-1.5 Mn, -4.0-5.5 Cr, -1.5-3.6 (Mo + W / 2), but at most 0.5 W, -4,8-6,3 (V + Nb / 2), but at most 2 Nb, and not more than 0,3 S, where the content of (C + Ν), on the one hand, and of (V + Nb / 2), on the other hand, are balanced relative to each other so that the contents of these elements are within an area that is defined by the coordinates A, B, C, D, A in the coordinate system of Figure 11, where the coordinates of [ (C + Ν), (V + Nb / 2)] for these points are A: [1.38, 4.8] B: [1.78, 4.8] C: [2.32, 6.3] D: [1.92, 6.3], as balance essentially only Fe and impurities in normal quantities. 2. A cold-working steel according to claim 1, characterized in that the content of (C + Ν) on the one hand and (V + Nb / 2) on the other hand are balanced with respect to another is that the contents of these elements are within an area that is defined by the coordinates E, F, G, Η, and the coordinate system of Figure 11, where the coordinates of [(C + Ν), (V + Nb / 2)] for these points E: [1.48, 4.8] F: [1.68, 4.8] G: [2.22, 6.3] H: [2.02, 6.3] 3. A cold-working steel according to claim 2, characterized in that the content of (C + Ν), on the one hand, and (V + Nb / 2), on the other hand, are balanced against one another. another is that the contents of these elements are within an area that is defined by the coordinates K, L, Μ, Ν, K in the coordinate system of Figure 11, where the coordinates of [(C + Ν), (V + Nb / 2)] for these points K: [1.62, 5.2] L: [1.82, 5.2] M: [2.05, 5.8] N: [1.85, 5.8] A cold-working steel according to any one of the preceding claims, characterized in that the content of (C + Ν) on the one hand and (V + Nb / 2) on the other hand are balanced. relative to each other so that the contents of these elements satisfy the condition 0.32 ≤ (C + Ν) / (V + Nb / 2) ≤ 0.35. A steel according to any one of the preceding claims, characterized in that it contains 0.1-1.2% Si, preferably 0.2-0.9% Si. A steel according to claim 5, characterized in that it contains 0.4% Si. A steel according to any one of the preceding claims, characterized in that it contains 0.1-1.3% Mn, preferably 0.1-0.9% Mn. A steel according to claim 7, characterized in that it contains 0.4% Mn. A steel according to any of the preceding claims, characterized in that it contains 4.5--5.1% Cr. A steel according to claim 9, characterized in that it contains 4.8% Cr. A steel according to any one of the preceding claims, characterized in that it contains 1.5--2.6% (Mo + W / 2). A steel according to any one of the preceding claims, characterized in that it contains 1.6 - 2.0% (Mo + W / 2). A steel according to claim 12, characterized in that it contains 1.8% (Mo + W / 2). A steel according to any one of the preceding claims, characterized in that it contains at most 0.3% W, preferably at most 0.1% W. A steel according to any one of the preceding claims, characterized in that it contains at most 0.3% Nb, preferably at most 0.1% Nb. A steel according to any one of the preceding claims, characterized in that it contains at most 0.15% S. A steel according to any one of the preceding claims, characterized in that the steel has a hardness in the range of 58-63 HRC reached after hardening from a temperature between 980 and -1050 ° C, preferably 59-62 HRC reached after hardening. from a temperature between 980 and -102 ° C, and a temperature between 500--560 ° C / 2x2 h. A steel according to any one of the preceding claims, characterized in that the steel has a microstructure after hardening from 1050 ° C and tempering containing 8-13% by volume of MXi carbides, nitrides and / or carbonitrides which are evenly distributed. in the steel matrix, where M is essentially vanadium and X is carbon and / or nitrogen, of which carbides, nitrides and / or carbonitrides at least 90% by volume have an equivalent diameter, Dekv / less than 3.0 μm, and is essentially free of M7C3 carbides, nitrides and / or carbonitrides. A steel according to claim 18, characterized in that at least 90% by volume of the MX disks have a maximum length of 2.0 μm. A method for cold cutting, shearing, punching and / or molding a metalworking material by a tool comprising a core according to any one of claims 1-19. A method for pressing a metal powder by a tool comprising a steel according to any one of claims 1-19. 22. A method for the manufacture of a steel, comprising the following production steps: a) production of a metal powder from a molten metal, b) isostatic hot pressing of the powder at a temperature and pressure between 950-1200 ° C and 90 ° C. -150 MPa1 respectively, to form a consolidated body, c) hot application of said consolidated body to an initial temperature between 1050 and 1150 ° C, d) soft annealing at approximately 900 ° C, e) hardening from a temperature between 980 and 1050 ° C and tempering at a temperature between 500 and 560 ° C to a hardness in the range 58-66 HRC, preferably 61-63 HRC, characterized in that the metal powder has a composition according to claim 1.