JP5323679B2 - Cold work steel - Google Patents

Abstract

The invention relates to a cold-working steel having a chemical composition, in % by weight, of 1.3-2.4 (C+N), whereof 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 max 0.5 W, 4.8-6.3 (V+Nb/2), but max 2 Nb, and max 0.3 S, in which the content of (C+N) and of (V+Nb/2) are balanced in relation to each other such that the contents of these elements are within an area that is defined by the coordinates A, B, C, D, A in the system of coordinates in FIG. 11, where the coordinates of [(C+N), (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], and a balance essentially only iron and impurities at normal contents.

Description

TECHNICAL FIELD The present invention relates to cold-working steel, ie steel intended for use in the processing of working materials at low temperature conditions. Typical applications for this steel are tools for cutting and punching, threading (eg threading dies and thread taps), cold extrusion, pressing of powder, deep drawing, cold forging. It is. The invention also relates to a method of processing a metal work material or a powder pressing method with a tool comprising this steel, as well as a method of manufacturing this steel.

BACKGROUND OF THE INVENTION High quality cold work ropes have many requirements such as adequate hardness for their application, good wear resistance, and high toughness / ductility. Meeting these properties is important for optimal tool performance. VANADIS® 4 is a cold work manufactured by powder metallurgy that combines the wear resistance and toughness / ductility for high performance tools that are manufactured and sold by the Applicant and considered to be superior. It is a steel rope. The nominal composition of the steel is C1.5, Si1.0, Mn0.4, Cr8.0, Mo1.5, V4.0 by weight%, and the rest is iron and inevitable impurities. . This steel is used in applications where adherent / abrasive wear or chipping is a major problem: soft / tacky work materials such as austenitic stainless steel, simple carbon steel, aluminum, copper, and thick work materials Especially suitable for. Typical examples of cold working tools that can use this steel are described in the introduction above. In general, VANADIS® 4 which is the subject of Swedish Patent No. 457,356 has good wear resistance, high compressive strength, good hardenability, excellent toughness, excellent dimensional stability with respect to heat treatment, and good All of these properties are important for high performance cold work steel, which can be characterized by high tempering resistance.

  The applicant manufactures and sells another cold work steel VANADIS® 6 manufactured by powder metallurgy, which is characterized by excellent wear resistance and relatively good toughness, Therefore, this rope is suitable for applications in which the abrasive wear is a major feature and the production process lasts long. The nominal composition of this steel is C2.1, Si1.0, Mn0.4, Cr6.8, Mo1.5, V5.4 by weight%, the rest being iron and inevitable impurities. Chipping resistance, machinability, and ease of polishing are not as good as VANADIS® 4.

  Subsequent to the above VANADIS (R) 4 is sold under the name VANADIS (R) 4 Extra and is characterized by better toughness than VANADIS (R) 4, other performance characteristics The field of application is in principle the same. This steel was very successful commercially and has the following chemical composition in weight percent: C 1.38%, Si 0.4%, Mn 0.4%, Cr 4.7%, Mo 3.5%, V 3.7%.

  Several commercially available steels are known that fall within the broad composition range specified in US Pat. No. 4,249,945. Steels having chemical compositions of C2.45, Mn0.50, Si0.90, Cr5.25, V9.75, Mo1.30, and S0.07 are commercially available, C1.80, Mn0.50, Si0. Also included are steels containing 90, Cr 5.25, Mo 1.30, and V 9.00. These steels are manufactured by powder metallurgy and are sold for use in applications requiring good wear resistance and sufficient toughness.

  Due to its superior properties, the above VANADIS® steel has gained an industry-leading position among high performance cold work steel. The competing steels described above have been successful in the same industry. VANADIS® 4 Extra has been found to have particularly good properties.

The Applicant is therefore eager to provide yet another high performance cold work steel that has a much better property profile than the steels described above. According to one aspect of the present invention, this steel should have generally improved practical properties, especially compared to VANADIS® 6. According to another aspect, it has good wear resistance beneficial to the same level as VANADIS® 6 and VANADIS® 10, but significantly improved toughness / ductility compared to these steels. It has been desired to provide steel with According to yet another aspect, the steel is characterized by good machinability and improved wear resistance. According to yet another aspect of the present invention, it is an object to provide a steel having high hardness, preferably in combination with good hardenability. The field of application of this steel is essentially the same as VANADIS® 4.
Swedish Patent No. 457,356 U.S. Pat. No. 4,249,945

DESCRIPTION OF THE INVENTION It is an object of the present invention to provide a steel that meets at least some of the above high requirements for high performance cold work steels. This is achieved by cold work steel having the following chemical composition in weight percent: That is, (C + N) 1.3 to 2.4 (of which C is at least 0.5), Si 0.1 to 1.5, Mn 0.1 to 1.5, Cr 4.0 to 5.5, (Mo + W / 2 ) 1.5 to 3.6 (W is a maximum of 0.5), (V + Nb / 2) 4.8 to 6.3 (Nb is a maximum of 2), and S is a maximum of 0.3, The content of (C + N) and the other (V + Nb / 2) is such that the content of these elements is in the region defined by the coordinates A, B, C, D, A in the coordinate system of FIG. Where the coordinates [(C + N), (V + Nb / 2)] of these points are A: [1.38,4.8], B: [1.78,4.8], C: [2.32, 6.3], D: [1.92, 6.3], the rest being essentially iron and the normal amount (at normal con ents) is only impurities. A method of cutting, shearing, stamping, and / or forming working of a metal workpiece at low temperature conditions with a tool comprising steel according to the invention, a method of pressing metal powder with a tool comprising steel according to the invention, It is also an object to provide a method for producing the steel according to the invention.

  The steel according to the invention is produced by powder metallurgy, which is a precondition because the steel is highly free of oxide content. Preferably, powder metallurgy production includes a gas spray of molten steel using nitrogen as the atomizing gas, whereby the alloy steel will achieve a minimum nitrogen content. If desired, the steel powder can be nitrided in the solid phase to further increase the nitrogen content in the steel. Thereafter, consolidation is performed by hot isostatic pressing. Steel can be used in this state or after forging / rolling to final dimensions.

Unless otherwise stated, this description always represents weight percent with respect to the chemical composition of the steel and volume percent with respect to the structural components of the steel. Unless otherwise stated, the designations MX carbide, M ₇ X ₃ carbide, or simply carbide always mean nitride and / or carbonitride in addition to carbide. M ₆ C carbide always means only carbide.

  The following applies for the individual alloy materials and their interrelationships, as well as for the structure and heat treatment of the steel.

Carbon, and an amount of nitrogen is also necessary, from typically of 1050 ° C. austenitizing temperature T _A, in a state in which the cured and tempered steel, vanadium and so as to form a 8-13 wt% of MX carbides Should be present in the steel in sufficient amounts with niobium if necessary, where M is essentially vanadium, X is carbon and nitrogen, preferably mostly carbon, at least 90 volume of the carbide. % Have an equivalent diameter of at most 2.5 μm, preferably at most 2.0 μm. Such MX carbide contributes to providing the steel with the desired wear resistance in a manner known per se to those skilled in the art, and MX carbide also provides finer particles and a certain amount of secondary hardening. Has a certain effect. By selecting a suitable heat treatment, ie austenitizing temperature and tempering temperature, the MX carbide content of the steel can be varied within the above range so as to obtain a microstructure suitable for the purpose, which is Described in more detail in the experimental description and accompanying figure description. In addition to these MX carbides, the steel should essentially contain no other primary precipitated carbides such as M ₇ X ₃ carbides and M ₆ C carbides.

  Preferably, the steel does not contain nitrogen inevitably and naturally contained by absorption from the environment and / or added raw materials, ie up to about 0.12%, preferably up to about 0.10%. However, in contemplated embodiments, the steel may contain a higher amount of intentionally added nitrogen that can be supplied by solid phase nitriding of the steel powder used in the manufacture of the steel. In this case, the majority of (C + N) may be nitrogen, in which case said M is mainly vanadium carbonitride, in which nitrogen is the main component together with vanadium, or even pure vanadium nitride. On the other hand, carbon essentially means that it is present simply as dissolved in the quenched and tempered steel matrix.

  Vanadium contains at least 4.8% but up to 6.3% in steel to form the above MX carbides with a total content of 8-13% by volume in the use of quenched and tempered steel It should be present in steel with carbon and nitrogen present in quantity. Vanadium can in principle be replaced by niobium, but it requires twice the amount of niobium compared to vanadium, which is a disadvantage. Niobium also causes sharper MX carbide shapes, which are larger than pure vanadium carbide. Thereby, crushing or fragmentation can start, thus reducing the toughness of the material, which is a disadvantage. Niobium should therefore not be present in a content exceeding 2%, preferably a maximum of 1%, suitably a maximum of 0.1%. Most preferably, the steel does not contain any intentionally added niobium, and niobium should not be tolerated at a content exceeding the impurity content in the form of residual elements resulting from the raw materials involved in the production of the steel.

  According to one aspect of the present invention, the content of one (C + N) and the other (V + Nb / 2) in the steel is such that the contents of these elements are coordinates A, B, C, in the coordinate system of FIG. Should be balanced with respect to each other so that they lie within the region defined by D, A, where the coordinates [(C + N), (V + Nb / 2)] of these points are A: [1. 38, 4.8], B :, 1.78, 4.8], C: [2.32, 6.3], and D: [1.92, 6.3]. Within this range, steels with very useful property profiles can be provided. With an adapted heat treatment, an adapted combination of hardness, wear resistance, ductility, and machinability can be obtained. Within this broadest composition range, hardness and wear resistance improve as the total amount of (C + N) and (V + Nb / 2) in the steel increases, while ductility may be advantageous as the total amount of these elements decreases. Generally applicable.

  According to a more preferred embodiment, the content of these elements should be in the region defined by the coordinates E, F, G, H, E in the coordinate system of FIG. 11, where the coordinates of these points are [(C + N), (V + Nb / 2)] is 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 content of one (C + N) and the other (V + Nb / 2) is such that the content of these elements is the coordinates K, L, M, N, K in the coordinate system of FIG. Should be balanced with respect to each other so that they lie within the region defined by, where the coordinates [(C + N), (V + Nb / 2)] of these points are K: [1.62,5 .2], L: [1.82, 5.2], M: [2.05, 5.8], and N: [1.85, 5.8].

  According to still another aspect of the present invention, the content of one (C + N) and the other (V + Nb / 2) is such that the content of these elements is 0.32 ≦ (C + N) / (V + Nb / 2) ≦. Should be balanced with each other to meet the 0.35 requirement.

According to still another aspect of the present invention, the content of one (C + N) and the other (V + Nb / 2) is such that the content of these elements is the coordinates A ′, B ′, C in the coordinate system of FIG. Should be balanced with respect to each other so that they lie within the region defined by ', D', A ', where the coordinates [(C + N), (V + Nb / 2)] of these points are A ': [1.52, 5.2], B ' : [1.93, 5.2], C ' : [2.18, 5.9], D ' : [1.77, 5.9] It is.

Carbon also in solid solution in the matrix of the steel hardened and tempered condition, the presence in a content of 0.4 to 0.6 wt% at austenitizing temperature T _A of 980～1050C, contribute to the hardness To do.

  Silicon is present as a residual element from the production of steel in a content of at least 0.1%, usually at least 0.2%. Silicon increases the activity of carbon in the steel and thus contributes to giving the steel adequate hardness. A too high content can lead to brittleness problems due to solid solution hardening, so the maximum content in silicon steel is 1.5%, preferably up to 1.2%, suitably up to 0.9% It is. The Si content useful for steel is 0.2 to 0.5 Si. This steel has a nominal content of 0.4% Si.

  Manganese is added to the steel at a content of at least 0.1% in order to combine with the amount of sulfur that may be present in the steel by forming manganese sulfide. Manganese, as well as elemental chromium and molybdenum, also contribute to imparting adequate hardenability to the steel, which means that a manganese content of 0.1% is acceptable without any negative effect on the properties of the steel. It means that it can be done. At high contents, manganese can cause undesired stabilization of retained austenite, which leads to a decrease in hardness. Residual austenite can also destabilize the steel, which is a major drawback. The manganese content should therefore not exceed 1.2% Mn, and the manganese content useful for steel is in the range of 0.1-0.9% Mn. This steel has a nominal content of 0.4% Mn.

As mentioned above, chromium contributes to the hardenability of the steel and therefore should be present at a content of at least 4.0%, preferably at least 4.5%. Chromium is also a carbide forming element and is used to contribute to the wear resistance of many steels by forming M ₇ X ₃ carbides. Such carbides can be dissolved to varying degrees by selecting the appropriate austenitizing temperature for quenching, and chromium and carbon dissolved in such form in austenite, and then to varying degrees. It can be precipitated to form very small secondary precipitated carbides that will effectively contribute to giving the steel the desired hardness in connection with tempering.

The steel according to the invention should exhibit very good wear resistance, among other things, and should be able to be hardened to a relatively high hardness. It has now been shown that this can be achieved at the same time that the steel is given surprisingly good ductility, surpassing some of Applicants' own steels sold for similar applications. By limiting the chromium content, it was possible to prevent or at least minimize the formation of M ₇ X ₃ carbides in favor of the formation of primary precipitated MX carbides. In order to achieve such a beneficial carbide composition, the chromium content should therefore be limited to a maximum of 5.5%, even more preferably a maximum of 5.1%. The beneficial chromium content for steel is 4.8%.

Most of the chromium added to the steel will be dissolved in the steel so as to contribute to the hardenability of the steel. According to the concept of the present invention, this steel should have the hardenability essential to hardening throughout in various dimensions, and if this steel is to be used in large dimensions, the hardenability is This is a particularly important aspect. Therefore, molybdenum should be present in the steel at a content of at least 1.5%. Molybdenum content up to 3.6% Mo can be tolerated without risking undesirable M ₆ C carbide precipitation. Preferably the steel contains between 1.5-2.6% Mo, and even more preferably 1.6-2.0% Mo.

  Molybdenum can be replaced with tungsten to some extent, but this requires twice the amount of tungsten compared to molybdenum, which is a disadvantage. It also makes scrap handling more difficult. Accordingly, tungsten should not be present at a content exceeding 0.5% maximum, preferably 0.3% maximum and suitably 0.1% maximum. It is most preferred that the steel does not contain any intentionally added tungsten, and in the most preferred embodiment tungsten is acceptable at a content exceeding the impurity level in the form of residual elements arising from the raw materials involved in the manufacture of the steel. Should not be done.

  Sulfur is mainly present in the steel as an impurity with a maximum content of 0.03%. However, according to one embodiment, to improve the machinability of the steel, the steel contains intentionally added sulfur with a content of up to 0.3%, preferably up to 0.15%. It is possible.

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

  The following composition is an example of possible variations of this steel within the scope of the present invention. C1.9%, Si 0.4%, Mn 0.4%, Cr 4.8%, Mo 3.5%, V5.8%, and the rest is essentially iron.

  The following composition is yet another example of a possible variant of this steel. C1.67%, Si0.4%, Mn0.4%, Cr4.8%, Mo2.3%, V5.2%, and the rest essentially iron.

  The following composition is yet another example of a possible variant of this steel. C1.80%, Si0.4%, Mn0.4%, Cr4.8%, Mo1.8%, V5.8%, the rest being essentially iron.

  The above variant is to obtain a slightly different property profile so that steels with increased contents of the carbide-forming materials molybdenum and vanadium get better wear resistance at the cost of a slight decrease in ductility. Optimized for. Steel with a reduced content of these two elements will obtain higher ductility at the expense of a slight decrease in wear resistance.

  In the production of steel, it contains a certain amount of carbon, silicon, manganese, chromium, molybdenum, optionally tungsten, vanadium, optionally niobium, possibly more sulfur than the impurity content, unavoidable nitrogen, the remainder iron and impurities The molten steel to be prepared is first prepared. Powder is produced from this melt by nitrogen gas spraying. The vanadium carbide formed and / or the mixed carbide of vanadium and niobium does not have time to grow and has a thickness not exceeding one micrometer piece so that it becomes very thin, and the droplets solidify to form powder particles. Prior to forming the droplets, the droplets formed by gas spray are quenched to obtain a noticeable irregular shape resulting from the carbides deposited in the region of residual melt in the dendritic network in the small solidified droplets To do. If the steel contains nitrogen above the inevitable impurity content, this is achieved, for example, by nitriding the powder as described in Swedish patent 462,837.

  After sieving (if the powder is nitrided, suitably done before nitriding), the powder is filled into capsules, which are then degassed and sealed, usually at high temperatures and high pressures of 950-1200 ° C. and 90-150 MPa. Is subjected to hot isostatic pressing or HIP treatment (known per se) at about 1150 ° C. and 100 MPa so that the powder is baked to form a complete compact.

  The HIP process will give the carbide a more regular shape than it has in the powder state. The majority of the volume has a maximum size of about 1.5 μm and a rounded shape. Occasionally there are still long and slightly long (up to about 2.5 μm) particles. This deformation is most likely due to a combination of the decomposition and coalescence of very thin particles in the powder.

  This steel can be used in a HIP-treated state. Usually, however, this steel is hot worked by forging and / or hot rolling after the HIP treatment. This is done at an onset temperature between 1050-1150 ° C, preferably about 1100 ° C. This results in further coalescence of the carbides and especially spheroidization. After forging and / or rolling, at least 90% by volume of the carbide has a size of at most 2.5 μm, preferably at most 2.0 μm.

The steel must first be soft annealed so that it can be machined with a cutting tool. This is done at a temperature below 950 ° C, preferably about 900 ° C. Once the tool is finalized by cutting, it is quenched and tempered. In austenitizing, MX carbides are dissolved to some extent so that they are secondary precipitated during annealing. Besides these MX carbides, the steel should not contain any other carbides. Quenching thereby reduces the austenitizing temperature, usually 980-1150 ° C., much lower than the conventional austenitizing temperature for steels with corresponding wear resistance, in order to prevent unnecessarily large amounts of MX carbide from dissolving. In the meantime, it can be carried out preferably from less than 1100 ° C. A suitable austenitizing temperature is 1000 to 1050 ° C. This is a decisive advantage for tool manufacturers because the steel can then be heat treated with most other tool steels available on the market. In the state where T _A 980-1050 ° C. steel is quenched, the matrix consists essentially of martensite containing 0.4-0.6% carbon in the solid solution.

Subsequent tempering can be carried out at temperatures between 200 and 600 ° C, preferably between 500 and 560 ° C. The final result is a microstructure typical of the present invention, consisting of tempered martensite, 8-13% by volume of the tempered martensite being MX carbide, where M is essentially vanadium. , X is carbon and nitrogen, preferably mainly carbon, of which at least 90% by volume has an equivalent diameter of at most 2.5 μm, preferably at most 2.0 μm. The carbides have mostly round or rounded shapes, but occasionally long carbides can be present. In this description, the equivalent diameter D _ekv is defined as D _ekv = 2√A / π, where A is the area of the carbide particles in the cross section being examined. Typically, at least 96% by volume of MX carbide, MX nitride, and / or carbonitride has D _ekv <3.0 μm. Usually, the carbide is also spheroidized so that there is no carbide with an actual length exceeding 3.0 μm in the observed cross section. After hardening and tempering, the steel has a hardness of 58-66 HRC.

  Other features and aspects of the present invention will be apparent from the appended claims and from the description of experiments performed below.

BRIEF DESCRIPTION OF THE DRAWINGS In the following description of experiments performed, reference will be made to the accompanying drawings.

  FIG. 1 shows the microstructure of the steel according to the invention after quenching and tempering.

  FIG. 2 is a diagram showing the microstructure of a commercially available comparative material after quenching and tempering.

  FIG. 3 shows the microstructure of a further commercially available comparative material after quenching and tempering.

  FIG. 4 is a graph showing the hardness of the steel according to the invention as a function of the austenitizing temperature.

  FIG. 5 is a graph showing the hardness of the steel according to the invention as a function of the tempering temperature at different austenite temperatures.

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

  FIG. 7 is a graph showing the machinability of steel according to the present invention as well as some comparative materials.

  FIG. 8 is a further graph showing the machinability of the steel according to the invention and the comparative material.

  FIG. 9 shows a combination of non-notch impact energy and wear resistance for steel according to the present invention and several comparative materials.

  FIG. 10 shows the wear rate in the wear test of the steel according to the invention and several comparative materials.

  FIG. 11 is a graph of the relationship between the content of carbon and nitrogen present versus the content of vanadium and niobium present.

  FIG. 12 is a graph of edge wear on the upper and lower knives after the cutting test.

  13a and 13b are views showing the side surface of the upper knife after the cutting test.

  14a and 14b are views showing the front surface of the upper knife after the cutting test.

  15a and 15b are views showing the front surface of the lower knife after the cutting test.

Description of Experiments Performed Table 1 shows the chemical composition of the investigated steels. In this table, sulfur shown for some steels is an impurity. Other impurities are not accounted for but do not exceed normal impurity levels. The rest is iron. In Table 1, steel 7 has a chemical composition according to the present invention. Steels 1-5 are reference materials.

  Steels 1 to 5 are commercially available steels, all of which are applicant's steels except steel number 1. Samples of these steel materials were ordered and analyzed for chemical composition. All of these steels were manufactured by powder metallurgy and ordered with soft annealing. A 6 ton melt was produced from Steel No. 7 according to conventional metallurgical melting techniques. Molten powder was produced from the melt by nitrogen gas spraying of the melt jet. The formed small droplet was quenched.

  Two ton blanks each having the chemical composition according to Table 1 were produced from steel 7 powder. The steel powder was placed in a sheet metal capsule, then sealed, degassed and heated to about 1150 ° C., followed by hot isostatic pressing (HIP) at about 1150 ° C. and a pressure of 100 MPa. The carbide structure of the initially obtained powder was decomposed during the HIP process, while the carbides were coalesced. In the state where the steel was HIP treated, the carbides obtained a more regular shape close to the spheroidized shape. They are still very small. Most of the over 90% by volume have an equivalent diameter of up to 2.5 μm, preferably up to about 2.0 μm.

  Thereafter, the blank was forged into a round bar having a size of 100 mm at a temperature of 1100 ° C. Steel No. 7 was soft annealed at 900 ° C., its microstructure was examined, and a hardness test was performed. The carbides are still present in the material in the form of very small, essentially spheroidized MX carbides up to about 2.0 μm in terms of equivalent diameter. After soft annealing, test samples were taken from steel number 7 for subsequent testing. Test samples of the same type were taken from reference materials 1-5 ordered in the soft annealed state.

  Table 2 shows the heat treatment associated with the quenching and tempering of various steels. The microstructure in the hardened and annealed state is represented by three of these steels, more specifically steel number 7 according to the invention shown in FIG. 1 and the references shown in FIGS. 2 and 3, respectively. Steel numbers 4 and 1 were examined. The steel according to the invention (FIG. 1) contained 11.7% by volume of MX carbide in the matrix consisting of tempered martensite. In addition to MX carbide, no carbide was detected. In the quenched and tempered steel according to the invention, carbides having an equivalent diameter of more than 3.0 μm could occasionally be found.

Reference steel number 4 (FIG. 2), when quenched and tempered, contains a total of about 14.4% by volume of carbides, of which about 9.2% by volume is MC carbides, and about 5.2% by volume. Was M ₇ C ₃ carbide. As is apparent from the figure, M ₇ C ₃ carbide is relatively large and generally larger than MC carbide. This mainly has a negative effect on ductility. Reference steel number 1 (FIG. 3) contained about 15.7% by volume MC carbides when quenched and tempered. Other carbides were not detected. A high content of carbide provides relatively good wear resistance in steel, but results in reduced ductility.

  Table 2 also shows the hardness after the heat treatment defined in Table 2. Following high temperature tempering, the steel 7 according to the invention obtained a hardness comparable to the reference material number 5, which is a high alloy. Its hardness was about 1 HRC unit higher than the investigated reference material numbers 2-4.

  The impact strength of the above materials was also examined, and the results are shown in FIG. Measured impact energy (J) absorbed in both the LC2 and CR2 directions, a dramatic improvement in Steel No. 7 according to the present invention, mainly compared to Reference Material No. 4, a material intended for further development Was measured. The best value for steel number 7 according to the invention is 37 J in the transverse direction (CR2), which was measured after high temperature tempering. This represents an improvement of about 60% compared to reference material number 4.

  Even when taking hardness into account, it is clear that steel number 7 according to the invention has a unique combination of high hardness and very good ductility, which is closest to reference material number 5 with comparable hardness, This is shown in FIG. The sample bar was cut and polished, and an unnotched sample bar having dimensions of 7 × 10 mm and a length of 55 mm was cured to the hardness of Table 2.

  The hardness of steel number 7 according to the invention was also examined after various austenitizing and tempering temperatures. The results are shown in the graphs of FIGS. Already at a relatively low austenitizing temperature of 1030 ° C., steel number 7 exhibits the greatest hardness, which is very advantageous from the point of view of heat treatment, since most of the commercial tool steel is heat treated at this temperature. You must think that there is. Most of the reference steel must be heated to about 1060-1070 ° C. to obtain maximum hardness. For reference steel number 1, the maximum hardness was not obtained up to a temperature of 1100-1150 ° C.

  As is apparent from FIG. 5, significant secondary curing is achieved by tempering at temperatures between 500 and 550 ° C. This steel also provides the possibility of low temperature tempering at about 200-250 ° C. It is also clear from the figure that residual austenite can be removed by high temperature tempering.

The wear resistance of the steel according to the invention is also compared with some reference materials and the results are shown in FIG. In the abrasion test, a sample rod having a size of φ15 mm and a length of 20 mm was used. The test was conducted as a pin-on-disk test using SiO ₂ as an abrasive wear agent. Prior to the abrasion test, reference steel numbers 2-5 and steel number 7 according to the invention were tempered to a hardness of 62.5 HRC. Reference steel number 1 had a slightly higher hardness of 62.7 HRC, obtained by quenching from 1120 ° C./30 minutes and tempering at 540 ° C./3×2 h. The wear rate in mg / min is also shown in Table 2. Steel number 7 was found to have good wear resistance similar to reference steel number 4, and was superior to reference steel numbers 2 and 3. Reference steel number 5 has slightly better wear resistance than steel number 7. Reference steel number 1 had the best wear resistance of all the steels.

  In two different experiments, the machinability of steel No. 7 according to the present invention was compared with reference steels 2-5, and the results are also shown in Table 2 and FIGS. FIG. 7 shows the results of testing the machinability of a soft annealed test sample by lathing with a cemented carbide cutting edge, and FIG. 8 shows the drill test of the material with an uncoated drill. The results of these tests show that steel number 7 according to the invention has very good machinability, i.e. high values of V30 and V1000 which are almost double compared to the reference material 4 in particular.

  In the practical test, the edge wear resistance was examined by a cutting test. Cutting knives were manufactured from Steel No. 4 and Steel No. 7. These knives were quenched and tempered to a hardness of 60.5 HRC and 60.0 HRC, respectively. The cutting test was conducted on an ESSA eccentric press with a maximum cutting load capacity of 15 tons and a cutting speed of 200 cuts per minute. Cutting was performed on a high-strength steel strip having a steel grade Docol 1400M, a width of 50 mm, and a thickness of 1 mm. The clearance for cutting was 0.05 mm.

  The edge wear of the upper and lower knives was measured and the results are shown in FIG. In FIG. 12, the graph shows edge wear after 100,000 cuts and after the end of the test. For knives made from steel number 5, the test had to be stopped after 150,000 cuts for edge chipping. The knife made from steel number 7 did not show any chipping tendency after 315,000 cuts at the end of the test. It is clear that Steel No. 7 showed much better edge wear resistance than Steel No. 5.

  In FIGS. 13a, b, the side of the upper knife of steel number 5 after the 150,000 cut and steel number 7 after the 315000 cut, ie the surface of the cutting tool parallel to the cutting direction, is shown after the end of the test. It can be seen from the figure that steel number 5 shows significantly greater abrasive wear after 150,000 cuts compared to steel number 7 after more than twice the cut.

  FIGS. 14a, b show the front of steel number 5 and steel number 7 upper knives after 150,000 and 315000 cuts, respectively, and FIGS. 15a, b show the front of steel number 5 and steel number 7 lower knives, The surface of the cutting tool perpendicular to the cutting direction of the steel sheet is shown. It can be seen that both the upper and lower knives made from steel number 5 show edge chipping, while the steel number 7 edge shows no tendency to chipping.

  Practical tests show that the steel of the present invention has better toughness and better wear resistance than reference steel number 5. In particular, resistance to chipping is advantageous.

  According to the inventive concept, the steel should have good hardenability. It has been found that the hardenability of the steel according to the invention can be varied within a wide range of steel compositions. This means that a steel according to the invention with a molybdenum content close to or close to the lower limit of its range obtains a relatively low hardenability compared to a steel according to the invention with a molybdenum content close to or close to its upper limit. In fact, it is possible to change the molybdenum content within a predetermined limit so that a hardenability exceeding the hardenability of the reference material numbers 1 and 4 can be obtained in the entire range of the molybdenum content. On a relative scale between 1 and 10 (1 = poor hardenability and 10 = best hardenability), steel number 7 according to the invention has a rating of 10. A steel variant according to the invention with a molybdenum content of 2.3% will get a rating of 4. These ratings and reference material ratings are shown in Table 2.

  By means of known theoretical calculations, ie Thermo Calc calculations, the carbide content and the amount of molybdenum in the solid solution of the matrix at equilibrium are calculated for a steel variant of the invention designated as steel number 6, steel number 4 and 7 compared. 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 alloyed Designed to further reduce elemental costs. The results are shown in Table 3 below.

  Compared to steel number 7, steel number 6 has a lower amount of molybdenum in the solid solution of the matrix, which results in reduced hardenability. However, the hardenability is on the order of steel number 4 and is sufficient for the quenching and tempering of round bars of φ250 mm or square bars with dimensions up to 400 × 200 mm, which is the dimension of the tool for the intended field of application. Is covered. Due to the lower amount of MC carbide in the matrix, Steel No. 6 will have higher ductility at the expense of less abrasive wear than Steel No. 7. Compared to steel number 4, steel numbers 6 and 7 of the present invention will have higher ductility and better abrasive wear resistance.

  In conclusion, with the steel according to the invention, a material with high hardness and very good wear resistance is obtained, which is cut and stamped, threaded (eg threaded dies and thread taps), cold It can be said to be suitable for use in extrusion, powder pressing, cold working tools for deep drawing, and mechanical knives. Steel that also exhibits surprisingly good ductility, relatively good machinability, and in the most preferred embodiment, allows the steel to be quenched with good results throughout, even at very large dimensions Steels that also exhibit very good hardenability can provide steels that are very suitable for practical applications and that have a remarkably good property profile. Within the scope of the present invention, steels that are not very good in hardenability but are otherwise equally good can be provided, and tools with thinner dimensions are to be produced. This is still advantageous from a cost standpoint.

2 shows the microstructure of the steel according to the invention after quenching and tempering. FIG. It is a figure which shows the microstructure of the commercially available comparative material after hardening and tempering. FIG. 4 shows the microstructure of a further commercially available comparative material after quenching and tempering. 2 is a graph showing the hardness of a steel according to the invention as a function of austenitizing temperature. 4 is a graph showing the hardness of the steel according to the invention as a function of the tempering temperature at different austenite temperatures. 1 is a graph showing the ductility of a steel according to the invention which has been tempered at high temperature and several comparative materials. 2 is a graph showing the machinability of steel according to the invention and several comparative materials. 4 is a further graph showing the machinability of the steel according to the invention and the comparative material. FIG. 3 shows a combination of non-notch impact energy and wear resistance for steel according to the invention and some comparative materials. FIG. 3 shows the wear rate in the wear test of the steel according to the invention and some comparative materials. FIG. 3 is a graph of the relationship between the content of carbon and nitrogen present versus the content of vanadium and niobium present. It is a graph about edge wear in an upper knife and a lower knife after a cutting test. a and b are side views of the upper knife after the cutting test. a and b are diagrams showing the front surface of the upper knife after the cutting test. a and b are diagrams showing the front surface of the lower knife after the cutting test.

Claims (24)

Mass% (C + N) 1.52~2.32,
N 0.12 or less,
Si 0.1-1.5,
Mn 0.1-1.5,
Cr 4.0-5.5,
(Mo + W / 2) 1.6-2.0 ,
W 0.3 or less,
(V + Nb / 2) 5.2 to 6.3 ,
Nb 0.3 or less,
S 0.3 or less Here, the content of one (C + N) and the other (V + Nb / 2) is such that the content of these elements is the coordinates A ′ , B ′ , C in the coordinate system of FIG. , D, A ′ are balanced relative to each other so as to be within the region defined by
Here, the coordinates [(C + N), (V + Nb / 2)] of these points are A ′ : [ 1.52, 5.2 ].
B ′ : [ 1.93, 5.2 ]
C: [2.32, 6.3]
D: [1.92, 6.3]
And
As well as, the rest of iron and non-pure product
Steel for cold work tool consisting. The content of one (C + N) and the other (V + Nb / 2) is such that the content of these elements is in the region defined by the coordinates K, L , G, H, K in the coordinate system of FIG. Balanced with each other,
Here, the coordinates [(C + N), (V + Nb / 2)] of these points are
K: [1.62, 5.2]
L: [1.82, 5.2]
G: [2.22, 6.3]
H: [2.02, 6.3]
And characterized in that the steel iron according to claim 1. The content of one (C + N) and the other (V + Nb / 2) is such that the content of these elements is in the region defined by the coordinates K, L, M, N, K in the coordinate system of FIG. Balanced with each other,
Here, the coordinates [(C + N), (V + Nb / 2)] of these points are K: [1.62, 5.2].
L: [1.82, 5.2]
M: [2.05, 5.8]
N: [1.85, 5.8]
And characterized in that the steel iron according to claim 2. The contents of one (C + N) and the other (V + Nb / 2) are mutually adjusted so that the contents of these elements satisfy the condition of 0.32 ≦ (C + N) / (V + Nb / 2) ≦ 0.35 Related characterized in that it is balanced, steel iron according to any one of claims 1 to 3. Characterized in that it contains 0.1 to 1.2% of S i, steel according to any one of claims 1-4. Steel according to claim 5, characterized in that it contains 0.2-0.9% Si.   6. Steel according to claim 5, characterized in that it contains 0.4% Si. Steel according to any one of claims 1 to 7 , characterized in that it contains 0.1 to 1.3% of Mn . Steel according to claim 8, characterized in that it contains 0.1-0.9% Mn. 9. Steel according to claim 8 , characterized in that it contains 0.4% Mn. Steel according to any one of claims 1 to 10 , characterized in that it contains 4.5 to 5.1% Cr. 12. Steel according to claim 11 , characterized in that it contains 4.8% Cr. The steel according to any one of claims 1 to 12 , characterized in that it contains 1.8% (Mo + W / 2). Characterized in that it contains a maximum of 0.1% of W, steel according to any one of claims 1 to 13. Characterized in that it contains a maximum of 0.1% of Nb, steel according to any one of claims 1 to 14. Steel according to any one of claims 1 to 15 , characterized in that it contains up to 0.15% S. Characterized by having a 980 to 1,050 quenching from temperatures between ° C., and 500 to 560 Hardness ranging obtained 58~63HRC after tempering twice for 2 hours at a temperature of ° C., according to claim 1 steel according to one wherein one to 16 of. It has a hardness in the range of 59-62 HRC obtained after quenching from a temperature between 980-1020 ° C and two tempers for 2 hours at a temperature of 500-560 ° C. The steel according to any one of 16 above. After quenching and tempering from 1050 ° C., it has a microstructure containing 8-13% by volume of MX carbide, MX nitride and / or MX carbonitride uniformly dispersed in the steel matrix, where M is a vanadium, X is carbon and / or nitrogen, this carbide, of nitrides and / or carbonitrides at least 90 volume% has a considerable diameter _{D EKV} less than 3.0 [mu] m, _M 7 C ₃ carbides, characterized in that it contains no M ₇ C ₃ nitrides and / or carbonitrides, steel according to any one of claims 1 to 18. 20. Steel according to claim 19 , characterized in that at least 90% by volume of the MX carbide has a maximum length of 2.0 [mu] m. 21. A method of cutting, shearing, stamping and / or forming metalworking material at low temperature conditions using a tool comprising the steel according to any one of claims 1-20 . A method for pressure forming metal powder using the steel-containing tool according to any one of claims 1 to 20 . The following production steps: a) producing metal powder from a metal melt;
b) hot isostatic pressing the powder at a temperature between 950 and 1200 ° C. and a pressure between 90 and 150 MPa to form a baked solid;
c) hot working the calcined solid at an initial temperature between 1050 and 1150 ° C .;
d ) soft annealing at 900 ° C .;
e) quenching from a temperature between 980-1050 ° C. and tempering at a temperature between 500-560 ° C. to a hardness in the range of 58-66 HRC, comprising the steps of: The method of claim 1, wherein the metal powder has the composition of claim 1. The method according to claim 23, wherein the hardness range in step e is 61 to 63HRC.

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