CN115505838A - High-strength-toughness low-alloy die steel and preparation method thereof - Google Patents
High-strength-toughness low-alloy die steel and preparation method thereof Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 182
- 239000010959 steel Substances 0.000 title claims abstract description 182
- 229910045601 alloy Inorganic materials 0.000 title claims abstract description 27
- 239000000956 alloy Substances 0.000 title claims abstract description 27
- 238000002360 preparation method Methods 0.000 title abstract description 6
- 238000005452 bending Methods 0.000 claims abstract description 36
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 11
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 10
- 229910052729 chemical element Inorganic materials 0.000 claims abstract description 5
- 238000005242 forging Methods 0.000 claims description 38
- 238000000034 method Methods 0.000 claims description 25
- 238000010438 heat treatment Methods 0.000 claims description 23
- 238000005496 tempering Methods 0.000 claims description 23
- 238000010791 quenching Methods 0.000 claims description 20
- 230000000171 quenching effect Effects 0.000 claims description 20
- 229910052799 carbon Inorganic materials 0.000 claims description 17
- 229910052720 vanadium Inorganic materials 0.000 claims description 17
- 229910052750 molybdenum Inorganic materials 0.000 claims description 16
- 229910052759 nickel Inorganic materials 0.000 claims description 14
- 239000000126 substance Substances 0.000 claims description 14
- 229910052710 silicon Inorganic materials 0.000 claims description 11
- 229910052804 chromium Inorganic materials 0.000 claims description 10
- 229910052748 manganese Inorganic materials 0.000 claims description 6
- 239000002893 slag Substances 0.000 claims description 6
- 238000003723 Smelting Methods 0.000 claims description 3
- 230000006698 induction Effects 0.000 claims description 3
- 229910001338 liquidmetal Inorganic materials 0.000 claims description 3
- 238000004321 preservation Methods 0.000 claims 2
- 239000000463 material Substances 0.000 description 28
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 27
- 239000011651 chromium Substances 0.000 description 19
- 230000008569 process Effects 0.000 description 18
- 239000011159 matrix material Substances 0.000 description 16
- 229910000734 martensite Inorganic materials 0.000 description 13
- 239000000203 mixture Substances 0.000 description 13
- 150000001247 metal acetylides Chemical class 0.000 description 10
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- 238000005516 engineering process Methods 0.000 description 6
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- 239000011733 molybdenum Substances 0.000 description 5
- 239000010703 silicon Substances 0.000 description 5
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- 238000000354 decomposition reaction Methods 0.000 description 4
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- UFGZSIPAQKLCGR-UHFFFAOYSA-N chromium carbide Chemical compound [Cr]#C[Cr]C#[Cr] UFGZSIPAQKLCGR-UHFFFAOYSA-N 0.000 description 2
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- 238000009628 steelmaking Methods 0.000 description 2
- 230000008646 thermal stress Effects 0.000 description 2
- 229910003470 tongbaite Inorganic materials 0.000 description 2
- INZDTEICWPZYJM-UHFFFAOYSA-N 1-(chloromethyl)-4-[4-(chloromethyl)phenyl]benzene Chemical compound C1=CC(CCl)=CC=C1C1=CC=C(CCl)C=C1 INZDTEICWPZYJM-UHFFFAOYSA-N 0.000 description 1
- QIJNJJZPYXGIQM-UHFFFAOYSA-N 1lambda4,2lambda4-dimolybdacyclopropa-1,2,3-triene Chemical compound [Mo]=C=[Mo] QIJNJJZPYXGIQM-UHFFFAOYSA-N 0.000 description 1
- 229910039444 MoC Inorganic materials 0.000 description 1
- 229910018487 Ni—Cr Inorganic materials 0.000 description 1
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- 125000004432 carbon atom Chemical group C* 0.000 description 1
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- 239000003795 chemical substances by application Substances 0.000 description 1
- VNNRSPGTAMTISX-UHFFFAOYSA-N chromium nickel Chemical compound [Cr].[Ni] VNNRSPGTAMTISX-UHFFFAOYSA-N 0.000 description 1
- 238000010835 comparative analysis Methods 0.000 description 1
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- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
- B21J5/00—Methods for forging, hammering, or pressing; Special equipment or accessories therefor
- B21J5/002—Hybrid process, e.g. forging following casting
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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Abstract
The invention relates to high-strength low-toughness low-alloy die steel and a preparation method thereof：C0.78～0.88％,Si0.90～1.05％,Mn1.10～1.30％,P<0.02％,S<0.02 percent, cr2.80 to 3.60 percent, mo0.30 to 0.40 percent, V0.30 to 0.45 percent, ni0.50 to 0.70 percent and the balance of Fe; and the content of the main chemical elements is in accordance with the following mathematical relation: c =0.45Mn +0.10Cr. After the steel is quenched at 930 ℃ and tempered at 180 ℃, the bending strength reaches 3350MP-3500MP and the impact toughness is 140J/cm 2 ‑155J/cm 2 The bending strength is improved by 30 percent, and the impact toughness is improved by 100 percent.
Description
Technical Field
The invention relates to high-strength low-alloy die steel and a preparation method thereof, in particular to a matched cold punching die material which has the advantages of good hardenability, lower quenching temperature, small heat treatment deformation, low alloy cost, better bending strength and toughness, and is used for cold punching forming and manufacturing of complex dies with high bending strength and toughness.
Background
The cold punching die is used for the working procedures of punching load, impact forming, bending, cold heading and the like of metal or nonmetal materials. The working object is in a room temperature state, and the working condition of the die is quite bad. The cold die steel generally selected requires sufficient strength, toughness, bending resistance, and wear resistance. For cold extrusion and cold upset body forming dies with large loads, the material is required to have higher bending resistance and fracture resistance.
At present, the bending-resistant cold work die steel material which is most widely applied to the domestic and foreign die material markets is high-carbon high-chromium cold work die steel 1.2379 steel (the mass percentages of the components are, C1.5-1.6%, si 0.10-0.40%, mn 0.15-0.45%, cr 11.0-12.0%, mo 0.60-0.80%, V0.90-1.10%, P is less than 0.030%, S is less than 0.030%), the bending-resistant cold work die steel belongs to ledeburite steel, has high hardenability, hardenability and wear resistance, and can be used as a general cold punch die steel material for manufacturing cold punch dies for various purposes, such as punching female dies with complex shapes, cold extrusion dies, rolling screw wheels, cold shearing knives, precision measuring tools and the like. However, the Cr content in the alloy element composition of the general cold-work die steel material reaches Cr11.0-12.0%, and the excessive Cr content can cause the existence of network ledeburite carbide in the material microstructure, which results in low toughness of the material. 1.2379 the performance index of the steel is that the impact toughness is 77J/cm after quenching at 1030 ℃ and tempering at 180 DEG C 2 The hardness was 61.5HRC and the bending strength was 2700MP. The performance indexes are key technical indexes of the bending-resistant cold stamping die steel. The bending-resistant cold punching die is mainly used for cold forming of metal or nonmetal materials, including cold formingStamping, cold extrusion, cold heading, and the like. The cold punching die has the advantages of large working load, high dimensional precision and high surface quality requirement. The cold die steel generally selected requires sufficient flexural strength, toughness, and hardness. On the other hand, the 1.2379 steel contains uneven ledeburite carbide in the structure, although the steel has higher hardness and wear resistance after quenching and tempering, the steel has lower toughness and unsatisfactory bending strength, so the steel is easy to crack and collapse in practical use.
The 1.2379 steel is smelted by an electric arc furnace, cast into a steel ingot, forged and cogging, and the specific steps comprise steelmaking, forging and heat treatment in sequence to finally form a product. The heating temperature of the forging is 1100-1140 ℃, the finish forging temperature is more than or equal to 880 ℃, and the cooling mode adopts high-temperature annealing, pit cooling or sand cooling. The 1.2379 steel forms a large amount of coarse eutectic carbides in a continuous network distribution. The netlike eutectic carbide severely cuts the matrix and can also be used as a crack source and a crack propagation path when the die steel is broken, so that the grain boundary of the die steel is severely embrittled and the toughness is very low. In addition, during forging, because the limit of the forging ratio is applied, the eutectic carbide at the core part of a large-size casting blank is difficult to break, and therefore, the strip-shaped carbide segregation often exists in the die steel structure after forging, so that the performance of the die steel is anisotropic, and the forging cracking is caused.
Disclosure of Invention
The invention mainly aims to provide the high-strength low-alloy cold-work die steel and the preparation method thereof, which can comprehensively improve the comprehensive performance of the cold-work die material. The cold punching die steel with high strength and toughness, namely bending strength and high toughness, is invented by a newly designed chemical component proportion, and the low alloy element proportion is adopted to improve the manufacturing cost and improve the product competitiveness of manufacturing enterprises.
In order to achieve the purpose, the technology of the invention firstly provides the low-alloy cold-work die steel with high strength and toughness, which comprises the following components in percentage by weight:
0.78 to 0.88 percent of C, 0.90 to 1.05 percent of Si, 1.10 to 1.30 percent of Mn, less than 0.02 percent of P, less than 0.02 percent of S, 2.80 to 3.60 percent of Cr, 0.30 to 0.40 percent of Mo, 0.30 to 0.45 percent of V, 0.50 to 0.70 percent of Ni and the balance of Fe. And the content of the main chemical elements is in accordance with the following mathematical relation: c =0.45Mn +0.10Cr, because in the technology of the invention, mn is an austenite structure forming element, and the stable austenite structure can be formed only by the relationship between Mn and C, so that the steel body can obtain the stable austenite structure, and the microstructure obtains the effect that fine alloy carbide is distributed in the austenite machine matrix structure, so that the austenite body is strengthened, and the bending strength and the impact toughness property of the steel can be greatly improved.
The following are descriptions of the role and limitations of the main elements of the present invention:
C 0.78～0.88％
the C-C element is one of main chemical elements of the high-strength and high-toughness cold-work die steel, is an indispensable basic element for forming various carbides such as vanadium carbide, molybdenum carbide and chromium carbide, is an important element for influencing the composition segregation of the steel and the structural uniformity of the steel, and can ensure that the martensite has good strength and hardenability when dissolved in the martensite. The carbon content in the steel increases, the yield point and tensile strength increase, but the plasticity and impact properties decrease. In addition, carbon can increase the cold brittleness and age sensitivity of the steel. The steel composition of the present design has a greater reduction in carbon content compared to 1.2379 steel, with the aim of improving the distribution and properties of carbides in the steel microstructure, improving the level of network carbides of the steel. The lower carbon content can prevent the steel from generating segregation structure in the solidification process so as to cause the reduction of the bending strength and the impact toughness of the steel. Therefore, if the carbon content is higher than the upper limit of the composition design, excessive carbide formation and segregation of the structure will occur, which will affect the net-like properties of the steel, especially the bending strength and impact toughness of the steel will be reduced; however, the design range of the carbon element lower than the composition will cause the deviation of the equivalent weight of the carbide formed by combining the carbon element and other alloy elements, and the stable fine carbide and the compound action of the carbide can not be effectively formed, thereby affecting the strength of the steel and the hardenability of the steel.
Si 0.90～1.05％
Si is dissolved in the matrix to improve the matrix strength, can block the decomposition of martensite during tempering, improves the tempering stability of steel, and can play the role of a reducing agent and a deoxidizing agent in the steelmaking process. The silicon content of the steel is taken as an alloy element. Silicon can significantly improve the elastic limit, yield point and tensile strength of steel. Silicon can effectively block the decomposition of martensite during the tempering process after the transformation from austenite to martensite, and the transformation from epsilon carbide to Fe3C is delayed mainly by simulating the growth of epsilon carbide particles and enlarging epsilon carbide stable zone. The control of the silicon content of the invention is slightly improved compared with the prior 1.2379 steel, and the aim is to further prevent the decomposition of the martensite transformation in the tempering process and have certain effect on improving the bending strength and the impact property value of the steel after quenching.
Mn 1.10～1.30％
Most of Mn is dissolved into the matrix in the austenitizing process, so that the alloy content in the matrix is increased, and the solid solution strengthening effect is enhanced, thereby improving the strength of the matrix. However, mn has a serious positive segregation tendency, and can be enriched at eutectic cell grain boundaries to form intergranular carbides, so that the toughness of the material can be reduced. Compared with the steel 1.2379, the content of Mn in the steel of the invention is slightly improved and controlled within a certain range. The aim is to increase the strength of the matrix and to stabilize the properties of the material.
Cr 2.80～3.60％
Cr is a strong carbide forming element, can improve the hardenability of the material, and is low in price. However, cr is also a main cause of the formation of network carbide and affects the toughness of the material, so that the content of Cr is not preferably too high. The steel 1.2379 contains 11.0-12.0% of Cr, which forms network ledeburite carbide with C, the chromium carbide is unevenly distributed in the crystallization process of the steel, which not only influences the effect of improving the hardenability of the chromium element in the steel, but also reduces the bending strength and impact toughness index of the steel. Compared with the steel 1.2379, the steel of the invention greatly reduces the Cr content, the proportioning of the Cr content can not cause the material to generate massive ledeburite structure, and the internal factors of coarse structure and low impact toughness are fundamentally eliminated, thus aiming at ensuring the structure of the material to be uniform and improving the toughness of the material.
Mo 0.30～0.40％；V 0.30～0.45％
Mo and V form dispersed second-phase precipitates in steel, and the dispersed precipitates can play a role in precipitation strengthening and can effectively inhibit the growth of austenite grains so as to improve the toughness of the material. And because Mo and V have strong affinity with carbon atoms, the decomposition speed of martensite is reduced in the tempering process, and the stability of the steel is improved. Both Mo and V in the steel of the present invention are reduced compared to the steel of 1.2379 because the C content in the steel of the present invention is lower than that in the steel of 1.2379. Too much Mo and V will consume C in the matrix and reduce the C content in the martensite, thereby reducing the strength of the material. Therefore, mo and V of the steel are controlled within a certain range, so that more secondary carbides are dispersed and precipitated in the structure, and the martensite keeps enough strength, so that the bending strength of the cold-punching die steel can be improved.
Ni 0.50～0.70％
Ni can improve the strength of steel and maintain good plasticity and toughness. The nickel has higher corrosion resistance to acid and alkali and has antirust and heat-resisting capabilities at high temperature. However, since nickel is a scarce resource, other alloy elements should be used as far as possible to replace nickel-chromium steel. The nickel element in the design is controlled in a small amount range, the nickel element is not a carbide forming element and cannot play a role in strengthening in a matrix of the steel, but the excessive nickel element can cause the combination effect of intermetallic compounds, so that the performance of the steel is reduced, and the control of the content of the nickel element in the steel grade plays a certain role in preventing the performance of the steel from being reduced. Compared with 1.2379 steel, the steel of the invention contains 0.50-0.70% of Ni content, and can well toughen the matrix.
P≤0.02wt％
Phosphorus is a harmful element in steel, increases the brittleness of the steel, and reduces the impact toughness of the steel, so that the control of the phosphorus element is lower than that of the steel of the prior art 1.2379, and the phosphorus element has a certain effect on improving the performance index value.
S≤0.02wt％
The sulfur element easily causes deterioration of the workability of the steel to some extent, and easily causes an overheating phenomenon in the hot working process of the steel. Therefore, the control of the sulfur content is lower than that of the prior art 1.2379 steel, the processing performance and the mechanical performance of the steel can be improved, and the control method plays a role in simulating the overheating phenomenon generated by continuous forging processing when a radial forging machine performs forging and cogging.
In order to realize the aim, the invention also provides a preparation method of the low-alloy cold-work die steel with high strength and toughness, which comprises the following steps:
according to the chemical component proportion of the invention, a steel ingot cast after smelting in an induction furnace is used as a consumable electrode and is placed in an electroslag remelting device for electroslag remelting, liquid metal falls into a lower water-cooled crystallizer through a slag layer of a slag bath and is re-solidified into a steel ingot of 0.5-1.0 t; heating the steel ingot to 1180-1200 ℃, and performing forging processing after keeping the temperature for 1.5-2.5 hours; initial forging temperature: 1030-1080 ℃ and the final forging temperature is more than or equal to 880 ℃.
The main process parameters are controlled as follows:
heating the steel ingot to 1180-1200 ℃ at a heating rate of 80-110 ℃/h in a heating furnace of a radial forging machine, and then preserving heat for 1.5-2.5 hours:
the steel ingot has high thermal stress sensitivity in the heating process and is easy to generate stress cracks, the temperature of the steel ingot entering the furnace is controlled to be 700-800 ℃, the heating rate is controlled to be 80-110 ℃/h, the thermal stress cracks can be prevented from being generated in the heating process of the steel ingot, the temperature is kept for 1.5-2.5 hours after the steel ingot is heated to 1180-1200 ℃, the temperature from the whole surface to the core of the steel ingot can be kept uniform, the forgeability of the steel ingot can be improved, the cracking tendency of the steel in the forging process can be prevented, the microstructure index of the steel can be improved, and the strength and the toughness of the steel can be improved.
Forging and cogging temperature of 1030-1080 ℃ by a forging machine:
the steel is an austenite single-phase structure area of the steel at the temperature range of 1030-1080 ℃, has optimal high-temperature thermoplasticity, is beneficial to high-temperature deformation processing and is not easy to generate high-temperature hot processing cracking.
The stop forging temperature of the radial forging machine of the steel is more than or equal to 880 ℃:
the finish rolling temperature of the steel ingot has important influence on the rolling quality of the steel ingot, the forging stop temperature of the radial forging machine is lower than the specified control range, the steel ingot is very easy to crack in the forging and cogging process of the radial forging machine, but the forging stop temperature higher than the control range is easy to cause the coarse crystal phenomenon of a steel structure of the steel after the forging and cogging of the radial forging machine, and serious net-shaped carbide is formed to reduce the performance of the steel.
Compared with the prior art, the invention has the following advantages:
1. the proportion of chemical components is more reasonable, and the contents of carbon and chromium elements are reduced, so that the structure segregation condition of the steel is greatly improved. Thereby improving the performance indexes of the high-strength and high-toughness cold-work die steel, such as bending strength, net-shaped carbide and the like; molybdenum and vanadium in the patented steel are reduced compared to 1.2379 steel because the C content in the steel of the present invention is lower than that of 1.2379 steel. Too much molybdenum and vanadium will consume the C in the matrix and reduce the C content in the martensite, thus reducing the strength of the material. Therefore, the molybdenum and the vanadium of the steel are controlled within a certain range, so that more secondary carbides are dispersed and separated out in the structure, and enough strength is kept in the martensite; properly increasing the silicon content in the steel can further prevent the steel from decomposing in the tempering process after the martensite transformation, and has certain effect on improving the bending strength and the impact property value of the steel after quenching; the content of the nickel element is controlled to be a certain low value, so that the brittleness and intermetallic compounds can be prevented from being generated, and the performance of the steel is improved; the reduction of the contents of phosphorus and sulfur can ensure that molten steel is purer, reduce the forming trend of non-metallic inclusions of steel and reduce the tempering brittleness of steel quenching and tempering.
2. Compared with the steel 1.2379, the steel of the invention has low content of alloy elements, reduces the manufacturing cost, improves the market competitiveness of products, and greatly improves the distribution of carbides in the microstructure and the grade of nature net-shaped carbides. Therefore, under the condition of the same forging ratio, compared with 1.2379, the steel of the invention can better crush the dendritic carbide in the cast structure, thin the microstructure of the steel and improve the performance of the steel.
3. Rational chemistryThe performance index of the steel is obviously improved by the component proportion and the advanced manufacturing process (such as a heating mode and a forging temperature control process), and after the traditional 1.2379 steel is quenched at 1030 ℃ and tempered at 200 ℃, the bending strength is 2700MP, and the impact toughness is 77J/cm 2 After the steel is quenched at 930 ℃ and tempered at 180 ℃, the bending strength of the steel reaches 3350MP-3500MP and the impact toughness is 140J/cm 2 -155J/cm 2 The bending strength is improved by 30 percent, and the impact toughness is improved by 100 percent.
Drawings
FIG. 1 is a comparison of the metallographic structure of the steel of the present invention and that of the steel 1.2379 after quenching and tempering. FIG. 1 (a) is a metallographic photograph of a steel of the present invention after being tempered by quenching at 180 ℃ with a heat treatment of 930 ℃. FIG. 1 (b) is a metallographic photograph of 1.2379 steel after quenching at 1030 ℃ and tempering at 180 ℃.
FIG. 2 shows the impact toughness and bending strength of the steel of the present invention after the heat treatment process of 930 ℃ quenching and 180 ℃ tempering compared with the 1.2379 steel after the quenching and 180 ℃ tempering at 1030 ℃.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way.
Example 1
In this example, the cold-work die steel comprises the following components in percentage by weight:
0.78 to 0.88 percent of C, 0.90 to 1.05 percent of Si, 1.10 to 1.30 percent of Mn, less than 0.02 percent of P, less than 0.02 percent of S, 2.80 to 3.60 percent of Cr, 0.30 to 0.40 percent of Mo, 0.30 to 0.45 percent of V, 0.50 to 0.70 percent of Ni and the balance of Fe.
In this embodiment, the process and steps of cold-working die steel are as follows:
the steel ingot cast after smelting in an induction furnace is used as a consumable electrode and placed in an electroslag remelting device for electroslag remelting, and liquid metal falls into a water-cooled crystallizer below through a slag layer of a slag bath and is re-solidified into a 0.5 ton steel ingot; controlling the charging temperature of the steel ingot to be 790 ℃, controlling the heating rate to be 90 ℃/h, heating to 1150 ℃, preserving heat for 1.5 hours, and then forging; initial forging temperature: 1050 ℃ and the finish forging temperature is 890 ℃.
The bending strength of the high-strength and high-toughness cold-work die steel of the embodiment reaches 3500MP, and the impact toughness is improved to 155J/cm 2 。
The specific chemical components (Wt%) of examples 2 to 6 are shown in table 1, the process parameter control is shown in table 2, and the performance index is shown in table 3.
TABLE 1
| Examples | C | Mn | Cr | Ni | Si | Mo | V | P | S |
| 2 | 0.79 | 1.13 | 2.80 | 0.50 | 0.99 | 0.32 | 0.31 | 0.013 | 0.011 |
| 3 | 0.85 | 1.10 | 2.95 | 0.55 | 0.90 | 0.30 | 0.30 | 0.015 | 0.009 |
| 4 | 0.81 | 1.00 | 3.39 | 0.60 | 1.00 | 0.33 | 0.43 | 0.012 | 0.015 |
| 5 | 0.78 | 1.30 | 3.46 | 0.70 | 1.01 | 0.40 | 0.38 | 0.009 | 0.012 |
| 6 | 0.88 | 1.21 | 3.60 | 0.65 | 1.05 | 0.35 | 0.45 | 0.007 | 0.010 |
TABLE 2
TABLE 3
| Examples | Bending strength sigma bb (MP) | Impact toughness Ak (J/cm) 2 ) |
| 2 | 3380 | 152 |
| 3 | 3350 | 140 |
| 4 | 3460 | 148 |
| 5 | 3500 | 143 |
| 6 | 3390 | 151 |
FIG. 1 is a comparison of the metallographic structure of the steel of the invention (example 1) and that of the steel 1.2379 after quenching and tempering. FIG. 1 (a) is a metallographic photograph of a steel of the present invention after being tempered by quenching at 180 ℃ with a heat treatment of 930 ℃. It is seen that finely dispersed carbide particles are uniformly distributed on the martensite matrix. Such a structure ensures excellent toughness matching of the steel of the present invention. FIG. 1 (b) is a metallographic photograph of 1.2379 steel after quenching at 1030 ℃ and tempering at 180 ℃. It is seen in the figures that the presence of ledeburitic carbide segregation leads to a decrease in the toughness of the material.
FIG. 2 shows the impact toughness and bending strength of the steel of the present invention (example 1) after the heat treatment process of 930 ℃ quenching and 180 ℃ tempering compared with the 1.2379 steel after the quenching and 180 ℃ tempering at 1030 ℃. As can be seen in the figure, the bending strength of the steel reaches 3350MP-3500MP, and the bending strength of the traditional 1.2379 steel is only 2700MP; the impact toughness of the steel of the invention is greatly improved compared with that of 1.2379 steel, and the impact toughness of the 1.2379 steel is 77J/cm 2 The toughness of the steel of the invention is 140J/cm 2 -155J/cm 2 . This is because after quenching and tempering the carbides of the steel according to the invention are all very finely dispersed secondary carbidesThe segregation of carbide does not occur as in the case of 1.2379 steel.
All the products of the invention have the metallographic structure shown in fig. 1 after quenching and tempering, and the impact toughness and the bending strength of the products shown in fig. 2 after the heat treatment process is that the products are quenched at 930 ℃ and tempered at 180 ℃ and the products shown in fig. 2 are quenched at 1030 ℃ and tempered at 180 ℃, are compared and are not repeated herein.
The steel of the invention is mainly characterized in that in the design of chemical components, the contents of C and Cr are reduced and controlled in a reasonable range, a certain amount of carbide forming elements such as Mo, V and the like are added, and a small amount of Ni and Si are added, so that the cost of alloy elements can be controlled for strengthening and toughening a matrix. The carbide form of the cold-work die steel in a casting state is improved, so that a larger deformation amount can be obtained by a smaller forging ratio during forging, namely, the carbide can be better distributed under the condition of the same forging ratio. The invention develops the matching of good hardenability, lower quenching temperature, small heat treatment deformation, low price, better bending strength and impact toughness, and is suitable for manufacturing the steel for precise complex dies. Can replace the common 1.2379 type cold punching die steel in a larger range.
After the bending-resistant cold stamping die steel is heated to 890-930 ℃ for austenitizing, a large amount of alloy elements are promoted to be dissolved into a matrix, the degree of alloying is improved, and the solid solution strengthening effect is enhanced. Meanwhile, in the process of secondary tempering, fine and uniform second-phase particles are dispersed and separated out, and the bending strength and the impact toughness of the material are improved through precipitation strengthening.
Further retrieval content analysis is carried out by Chinese and foreign patents of the related art:
through searching the documents of the middle and external patents and the related cold-work die steel by inputting the keywords related to the content of the invention, the patent number related to the die material and the metallurgical manufacturing technology thereof related to the invention is shown as
1) Patent number < application number > =200710171694.5< publication (publication) number > = CN101182619A. The weight percentage of the chemical components is as follows: 0.9 to 1.0 percent of C, 1.0 percent of Si, 0.5 to 0.8 percent of Mn, less than 0.02 percent of P, less than 0.02 percent of S, 9 to 10 percent of Cr, 0.8 to 1.0 percent of Cu, 2.0 percent of Mo2, 0.8 to 1.0 percent of V, and the balance of Fe.
The invention relates to a novel high-strength tough low-alloy cold-work die steel, which comprises the following chemical components in design: 0.78 to 0.88 percent of C, 0.90 to 1.05 percent of Si, 1.10 to 1.30 percent of Mn, less than 0.02 percent of P, less than 0.02 percent of S, 2.80 to 3.60 percent of Cr, 0.30 to 0.40 percent of Mo, 0.30 to 0.45 percent of V, 0.50 to 0.70 percent of Ni and the balance of Fe.
A comparison of the two chemical compositions is shown in the following table:
comparative analysis is as follows: it can be seen from the comparison of the components that the content of carbon, chromium, molybdenum, vanadium and the like in the element content of the chemical components of the invention is lower than that of the retrieved patent CN101182619A, and a small amount of nickel element is added, so that the mechanism of the function of the nickel element on the performance of the material is different, and the performance characteristics of the material are also different. The chemical composition of patent CN101182619A is characterized by containing high chromium element, molybdenum and vanadium element compared with the chemical composition designed by the present invention, and chromium element is one of the main causes of carbide non-uniformity, and is easy to form network carbide, which reduces the toughness of the material. The chemical composition of the technology of the invention contains lower chromium content and adds a small amount of Ni content to replace Mo and V. Ni can improve the strength of steel while maintaining good plasticity and toughness. Mo and V form dispersed second-phase precipitates in steel, and the dispersed precipitates can play a role in precipitation strengthening and can effectively inhibit the growth of austenite grains so as to improve the toughness of the material. In the chemical composition design of the related patent CN101250667, compared with the chemical element design of the traditional cold-work steel, the content of Cr is properly reduced (but is much higher than the Cr element composition design in the technology of the present invention), and tungsten element is added to improve the performance of the steel, but the technology of the present invention adopts Ni element to strengthen the matrix strength of the steel, reduce the content of C and the content of alloy elements to reduce the manufacturing cost, improve the microstructure, and improve the performance index of the steel, the mechanism of the action and the design concept of the composition are different, and the composition design has a larger difference.
Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (5)
1. The high-strength-toughness low-alloy die steel is characterized by comprising the following components in percentage by weight:
0.78 to 0.88 percent of C, 0.90 to 1.05 percent of Si, 1.10 to 1.30 percent of Mn, less than 0.02 percent of P, less than 0.02 percent of S, 2.80 to 3.60 percent of Cr, 0.30 to 0.40 percent of Mo, 0.30 to 0.45 percent of V, 0.50 to 0.70 percent of Ni, and the balance of Fe; and the content of the main chemical elements is in accordance with the following mathematical relation: c =0.45Mn +0.10Cr.
2. A method for preparing the high-toughness low-alloy die steel as claimed in claim 1, comprising the following steps:
according to the proportion of the chemical components in the claim 1, a steel ingot cast after smelting in an induction furnace is used as a consumable electrode and is placed in an electroslag remelting device for electroslag remelting, liquid metal falls into a lower water-cooled crystallizer through a slag layer of a slag bath and is re-solidified into the steel ingot with 0.5-1.0 t; heating the steel ingot to 1180-1200 ℃, and performing forging processing after heat preservation for 1.5-2.5 hours; initial forging temperature: 1030-1080 ℃ and the final forging temperature is more than or equal to 880 ℃.
3. The method for preparing the high-strength-toughness low-alloy die steel according to claim 2, wherein the steel ingot is heated to 1180-1200 ℃ in a radial forging machine heating furnace at a heating rate of 80-110 ℃/h and then is subjected to heat preservation for 1.5-2.5 hours.
4. The method for preparing the high-strength low-toughness low-alloy die steel according to claim 2, wherein the charging temperature of the steel ingot is controlled to be 700-800 ℃.
5. The method for preparing the high-strength-toughness low-alloy die steel as claimed in claim 2, wherein the bending strength of the high-strength-toughness low-alloy die steel prepared by the method reaches 3350MP-3500MP and the impact toughness is 140J/cm after the high-strength-toughness low-alloy die steel is subjected to the tempering heat treatment of 930 ℃ quenching and 180 ℃ tempering 2 -155J/cm 2 。
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