CN116287982A - Low-alloy high-toughness ultrahigh-strength steel - Google Patents

Low-alloy high-toughness ultrahigh-strength steel Download PDF

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CN116287982A
CN116287982A CN202310120453.7A CN202310120453A CN116287982A CN 116287982 A CN116287982 A CN 116287982A CN 202310120453 A CN202310120453 A CN 202310120453A CN 116287982 A CN116287982 A CN 116287982A
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equal
strength steel
forging
steel
toughness
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胡春东
曹鑫
曹鹏敏
崔晓宁
王子君
许婷婷
董瀚
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Shanghai University Zhejiang High End Equipment Basic Materials Research Institute
Henan Zhongyuan Special Steel Equipment Manufacturing Co Ltd
University of Shanghai for Science and Technology
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Shanghai University Zhejiang High End Equipment Basic Materials Research Institute
Henan Zhongyuan Special Steel Equipment Manufacturing Co Ltd
University of Shanghai for Science and Technology
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
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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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    • 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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    • 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
    • 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
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • 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
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • 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
    • C22C38/18—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
    • 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
    • C22C38/18—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
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract

Compared with the A1SI4340 steel or the D6AC steel, the low-alloy high-toughness ultrahigh-strength steel adjusts the conditions that the C content is too high and the Ni content is too low, so that the balance effect realized by low cost, high toughness and ultrahigh strength is better considered, and the ultrahigh strength and the high toughness are tested according to the national standards GB/T228.1-2018 and GB/T229-2007 as follows: the tensile strength is more than or equal to 1950MPa, the yield strength is more than or equal to 1500MPa, the elongation is more than or equal to 10.0%, the surface shrinkage is more than or equal to 40%, and the impact energy is more than or equal to 60J, and is characterized by comprising the following chemical element components in percentage by weight: c=0.22 to 0.38, si=1.10 to 2.20, mn=0.80 to 2.20, cr=0.70 to 1.20, ni=2.25 to 4.50, mo=0.50 to 1.35, v=0.09 to 0.35, nb=0.01 to 0.04, s is less than or equal to 0.0015, p is less than or equal to 0.005, and fe=balance.

Description

Low-alloy high-toughness ultrahigh-strength steel
Technical Field
The invention relates to the technical field of low alloy steel, in particular to low alloy high toughness and ultrahigh strength steel, which is reduced in Ni content by times and does not use Co compared with AerMet100 steel and the like, and is regulated to have too high C content and too low Ni content compared with A1SI4340 steel or D6AC steel and the like, so that the balanced effect of low cost, high toughness and ultrahigh strength is better considered, and the high toughness and the ultrahigh strength are the following test results according to national standards GB/T228.1-2018 and GB/T229-2007: the tensile strength is more than or equal to 1950MPa, the yield strength is more than or equal to 1500MPa, the elongation is more than or equal to 10.0%, the surface shrinkage is more than or equal to 40%, and the impact energy is more than or equal to 60J.
Background
Ultra-high strength steel generally refers to alloy steels having tensile strengths in excess of 1400MPa and yield strengths in excess of 1300 MPa. In addition to the ultra-high strength, it is also required to have sufficient toughness, fatigue resistance, and other requirements such as corrosion resistance, creep resistance, etc. according to the service conditions. The high-strength bolt is widely applied to aircraft landing gear, high-strength bolts, bulletproof steel plates, rocket engine shells, high-pressure containers, automobile key parts, firearm parts, penetration shell and the like. With the development of high and new technologies and the demand for resource saving, ultra-high strength steel is required to have high toughness and low cost.
At present, a great amount of Co and Ni are added into the steel with ultra-high toughness, such as AerMet100 (Ni=11-12%, co=13-14%), 9Ni-5Co, AF1410 (Ni=9.5-10.5%, co=13.5-14.5%), 18Ni (250), G99 (Ni=9.68%, co=9.94%), and the like, co can promote the distribution of fine dispersion of precipitated phase particles by influencing dislocation substructure, so that obvious precipitation strengthening effect is achieved, the toughness of the steel is improved, ni can improve the matrix fault energy of carbon steel, so that screw dislocation is convenient for cross sliding, and the toughness of the steel is improved, however, co and Ni are all rare strategic resources in China, so that the cost is very expensive, a great deal of application is difficult to obtain, low-cost ultra-high strength steel A1SI4340 (C=0.38-0.43%, ni=1.65-2.0%), 300M (C=0.41-0.46%, ni=1.6-2.0D 6%, and the content of C=0.43% is very poor after quenching, and the content of Ni=0.65-0.0.43%) is very poor. Therefore, from the aspects of saving resources and improving the overall quality of domestic ultra-high-strength and toughness steel, it is necessary to develop ultra-high-strength steel with lower alloy content and excellent toughness.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention provides low-alloy high-toughness ultrahigh-strength steel, which is reduced in Ni content by times and does not use Co compared with AerMet100 steel and the like, and compared with A1SI4340 steel or D6AC steel and the like, the balanced effect of low cost, high toughness and ultrahigh strength is better considered, and the ultrahigh strength and the high toughness are tested according to the national standards GB/T228.1-2018 and GB/T229-2007 as follows: the tensile strength is more than or equal to 1950MPa, the yield strength is more than or equal to 1500MPa, the elongation is more than or equal to 10.0%, the surface shrinkage is more than or equal to 40%, and the impact energy is more than or equal to 60J.
The technical scheme of the invention is as follows:
the low-alloy high-toughness ultrahigh-strength steel is characterized by comprising the following chemical element components in percentage by weight: c=0.22 to 0.38, si=1.10 to 2.20, mn=0.80 to 2.20, cr=0.70 to 1.20, ni=2.25 to 4.50, mo=0.50 to 1.35, v=0.09 to 0.35, nb=0.01 to 0.04, s is less than or equal to 0.0015, p is less than or equal to 0.005, and fe=balance.
The ultra-high strength and high toughness refer to the following test results according to the national standards GB/T228.1-2018 and GB/T229-2007: the tensile strength is more than or equal to 1950MPa, the yield strength is more than or equal to 1500MPa, the elongation is more than or equal to 10.0%, the surface shrinkage is more than or equal to 40%, and the impact energy is more than or equal to 60J.
After the low-alloy high-toughness ultrahigh-strength steel is subjected to a quenching and tempering heat treatment process, the metallographic structure of the low-alloy high-toughness ultrahigh-strength steel can be seen to be lath martensite, retained austenite and fine spherical carbide under the magnification of 500 times by an optical microscope, and the prior austenite crystal grain size is relatively fine, wherein the metallographic structure is shown as a figure 1 in the attached drawing of the specification.
After the low-alloy high-toughness ultrahigh-strength steel is subjected to a quenching and tempering heat treatment process, the microstructure of the low-alloy high-toughness ultrahigh-strength steel can be seen to be dispersed and distributed on a lath martensite matrix under 10000 times of magnification of a scanning electron microscope, and the microstructure is shown as a figure 2 in an attached drawing of the specification.
The heat treatment process of quenching and tempering comprises the following steps: 1050 ℃ multiplied by 1 h+oil quenching, 260 ℃ multiplied by 2 h+air cooling tempering, wherein the chemical element components and the weight percent content of the low alloy high toughness ultra-high strength steel are as follows: c=0.24, si=1.18, mn=1.12, cr=0.95, ni=2.35, mo=1.08, v=0.11, nb=0.028, s.ltoreq.0.0015, p.ltoreq.0.005, fe=balance.
The low-alloy high-toughness ultrahigh-strength steel is subjected to a smelting process, a forging process and a post-forging annealing process in sequence from front to back before being subjected to a quenching and tempering heat treatment process.
The smelting process comprises adopting a vacuum induction furnace for smelting or adopting an electric arc furnace for smelting and adopting an external furnace for refining, and then carrying out vacuum consumable remelting or electroslag remelting; the forging process is to perform three piers and three pulls on the smelted steel ingot, and specifically comprises the following steps: step 1, forging at 1080+/-10 ℃ to 1/2 of the original height, and drawing to 4/5 of the original height; step 2, heating to 1080+/-10 ℃, upsetting to 1/2 of the original height, and drawing to 4/5 of the original height; step 3, heating to 1080+/-10 ℃, upsetting to 1/2 of the original height, forging or rolling into bars or billets with corresponding sizes according to the product requirement, wherein the final forging temperature of each step is more than or equal to 860 ℃; the post-forging annealing process comprises the following steps: the forging is heated to 640-660 ℃ for 10h, then cooled to 250-280 ℃ for 10h, then heated to 880 ℃ for more than or equal to 12h, cooled to 250-280 ℃ for 10h, finally heated to 665 ℃ for more than or equal to 20h, cooled to 150 ℃ along with the furnace, and discharged for air cooling.
The invention has the following technical effects: according to the low-alloy high-toughness ultrahigh-strength steel, the addition of Cr, mo, ni, V, nb for alloying can play roles of solid solution strengthening and alloy carbide strengthening; ni can form film austenite among martensite laths, and the screw dislocation is not easy to decompose, so that the cross sliding is smoothly carried out, and the toughness of the steel is improved; a small amount of V, nb can form nanoscale MC to block grain boundary migration so as to refine grains, the content of impurity elements is controlled through vacuum induction and vacuum self-consumption/electroslag remelting, and after corresponding heat treatment, the microstructure of steel is ensured to be lath martensite, film austenite, epsilon-carbide and fine dispersed MC, so that the material has ultrahigh strength and good toughness, meanwhile, the Ni content in the components is lower and Co is not contained, and the cost is reduced by more than 30 percent compared with A-100 (AerMet 100). According to the invention, the mechanical properties of the steel are respectively subjected to quasi-static stretching according to national standards (GB/T228.1-2018, GB/T229-2007), and the impact toughness test meets the following requirements: the tensile strength reaches more than 1950MPa, the yield strength reaches more than 1500MPa, the elongation reaches more than 10.0%, the surface shrinkage reaches more than 40%, and the impact energy reaches more than 60J.
Drawings
FIG. 1 is an optical microscope photomicrograph of sample number 4 of an example of a low alloy, high toughness, ultra high strength steel according to the present invention. In FIG. 1, the magnification of the metallographic structure is 500 times, from which lath martensite+retained austenite+fine spherical carbides can be seen, and the prior austenite grain size is finer. The chemical element content in weight percent in sample # 4 is c=0.24, si=1.18, mn=1.12, cr=0.95, ni=2.35, mo=1.08, v=0.11, nb=0.028, s is less than or equal to 0.0015, p is less than or equal to 0.005, and fe=the balance. The heat treatment process parameters of the sample No. 4 are as follows: 1050 ℃ for 1h, and oil-cooling quenching; and (3) air cooling and tempering at 260 ℃ for 2 h. The quasi-static mechanical performance index of the sample No. 4 is as follows: tensile strength 1969MPa, yield strength 1683MPa, elongation after break 10.0%, reduction of area 45% and impact energy 64J.
FIG. 2 is a photograph of the microstructure morphology of sample No. 4 scanning electron microscope in the example of the present invention. In fig. 2, the microstructure magnification is 10000 times, from which it can be seen that lath martensite + fine spherical carbides are arranged in parallel, the fine spherical carbides being dispersed on the lath martensite matrix. The chemical element content in weight percent in sample # 4 is c=0.24, si=1.18, mn=1.12, cr=0.95, ni=2.35, mo=1.08, v=0.11, nb=0.028, s is less than or equal to 0.0015, p is less than or equal to 0.005, and fe=the balance. The heat treatment process parameters of the sample No. 4 are as follows: 1050 ℃ for 1h, and oil-cooling quenching; and (3) air cooling and tempering at 260 ℃ for 2 h. The quasi-static mechanical performance index of the sample No. 4 is as follows: tensile strength 1969MPa, yield strength 1683MPa, elongation after break 10.0%, reduction of area 45% and impact energy 64J.
Detailed Description
The invention is described below with reference to the figures (fig. 1-2) and examples.
FIG. 1 is an optical microscope photomicrograph of sample number 4 of an example of a low alloy, high toughness, ultra high strength steel according to the present invention. FIG. 2 is a photograph of the microstructure morphology of sample No. 4 scanning electron microscope in the example of the present invention. Referring to fig. 1 to 2, a low alloy high toughness ultra high strength steel comprises the following chemical element components in wt%: c=0.22 to 0.38, si=1.10 to 2.20, mn=0.80 to 2.20, cr=0.70 to 1.20, ni=2.25 to 4.50, mo=0.50 to 1.35, v=0.09 to 0.35, nb=0.01 to 0.04, s is less than or equal to 0.0015, p is less than or equal to 0.005, and fe=balance. The ultra-high strength and high toughness refer to the following test results according to the national standards GB/T228.1-2018 and GB/T229-2007: the tensile strength is more than or equal to 1950MPa, the yield strength is more than or equal to 1500MPa, the elongation is more than or equal to 10.0%, the surface shrinkage is more than or equal to 40%, and the impact energy is more than or equal to 60J.
After the low-alloy high-toughness ultrahigh-strength steel is subjected to a quenching and tempering heat treatment process, the metallographic structure of the low-alloy high-toughness ultrahigh-strength steel can be seen to be lath martensite, retained austenite and tiny spherical carbide under the magnification of 500 times by an optical microscope, and the prior austenite crystal grain size is finer, wherein the metallographic structure is shown as a figure 1 in the attached drawing of the specification. After the low-alloy high-toughness ultrahigh-strength steel is subjected to a quenching and tempering heat treatment process, the microstructure of the low-alloy high-toughness ultrahigh-strength steel can be seen to be dispersed and distributed on a lath martensite matrix under 10000 times of magnification of a scanning electron microscope, and the microstructure is shown as a figure 2 in an attached drawing of the specification. The heat treatment process of quenching and tempering comprises the following steps: 1050 ℃ multiplied by 1 h+oil quenching, 260 ℃ multiplied by 2 h+air cooling tempering, wherein the chemical element components and the weight percent content of the low alloy high toughness ultra-high strength steel are as follows: c=0.24, si=1.18, mn=1.12, cr=0.95, ni=2.35, mo=1.08, v=0.11, nb=0.028, s.ltoreq.0.0015, p.ltoreq.0.005, fe=balance.
The low-alloy high-toughness ultrahigh-strength steel is subjected to a smelting process, a forging process and a post-forging annealing process in sequence from front to back before being subjected to a quenching and tempering heat treatment process. The smelting process comprises adopting a vacuum induction furnace for smelting or adopting an electric arc furnace for smelting and adopting an external furnace for refining, and then carrying out vacuum consumable remelting or electroslag remelting; the forging process is to perform three piers and three pulls on the smelted steel ingot, and specifically comprises the following steps: step 1, forging at 1080+/-10 ℃ to 1/2 of the original height, and drawing to 4/5 of the original height; step 2, heating to 1080+/-10 ℃, upsetting to 1/2 of the original height, and drawing to 4/5 of the original height; step 3, heating to 1080+/-10 ℃, upsetting to 1/2 of the original height, forging or rolling into bars or billets with corresponding sizes according to the product requirement, wherein the final forging temperature of each step is more than or equal to 860 ℃; the post-forging annealing process comprises the following steps: the forging is heated to 640-660 ℃ for 10h, then cooled to 250-280 ℃ for 10h, then heated to 880 ℃ for more than or equal to 12h, cooled to 250-280 ℃ for 10h, finally heated to 665 ℃ for more than or equal to 20h, cooled to 150 ℃ along with the furnace, and discharged for air cooling.
The invention aims to provide ultra-high strength steel with low cost and high strength and toughness. The invention aims at realizing the following technical scheme: the invention relates to low-alloy high-toughness ultrahigh-strength steel, which comprises the following chemical components in percentage by mass: 0.22 to 0.38 percent of C, 1.10 to 2.20 percent of Si, 0.80 to 2.20 percent of Mn, 0.70 to 1.20 percent of Cr, 2.25 to 4.50 percent of Ni, 0.50 to 1.35 percent of Mo, 0.09 to 0.35 percent of V, 0.01 to 0.04 percent of Nb, less than or equal to 0.0015 percent of S, less than or equal to 0.005 percent of P and the balance of: fe.
C: as a main solid solution strengthening element of the steel, epsilon-carbide precipitated by solid solution of interstitial atoms after martensitic transformation and low-temperature tempering is strengthened. When the C content is lower, the strength is insufficient, and when the C content exceeds 0.5%, brittle fracture is likely to occur at the original austenite grain boundary. Comprehensively considering that the C content of the invention is between 0.22 and 0.38 percent.
Si: the Si can prevent cementite from forming and improve the tempering resistance of the steel, so that the tempering temperature of the steel is lower than a brittleness temperature range. However, when the Si content is in the range of 0.8% -1.0%, the shaping and toughness of the steel are obviously reduced, and when the Si content is too high, the solubility of Mo element in a steel matrix is reduced, so that alloy carbide remains during quenching and heating, and the toughness of the steel is damaged. Comprehensively considering that the Si content is controlled between 1.10 and 2.20 percent.
Mn: mn is added into the steel as the element for removing O and S, so that the deoxidization effect of Si can be enhanced, the hardenability of the steel can be obviously improved, and the addition of Mn has the comprehensive effects of solid solution strengthening, formation of dislocation martensite and film-shaped residual austenite, inhibition of network cementite and improvement of the strength and toughness of the steel. However, too high a Mn content lowers the Ms point and reduces the strength of the steel. Comprehensively considering that the Mn content of the invention is controlled between 0.80 and 2.20 percent.
Cr: as the addition of Cr to the steel for improving the hardenability of the steel of the invention, the addition of Cr has the comprehensive effect of solid solution strengthening and forming alloy carbide, and the strength of the steel is further improved. However, the higher Cr content forms coarse eutectic carbide, which reduces the ductility and toughness of the steel, and when the Cr content is in the range of 0.5% -1.65%, the alloy steel has high strength, high wear resistance, and good hardenability and fatigue resistance. Comprehensively considering that the Cr content is controlled between 0.70 and 1.20 percent.
Ni: as an alloy element for expanding a gamma-phase region, screw dislocation is not easy to decompose, so that the slip is smoothly carried out, and the toughness of steel is remarkably improved. In addition, ni can improve the hardenability of steel and reduce the ductile-brittle transition temperature. However, ni is a scarce resource in China, and the excessive content not only increases the cost but also reduces the Ms point. Comprehensively considering that the Ni content is controlled between 2.25 and 4.50 percent.
Mo: as a strong carbide forming element, the tempering stability of the steel of the present invention can be improved, and when Mn and Cr are present together, mo can suppress or reduce tempering brittleness caused by other elements. When the Mo content is about 0.5%, the tempering brittleness of the steel can be basically eliminated, and the second tempering brittleness of the steel can be effectively prevented, however, mo is an alloy element for expanding an alpha phase region, and too high Mo can reduce the plasticity and toughness of the steel and increase the cost of the steel. Comprehensively considering that the Mo content of the invention is controlled between 0.50 and 1.35 percent.
V: as a microalloying element, a small amount of V is added to form MC type carbide, which hinders migration of prior austenite grain boundaries during quenching to refine grains, thereby improving strength of steel and toughness of steel, but an excessively high content of V reduces toughness. Comprehensively considering that the V content is controlled between 0.09 and 0.35 percent.
Nb: as a microalloying element, a small amount of Nb is added to form nano-sized NbC to inhibit grain growth, but Nb and strong carbide elements such as Ti, V are easily combined into large-sized liquid-out carbide to reduce toughness of steel. Comprehensively considering, the Nb content is controlled to be 0.01-0.04 percent.
The control requirement of the content of harmful impurities in the steel is as follows: s is less than or equal to 0.0015%, and P is less than or equal to 0.005%.
The invention relates to a preparation process for processing low-alloy high-toughness ultrahigh-strength steel by adopting the formula, which comprises the following specific treatment processes:
1) The smelting process comprises the following steps: smelting by adopting a vacuum induction furnace, or adopting arc furnace smelting and external refining, and then carrying out vacuum consumable remelting or electroslag remelting;
2) The forging process comprises the following steps: the smelted steel ingot is subjected to a forging process of three piers and three pulls; the method comprises the following specific steps: step 1: the initial forging temperature is 1080+/-10 ℃, upsetting is carried out to 1/2 of the original height, and drawing is carried out to 4/5 of the original height; step 2: heating to 1080+ -10deg.C, upsetting to 1/2 of the original height, and drawing to 4/5 of the original height; and step 3: heating to 1080+/-10 ℃, upsetting to 1/2 of the original height, forging or rolling into bars or billets with corresponding dimensions according to the product requirement, and the final forging temperature of the process is more than or equal to 860 ℃.
3) The annealing process after forging: the forging is heated to 640-660 ℃ for 10h, then furnace cooled to 250-280 ℃ for 10h, then heated to 880 ℃ for more than or equal to 12h, air cooled to 250-280 ℃ for 10h, finally heated to 665 ℃ for more than or equal to 20h, and then discharged from the furnace for air cooling along with furnace cooling to 150 ℃.
4) The heat treatment process comprises the following steps: and heating the annealed forging to 950-1100 ℃, preserving heat for 1-2 h, then quenching oil to room temperature, then heating to 200-300 ℃, preserving heat for 2-3 h, taking out, and cooling to room temperature.
Examples: the test steels numbered 1 and 2 were smelted by vacuum induction and electroslag remelting, the test steels numbered 3 and 4 were smelted by vacuum induction and vacuum consumable supply, and the chemical compositions are shown in Table 1. The smelted steel ingot is subjected to a forging process of three piers and three pulls; the method comprises the following specific steps: step 1: the initial forging temperature is 1080 ℃, the upsetting is 1/2 of the original height, and the drawing is 4/5 of the original height; step 2: heating to 1080 ℃, upsetting to 1/2 of the original height, and drawing to 4/5 of the original height; and step 3: heating to 1080 ℃, upsetting to 1/2 of the original height, and finally finish forging to obtain a round ingot with the diameter of 390mm and the length of 3100mm, wherein the final forging temperature of the process is more than or equal to 860 ℃. The forging is heated to 640-660 ℃ for 10h, then furnace cooled to 250-280 ℃ for 10h, then heated to 880 ℃ for more than or equal to 12h, air cooled to 250-280 ℃ for 10h, finally heated to 665 ℃ for more than or equal to 20h, cooled to 150 ℃ along with furnace cooling, discharged from the furnace for air cooling, and then heat treated by adopting a heat treatment system in table 2.
TABLE 1 chemical composition (wt.%)
Numbering device C Si Mn Cr Ni Mo V Nb Co
1# 0.38 2.20 2.10 1.10 3.95 1.15 0.28 0.033 —
2# 0.28 2.10 1.98 1.04 2.85 0.95 0.24 0.012 —
3# 0.34 1.10 0.85 0.75 2.26 0.65 0.34 0.031 —
4# 0.24 1.18 1.12 0.95 2.35 1.08 0.11 0.028 —
Comparative example 1 0.23 — — 2.91 11.59 1.20 — — 13.60
TABLE 2 heat treatment process parameters
Numbering device Quenching Cold treatment Tempering
1# 960 ℃ for 1h, oil cooling — 220 ℃ x 2h, air cooling
2# 960 ℃ for 1h, oil cooling — 300 ℃ x 2h, air cooling
3# 960 ℃ for 1h, oil cooling — 260 ℃ x 2h, air cooling
4# 1050 ℃ for 1h, oil cooling — 260 ℃ x 2h, air cooling
Comparative example 1 885 ℃ for 1h, oil cooling -73 ℃ for 1h, air cooling 482 ℃ for 5h, air cooling
TABLE 3 quasistatic mechanical Properties
Numbering device Tensile strength/MPa Yield strength/MPa Elongation after break/% Area reduction/% Impact energy/J
1# 2024 1605 12.5 47 67
2# 1950 1602 10.0 48 66
3# 2020 1625 12.5 52 66
4# 1969 1683 10.0 45 64
Comparative example 1 1940 1726 11.5 59 76
Table 3 shows the quasi-static mechanical properties of the steels of examples 1-4, which are comparable to those of comparative example 1 (AerMet 100) and A-100 (AerMet 100), but the composition is free of Co and has a lower Ni content, resulting in a 30% reduction in cost.
What is not described in detail in the present specification belongs to the prior art known to those skilled in the art. It is noted that the above description is helpful for a person skilled in the art to understand the present invention, but does not limit the scope of the present invention. Any and all such equivalent substitutions, modifications and/or deletions as may be made without departing from the spirit and scope of the invention.

Claims (7)

1. The low-alloy high-toughness ultrahigh-strength steel is characterized by comprising the following chemical element components in percentage by weight: c=0.22 to 0.38, si=1.10 to 2.20, mn=0.80 to 2.20, cr=0.70 to 1.20, ni=2.25 to 4.50, mo=0.50 to 1.35, v=0.09 to 0.35, nb=0.01 to 0.04, s is less than or equal to 0.0015, p is less than or equal to 0.005, and fe=balance.
2. The low alloy high toughness ultra high strength steel according to claim 1, wherein the ultra high strength and high toughness are according to the national standards GB/T228.1-2018 and GB/T229-2007 as follows: the tensile strength is more than or equal to 1950MPa, the yield strength is more than or equal to 1500MPa, the elongation is more than or equal to 10.0%, the surface shrinkage is more than or equal to 40%, and the impact energy is more than or equal to 60J.
3. The low alloy high toughness ultra high strength steel according to claim 1, wherein after the heat treatment process of quenching and tempering, the metallographic structure of the low alloy high toughness ultra high strength steel is capable of seeing lath martensite + retained austenite + fine spherical carbides under 500 times magnification of an optical microscope, the metallographic structure being as shown in fig. 1 of the accompanying drawings of the specification.
4. The low alloy high toughness ultra high strength steel according to claim 1, wherein after the heat treatment process of quenching and tempering, the microstructure of the low alloy high toughness ultra high strength steel can see fine spherical carbides dispersed and distributed on lath martensite matrix under 10000 times of magnification of scanning electron microscope, the microstructure is as shown in figure 2 of the accompanying drawings.
5. The low alloy high toughness ultra high strength steel according to claim 3 or 4, wherein the quenching+tempering heat treatment process is as follows: 1050 ℃ multiplied by 1 h+oil quenching, 260 ℃ multiplied by 2 h+air cooling tempering, wherein the chemical element components and the weight percent content of the low alloy high toughness ultra-high strength steel are as follows: c=0.24, si=1.18, mn=1.12, cr=0.95, ni=2.35, mo=1.08, v=0.11, nb=0.028, s.ltoreq.0.0015, p.ltoreq.0.005, fe=balance.
6. The low alloy high toughness ultra high strength steel according to claim 3 or 4, wherein the low alloy high toughness ultra high strength steel is subjected to a smelting process, a forging process, and a post-forging annealing process in this order from front to back before being subjected to a heat treatment process of quenching and tempering.
7. The low alloy high toughness ultra high strength steel according to claim 6, wherein the smelting process comprises melting with a vacuum induction furnace or melting with an electric arc furnace + external refining followed by vacuum consumable remelting or electroslag remelting; the forging process is to perform three piers and three pulls on the smelted steel ingot, and specifically comprises the following steps: step 1, forging at 1080+/-10 ℃ to 1/2 of the original height, and drawing to 4/5 of the original height; step 2, heating to 1080+/-10 ℃, upsetting to 1/2 of the original height, and drawing to 4/5 of the original height; step 3, heating to 1080+/-10 ℃, upsetting to 1/2 of the original height, forging or rolling into bars or billets with corresponding sizes according to the product requirement, wherein the final forging temperature of each step is more than or equal to 860 ℃; the post-forging annealing process comprises the following steps: the forging is heated to 640-660 ℃ for 10h, then cooled to 250-280 ℃ for 10h, then heated to 880 ℃ for more than or equal to 12h, cooled to 250-280 ℃ for 10h, finally heated to 665 ℃ for more than or equal to 20h, cooled to 150 ℃ along with the furnace, and discharged for air cooling.
CN202310120453.7A 2023-02-14 2023-02-14 Low-alloy high-toughness ultrahigh-strength steel Pending CN116287982A (en)

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