High-strength steel with high delay fracture resistance and energy-saving preparation method and application thereof

Abstract

The application discloses a high-strength steel with high delay fracture resistance and an energy-saving preparation method and application thereof. The high-strength steel comprises the following components in percentage by mass: 0.2-0.4% of C, 1.2-2.0% of Si, 0.1-0.3% of Mn, 0.6-1.2% of Cr, 0.8-1.5% of Ni, 0.5-1.0% of Al, 0.8-1.2% of Mo, 0.3-0.5% of V, 0.06-0.10% of Nb, 0.2-0.5% of Cu, 0.02-0.05% of B, 0.02-0.05% of N, 0-0.015% of P, 0-0.010% of S, 0-0.00015% of H, 0-0.0015% of O, and the rest is Fe and impurities. The application can make carbides precipitate in different heat treatment process stages, form a microstructure composed of bainite, residual austenite and carbides, be beneficial to form hydrogen traps, increase the strength and toughness, improve the delay fracture resistance, shorten the process flow, save energy, reduce emissions and reduce the cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel manufacturing, and relates to a high-strength steel with high resistance to delayed fracture and an energy-saving preparation method and application thereof. BACKGROUND

[0002] In recent years, China's manufacturing industry has achieved unprecedented success, and the industrial system is more sound and the industrial chain is more complete. Some high-end equipment such as advanced rail transit equipment, new energy vehicles, ocean engineering equipment and high-tech ships, aerospace equipment and the like have made great progress. Because the working environment of these high-end equipment is more severe and the performance requirements are more stringent, a large number of ultra-high strength steel parts are used.

[0003] However, the challenge faced by the application of ultra-high strength steel parts is the problem of delayed fracture. When the strength of the steel is increased to more than 1200 MPa, the sensitivity of delayed fracture is greatly increased, which seriously limits the application of ultra-high strength steel parts. In addition, whether from the composition design or the subsequent processing and manufacturing of ultra-high strength steel parts, carbon emission problems are involved to varying degrees. China's steel products are mainly produced in the long process converter steel production mode, and the carbon emission per ton of steel is seriously over-standard. Moreover, the downstream industrial chain manufacturing process uses heat treatment processes such as quenching and tempering, annealing and the like many times, which seriously consumes energy such as electricity and pollutes the water environment. Taking the application of ultra-high strength steel in the fastener industry as an example, the 12.9 grade or above ultra-high strength fastener contains elements such as V, Mo, Ni and Cr, which mainly functions in improving hardenability, enhancing tempering stability and improving mechanical properties. The fastener manufacturing process is: raw material→spheroidizing annealing→drawing→spheroidizing annealing→drawing→cold heading head→machining (thread rolling) →quenching and tempering→surface treatment. Obviously, the current ultra-high strength steel products have the following characteristics in the manufacturing process: the alloy content in the raw material is high, and the cost is expensive; the raw material has high strength, and the process includes more than one spheroidizing annealing treatment, and the processing cost is high; the traditional quenching and tempering process causes unstable precipitation of second phase carbides, resulting in coarse grains, and finally the resistance to delayed fracture cannot meet the requirements of the use environment. SUMMARY

[0004] The purpose of the present application is to overcome the deficiencies in the prior art, and to provide a high-strength steel with high resistance to delayed fracture and an energy-saving preparation method and application thereof, which solves the technical problems of low resistance to delayed fracture of ultra-high strength steel wire products and emission reduction and carbon reduction.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] A high-strength steel with high resistance to delayed fracture, the high-strength steel has the following components in percentage by mass: 0.2-0.4% C, 1.2-2.0% Si, 0.1-0.3% Mn, 0.6-1.2% Cr, 0.8-1.5% Ni, 0.5-1.0% Al, 0.8-1.2% Mo, 0.3-0.5% V, 0.06-0.10% Nb, 0.2-0.5% Cu, 0.02-0.05% B, 0.02-0.05% N, 0-0.015% P, 0-0.010% S, 0-0.00015% H, 0-0.0015% O, and the rest is Fe and impurities.

[0007] Optionally, the high-strength steel has a metallographic structure including pearlite, bainite and residual austenite, and carbonitride is dispersedly distributed in the matrix of the high-strength steel.

[0008] Optionally, the high-strength steel has a grain size greater than 8, the bainite has a volume fraction of 90-95%, the residual austenite has a volume fraction of 3-5%, and the carbonitride has a volume fraction of 1-3%.

[0009] Optionally, the high-strength steel has a tensile strength R m ≥1510MPa, a yield strength Rp 0.2 ≥1410MPa, a surface reduction A ≥50%, an elongation ε ≥13%, and an impact toughness K V ≥38J, and a transverse load delayed fracture strength ratio greater than 0.73.

[0010] An energy-saving preparation method of a high-strength steel with high resistance to delayed fracture, the method comprises the following steps: sequentially performing drawing, spheroidizing annealing, cold deformation, preliminary heat treatment, quenching and tempering treatment and surface treatment on a workpiece to be processed.

[0011] Optionally, when the deformation amount of the first drawing is greater than 25% and the total drawing deformation amount is greater than 30% during the drawing process, the workpiece after drawing and before spheroidizing annealing is sequentially subjected to intermediate spheroidizing annealing and secondary drawing.

[0012] Optionally, the spheroidizing rate of the workpiece after spheroidizing annealing and before cold deformation is greater than 90%.

[0013] Optionally, the surface coating passivation film obtained by the surface treatment contains Al.

[0014] An application of a high-strength steel with high resistance to delayed fracture in long-axis type parts.

[0015] Compared with the prior art, the present application has the following beneficial effects:

[0016] The application provides a high-strength steel with high delay fracture resistance and an energy-saving preparation method and application thereof, the high-strength steel contains B, N, Cu, high content of Si, Al and other alloy chemical components, and a hot-rolled rod obtained through reasonable smelting and rolling processes has excellent strength and plasticity, the spheroidizing annealing process before cold drawing is eliminated, the heating temperature and holding time of spheroidizing annealing are reduced, carbon reduction, efficiency improvement and cost reduction are realized while the annealing process is saved;

[0017] Through reasonable heat treatment technology, the microstructure of bainite + residual austenite + carbonitride is formed, the microstructure has high strength and high toughness, the residual austenite film can reduce the diffusion rate of hydrogen atoms in the steel, and the dispersed carbonitride acts as a hydrogen trap, so that high strength and good delay fracture resistance can be obtained at the same time;

[0018] The ultrahigh-strength steel wire product has a grain size greater than 8 levels, a tensile strength R m ≥1510MPa, a yield strength Rp 0.2 ≥1410MPa, a surface reduction A ≥50%, an elongation ε ≥13%, an impact toughness K V ≥38J, and a delay fracture strength ratio greater than 0.73. BRIEF DESCRIPTION OF DRAWINGS

[0019] Fig. 1 Fig. 2 shows a microstructure diagram of the high-strength steel with high delay fracture resistance after spheroidizing annealing according to an embodiment of the application;

[0020] Fig. 2 Fig. 3 shows a schematic diagram of the grain size of the high-strength steel with high delay fracture resistance according to an embodiment of the application;

[0021] Fig. 3 Fig. 4 shows a microstructure diagram of the high-strength steel with high delay fracture resistance according to an embodiment of the application. DETAILED DESCRIPTION

[0022] The application will be further described below in combination with the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the application, and cannot be used to limit the protection scope of the application.

[0023] The endpoints of the ranges and any values in this disclosure are not limited to the precise values stated. The ranges and values should be interpreted as approximately between the stated values. For ranges, the endpoints are included between each respective range; the endpoints are included in the respective range and each respective range is a new range. These ranges are intended to cover all sub-ranges of the defined ranges.

[0024] For the purposes of the present description and the appended claims, unless otherwise stated, all numbers expressing quantities of ingredients, percentage or proportions, and other numerical values used in the description and the appended claims are to be understood as being modified in all instances by the term "about". Also, all ranges include endpoints unless otherwise stated.

[0025] A high strength steel with high resistance to delayed fracture, the high strength steel has a chemical composition comprising, by mass percent: 0.2-0.4% C, 1.2-2.0% Si, 0.1-0.3% Mn, 0.6-1.2% Cr, 0.8-1.5% Ni, 0.5-1.0% Al, 0.8-1.2% Mo, 0.3-0.5% V, 0.06-0.10% Nb, 0.2-0.5% Cu, 0.02-0.05% B, 0.02-0.05% N, 0-0.015% P, 0-0.010% S, 0-0.00015% H, 0-0.0015% O, and the balance of Fe and impurities.

[0026] The high strength steel has a microstructure comprising pearlite, bainite and residual austenite, and carbonitrides dispersedly distributed in the matrix of the high strength steel. The high strength steel has a grain size greater than 8, the bainite volume fraction is 90-95%, the residual austenite volume fraction is 3-5%, and the carbonitride volume fraction is 1-3%. The high strength steel has a tensile strength R m ≥1510 MPa, a yield strength Rp 0.2 ≥1410 MPa, a reduction of area A ≥50%, an elongation ε ≥13%, and an impact toughness K V ≥38 J, and a transverse load delayed fracture strength ratio greater than 0.73.

[0027] An energy-saving preparation method of a high strength steel with high resistance to delayed fracture, comprising the following steps:

[0028] S1, directly cold-drawing the hot-rolled wire rod, when the total cold-drawing deformation is greater than 30%, intermediate spheroidizing annealing is performed, the heating temperature is 660-690℃, the holding time is 0.5h-8h, then furnace cooling to 610-640℃, holding for 3-6h, furnace cooling to 480-530℃ at a rate of 10-15℃ / h, and then air cooling to room temperature, after the intermediate spheroidizing annealing, cold-drawing is performed again, the cold-drawing deformation is less than 30%, and finally spheroidizing annealing is performed to obtain the wire rod; when the cold-drawing deformation of the hot-rolled wire rod is less than 30%, intermediate spheroidizing annealing and drawing are not needed, spheroidizing annealing is performed after the cold-drawing, and the wire rod is obtained; the spheroidizing annealing heating temperature is 600-640℃, the holding time is 0.5h-3h, then furnace cooling to 560-590℃, holding for 0.5-3h, and then furnace cooling to 430-460℃ at a rate of 30-35℃ / h and air cooling; the spheroidizing rate of the wire rod is greater than 90%; the first cold-drawing deformation of the drawing is greater than 25%; the diameter of the hot-rolled wire rod is 1cm-4cm, and the diameter of the wire rod is 0.5-3.4cm;

[0029] S2, cold deformation treatment is performed on the wire rod, the cold deformation treatment includes cold heading, cold bending, cold rolling, thread rolling, and wire drawing processes;

[0030] S3, pre-heat treatment is performed on the wire rod after the cold deformation treatment, the heating temperature is 1050-1200℃, the holding time is 30-50min, the structure is completely austenitized and the carbides are completely dissolved, and the austenite grain size is greater than 8, then furnace cooling to 860-920℃, holding for 50-90min, so that the micro-alloy carbides of Mo, V, Nb, etc. are finely and uniformly dispersed in nanometer scale (~100nm), then furnace cooling to 500-550℃ and holding for 60-90min, in this process, the austenite structure is transformed into lower bainite structure, and the nanometer scale fine and dispersed Cr alloy carbides and Al, B nitrides are further precipitated, and finally furnace cooling to room temperature; then quenching and tempering treatment is performed, the quenching heating temperature is 920-960℃, the holding time is 40-60min, oil cooling to room temperature, the sub-micron scale (100nm-1000nm) carbonitrides are precipitated in the quenching and tempering process, then tempering treatment is performed at a temperature of 570-600℃ for 60-90min, after the quenching and tempering treatment, the wire rod is tempered again, the tempering temperature is 540-570℃, the holding time is 90-120min, the fine and dispersed Cr carbides and Al, B nitrides are further precipitated; finally, surface treatment is performed, the surface treatment includes phosphating treatment, blackening treatment, bluing treatment, galvanizing, Dacromet, and nickel plating methods, in the surface treatment process, the alloy steel contains Al element, the Al element promotes the passivation of the surface of the alloy steel, and the Al element contained in the surface coating passivation film is also beneficial to reducing the H diffusion rate and hindering the diffusion of H element.

[0031] Application of a high-strength steel with high resistance to delayed fracture in long shaft components, including fasteners and springs.

[0032] Example 1

[0033] like Figs. 1 to 3 As shown, a high-strength steel with high resistance to delayed fracture has the following chemical composition by mass percentage: 0.2% C, 2.0% Si, 0.3% Mn, 1.2% Cr, 1.5% Ni, 0.5% Al, 1.2% Mo, 0.5% V, 0.06% Nb, 0.2% Cu, 0.05% B, 0.05% N, 0.005% P, 0.008% S, 0.00012% H, 0.0007% O, with the remainder being Fe and impurities.

[0034] An energy-saving preparation method for high-strength steel with high resistance to delayed fracture includes the following steps:

[0035] S1. Hot-rolled wire rod with a diameter of 22mm is cold-worked and drawn. The first drawing deformation is 28%, the second drawing deformation is 20%, and the total cold-worked drawing deformation is 42.4%. Intermediate spheroidizing annealing is performed. The heating temperature is 660℃ and held for 8 hours, followed by furnace cooling to 610℃ and held for 6 hours. The wire is then furnace-cooled to 480℃ at a rate of 15℃ / h and then air-cooled to room temperature. After intermediate spheroidizing annealing, cold drawing is performed again, with a cold-worked drawing deformation of 21%. Finally, spheroidizing annealing is performed to obtain wire. The spheroidizing annealing temperature is 600℃ and held for 3 hours, followed by furnace cooling to 560℃ and held for 3 hours, and then furnace-cooled to 430℃ at a rate of 35℃ / h and then air-cooled. The spheroidization rate of the wire is 93%.

[0036] S2, the wire is cold-forged into a hexagonal shape for the bolt head and cold-rolled for the bolt shank to produce an M10 hexagonal head bolt;

[0037] S3. The bolts undergo preliminary heat treatment by heating to 1050℃ and holding for 50 minutes, then furnace cooling to 860℃ and holding for 90 minutes, then furnace cooling to 550℃ and holding for 60 minutes, and finally furnace cooling to room temperature. The bolts then undergo tempering treatment by quenching at 920℃ and holding for 60 minutes, oil cooling to room temperature, and then tempering at 600℃ and holding for 60 minutes. After tempering, the bolts undergo tempering again at 570℃ and holding for 90 minutes. The bolt surfaces are then phosphated, and the phosphated layers contain Al.

[0038] The M10 bolts prepared using this technique have a grain size of 8.5, a bainite volume fraction of 92%, a retained austenite volume fraction of 5%, and a carbonitride volume fraction of 3%. At room temperature, the tensile strength R... m =1595MPa, yield strength Rp 0.2= 1468 MPa, surface reduction A = 57%, elongation ε = 18%, impact toughness K V = 46 J, the transverse load delayed fracture strength ratio is 0.77.

[0039] Example Two

[0040] As Figs. 1 to 3 shown, a high-strength steel with high resistance to delayed fracture, the chemical composition of the high-strength steel includes the following components by mass percent: 0.4% C, 1.2% Si, 0.1% Mn, 0.6% Cr, 0.8% Ni, 1.0% Al, 0.8% Mo, 0.3% V, 0.10% Nb, 0.5% Cu, 0.02% B, 0.02% N, 0.005% P, 0.009% S, 0.0001% H, 0.0008% O, the rest is Fe and impurities.

[0041] An energy-saving preparation method of a high-strength steel with high resistance to delayed fracture, comprising the following steps:

[0042] S1, cold drawing deformation is performed on hot-rolled wire rod with a diameter of 12 mm, the first pass drawing deformation is 35%, the second pass drawing deformation is 22%, the total cold drawing deformation is 49.3%, intermediate spheroidizing annealing is performed, the heating temperature is 690 ℃ for 0.5 h, then furnace cooling to 640 ℃ for 3 h, furnace cooling to 530 ℃ at a rate of 10 ℃ / h, and then air cooling to room temperature, then cold drawing after intermediate spheroidizing annealing, the cold drawing deformation is 17.8%, and finally spheroidizing annealing is performed to obtain the wire rod; the spheroidizing annealing heating temperature is 640 ℃ for 0.5 h, then furnace cooling to 590 ℃ for 0.5 h, then furnace cooling to 460 ℃ at a rate of 30 ℃ / h, and then air cooling; the spheroidizing rate of the wire rod is 94%;

[0043] S2, the wire rod is cold coiled to obtain a coil-type spring with a diameter of 5 mm;

[0044] S3, the spring is subjected to preliminary heat treatment, the heating temperature is 1200 ℃ for 30 min, then furnace cooling to 920 ℃ for 50 min, then furnace cooling to 500 ℃ for 90 min, and finally furnace cooling to room temperature; then the bolt is subjected to quenching and tempering treatment, the quenching heating temperature is 960 ℃ for 40 min, oil cooling to room temperature, then tempering treatment at a temperature of 570 ℃ for 90 min, then once more tempering after quenching and tempering treatment, the tempering temperature is 540 ℃ for 120 min; the surface of the spring is subjected to phosphating treatment, and the surface phosphating layer film contains Al elements.

[0045] The spring prepared by the present technology has a grain size of 8.5, a volume fraction of bainite of 94%, a volume fraction of residual austenite of 5%, and a volume fraction of carbonitride of 1%. At room temperature, the tensile strength R m = 1653 MPa, the yield strength Rp0.2 = 1512 MPa, surface reduction A = 51%, elongation ε = 15%, impact toughness K V = 39 J, transverse load delayed fracture strength ratio is 0.76.

[0046] Example Three

[0047] As Figs. 1 to 3 shown, a high-strength steel with high resistance to delayed fracture, the chemical composition of the high-strength steel includes the following components by mass percent: 0.25% C, 1.6% Si, 0.16% Mn, 0.77% Cr, 0.91% Ni, 0.69% Al, 0.92% Mo, 0.41% V, 0.063% Nb, 0.45% Cu, 0.03% B, 0.03% N, 0.007% P, 0.009% S, 0.00011% H, 0.0009% O, and the balance of Fe and impurities.

[0048] An energy-saving preparation method of a high-strength steel with high resistance to delayed fracture, comprising the following steps:

[0049] S1, cold drawing deformation is performed on a hot-rolled wire rod with a diameter of 24 mm, the cold drawing deformation amount is 25%, and finally spheroidizing annealing is performed to obtain a wire rod, the spheroidizing annealing heating temperature is 630 ℃, the temperature is kept for 2.5 h, then furnace cooling is performed to 580 ℃, the temperature is kept for 1 h, and then furnace cooling is performed to 450 ℃ at a rate of 32 ℃ / h, and air cooling is performed; the spheroidizing rate of the wire rod is 93%;

[0050] S2, rod cold rolling is performed on the wire rod to obtain a stud with a diameter of 18 mm;

[0051] S3, preliminary heat treatment is performed on the stud, the heating temperature is 1080 ℃, the temperature is kept for 47 min, then furnace cooling is performed to 880 ℃, the temperature is kept for 58 min, then furnace cooling is performed to 520 ℃, the temperature is kept for 72 min, and finally furnace cooling is performed to room temperature; quenching and tempering treatment is performed on the stud, the quenching heating temperature is 930 ℃, the temperature is kept for 43 min, oil cooling is performed to room temperature, then tempering treatment is performed at a temperature of 585 ℃ for 75 min, after the quenching and tempering treatment, the stud is subjected to secondary tempering treatment, the tempering temperature is 550 ℃, and the temperature is kept for 105 min; phosphating treatment is performed on the surface of the stud, and the surface phosphating layer film contains Al elements.

[0052] The fastener stud prepared by the technology has a grain size of 8.5, a volume fraction of bainite of 95%, a volume fraction of residual austenite of 3%, and a volume fraction of carbonitride of 2%. At room temperature, the tensile strength R m = 1545 MPa, the yield strength Rp 0.2 = 1420 MPa, the surface reduction A = 51%, the elongation ε = 14%, and the impact toughness K V = 39 J, the transverse load delayed fracture strength ratio is 0.74.

[0053] Comparative Example

[0054] A high-strength bolt steel, the mass percentage of the chemical components is (wt%): C 0.35-0.45; Si 0.15-0.24; Mn 0.20-0.40%; Cr 0.75-1.35; Mo 0.55-1.00; V 0.08-0.30; Al 0.005-0.10; S 0-0.005, and the rest is Fe and impurities.

[0055] The preparation process is: smelting and casting → soaking treatment → roughing and cogging → rolling → rolling wire rod → quenching and tempering treatment → final product. The specific parameters are as follows: the wire rod is subjected to quenching and tempering treatment, the selected quenching temperature should satisfy log{[V][C]}>6.72-9500 / T (in the formula, [V] is the mass percentage of V in the high-strength bolt steel, [C] is the mass percentage of C in the high-strength bolt steel, and T is the quenching temperature, the unit of the quenching temperature T is K), the wire rod is quenched after being kept at the quenching temperature for 60-80 min, is cooled to below 80 ℃ by using mineral oil at 40-60 ℃, and is tempered by heating at a temperature not lower than 500 ℃ for more than 90 min, and the high-strength bolt steel is obtained by quenching after being kept at the quenching temperature T for 60-80 min and tempering by heating at a temperature not lower than 500 ℃ for more than 90 min and air cooling.

[0056] The fastener bolt prepared by the technology has microstructure of tempered sorbite, the size of the original austenite grains in the tempered sorbite is ≤20 μm, the tensile strength is above 1400 MPa, the yield strength reaches 1260 MPa, and the reduction of area is above 50%.

[0057] C: Carbon is the main element for obtaining strength of alloy steel, generally, the strength of ultrahigh-strength steel is greater than 1280 MPa, and the carbon content is greater than 0.2% or more, but when the C content increases to greater than 0.4%, although the strength increases, the plasticity and toughness will also decrease, especially the resistance to delayed fracture of the alloy steel significantly decreases. Therefore, in the present application, the C content is controlled to be 0.2-0.4%.

[0058] Si: Silicon element has solid solution strengthening effect in steel, is a non-carbide forming element, in addition, silicon element is beneficial to increase the amount of austenite, thereby reducing the hydrogen diffusion rate, and the Si element has good tempering resistance, so that the alloy steel can be tempered at a higher temperature. In addition, the addition of Si element can also promote the residual austenite film distributed between the bainite to reduce the diffusion rate of hydrogen atoms. Obviously, the Si element helps to improve the resistance to delayed fracture performance, but when the Si element content is greater than 2.0%, the plasticity and toughness of the steel will decrease sharply. Considering comprehensively, in the present application, the Si content is controlled to be 1.0-2.0%.

[0059] Mn: Manganese element can help remove oxygen, sulfur, etc., while manganese element is an austenite forming element, which is beneficial to the formation of austenite and hinders the transformation of austenite to form residual austenite. However, when the manganese content increases, it will promote the segregation of P element. Considering comprehensively, the content of Mn element in the application is controlled at 0.1-0.3%.

[0060] Cr: Chromium element is a carbide forming element, which can improve strength and resistance to delayed fracture when carbide precipitates, and chromium element also improves the hardenability of steel, but if the Cr content is too much, it will deteriorate the cold working performance, so the upper limit of Cr element needs to be controlled. Considering comprehensively, the content of Cr element in the application is controlled at 0.6-1.2%.

[0061] Ni: Nickel element is an austenite forming element, which can improve strength and promote the formation of residual austenite, and residual austenite film improves toughness and significantly improves resistance to delayed fracture. However, Ni is high in cost, which can be replaced by N and B. Considering comprehensively, the content of Ni in the application is controlled at 0.8-1.5%.

[0062] Al: Aluminum element can effectively remove oxygen, and aluminum element can form AlN, which is beneficial to improve strength and resistance to delayed fracture. In addition, aluminum element promotes the passivation of steel surface, and the Al element in the passivation film on the surface of the steel is also beneficial to hinder the diffusion of H element and reduce the diffusion rate of H. When the aluminum content is greater than 0.5%, the above-mentioned effect will be achieved. However, when the aluminum content is greater than 1.0%, the toughness and processing performance will be reduced. Considering comprehensively, the content of Al in the application is controlled at 0.5-1.0%.

[0063] Mo: Molybdenum element is a strong carbide forming element, which does not dissolve at a suitable temperature, and can precipitate to form secondary strengthening during tempering, thereby improving strength and resistance to delayed fracture. Molybdenum element is an indispensable element in ultra-high strength steel. Considering comprehensively, the content of Mo in the application is controlled at 0.8-1.2%.

[0064] V: Vanadium element can form stable carbide, refine grains, and play a secondary strengthening role during tempering, thereby improving strength and resistance to delayed fracture. Vanadium element is a common additive element in ultra-high strength steel, but when the content is greater than 0.5%, the processing performance will be deteriorated and the cost will be increased. Considering comprehensively, the content of V in the application is controlled at 0.3-0.5%.

[0065] Nb: Niobium element has the same effect as V element, mainly forming stable carbide, but its solubility in steel is lower than 0.10%, and the cost is higher. Considering comprehensively, the content of Nb is controlled at 0.06-0.10%.

[0066] Cu: Copper is an austenite forming element and can be used to replace part of the Ni element, while helping to promote the formation of residual austenite, improve toughness, and significantly improve the resistance to delayed fracture performance. However, the solubility of Cu in iron is limited, and high content will also deteriorate the hot working performance. Considering comprehensively, the Cu content in the present application is controlled to be 0.2-0.5%.

[0067] B: Boron increases the hardenability of steel, part of the boron element can replace nickel, chromium and other elements, reduce the manufacturing cost, and the boron has less tendency to form cracks when the alloy steel is quenched, in addition, B has strong affinity with N to form BN, which is beneficial to refine the grain, improve the strength and toughness and the resistance to delayed fracture performance. However, B slightly promotes the tendency of temper brittleness, and is easy to cause coarse grains. Considering comprehensively, the B content in the present application is controlled to be 0.02-0.05%.

[0068] N: is an austenite forming element, can replace Ni and C elements, in order to improve the strength, resistance to delayed fracture performance, the N content needs to be greater than 0.02%, however, when the content is greater than 0.05%, it will easily lead to steel porosity. Considering comprehensively, the N content in the present application is controlled to be 0.02-0.05%.

[0069] The above only describes the preferred embodiments of the present application, it should be noted that for those skilled in the art, without departing from the technical principles of the present application, a number of improvements and modifications can be made, these improvements and modifications should also be considered as the protection scope of the present application.

Claims

1. An energy-saving preparation method for high-strength steel with high resistance to delayed fracture, characterized in that, The workpiece is subjected to the following processes in sequence: drawing, spheroidizing annealing, cold deformation, pre-heat treatment, quenching and tempering, and surface treatment. The pre-heat treatment is as follows: heating to 1050~1200℃, holding for 30~50 min, then furnace cooling to 860~920℃, holding for 50~90 min, then furnace cooling to 500~550℃, holding for 60~90 min, and finally furnace cooling to room temperature. The chemical composition of the high-strength steel, by mass percentage, includes the following components: 0.2~0.4%C, 1.2~2.0%Si, 0.1~0.3%Mn, 0.6~1.2%Cr, 0.8~1.5%Ni, 0.5~1.0%Al, 0.8~1.2%Mo, 0.3~0.5%V, 0.06~0.10%Nb, 0.2~0.5%Cu, 0.02~0.05%B, 0.02~0.05%N, 0~0.015%P, 0~0.010%S, 0~0.00015%H, 0~0.0015%O, with the remainder being Fe and impurities.

2. The energy-saving preparation method of high-strength steel with high resistance to delayed fracture according to claim 1, characterized in that: The microstructure of high-strength steel consists of bainite, retained austenite, and carbonitrides dispersed in the high-strength steel matrix.

3. The energy-saving preparation method of high-strength steel with high resistance to delayed fracture according to claim 2, characterized in that: The high-strength steel has a grain size greater than grade 8, the volume fraction of bainite is 92-95%, the volume fraction of retained austenite is 3-5%, and the volume fraction of carbonitrides is 1-3%.

4. The energy-saving preparation method of high-strength steel with high resistance to delayed fracture according to claim 1, characterized in that: High-strength steel tensile strength R m ≥1510MPa, yield strength Rp 0.2 ≥1410MPa, reduction of area A≥50%, elongation ε≥13%, impact toughness K V ≥38J, transverse load delayed fracture strength ratio greater than 0.

73.

5. The energy-saving preparation method of high-strength steel with high resistance to delayed fracture according to claim 1, characterized in that: During the drawing process, if the deformation of the first drawing pass is greater than 25% and the total drawing deformation is greater than 30%, the workpiece to be processed after drawing and before spheroidizing annealing is subjected to intermediate spheroidizing annealing and secondary drawing in sequence.

6. The energy-saving preparation method of high-strength steel with high resistance to delayed fracture according to claim 1, characterized in that: The spheroidization rate of the workpiece before cold deformation after spheroidizing annealing is greater than 90%.

7. The energy-saving preparation method of high-strength steel with high resistance to delayed fracture according to claim 1, characterized in that: Nanoscale carbonitrides are precipitated during the preheating process, and submicron-scale carbonitrides are precipitated during the tempering process.

8. The energy-saving preparation method of high-strength steel with high resistance to delayed fracture according to claim 1, characterized in that: The passivation film obtained by the surface treatment contains Al.

9. A high-strength steel with high resistance to delayed fracture, characterized in that, Prepared by the method according to any one of claims 1-8.

10. The application of the high-strength steel with high resistance to delayed fracture as described in claim 9 in long shaft components.

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