CN115161550A - Steel for high-strength fastener for large hydraulic impact crusher and manufacturing method thereof - Google Patents
Steel for high-strength fastener for large hydraulic impact crusher and manufacturing method thereof Download PDFInfo
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Abstract
The invention relates to a steel for a high-strength fastener for a large hydraulic impact crusher and a manufacturing method thereof, wherein the steel comprises the following elements in percentage by mass: c:0.38 to 0.45%, si:0.15 to 0.35%, mn: 0.70-0.90%, P: less than or equal to 0.010%, S: less than or equal to 0.003 percent, cr:1.30 to 1.80%, mo:0.40 to 0.60%, ni:3.10 to 4.00%, O: less than or equal to 0.0010%, H: less than or equal to 0.0001%, N: less than or equal to 0.0040 percent, and the balance of Fe and inevitable impurity elements. The metallographic structure is a tempered sorbite. The method is manufactured by controlled rolling, annealing and quenching and tempering, and takes continuous casting round billets with the diameter of more than 600mm as blanks to produce round steel with the diameter of 45-200mm, so that the steel compression ratio is greatly improved, the compactness of the core of the material is better, the mechanical property is obviously improved, and compared with the traditional method of rolling small-specification continuous casting square billets, the compactness, the porosity and the segregation tendency of the steel are obviously improved.
Description
Technical Field
The invention relates to the technical field of alloy steel, in particular to high-strength bolt round steel applied to processing of a large hydraulic impact crusher and a manufacturing method thereof.
Background
The large hydraulic impact crusher supplies pressure oil through a pump station of an excavator or a loader, thereby effectively cleaning floating stones and soil in rock gaps in the operation of excavating mines and the like. The working process can generate strong vibration force and also needs enough breakdown force to effectively break the stones by the hammering energy of the piston, so the working environment is very bad. Important parts such as through bolts, guard plate bolts and the like for fixing upper, middle and lower cylinder bodies of a large hydraulic impact crusher are easy to wear during work, so that the guard plate bolts and the through bolts are loosened, the bolts are broken due to fatigue damage at the thread parts of the bolts, and in addition, the through bolts fail to work, so that the pistons and the cylinder bodies are not concentric to pull cylinders when being struck. The energy accumulator bolt and the external reversing valve bolt of the hydraulic impact crusher are made of materials with high obdurability and proper high-temperature resistance due to the particularity of working positions. At present, the common bolt materials such as 35-42CrMoA, 4140, B7, 32-36CrB4, 40CrNiMo and the like are far from meeting the high strength and toughness and certain high temperature resistance which are needed to be possessed by the bolt materials of a large-scale hydraulic impact crusher through bolt, a guard plate bolt, an energy accumulator bolt and an external reversing valve bolt, and a new material is urgently needed to be developed so as to meet the use requirements of high strength, high hardness, impact resistance and proper high temperature performance under the working state of the bolt of the large-scale hydraulic impact crusher.
The high-strength bolt raw material for processing the large hydraulic impact crusher and the manufacturing method thereof are developed and applied, and can meet the use requirements of high strength and toughness of important part through bolts, guard plate bolts, energy accumulator bolts and external reversing valve bolt materials of the large hydraulic impact crusher. With the increasing of new domestic capital construction projects, the market of the hydraulic impact crusher is more and more concerned, and the market application prospect of the high-strength bolt material on the hydraulic impact crusher is wider.
Disclosure of Invention
The invention aims to provide a high-strength bolt steel for producing a large hydraulic impact crusher by continuously casting round billets and a manufacturing method thereof, and compared with traditional bolt materials such as 35-42CrMoA, 4140, B7, 32-36CrB4, 40CrNiMo and the like, the high-strength bolt steel has the following advantages: (1) The novel element components are adopted, so that the use requirements of high-strength, high-toughness and high-temperature-resistant strength bolt materials urgently needed in the market are met; (2) The round steel with the specification of phi 45-200mm is produced by rolling the large-specification continuous casting round billet, the compression ratio of the material in the forming process is obviously increased, and the heat treatment mechanical property, particularly the core performance, of the material is obviously improved; (3) Compared with the traditional method of rolling round steel by adopting small-specification continuous casting square billets, the method has the advantages that the compactness, segregation tendency, porosity and other aspects of the internal structure of the steel are obviously improved.
The application is applicable to the steel for the high-strength fastener of the large-scale hydraulic impact crusher, and the element components of the steel satisfy the following requirements in percentage by mass: c:0.38 to 0.45%, si:0.15 to 0.35%, mn: 0.70-0.90%, P: less than or equal to 0.010%, S: less than or equal to 0.003 percent, cr: 1.30-1.80%, mo:0.40 to 0.60%, ni:3.10 to 4.00%, O: less than or equal to 0.0010%, H: less than or equal to 0.0001%, N: less than or equal to 0.0040 percent, and the balance of Fe and inevitable impurity elements.
The chemical components of the high-strength bolt material for the large hydraulic impact crusher are determined as follows:
c: the hardenability of the steel is remarkably improved, and the strength and hardness of the steel are improved, but the plasticity and the impact toughness of the steel are remarkably reduced along with the improvement of C. In order to ensure the requirements of high-strength bolt steel on strength, plasticity, toughness, wear resistance and the like, the content of C in the material is designed to be 0.38-0.45%.
Si: is a deoxidizing element in steel, improves the strength of the steel in a solid solution strengthening mode, has poor deoxidizing effect when the content of Si is lower than 0.10 percent, increases the brittleness of the steel when the content of Si is higher, and reduces the ductility and toughness of the steel. Considering the higher requirement of the ductility and toughness of the steel, the Si content of the design material is 0.15-0.35%.
Mn: is an important element for improving the hardenability and the wear resistance of the steel, and plays a role in solid solution strengthening to make up for the strength loss caused by the reduction of the content of C in the steel. The excessive Mn content easily causes the coarse tendency of the crystal grains of the steel and is unfavorable for the plasticity and the toughness of the material, and the Mn content of the designed material is 0.70 to 0.90 percent.
Ni: non-carbide forming elements exist in the steel in a solid solution form, improve the hardenability of the steel and have good effects on impact toughness and ductile-brittle transition temperature, ni can also improve the hardenability of the steel, reduce the critical point, increase the stability of austenite, and in addition, can significantly improve the fatigue properties of the steel. Considering the higher toughness requirement of the steel under high strength, the Ni content of the design material is 3.10-4.00%.
Cr: part of Cr in the steel replaces iron to form alloy cementite, so that the stability is improved; part of the ferrite is dissolved in the ferrite to play a role of solid solution strengthening, thereby improving the strength and the hardness of the ferrite. The addition of a certain amount of Cr in the heat-treated steel enables the strength and hardness of the steel after quenching and tempering to be obviously improved, the higher Cr can form a passive film on the surface of the steel to improve the corrosion resistance of the steel, in addition, the Cr is combined with carbon to form various carbides to increase the toughness of the material, but the Cr content is over high to be unfavorable for the toughness, and the Cr content in the design is in the range of 1.30-1.80%.
Mo: mo existing in solid solution and carbide of steel has solid solution strengthening effect, can obviously improve hardenability and tempering stability of steel, has solid solution strengthening effect on ferrite, and simultaneously improves carbide stability, thereby improving the strength of steel. Mo can also improve the ductility and the wear resistance of the steel, simultaneously has a beneficial effect on improving the corrosion resistance of the material, and can also refine crystal grains and improve the nonuniformity of carbide, thereby improving the strength and the toughness of the steel. In the design, the content of Mo is 0.40-0.60%.
S and P: s mainly exists in the form of MnS and FeS in steel, can cause hot brittleness of the steel, reduces mechanical properties of the steel, particularly yield strength, plasticity and wear resistance, and has adverse effect on corrosion resistance of the steel; p is easy to segregate in the steel at grain boundaries to cause segregation, thereby increasing the tempering brittleness of the steel and obviously reducing the plasticity and the toughness of the grain boundaries. Both P and S as impurity elements adversely affect the toughness of the steel, and the content thereof should be minimized. For this purpose, material P is designed: less than or equal to 0.010 percent, S: less than or equal to 0.003 percent.
H. O, N: h is a harmful element in steel, and the dissolution of H in the steel can cause the defects of hydrogen embrittlement, white spots and the like of the steel, so that the plasticity, toughness and fatigue strength of the steel are reduced rapidly, and hydrogen-induced cracking can be caused in serious cases, and the method comprises the following steps: h: less than or equal to 0.00010 percent; o is a harmful element in steel, and is FeO, mnO or SiO in steel 2 、Al 2 O 3 And the like exist in the form of inclusions, so that the strength and the plasticity of the steel are reduced, and the fatigue strength and the impact toughness of the steel are particularly seriously influenced, and the control is as follows: o: less than or equal to 0.0010 percent; n is an impurity element harmful to toughness in steel, and in order to obtain excellent toughness, N: less than or equal to 0.0040 percent.
The manufacturing method of the high-strength bolt round steel for the large hydraulic impact crusher comprises the following process steps: preparing smelting raw materials according to the chemical composition of the steel, and sequentially carrying out KR molten iron pretreatment, converter smelting, LF furnace refining, RH furnace refining and continuous casting to produce high-purity molten steel and continuous casting round billets with the diameter of more than or equal to 600mm, low center segregation and looseness, no cracks and shrinkage cavities and high purity.
In particular, the continuous casting round billet should satisfy: center segregation: grade ≦ 0.5, general and central loosening: not more than 0.5 grade, and has no central crack, intermediate crack and shrinkage cavity; non-metallic inclusions: class A coarse series =0 level, class A fine series is less than or equal to 0.5 level; the coarse line and the fine line of the B and the D are both less than or equal to 0.5 grade; class C coarse and fine systems both =0 level; ds class is less than or equal to 0.5 grade). The content of H in molten steel after RH treatment is less than or equal to 0.0001%.
And (3) after the continuous casting is finished, putting the continuous casting blank into a slow cooling pit for slow cooling to reduce the H content so as to avoid hydrogen induced cracking of the casting blank, preferably, putting the continuous casting blank into the pit at a temperature of more than or equal to 650 ℃, keeping the temperature of more than or equal to 72 hours in the pit, and cooling to the temperature of less than 180 ℃ to be discharged from the slow cooling pit.
And after the slow cooling is finished, performing shot blasting on the surface of the continuous casting billet to ensure that the surface crack defect of the steel bar is not generated in the rolling process due to the surface quality problem of the continuous casting billet.
The continuous casting round billet after the treatment is heated and insulated, so that alloy elements in the steel are fully dissolved in the solution, and the strengthening and toughening effects of the alloy elements are exerted, thereby ensuring the chemical composition and the tissue uniformity of the final product. Preferably, a natural gas heated continuous heating furnace is adopted for sectional heating, the temperature of a preheating section is 650-850 ℃, the temperature of a heating section I is 950-1050 ℃, the temperature of a heating section II is 1220 +/-30 ℃, the temperature of a soaking section is 1270 +/-30 ℃, the total heating time of the casting blank is more than 20 hours, and the time of a high-temperature soaking section is more than 8 hours.
After the heat preservation is finished, carrying out high-pressure water descaling treatment on the continuous casting billet to remove a surface oxide layer, and then rolling in two stages: the first stage rolling is rough rolling, the initial rolling temperature is 1100-1170 ℃, the total reduction rate is more than or equal to 43%, the maximum single-pass reduction rate is more than or equal to 19% by adopting the high-pressure rolling process, so that the core defects of the continuous casting billet are fully closed, and the large-diameter steel bar is ensured at the 1/2 radius and the core performance. The second stage of rolling is finish rolling, the initial rolling temperature is 940-980 ℃, the total compression rate is more than or equal to 22%, and the finished product diameter is achieved.
And (3) after rolling, conveying the steel bar into an annealing furnace for annealing, wherein the annealing heat preservation temperature is 670 +/-10 ℃, the heat preservation time is more than or equal to 30 hours, so as to further reduce or remove the H content in the rolled steel bar, further ensure the performance of the 1/2 diameter part and the core part of the finished steel bar, annealing the steel bar below 200 ℃, discharging and air cooling to room temperature.
And quenching and tempering the annealed steel bar to obtain the quenched and tempered steel bar. Alternatively, the quenching treatment uses continuous roller hearth furnace heating, the heating temperature: 925-950 ℃, in-furnace time: 2.1-2.5 min/mm multiplied by the diameter (mm) of the steel bar, and quenching by using a quenching machine; water flow is more than or equal to 30m 3 And h, the water pressure of the low-pressure section is more than or equal to 4bar, the water pressure of the high-pressure section is more than or equal to 8bar, and the steel bar is quenched to the surface temperature of less than or equal to 80 ℃ and then cooled to room temperature by air. The tempering treatment process comprises the following steps: tempering temperature: 470-570 ℃, holding time: 3.0-4.0 min/mm multiplied by the diameter (mm) of the steel bar, and air-cooled to room temperature after being taken out of the furnace.
Compared with the prior art, the invention has the advantages that:
the design adopts new material element components, and the problems that the existing domestic material cannot meet the high strength, high toughness and certain high temperature resistance required by the bolts for the large hydraulic impact crusher can be better solved.
The method adopts the continuous casting round billet with the diameter of more than or equal to 600mm, low center segregation and looseness, no crack and shrinkage cavity and ultra-pure, and produces round steel with the diameter of 45-200mm by continuous rolling, thereby greatly improving the steel compression ratio, leading the material core to have better compactness and obviously improved mechanical property, and compared with the traditional method of adopting small-specification continuous casting square billet rolling, obviously improving the compactness, the looseness and the segregation tendency of the steel.
The high-strength bolt round steel for the large hydraulic impact crusher, which is manufactured by the invention, is manufactured by using the continuous casting round billet as the blank, so that compared with the method of manufacturing the blank by using a die casting steel ingot, the cogging process in the rolling process is omitted, the production process is simplified, meanwhile, the yield of the steel bar is improved, and the production and manufacturing cost of the steel bar is reduced; compared with the traditional method, the thickness of the film is less than or equal to 390 multiplied by 510mm 2 Compared with the continuous rolling production of the continuous casting square billet with the specification, the density, the porosity and the deviation of the steelThe tendency to precipitate improves significantly. Therefore, the method has obvious technical advantages in industrial production.
A round steel product meeting the use requirement of the high-strength fastener is manufactured by adopting controlled rolling, annealing and thermal refining, the diameter of the round steel is 45-200mm, and the final metallographic structure is a tempered sorbite structure. The high-strength bolt for the large hydraulic impact crusher, which is manufactured by the invention, has the characteristics of full-section through quenching, high strength, high hardness, high toughness and certain high-temperature resistance. Performance indexes (tensile and impact are sampled at half of the radius of the bar) reached after round steel quenching and tempering treatment: the yield strength is more than or equal to 1100MPa, the tensile strength is more than or equal to 1220MPa, the elongation is more than or equal to 10 percent, the reduction of area is more than or equal to 44 percent, and the Charpy impact energy at minus 40 ℃ is more than or equal to 27J; after quenching and tempering, ensuring 100 percent of tempered sorbite tissues of the whole section; the hardness of the surface, the core and one half of the radius is in the range of 380-429HV10, the hardness difference of each position is less than or equal to 30HV10, and the surface hardness HV0.3 is less than or equal to 435. In addition, the tensile property at high temperature of 250 ℃ reaches: the yield strength is more than or equal to 1034MPa, the tensile strength is more than or equal to 1172MPa, the elongation is more than or equal to 8 percent, and the reduction of area is more than or equal to 40 percent.
Drawings
Fig. 1 is an in-situ analysis diagram of round steel in example 1 of the present invention: the density is 0.9753, and the porosity is 0.0182;
FIG. 2 shows a conventional 390X 510mm 2 In-situ analysis chart of round steel produced by square billet rolling and having the same specification as that of example 1: the compactness is 0.9349, and the looseness is 0.0742;
FIG. 3 is the microstructure of the round steel after annealing and quenching and tempering heat treatment in example 1 of the invention;
FIG. 4 shows the microstructure of the round steel after annealing and quenching and tempering heat treatment in example 2 of the present invention.
Detailed Description
The present invention is described in further detail below with reference to examples, which are illustrative and are intended to be illustrative of the present invention, but are not to be construed as limiting the present invention.
Example 1
The diameter of the high-strength bolt steel for the large hydraulic impact crusher related to the embodiment is 200mm, and the high-strength bolt steel comprises the following chemical components in percentage by mass: c:0.42%, si:0.27%, mn:0.77%, P:0.007%, S:0.002%, cr:1.73%, mo:0.51%, ni:3.25%, H:0.00007%, O:0.0008%, N:0.0031% and the balance of Fe and inevitable impurity elements.
The manufacturing process of the bolted steel comprises the steps of preparing smelting raw materials according to the chemical components of the finished product of the bolted steel, pretreating by KR molten iron, smelting in a converter, tapping P in the converter to be 0.006%, refining the molten steel by LF, finely adjusting the alloy content, adding a deoxidizing agent for deoxidation, conveying the molten steel to an RH station for vacuum degassing treatment, wherein the high vacuum time is 20 minutes, the soft argon blowing time is 25 minutes, and the RH oxygen content is 0.0007%, and then continuously casting to obtain a round billet which meets the chemical components, a macrostructure (central segregation: 0.5 grade, general porosity and central porosity: 0.5 grade, and no central crack, middle crack and shrinkage cavity) and ultra-pure degree (nonmetallic inclusion: A coarse =0 grade, A fine =0.5 grade, B coarse =0.5 grade, D coarse grade =0 grade, B and D fine grade =0.5 grade, D coarse grade =0 grade, D coarse grade and D fine grade = 0.00000 mm grade, and continuously casting the D coarse grade and fine grade D grade = 0mm D of the round billet in the molten steel after RH treatment, wherein the H content of the round billet is = 700mm, and the finished product of the steel is RH, and the H is subjected to be continuously cast. And (3) putting the casting blank into a slow cooling pit at a high temperature, wherein the offline temperature is 680 ℃, the slow cooling time is 76 hours, and the pit outlet temperature is 170 ℃.
Cold loading a continuous casting round billet with the diameter of 700mm into a heating furnace for heating, wherein the temperature of a preheating section is 670-830 ℃, the temperature of a heating section I is 980-1030 ℃, the temperature of a heating section II is 1210-1250 ℃, the temperature of a soaking section is 1260-1290 ℃, the total heating time of the casting blank is 22.5 hours, and the high-temperature soaking section is 10 hours for discharging; the high-pressure water descaling is carried out, then two-stage rolling is carried out, the first stage rolling is rough rolling, the initial rolling temperature is 1120-1170 ℃, the total compression rate is not less than 43%, the high-pressure rolling process is adopted, the maximum single-pass reduction rate is 19%, the second stage rolling is finish rolling, the initial rolling temperature is 960-980 ℃, and the total compression rate is 23%. After rolling to the diameter of a finished product, annealing the bar in red, annealing at the temperature of 670 +/-10 ℃ for 37 hours, annealing the steel bar at the temperature of 190 ℃, discharging the steel bar out of the furnace, and air cooling to room temperature.
Quenching and tempering the annealed steel bar, wherein the quenching and tempering heat treatment uses a continuous roller hearth furnace, and the quenching and heating temperature is as follows: 935 + -10 ℃, in-furnace time: 481min, quenching with water by using a quenching machine; water flow is more than or equal to 30m 3 The water pressure of the low-pressure section is more than or equal to 4bar, the water pressure of the high-pressure section is more than or equal to 8bar, and the steel bar is water-quenched to the surface temperature of less than or equal to 80 ℃ during quenching and then air-cooled to the room temperature; tempering temperature: 530 +/-8 ℃, and holding time: 645min, and air cooling to room temperature after discharging.
The mechanical properties of the bolt round steel prepared by the manufacturing process are shown in tables 1-1 and 1-2.
Table 1-1 example 1 Normal temperature mechanical Properties of round steel
Table 1-2 high temperature performance of round steel of example 1
And the tensile and impact properties are measured by sampling at the 1/4 diameter part of the cross section of the round steel, and the Vickers hardness is respectively measured at the surface of the cross section, the core part and the 1/4 diameter part.
The porosity, the compactness and the segregation tendency of each main element of the round steel prepared by the process are 390 multiplied by 510mm compared with the traditional round steel 2 The square billet is rolled into the same specification round steel pair as shown in the table 2.
Table 2 comparison of porosity, segregation and segregation of main element of round steel in example 1 with those of conventional process
Example 2
The diameter of the high-strength bolt steel for the large hydraulic impact crusher related to the embodiment is 110mm, and the high-strength bolt steel comprises the following chemical components in percentage by mass: c:0.41%, si:0.25%, mn:0.72%, P:0.008%, S:0.001%, cr:1.65%, mo:0.47%, ni:3.17%, H:0.00006%, O:0.0006%, N:0.00259%, and the balance of Fe and inevitable impurity elements.
The manufacturing process of the bolted steel comprises the steps of preparing smelting raw materials according to the chemical components of the finished bolted steel, pretreating by KR molten iron, smelting in a converter, tapping P in the converter for 0.007%, refining the molten steel by LF, finely adjusting the alloy content, adding a deoxidizing agent for deoxidation, conveying the molten steel to an RH station for vacuum degassing treatment, carrying out high vacuum time for 20 minutes, carrying out soft argon blowing for 25 minutes, and tapping RH for 0.0005%, and carrying out continuous casting to obtain the bolted steel which meets the chemical components, has a macroscopic structure (central segregation: 0.5 grade, general and central porosity: 0.5 grade, and has no central crack, intermediate crack and shrinkage) and ultra-purity (nonmetallic inclusion: A type coarse system =0 grade, and A type fine system =0.5 grade, B type and D type coarse systems =0 grade, B type and D fine systems both =0.5 grade, C type coarse system and fine system both =0 grade, ds type =0.5 grade), and has the specification of 600mm phi round billet, and has RH content = 0.6% in the molten steel after vacuum treatment. And (3) putting the casting blank into a slow cooling pit at a high temperature, wherein the offline temperature is 665 ℃, the slow cooling time is 72 hours, and the pit outlet temperature is 172 ℃.
Cold charging a continuous casting round billet with the diameter of 600mm into a heating furnace for heating, wherein the temperature of a preheating section is 660-840 ℃, the temperature of a heating section I is 970-1030 ℃, the temperature of a heating section II is 1210-1240 ℃, the temperature of a soaking section is 1250-1270 ℃, the total heating time of a casting blank is 20.5 hours, and the high-temperature soaking section is 8.7 hours; descaling by high-pressure water and then carrying out two-stage rolling, wherein the first stage rolling is rough rolling, the initial rolling temperature is 1120-1160 ℃, the total compression rate is more than or equal to 41%, the high-pressure process rolling is adopted, the maximum single-pass reduction rate is 20%, the second stage rolling is finish rolling, the initial rolling temperature is 960-980 ℃, the total compression rate is 23%, after rolling to the diameter of a finished product, a bar is subjected to red annealing, the annealing heat preservation temperature is 670 +/-10 ℃, the heat preservation time is 31 hours, and the steel bar is subjected to annealing at 170 ℃, discharged from a furnace and air-cooled to the room temperature.
Carrying out quenching and tempering treatment on the annealed steel bar, wherein the heat treatment uses a continuous roller hearth furnace, and the quenching heating temperature is as follows: 935 ± 10 ℃, in-furnace time: quenching in water for 265min by using a quenching machine; water flow is more than or equal to 30m 3 The water pressure of the low-pressure section is more than or equal to 4bar, the water pressure of the high-pressure section is more than or equal to 8bar, and the steel bar is water-quenched to the surface temperature of less than or equal to 80 ℃ during quenching and then air-cooled to the room temperature; tempering temperature: 530 +/-8 ℃, and holding time: and (5) taking the steel out of the furnace, and cooling the steel to room temperature in air.
The mechanical properties of the bolt round steel prepared by the manufacturing process are shown in tables 3-1 and 3-2.
TABLE 3-1 Normal temperature mechanical properties of round steel in example 2
Table 3-2 high temperature mechanical properties of example 2 round steel
And the tensile and impact properties are measured by sampling at the 1/4 diameter part of the cross section of the round steel, and the Vickers hardness is respectively measured at the surface of the cross section, the core part and the 1/4 diameter part.
Claims (9)
1. A high-strength steel for fasteners, characterized in that: the element components of the steel satisfy the following requirements in percentage by mass: c:0.38 to 0.45%, si:0.15 to 0.35%, mn: 0.70-0.90%, P: less than or equal to 0.010 percent, S: less than or equal to 0.003 percent, cr: 1.30-1.80%, mo:0.40 to 0.60%, ni:3.10 to 4.00%, O: less than or equal to 0.0010%, H: less than or equal to 0.0001%, N: less than or equal to 0.0040 percent, and the balance of Fe and inevitable impurity elements.
2. The steel for high-strength fasteners according to claim 1, characterized in that: the product is round steel with the diameter of 45-200mm, and the final metallographic structure is a tempered sorbite structure.
3. The steel for high-strength fasteners according to claim 1, characterized in that: the compactness and segregation of the product meet the following requirements: center segregation: grade less than or equal to 0.5, general and central loosening: not more than 0.5 grade, and has no central crack, intermediate crack and shrinkage cavity; the purity satisfies the following conditions: non-metallic inclusions: class A coarse series =0 level, class A fine series is less than or equal to 0.5 level; the coarse line and the fine line of the B type and the D type are both less than or equal to 0.5 grade; class C coarse and fine systems both =0 level; ds class is less than or equal to 0.5 grade.
4. The steel for high-strength fasteners according to claim 2, characterized in that: the product after quenching and tempering reaches the performance index, the yield strength is more than or equal to 1100MPa, the tensile strength is more than or equal to 1220MPa, the elongation is more than or equal to 10 percent, the reduction of area is more than or equal to 44 percent, and the Charpy impact energy at minus 40 ℃ is more than or equal to 27J; the hardness of the surface, the core and one half of the radius of the round steel is in the range of 380-429HV10, the hardness difference of each position is less than or equal to 30HV10, and the surface hardness HV0.3 is less than or equal to 435; the tensile property at high temperature of 250 ℃ reaches: the yield strength is more than or equal to 1034MPa, the tensile strength is more than or equal to 1172MPa, the elongation is more than or equal to 8 percent, and the reduction of area is more than or equal to 40 percent.
5. A method of manufacturing the steel for high-strength fasteners according to claim 1, characterized by: smelting molten steel according to element components, casting the molten steel into a continuous casting round billet with the diameter of more than or equal to 600mm, putting the continuous casting billet into a slow cooling pit for slow cooling after continuous casting is finished, wherein the temperature of the put continuous casting billet into the pit is more than or equal to 650 ℃, the heat preservation time of the continuous casting billet is more than or equal to 72 hours, and the continuous casting billet is cooled to be below 180 ℃ and then is taken out of the slow cooling pit; performing shot blasting on the surface of the continuous casting billet after the slow cooling is finished;
heating and preserving heat of the continuously cast round billet subjected to the treatment to fully dissolve alloy elements in the steel, performing high-pressure water descaling treatment after heat preservation, and then performing two-stage rolling: the first stage of rolling is rough rolling, the initial rolling temperature is 1100-1170 ℃, the total reduction rate is more than or equal to 43 percent, the maximum single-pass reduction rate is more than or equal to 19 percent, the second stage of rolling is finish rolling, the initial rolling temperature is 940-980 ℃, the total reduction rate is more than or equal to 22 percent, and the finished product diameter is achieved;
after rolling, the steel bar is sent to an annealing furnace for annealing, the annealing heat preservation temperature is 670 +/-10 ℃, the heat preservation time is more than or equal to 30 hours, the steel bar is annealed below 200 ℃, discharged from the furnace and cooled to room temperature;
and quenching and tempering the annealed steel bar to obtain the quenched and tempered round steel.
6. The method of manufacturing a steel for high-strength fasteners according to claim 5, wherein: the molten steel smelting relates to KR molten iron pretreatment, converter smelting, LF furnace refining and RH furnace refining, and the content of H in the molten steel after vacuum degassing treatment in the RH furnace is less than or equal to 0.0001%.
7. The method of manufacturing a steel for high-strength fasteners according to claim 5, wherein: the continuous casting round billet satisfies the following conditions: center segregation: grade ≦ 0.5, general and central loosening: not more than 0.5 grade, and has no central crack, intermediate crack and shrinkage cavity; non-metallic inclusions: class A coarse series =0 level, class A fine series is less than or equal to 0.5 level; the coarse line and the fine line of the B type and the D type are both less than or equal to 0.5 grade; class C coarse and fine systems both =0 level; ds class is less than or equal to 0.5 grade.
8. The method of manufacturing a steel for high-strength fasteners according to claim 5, wherein: the continuous casting round billet is heated by a continuous heating furnace heated by natural gas in a sectional mode, the temperature of a preheating section is 650-850 ℃, the temperature of a heating section I is 950-1050 ℃, the temperature of a heating section II is 1220 +/-30 ℃, the temperature of a soaking section is 1270 +/-30 ℃, the total heating time of the casting billet is more than 20 hours, and the time of a high-temperature soaking section is more than 8 hours, so that the alloy elements are fully dissolved.
9. The method of manufacturing a steel for high-strength fasteners according to claim 5, wherein: quenching heating temperature: 925-950 ℃, in-furnace time: 2.1-2.5 min/mm multiplied by the diameter mm of the steel bar, and water quenching; water flow is more than or equal to 30m 3 The water pressure of the low-pressure section is more than or equal to 4bar, the water pressure of the high-pressure section is more than or equal to 8bar, and the steel bar is quenched to the surface temperature of less than or equal to 80 ℃ and then cooled to room temperature in an air cooling mode during quenching; tempering and heating temperature: 470-570 ℃, holding time: 3.0-4.0 min/mm multiplied by the diameter mm of the steel bar, and air-cooled to room temperature after being taken out of the furnace.
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