CN115161550B - High-strength fastener steel for large hydraulic impact crusher and manufacturing method thereof - Google Patents
High-strength fastener steel for large hydraulic impact crusher and manufacturing method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/16—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling wire rods, bars, merchant bars, rounds wire or material of like small cross-section
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/46—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling metal immediately subsequent to continuous casting
- B21B1/463—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling metal immediately subsequent to continuous casting in a continuous process, i.e. the cast not being cut before rolling
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
- B21B37/58—Roll-force control; Roll-gap control
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
- B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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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
- C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
- C21D3/02—Extraction of non-metals
- C21D3/06—Extraction of hydrogen
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
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- 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
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- 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
- C21D2211/009—Pearlite
Abstract
The application relates to a high-strength fastener steel for a large hydraulic impact crusher and a manufacturing method thereof, wherein the steel comprises the following element components in percentage by mass: c:0.38 to 0.45 percent, si:0.15 to 0.35 percent, 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 to 1.80 percent, mo:0.40 to 0.60 percent, ni:3.10 to 4.00 percent, O: less than or equal to 0.0010 percent, H: less than or equal to 0.0001 percent, N: less than or equal to 0.0040 percent, and the balance of Fe and unavoidable impurity elements. The metallographic structure is tempered sorbite. The method adopts controlled rolling, annealing and quenching and tempering to manufacture, uses a continuous casting round billet with the diameter of more than 600mm as a blank to produce round steel with the diameter of 45-200mm, greatly improves the compression ratio of steel, ensures that the material core has better compactness and obviously improved mechanical property, and obviously improves the compactness, porosity and segregation tendency of the steel compared with the traditional method adopting small-specification continuous casting square billet rolling.
Description
Technical Field
The application relates to the technical field of alloy steel, in particular to high-strength bolt round steel for processing a large hydraulic impact crusher and a manufacturing method thereof.
Background
The large hydraulic impact breaker provides pressure oil through a pump station of an excavator or a loader, so that the floating stones and soil in rock gaps are effectively cleaned in the operations of mining and the like. When in operation, strong vibration force is generated, and enough breakdown force is needed to effectively crush stone by hammering energy of the piston, so that the working environment is very bad. Important parts such as a through bolt, a guard plate bolt and the like of the upper cylinder body, the middle cylinder body and the lower cylinder body of the large hydraulic impact crusher are fixed, the guard plate bolt and the through bolt are particularly easy to wear in working, the guard plate bolt and the through bolt are loosened, the bolt is broken due to fatigue damage at the thread of the bolt, and in addition, the piston and the cylinder body are not concentric and can be pulled when the through bolt fails. The accumulator bolts and the external reversing valve bolts of the hydraulic impact crusher have the advantages that due to the specificity of the working position, the material has to have higher toughness and proper high temperature resistance. At present, common bolt materials such as 35-42CrMoA, 4140, B7, 32-36CrB4, 40CrNiMo and the like can not meet the high toughness and certain high temperature resistance of the large hydraulic impact breaker through bolts, guard plate bolts, accumulator bolts and external reversing valve bolt materials, and new materials are urgently needed to be developed to meet the high strength, high hardness, impact resistance and proper high temperature performance use requirements under the working state of the large hydraulic impact breaker bolts.
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 high-strength and high-toughness use requirements of important parts of the large hydraulic impact crusher, such as through bolts, guard plate bolts, accumulator bolts and external reversing valve bolt materials. With the increasing of new civil construction projects, the market of the hydraulic impact crusher is more and more focused, and the market application prospect of the high-strength bolt material on the hydraulic impact crusher is wider.
Disclosure of Invention
The application aims to provide a high-strength bolt steel for producing a large hydraulic impact crusher by continuous casting round billets and a manufacturing method thereof, and compared with the 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 which are urgently needed in the market are met; (2) The round steel with the specification phi of 45-200mm is produced by adopting large-specification continuous casting round billet rolling, the compression ratio in the material forming process is obviously increased, and the heat treatment mechanical property, particularly the core property, of the material is obviously improved; (3) Compared with the traditional method for rolling round steel by adopting small-specification continuous casting billets, the method has the advantages that the internal tissue compactness, segregation tendency, porosity and the like of the steel are obviously improved.
The application is suitable for steel for high-strength fasteners of large hydraulic impact crushers, and the elemental components of the steel in percentage by mass are as follows: c:0.38 to 0.45 percent, si:0.15 to 0.35 percent, 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 to 1.80 percent, mo:0.40 to 0.60 percent, ni:3.10 to 4.00 percent, O: less than or equal to 0.0010 percent, H: less than or equal to 0.0001 percent, N: less than or equal to 0.0040 percent, and the balance of Fe and unavoidable impurity elements.
The chemical components of the high-strength bolt material for the large hydraulic impact crusher are determined in the following way:
c: the hardenability of the steel is obviously improved, the strength and the hardness of the steel are improved, but the plasticity and the impact toughness of the steel are obviously reduced along with the improvement of C. In order to ensure the requirements of strength, plasticity, toughness, wear resistance and the like of the high-strength bolt steel, the C content of the design material is 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 Si content is lower than 0.10 percent, increases the brittleness of the steel when the Si content is higher, and reduces the plasticity and toughness of the steel. Considering the high requirement of the 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 steel, and plays a role in solid solution strengthening to compensate the strength loss caused by the reduction of the C content in the steel. The Mn content is too high, which is easy to cause the coarse grain trend of steel, and is unfavorable for the plasticity and toughness of the material, and the Mn content of the designed material is 0.70-0.90%.
Ni: is a non-carbide forming element which exists in the steel in a solid solution form, improves the hardenability of the steel and has good influence on impact toughness and ductile-brittle transition temperature, ni can also improve the hardenability of the steel, reduces the critical point and increases the stability of austenite, and in addition, can remarkably improve the fatigue performance of the steel. Considering the requirement of high toughness of steel under high strength, the Ni content of the design material is 3.10-4.00%.
Cr: cr in the steel is partially substituted by iron to form alloy cementite, so that the stability is improved; part of the ferrite is dissolved into the ferrite to play a solid solution strengthening role, so that the strength and hardness of the ferrite are improved. The heat-treated steel is added with a certain amount of Cr to obviously improve the strength and hardness of the steel after quenching and tempering treatment, a passivation film can be formed on the surface of the steel by higher Cr, the corrosion resistance of the steel is improved, in addition, cr and carbon are combined to form various carbides, the toughness of the material is improved, but the toughness is unfavorable due to the excessively high Cr content, 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 also improves carbide stability, thereby improving strength of steel. Mo can also improve the ductility and wear resistance of steel, has a beneficial effect on improving the corrosion resistance of materials, and can refine grains and improve carbide non-uniformity, thereby improving the strength and toughness of steel. In the design, the Mo content is 0.40-0.60%.
S, P: s mainly exists in the form of MnS and FeS in steel, so that the hot brittleness of the steel can be caused, the mechanical properties of the steel, particularly the yield strength, the plasticity and the wear resistance of the steel are reduced, and the existence of S has adverse effects on the corrosion resistance of the steel; p in steel is easy to cause segregation by grain boundary segregation, increases the tempering brittleness of steel, and obviously reduces the plasticity and toughness of grain boundaries. P, S as the impurity element adversely affects the toughness of the steel material, and the content thereof should be reduced as much as possible. The material P is designed for this purpose: 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, H is dissolved in the steel to cause defects of hydrogen embrittlement, white spots and the like of the steel, so that the plasticity, toughness and fatigue strength of the steel are drastically reduced, and hydrogen induced cracking is caused when serious, and the control is performed: h: less than or equal to 0.00010 percent; o is a harmful element in steel, and is FeO, mnO, siO in steel 2 、Al 2 O 3 The existence of the inclusion forms reduces the strength and plasticity of the steel, has serious influence on the fatigue strength and impact toughness of the steel, and controls the following steps: o: less than or equal to 0.0010 percent; n is an impurity element in steel which is detrimental to toughness, and in order to obtain excellent toughness, N is controlled: 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, porosity, no cracks and shrinkage cavities and high purity.
In particular, the round billet for continuous casting should satisfy: center segregation: grade no more than 0.5, general and central loose: no central crack, middle crack and shrinkage cavity are generated in the level of less than or equal to 0.5; nonmetallic inclusion: class a coarse system=0 level, class a fine system is less than or equal to 0.5 level; class B and class D coarse systems and fine systems are all less than or equal to 0.5 level; class C coarse and fine lines all = level 0; class Ds.ltoreq.0.5). The H content in the molten steel after RH treatment is less than or equal to 0.0001 percent.
After continuous casting is finished, the continuous casting blank is put into a slow cooling pit for slow cooling so as to reduce the H content in the continuous casting blank and avoid hydrogen induced cracking of the casting blank, preferably, the temperature of the continuous casting blank put into the pit is more than or equal to 650 ℃, the heat preservation time of the continuous casting blank put into the pit is more than or equal to 72 hours, and the continuous casting blank is cooled to below 180 ℃ and then is taken out of the slow cooling pit.
After the slow cooling is finished, the surface of the continuous casting billet is subjected to shot blasting to ensure that the surface crack defect of the steel rod in the rolling process is not generated due to the surface quality problem of the continuous casting billet.
The processed continuous casting round billet is heated and kept at the temperature, so that alloy elements in the steel are fully dissolved in solid, and the toughening effect of the alloy elements is exerted, so that the chemical components and the structural uniformity of the final product are ensured. Preferably, the continuous heating furnace heated by natural gas can be adopted for sectional heating, the temperature of the preheating section is 650-850 ℃, the temperature of the heating section I is 950-1050 ℃, the temperature of the heating section II is 1220+/-30 ℃, the temperature of the soaking section is 1270+/-30 ℃, the total heating time of the casting blank is more than 20 hours, and the time of the high-temperature soaking section is more than 8 hours.
After heat preservation is completed, performing high-pressure water descaling treatment on the continuous casting billet to remove a surface oxide layer, and then adopting two-stage rolling: the first stage is rolling to rough rolling, the initial rolling temperature is 1100-1170 ℃, the total compression rate is more than or equal to 43 percent, and the rolling is carried out by adopting a strong rolling process, the maximum single pass rolling rate is more than or equal to 19 percent, so as to ensure that the defects of the core part of the continuous casting billet are fully bridged, and the performances of the large-diameter steel bar at the radius of 1/2 and the core part are ensured. The second stage is finish rolling, the initial rolling temperature is 940-980 ℃, the total compression ratio is more than or equal to 22%, and the finished product diameter is obtained by rolling.
And (3) after rolling, conveying the steel rod into an annealing furnace for annealing, wherein the annealing heat preservation temperature is 670+/-10 ℃, and the heat preservation time is more than or equal to 30 hours, so that the H content in the rolled steel rod is further reduced or removed, the properties of the 1/2 diameter part and the core part of the finished steel rod are further ensured, and the steel rod is annealed below 200 ℃ and discharged from the furnace for 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 is heated using a continuous hearth furnace at a temperature of: 925-950 ℃, atFurnace time: 2.1-2.5 min/mm×steel bar diameter (mm), and water quenching by using a quenching machine; the 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 by water until the surface temperature is less than or equal to 80 ℃ and then cooled to room temperature. The tempering treatment process comprises the following steps: tempering temperature: 470-570 ℃, and the heat preservation time is as follows: 3.0-4.0 min/mm×steel bar diameter (mm), and air cooling to room temperature after tapping.
Compared with the prior art, the application has the advantages that:
the novel material element components are adopted in the design, so that the problems that the existing domestic material cannot meet the requirements of high strength, high toughness and certain high temperature resistance of the bolts for large hydraulic impact crushers are solved.
The continuous casting round billet with the diameter of more than or equal to 600mm, low center segregation, porosity, no cracks and shrinkage holes and ultra purity is adopted, the 45-200mm round steel is produced by continuous rolling, the steel compression ratio is greatly improved, the material core compactness is better, the mechanical property performance is obviously improved, and compared with the traditional rolling of a small-specification continuous casting square billet, the compactness, the porosity and the segregation tendency of the steel are obviously improved.
The high-strength bolt round steel for the large hydraulic impact crusher is manufactured by using the continuous casting round billet as a blank, and compared with the manufacturing by using a die-casting steel ingot as the blank, the method omits the cogging processing process in the rolling process, simplifies the production process, improves the yield of the steel rod, and reduces the production and manufacturing cost of the steel rod; compared with the traditional method, the thickness of the material is less than or equal to 390 multiplied by 510mm 2 Compared with the standard continuous casting square billet continuous rolling production, the compactness, the porosity and the segregation tendency of the steel are obviously improved. Therefore, the method has obvious technical advantages in industrial production.
The round steel product meeting the use requirement of the high-strength fastener is manufactured by adopting controlled rolling, annealing and quenching and tempering, 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 has the characteristics of full-section hardenability, high strength, high hardness, high toughness and certain high temperature resistance. Performance index (tensile and impact samples at one half of the radius of the bar) achieved after the round steel is quenched and tempered: 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%, the area shrinkage is more than or equal to 44%, and the Charpy impact energy at minus 40 ℃ is more than or equal to 27J; after quenching and tempering, ensuring 100% tempered sorbite structure of the whole cross section; the hardness of each position of the surface, the core and 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 high-temperature tensile property at 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%, and the area shrinkage is more than or equal to 40%.
Drawings
FIG. 1 is an in-situ analysis chart of round steel in example 1 of the present application: density 0.9753, fluffiness 0.0182;
FIG. 2 shows the conventional 390X 510mm 2 In-situ analysis chart of round steel with the same specification as in example 1 produced by square billet rolling: density 0.9349, porosity 0.0742;
FIG. 3 shows the microstructure of the round steel of example 1 after annealing and tempering heat treatment according to the present application;
FIG. 4 shows the microstructure of the round steel of example 2 after annealing and tempering heat treatment.
Detailed Description
The application is described in further detail below in connection with the following examples, which are exemplary and intended to illustrate the application, but are not to be construed as limiting the application.
Example 1
The diameter of the high-strength bolt steel for the large hydraulic impact crusher 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 unavoidable impurity elements.
The manufacturing process of the bolt steel comprises the steps of preparing smelting raw materials according to chemical components of a bolt steel finished product, carrying out KR molten iron pretreatment, converter smelting, converter tapping P content of 0.006%, carrying out LF refining on molten steel, fine adjusting alloy content, adding deoxidizer for deoxidization, carrying out vacuum degassing treatment on the molten steel to an RH station, carrying out high vacuum time for 20 minutes, soft argon blowing time for 25 minutes, and RH tapping oxygen content of 0.0007%, and carrying out continuous casting to obtain a continuous casting round billet with phi 700mm, wherein the continuous casting round billet meets chemical components, low-power tissues (center segregation: 0.5 grade, general porosity and center porosity: 0.5 grade, no center crack, middle crack and shrinkage cavity) and ultra-purity (nonmetallic inclusion: class A coarse system=0 grade, class A fine system=0.5 grade, class B coarse system=0.5 grade, class D coarse system=0 grade, class B and class D fine system=0.5 grade, class C coarse system and fine system=0 grade, class=0.00007% of H content in the molten steel after RH treatment. And (3) introducing the casting blank into a slow cooling pit at a high temperature, wherein the temperature of the casting blank is 680 ℃, the slow cooling time is 76 hours, and the temperature of the casting blank is 170 ℃.
Cold charging a phi 700mm continuous casting round billet 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 a casting blank is 22.5 hours, and the casting blank is discharged from the heating furnace after the time of a high-temperature soaking section is 10 hours; the first stage rolling is rough rolling, the initial rolling temperature is 1120-1170 ℃, the total compression rate is more than or equal to 43%, the rolling is carried out by adopting a strong pressing process, 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%. And (3) after rolling to the diameter of a finished product, carrying out red conveying annealing on the bar, wherein the annealing heat preservation temperature is 670+/-10 ℃, the heat preservation time is 37 hours, and taking the steel bar out of the annealing furnace and cooling to room temperature.
Quenching and tempering the annealed steel rod, wherein the quenching and tempering heat treatment uses a continuous roller hearth furnace, and the quenching and heating temperature is as follows: 935±10 ℃, at furnace time: 481min, using a quenching machine for water quenching; the 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 air-cooled to room temperature during quenching; tempering treatment temperature: 530 ℃ +/-8 ℃ and heat preservation time: 645min, and air cooling to room temperature after discharging.
The mechanical properties of the round bolt steel prepared by the manufacturing process are shown in tables 1-1 and 1-2.
Table 1-1 example 1 round steel normal temperature mechanical properties
TABLE 1-2 high temperature Properties of round steel example 1
The tensile and impact properties of the steel are measured by sampling the 1/4 diameter part of the cross section of the round steel, and the Vickers hardness is respectively tested on the surface of the cross section, the core part and the 1/4 diameter part.
The porosity, density and segregation tendency of each main element of the round steel prepared by the process are equal to those of the round steel prepared by the traditional 390 multiplied by 510mm 2 Square billet rolling the same specification round steel pair is shown in table 2.
TABLE 2 example 1 round steel porosity, segregation degree and main element segregation vs. conventional Process
Example 2
The diameter of the high-strength bolt steel for the large hydraulic impact crusher 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 unavoidable impurity elements.
The manufacturing process of the bolt steel comprises the steps of preparing smelting raw materials according to chemical components of a bolt steel finished product, carrying out KR molten iron pretreatment, converter smelting, converter tapping P content of 0.007%, carrying out LF refining on molten steel, finely adjusting alloy content, adding deoxidizer for deoxidization, carrying out vacuum degassing treatment on the molten steel to an RH station, carrying out high vacuum time for 20 minutes, soft argon blowing time for 25 minutes, carrying out RH tapping oxygen content of 0.0005%, and carrying out continuous casting to obtain a continuous casting round billet with the specification of phi 600mm meeting the chemical components, low-power structure (center segregation: 0.5 grade, general and center porosity: 0.5 grade, no center crack, middle crack and shrinkage cavity) and ultra-purity (nonmetallic inclusion: A coarse system=0 grade, A fine system=0.5 grade, B coarse system and D coarse system=0 grade, B fine system and D fine system=0.5 grade, C coarse system and fine system=0 grade, and Ds=0.5 grade), and carrying out RH vacuum treatment to obtain the continuous casting round billet with H content=0.00006 percent in the molten steel. And (3) introducing the casting blank into a slow cooling pit at a high temperature, wherein the temperature of the casting blank 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 time of a high-temperature soaking section is 8.7 hours for discharging; the steel bar is subjected to two-stage rolling after descaling by high-pressure water, the first stage rolling is rough rolling, the initial rolling temperature is 1120-1160 ℃, the total compression ratio is more than or equal to 41%, the rolling is carried out by adopting a strong pressing process, the maximum single-pass secondary rolling reduction ratio is 20%, the second stage rolling is finish rolling, the initial rolling temperature is 960-980 ℃, the total compression ratio is 23%, the bar is subjected to red feeding annealing after being rolled to the diameter of a finished product, the annealing heat preservation temperature is 670+/-10 ℃, the heat preservation time is 31 hours, and the steel bar is annealed at 170 ℃ and is discharged from a furnace for air cooling to room temperature.
Quenching and tempering the annealed steel bar, wherein a continuous roller hearth furnace is used for heat treatment, and the quenching and heating temperature is as follows: 935±10 ℃, at furnace time: 265min, using a quenching machine for water quenching; the 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 air-cooled to room temperature during quenching; tempering treatment temperature: 530 ℃ +/-8 ℃ and heat preservation time: 370min, and air cooling to room temperature after discharging.
The mechanical properties of the round bolt steel prepared by the manufacturing process are shown in tables 3-1 and 3-2.
Table 3-1 example 2 round steel normal temperature mechanical properties
TABLE 3-2 high temperature mechanical Properties of round Steel example 2
The tensile and impact properties of the steel are measured by sampling the 1/4 diameter part of the cross section of the round steel, and the Vickers hardness is respectively tested on the surface of the cross section, the core part and the 1/4 diameter part.
Claims (7)
1. A high strength fastener steel, characterized by: the steel comprises the following element components in percentage by mass: c:0.38 to 0.45 percent, si:0.15 to 0.35 percent, 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 to 1.80 percent, mo:0.40 to 0.60 percent, ni:3.10 to 4.00 percent, O: less than or equal to 0.0010 percent, H: less than or equal to 0.0001 percent, N: less than or equal to 0.0040 percent, and the balance being Fe and unavoidable impurity elements;
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, after continuous casting, slowly cooling the continuous casting billet in a slow cooling pit, wherein the pit temperature is more than or equal to 650 ℃, preserving heat of the continuous casting billet for more than or equal to 72 hours, cooling to below 180 ℃, and discharging the continuous casting billet from the slow cooling pit; after the slow cooling is finished, performing shot blasting cleaning on the surface of the continuous casting billet;
heating and preserving heat of the continuous casting round billet treated by the method to enable alloy elements in steel to be fully dissolved in solid, after preserving heat, carrying out high-pressure water descaling treatment, and then carrying out two-stage rolling: the first stage rolling is rough rolling, the initial rolling temperature is 1100-1170 ℃, the total compression rate is more than or equal to 43%, the maximum single pass rolling reduction is more than or equal to 19%, the second stage rolling is finish rolling, the initial rolling temperature is 940-980 ℃, the total compression rate is more than or equal to 22%, and the rolling is carried out until the diameter of a finished product is reached;
after rolling, the steel bar is sent into 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, and the steel bar is discharged from the annealing furnace for air cooling to room temperature under 200 ℃;
quenching and tempering the annealed steel rod to obtain quenched and tempered round steel;
the product is round steel with the diameter of 45-200mm, and the final metallographic structure is a tempered sorbite structure; the product after the quenching and tempering treatment achieves 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%, the area shrinkage is more than or equal to 44%, and the Charpy impact energy at minus 40 ℃ is more than or equal to 27J; the hardness of each part of the surface, the core and the radius of the round steel is in the range of 380-429HV10, the hardness difference of each part is less than or equal to 30HV10, and the surface hardness HV0.3 is less than or equal to 435; the high-temperature tensile property at 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%, and the area shrinkage is more than or equal to 40%.
2. The high strength fastener steel according to claim 1, wherein: the compactness and segregation of the product are as follows: center segregation: grade no more than 0.5, general and central loose: no central crack, middle crack and shrinkage cavity are generated in the level of less than or equal to 0.5; the purity is as follows: nonmetallic inclusion: class a coarse system=0 level, class a fine system is less than or equal to 0.5 level; class B and class D coarse systems and fine systems are all less than or equal to 0.5 level; class C coarse and fine lines all = level 0; ds class is less than or equal to 0.5 level.
3. A method of manufacturing the high strength fastener stock steel of 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, after continuous casting, slowly cooling the continuous casting billet in a slow cooling pit, wherein the pit temperature is more than or equal to 650 ℃, preserving heat of the continuous casting billet for more than or equal to 72 hours, cooling to below 180 ℃, and discharging the continuous casting billet from the slow cooling pit; after the slow cooling is finished, performing shot blasting cleaning on the surface of the continuous casting billet;
heating and preserving heat of the continuous casting round billet treated by the method to enable alloy elements in steel to be fully dissolved in solid, after preserving heat, carrying out high-pressure water descaling treatment, and then carrying out two-stage rolling: the first stage rolling is rough rolling, the initial rolling temperature is 1100-1170 ℃, the total compression rate is more than or equal to 43%, the maximum single pass rolling reduction is more than or equal to 19%, the second stage rolling is finish rolling, the initial rolling temperature is 940-980 ℃, the total compression rate is more than or equal to 22%, and the rolling is carried out until the diameter of a finished product is reached;
after rolling, the steel bar is sent into 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, and the steel bar is discharged from the annealing furnace for air cooling to room temperature under 200 ℃;
and quenching and tempering the annealed steel rod to obtain the quenched and tempered round steel.
4. A method of manufacturing a high strength fastener steel according to claim 3, wherein: the molten steel smelting comprises KR molten iron pretreatment, converter smelting, LF furnace refining and RH furnace refining, wherein the H content in the molten steel after the RH furnace vacuum degassing treatment is less than or equal to 0.0001 percent.
5. A method of manufacturing a high strength fastener steel according to claim 3, wherein: the continuous casting round billet meets the following conditions: center segregation: grade no more than 0.5, general and central loose: no central crack, middle crack and shrinkage cavity are generated in the level of less than or equal to 0.5; nonmetallic inclusion: class a coarse system=0 level, class a fine system is less than or equal to 0.5 level; class B and class D coarse systems and fine systems are all less than or equal to 0.5 level; class C coarse and fine lines all = level 0; ds class is less than or equal to 0.5 level.
6. A method of manufacturing a high strength fastener steel according to claim 3, 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 a casting blank 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 in a solid state.
7. A method of manufacturing a high strength fastener steel according to claim 3, wherein: quenching heating temperature: 925-950 ℃, and the furnace time is as follows: 2.1-2.5 min/mm×steel bar diameter mm, water quenching; the 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 by water until the surface temperature is less than or equal to 80 ℃ and then cooled to room temperature; tempering heating temperature: 470-570 ℃, and the heat preservation time is as follows: 3.0-4.0 min/mm×steel bar diameter mm, and air cooling to room temperature after tapping.
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