CN114231840A - Wire rod for high-hardenability medium-carbon cold heading steel and production process thereof - Google Patents

Wire rod for high-hardenability medium-carbon cold heading steel and production process thereof Download PDF

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Publication number
CN114231840A
CN114231840A CN202111404325.2A CN202111404325A CN114231840A CN 114231840 A CN114231840 A CN 114231840A CN 202111404325 A CN202111404325 A CN 202111404325A CN 114231840 A CN114231840 A CN 114231840A
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wire rod
steel
rolling
medium
hardenability
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李金波
翟晓毅
韩广杰
孙彩凤
肖国华
高建
徐学良
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Handan Iron and Steel Group Co Ltd
HBIS Co Ltd Handan Branch
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Handan Iron and Steel Group Co Ltd
HBIS Co Ltd Handan Branch
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Priority to CN202111404325.2A priority Critical patent/CN114231840A/en
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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
    • 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
    • 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
    • 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
    • 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
    • B21B37/76—Cooling control on the run-out table
    • 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
    • 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
    • B22D11/10—Supplying or treating molten metal
    • B22D11/11—Treating the molten metal
    • B22D11/111—Treating the molten metal by using protecting powders
    • 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
    • B22D11/16—Controlling or regulating processes or operations
    • B22D11/18—Controlling or regulating processes or operations for pouring
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/28—Manufacture of steel in the converter
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/06—Deoxidising, e.g. killing
    • 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
    • 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
    • C21D11/00—Process control or regulation for heat treatments
    • C21D11/005—Process control or regulation for heat treatments for cooling
    • 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
    • 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
    • C22C33/06—Making ferrous alloys by melting using master alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • 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
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • 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 invention discloses a wire rod for high-hardenability medium carbon cold heading steel and a production process thereof, belonging to the field of ferrous metallurgy and rolling. The wire rod comprises the following chemical components in percentage by mass: c: 0.37% -0.40%, Si: 0.15-0.30%, Mn: 0.70 to 0.90 percent of Cr, 0.10 to 0.20 percent of Cr, less than or equal to 0.020 percent of P, less than or equal to 0.020 percent of S, 0.010 to 0.030 percent of Als, and the balance of iron and inevitable impurity elements. The production process of the wire rod comprises the working procedures of converter smelting, LF refining, continuous casting, heating, rolling and controlled cooling. The invention avoids quenching cracks of the water quenching process and quality risks of quenching imperviousness of the oil quenching process, obviously improves the stability and reliability of the product quality under the condition of not greatly increasing the cost, and reduces the quality risks and quality loss.

Description

Wire rod for high-hardenability medium-carbon cold heading steel and production process thereof
Technical Field
The invention belongs to the technical field of ferrous metallurgy and rolling, and particularly relates to a wire rod for high-hardenability medium-carbon cold heading steel and a production process thereof.
Background
The quenched and tempered steel is medium carbon steel or steel which is obtained by adding alloy elements such as Cr, Ti, Mo and the like into the medium carbon steel to improve the hardenability of the medium carbon steel and then achieving a certain strong plasticity index through a user quenching and tempering process. When the oil quenching process is adopted, oil belongs to a medium with weaker cooling capacity, the problem of quenching cracking can be avoided by using oil quenching, but the oil quenching also causes poor quenching performance, the hardness index does not reach the standard, the phenomenon of quenching impermeability of parts with critical specification (phi 12mm) exists, the performance of the bolt is unqualified, and the quality risk exists.
The hardenability of the steel mainly depends on the critical cooling speed, the critical cooling speed mainly depends on the stability of the undercooled austenite, and factors influencing the stability of the austenite comprise chemical composition, austenite grain size, austenite uniformity, original structure state and the like.
The influence of chemical components on the hardenability of the steel is mainly the influence of carbon element, when the C% is less than 0.77%, the critical cooling speed is obviously reduced along with the increase of the carbon concentration in austenite, the C curve is shifted to the right, and the hardenability of the steel is increased. The actual grain size of austenite has a large influence on the hardenability of steel, and the coarse austenite grains can shift the C curve to the right, so that the critical cooling speed of the steel is reduced. Under the same cold condition, the more uniform the austenite component, the lower the nucleation rate of pearlite, the longer the inoculation period of transformation, the right shift of the C curve, the slower the critical cooling speed and the higher the hardenability of steel.
The prior medium carbon steel has the problems of low carbon content, coarse austenite grains, uneven components, coarse hot rolling structure and the like, so that the hardenability of the medium carbon steel is poor. Therefore, the development of the medium carbon steel with high hardenability has wide application prospect.
Disclosure of Invention
The invention aims to solve the technical problem of providing a wire rod for medium carbon cold forging steel with high hardenability, and solving the problem of poor hardenability of medium carbon steel. The invention produces the material with higher quenching stability by controlling the content of proper C, Si, Mn, Cr, Als, P, S and other alloy elements and combining the optimization of steel making, LF refining, continuous casting and rolling processes, the hardenability of the oil quenching process is stable, the occurrence of quenching cracks is avoided, meanwhile, the performance requirement of 8.8-grade bolts of wires with critical specification (phi 12mm) and below can be ensured by the oil quenching process, and the quality risk and loss are obviously reduced.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a wire rod for high-hardenability medium carbon cold heading steel comprises the following chemical components in percentage by mass: c: 0.37% -0.40%, Si: 0.15-0.30%, Mn: 0.70 to 0.90 percent of Cr, 0.10 to 0.20 percent of Cr, less than or equal to 0.020 percent of P, less than or equal to 0.020 percent of S, 0.010 to 0.030 percent of Als, and the balance of iron and inevitable impurity elements; the Jominy test result of the medium carbon cold heading steel with high hardenability is as follows: j51/56-1.5, J45/52-3, J30/37-5, J26/33-7, J25/27-9, J23/25-11, J22/24-13, J21/23-15, J20/22-20 and J18/20-25.
Further, the austenite grain size of the wire rod is more than or equal to 9 grades, the critical quenching specification of the oil quenching process of the wire rod is phi 12mm, the core hardness of the wire rod after oil quenching is more than or equal to 45HRC, and the core hardness of the wire rod after tempering is 28-30 HRC.
The invention also provides a production process of the wire rod for the high-hardenability medium-carbon cold heading steel, wherein the production process of the wire rod comprises the working procedures of converter smelting, LF refining, continuous casting, heating, rolling and controlled cooling; in the converter smelting process, the end point C is controlled to be 0.10-0.20%, the end point O is controlled to be 200-600ppm, the alloying deoxidation is carried out after the carbon powder is adopted for pre-deoxidation during the deoxidation, and the alloying addition sequence is aluminum deoxidizer-ferrosilicon-ferromanganese-ferrochrome.
Furthermore, in the LF refining process, the alkalinity of the refining slag is 4.0-5.0, the content of total ferrous oxide is less than or equal to 1.0%, and the nitrogen content of the outbound molten steel is less than or equal to 50 ppm.
Further, in the continuous casting process, the superheat degree of the molten steel is 20-50 ℃, the medium drawing speed is controlled to be 2.0-2.5m/min, the secondary cooling adopts the medium cooling strength, the specific water amount is controlled to be 0.7-0.9L/kg.min, the secondary cooling 1 area is water cooling, and the secondary cooling 2-4 area is gas spray cooling.
Further, in the heating procedure, the continuous casting blank is heated to 1050-1150 ℃ before rolling, and the temperature is kept for 90-120 min; the rolling procedure is high-speed wire rod rolling; descaling a square billet by using high-pressure water, and then sequentially carrying out rough rolling, medium rolling, finish rolling and sizing reduction, wherein the inlet temperature of the sizing reduction is 850-890 ℃, and the spinning temperature is 880-910 ℃.
Further, in the cold control procedure, after rolling, the steel wire enters a stelmor cooling line, the heat-insulating cover is fully closed, the fan is fully closed, the temperature of the steel wire rod entering the heat-insulating cover is 820-.
Further, in the converter smelting process, the molten iron ratio is 850-1000 kg/ton steel, the lime consumption is 20-30 kg/ton steel, the light-burned dolomite is 15-25 kg/ton steel, and the sintered return ores are 15-25 kg/ton steel; the blowing adopts a low-high-low lance position, the working oxygen pressure is 0.6-0.8MPa, and 500-800kg of premelted slag is added for premelting when 3/4 steel is tapped.
In the LF refining process, the adding amount of slag materials is 5.7-10.7kg of lime per ton of steel and 0.6kg of fluorite per ton of steel, ferrosilicon powder is adopted for slag surface deoxidation in the slagging process, the adding amount of an aluminum wire is calculated according to the aluminum content of steel types and a calculation model and is fed in the initial stage of refining, and the aluminum wire is not fed in the later stage.
Further, in the continuous casting process, the steel ladle adopts a whole-process capping process, the molten steel in the tundish is covered by double-layer slag, argon is blown into the tundish for 2-5 minutes before casting for replacing air in the tundish, the continuous casting tundish adopts an integral submerged nozzle for casting, the insertion depth of the nozzle is automatically adjusted within the range of 70-150mm according to the set parameters of a model, and the crystallizer adopts non-sinusoidal vibration; the continuous casting adopts square billet continuous casting. The continuous billet casting section specification is preferably any one of 150mm × 150mm, 160mm × 160mm, and 280mm × 320 mm.
The theoretical analysis of the component proportion and the process adjustment is as follows:
1. according to the invention, the content of C, Si and Mn in the medium carbon manganese steel is controlled to be at the upper limit of the standard component, so that the quenching permeability of the hot rolled wire rod can be effectively improved, a small amount of Cr element is added, the hardenability of the material can be effectively improved, the oil quenching process of a user is met, the production cost is greatly reduced, and the quality assurance level of the user is improved;
2. in the converter steelmaking process, the terminal point [ O ] of the converter is controlled to be 200-600ppm, so that the oxidability of the molten steel at the terminal point can be effectively reduced; the total oxygen content of the steel is less than or equal to 20ppm, and the purity of the molten steel is improved; the nitrogen content of the steel is less than or equal to 50ppm, the content of harmful gas is reduced, the risk of quenching cracking is reduced, the yield of alloy elements can be improved, the yield of Mn elements is more than or equal to 95%, the yield of Si elements is more than or equal to 93%, and the production cost is reduced.
3. The content of S and O, N in the molten steel is reduced to the maximum extent in the LF refining process, the purity of the material is effectively improved, and the quenching cracking risk is reduced.
4. The internal quality of the casting blank is effectively controlled in the continuous casting process, the secondary oxidation of molten steel is reduced, and the defects of slag entrapment and casting blank structure are prevented, so that the subsequent process treatment is difficult.
5. And the optimal rolling process control parameters are adopted, multiple recovery recrystallization processes are completed in the rolling process, the structure grains are refined, and the cooling speed condition required by subsequent control cooling is met.
6. The best cooling speed is obtained by adopting the controlled cooling of a stelmor cooling line, which is beneficial to obtaining the moderate austenite grain size, improving the hardenability of the material and meeting the requirements of the oil quenching process.
Adopt the produced beneficial effect of above-mentioned technical scheme to lie in:
1. the chemical composition design of the hot-rolled wire rod produced by the method controls C, Si, Mn and Cr elements according to the upper limit of the standard so as to improve the hardenability of the material, avoids adding expensive alloy elements such as Mo, V, Ti, Nb and the like, reduces the production cost 2 of a steel mill, effectively controls the contents of impurities and harmful gases in steel through reasonable steelmaking, refining and continuous casting processes, improves the purity of molten steel, controls the internal structure of proper steel billets, and provides guarantee for improving the quenching performance of the material and reducing quenching cracks; 3. reasonable heating, rolling and controlled cooling of a stelmor cooling line are adopted, so that ferrite and pearlite structures with proper austenite grain sizes can be obtained, and the hardenability of the material is improved. 5. By drawing and cold heading forming the hot-rolled wire rod produced by the invention, the cold deformation is gradually accumulated, the strength is gradually improved, and finally the strength requirement of the 8.8-grade power bolt can be met.
Drawings
FIG. 1 is a hot rolled metallographic structure of a wire rod of diameter 12mm according to example 1;
FIG. 2 is a graph of austenite grains for the wire rod of example 1. phi.12 mm;
FIG. 3 is a metallographic structure diagram of a core portion of an oil-quenched wire rod of example 1. phi.12 mm.
Detailed Description
The present invention will be described in further detail with reference to specific examples.
A wire rod for high-hardenability medium carbon cold heading steel comprises the following chemical components in percentage by mass: c: 0.37% -0.40%, Si: 0.15-0.30%, Mn: 0.70 to 0.90 percent of Cr, 0.10 to 0.20 percent of Cr, less than or equal to 0.020 percent of P, less than or equal to 0.020 percent of S, 0.010 to 0.030 percent of Als, and the balance of iron and inevitable impurity elements.
The austenite grain size of the wire rod is more than or equal to grade 9, the critical through quenching specification of the oil quenching process is phi 12mm, the core hardness of the wire rod after oil quenching is more than or equal to 45HRC, and the tempering hardness is 28-30 HRC.
A production process of a wire rod for high-hardenability medium carbon cold heading steel comprises the working procedures of converter smelting, LF refining, continuous casting, heating, rolling and controlled cooling;
(1) a converter smelting process, wherein the molten iron ratio is 850-; the blowing adopts low-high-low lance position, the working oxygen pressure is 0.6-0.8MPa, the end point C is controlled at 0.10-0.20%, the end point O is controlled at 600ppm, the alloying deoxidation is carried out after the carbon powder is used for pre-deoxidation during the deoxidation, the alloy addition sequence is aluminum deoxidizer-ferrosilicon-ferromanganese-ferrochrome, and 500kg of pre-melted slag charge is added for pre-slagging during the steel tapping of 3/4.
(2) And in the LF refining process, the adding amount of slag is 5.7-10.7kg of lime per ton of steel and 0.6kg of fluorite per ton of steel, ferrosilicon powder is adopted for slag surface deoxidation in the slagging process, the adding amount of an aluminum wire is calculated according to the aluminum content of steel types and is fed in the initial stage of refining, the aluminum wire is not fed in the later stage, the alkalinity of refining slag is 4.0-5.0, the content of total ferrous oxide is less than or equal to 1.0%, and the nitrogen content of the discharged molten steel is less than or equal to 50 ppm.
(3) The continuous casting process is carried out by covering the steel ladle in the whole process, wherein the superheat degree of the molten steel is 20-50 ℃, the molten steel in the tundish is covered by double-layer slag, argon is blown into the tundish for 2-5 minutes before casting for replacing air in the tundish, the continuous casting tundish is cast by an integral submerged nozzle, the insertion depth of the nozzle is automatically adjusted within the range of 70-150mm according to the set parameters of a model, the casting speed is controlled at 2.0-2.5m/min, the secondary cooling adopts intercooling strength, the specific water amount is controlled at 0.7-0.9L/kg.min, the secondary cooling 1 area is water cooling, the 2-4 area is gas spray cooling, the crystallizer adopts non-sinusoidal vibration, and the continuous casting adopts square billet continuous casting.
(4) A heating procedure, namely heating the continuous casting blank to 1050-1150 ℃ before rolling, and keeping the temperature for 90-120 min;
(5) a rolling step of high-speed wire rod rolling; descaling a square billet by using high-pressure water, and then sequentially carrying out rough rolling, medium rolling, finish rolling and sizing reduction, wherein the inlet temperature of the sizing reduction is 850-890 ℃, and the spinning temperature is 880-910 ℃.
(6) And (5) a cooling control procedure, namely, after rolling is finished, entering a stelmor cooling line, fully closing the heat-insulating cover and fully closing the fan.
Example 1
A wire rod for high-hardenability medium-carbon cold forging steel comprises the chemical components and the mass percentage content shown in table 1, and the specification is a hot-rolled wire rod with the diameter of 12 mm.
A production process of a wire rod for high-hardenability medium carbon cold heading steel comprises the working procedures of converter smelting, LF refining, continuous casting, heating, rolling and controlled cooling;
(1) a converter smelting process, wherein the molten iron ratio is 850kg/t steel, the lime consumption is 20 kg/t steel, the light-burned dolomite is 15 kg/t steel, and the sintered return mine is 15 kg/t steel; the blowing adopts low-high-low gun position, the working oxygen pressure is 0.7MPa, the end point C is controlled at 0.20 percent, the end point O is controlled at 560ppm, carbon powder is adopted for pre-deoxidation during deoxidation, alloying deoxidation is carried out, the alloy addition sequence is aluminum deoxidizer-ferrosilicon-ferromanganese-ferrochrome, 800kg of pre-melted slag charge is added for pre-slagging during the tapping of 3/4.
(2) And in the LF refining process, the adding amount of slag is 5.7kg of lime per ton of steel and 0.6kg of fluorite per ton of steel, ferrosilicon powder is adopted for slag surface deoxidation in the slagging process, the adding amount of an aluminum wire is calculated according to the aluminum content of steel types and a calculation model and is fed in the initial stage of refining, the aluminum wire is not fed in the later stage, the alkalinity of refining slag is 4.0-5.0, the content of total ferrous oxide is 1.0%, and the nitrogen content of the discharged molten steel is 50 ppm.
(3) The continuous casting process comprises the steps that a steel ladle adopts a whole-process covering process, the superheat degree of molten steel is 35 ℃, molten steel of a tundish is covered by double-layer slag, argon is blown into the tundish for 2-5 minutes before casting for replacing air in the tundish, the continuous casting tundish adopts an integral submerged nozzle for casting, the insertion depth of the nozzle is automatically adjusted within the range of 70-150mm according to set parameters of a model, the casting speed is controlled to be 2.4m/min, the secondary cooling adopts intercooling strength, the specific water amount is controlled to be 0.8L/kg.min, a secondary cooling 1 area is water-cooled, a 2-4 area is gas mist cooling, and a crystallizer adopts non-sinusoidal vibration. Continuously casting into square billet with the size of 150mm by 150 mm.
(4) A heating procedure, namely heating the continuous casting slab to 1150 ℃ before rolling, and keeping the temperature for 100 min;
(5) and a rolling step of high-speed wire rod rolling. Descaling a square billet by using high-pressure water, wherein the descaling high-pressure water pressure is not lower than 15MPa, and after surface descaling, carrying out rough rolling, medium rolling, finish rolling and reducing sizing in sequence, wherein the reducing sizing inlet temperature is 890 ℃, and the spinning temperature is 910 ℃.
(6) A cooling control procedure, namely, entering a stelmor cooling line after rolling, fully closing the heat-insulating cover and fully closing the fan; the temperature of the wire rod entering the heat preservation cover is 860 ℃, the temperature of the wire rod exiting the heat preservation cover is 600 ℃, and the cooling speed is 0.7 ℃/s.
The hot rolled wire rod with the diameter of 12mm is basically detected to be ferrite and pearlite, the austenite grain size is 9 grades, the core hardness of the wire rod after oil quenching is 48HRC, and the tempering hardness is 30 HRC. A middle rolling process sample is taken for Jominy test, and the result is as follows: j55-1.5, J49-3, J30/37-5, J33-7, J27-9, J25-11, J22-13, J21-15, J20-20 and J19-25.
FIG. 1 is a hot-rolled metallographic structure diagram of a wire rod with a diameter of 12 mm; FIG. 2 is a diagram of austenite grains of a wire rod with a diameter of 12 mm; FIG. 3 is a metallographic structure of an oil-quenched core of a wire rod having a diameter of 12mm (the same as that of the other embodiments, and therefore, omitted). Through the attached drawings 1-3, the hot-rolled structure of the phi 12mm wire rod is uniform and fine and is in an equiaxial crystal shape, the austenite grain size of the wire rod is more than or equal to 9 grade, the center of the wire rod after oil quenching is completely quenched, the structure is all lath martensite, no retained austenite exists, and the hardenability is excellent.
Example 2
A wire rod for high-hardenability medium-carbon cold forging steel comprises the chemical components and the mass percentage content shown in table 1, and the specification is a hot-rolled wire rod with the diameter of 10 mm.
A production process of a wire rod for high-hardenability medium carbon cold heading steel comprises the working procedures of converter smelting, LF refining, continuous casting, heating, rolling and controlled cooling;
(1) a converter smelting process, wherein the molten iron ratio is 1000kg/t steel, the lime consumption is 30 kg/ton steel, the light-burned dolomite is 25 kg/ton steel, and the sintered return mine is 25 kg/ton steel; the blowing adopts low-high-low gun position, the working oxygen pressure is 0.6MPa, the end point C is controlled at 0.10 percent, the end point O is controlled at 390ppm, the alloying deoxidation is carried out after carbon powder is adopted for pre-deoxidation during the deoxidation, the alloy addition sequence is aluminium deoxidizer-ferrosilicon-ferromanganese-ferrochrome, 500kg pre-melted slag charge is added for pre-slagging during the tapping of 3/4.
(2) And in the LF refining process, the addition of slag materials is 10.7kg of lime per ton of steel and 0.6kg of fluorite per ton of steel, ferrosilicon powder is adopted for slag surface deoxidation in the slagging process, the addition of an aluminum wire is calculated according to the aluminum content of steel types and a calculation model and is fed in the initial stage of refining, the aluminum wire is not fed in the later stage, the alkalinity of refining slag is 4.0-5.0, the content of total ferrous oxide is 0.9%, and the nitrogen content of the discharged molten steel is 48 ppm.
(3) The continuous casting process comprises the steps that a steel ladle adopts a whole-process covering process, the superheat degree of molten steel is 30 ℃, the molten steel of a tundish is covered by double-layer slag, argon is blown into the tundish for 2-5 minutes before casting for replacing air in the tundish, the continuous casting tundish adopts an integral submerged nozzle for casting, the insertion depth of the nozzle is automatically adjusted within the range of 70-150mm according to set parameters of a model, the casting speed is controlled at 2.0m/min, the secondary cooling adopts intercooling strength, the specific water amount is controlled at 0.7L/kg.min, a secondary cooling 1 area is water-cooled, a 2-4 area is gas fog cooled, and a crystallizer adopts non-sinusoidal vibration. Continuously casting into square billet with the size of 160mm by 160 mm.
(4) Heating, namely heating the continuous casting slab to 1100 ℃ before rolling, and keeping the temperature for 90 min;
(5) and a rolling step of high-speed wire rod rolling. Descaling a square billet by using high-pressure water, wherein the descaling high-pressure water pressure is not lower than 15MPa, and after surface descaling, carrying out rough rolling, medium rolling, finish rolling and reducing sizing in sequence, wherein the inlet temperature of the reducing sizing is 880 ℃, and the spinning temperature is 900 ℃.
(6) A cooling control procedure, namely, entering a stelmor cooling line after rolling, fully closing the heat-insulating cover and fully closing the fan; the temperature of the wire rod entering the heat preservation cover is 850 ℃, the temperature of the wire rod exiting the heat preservation cover is 580 ℃, and the cooling speed is 0.6 ℃/s.
The hot rolled wire rod with the diameter of 10mm is basically tested to be ferrite and pearlite, the austenite grain size is 9.5 grade, the center hardness of the wire rod after oil quenching is 47HRC, and the tempering hardness is 28 HRC. A middle rolling process sample is taken for Jominy test, and the result is as follows: j56-1.5, J52-3, J35-5, J31-7, J27-9, J25-11, J23-13, J21-15, J20-20 and J18-25.
Example 3
A wire rod for high-hardenability medium-carbon cold forging steel comprises the chemical components and the mass percentage shown in table 1, and the specification is a hot-rolled wire rod with the diameter of 8 mm.
A production process of a wire rod for high-hardenability medium carbon cold heading steel comprises the working procedures of converter smelting, LF refining, continuous casting, heating, rolling and controlled cooling;
(1) converter smelting, wherein the molten iron ratio is 900kg/t steel, the lime consumption is 24 kg/t steel, the light-burned dolomite is 20 kg/t steel, and the sintered return mine is 18 kg/t steel; the blowing adopts low-high-low gun position, the working oxygen pressure is 0.8MPa, the end point C is controlled at 0.17 percent, the end point O is controlled at 280ppm, the alloying deoxidation is carried out after carbon powder is adopted for pre-deoxidation during the deoxidation, the alloy addition sequence is aluminum deoxidizer-ferrosilicon-ferromanganese-ferrochrome, and 600kg pre-melted slag charge is added for pre-slagging during the tapping of 3/4.
(2) And in the LF refining process, the addition of slag materials is 6.9kg of lime per ton of steel and 0.6kg of fluorite per ton of steel, ferrosilicon powder is adopted for slag surface deoxidation in the slagging process, the addition of an aluminum wire is calculated according to the aluminum content of steel types and a calculation model and is fed in the initial stage of refining, the aluminum wire is not fed in the later stage, the alkalinity of refining slag is 4.0-5.0, the content of total ferrous oxide is 0.8%, and the nitrogen content of the discharged molten steel is 45 ppm.
(3) The continuous casting process comprises the steps that a steel ladle adopts a whole-process covering process, the superheat degree of molten steel is 20 ℃, the molten steel of a tundish is covered by double-layer slag, argon is blown into the tundish for 2-5 minutes before casting for replacing air in the tundish, the continuous casting tundish adopts an integral submerged nozzle for casting, the insertion depth of the nozzle is automatically adjusted within the range of 70-150mm according to set parameters of a model, the casting speed is controlled at 2.5m/min, the secondary cooling adopts intercooling strength, the specific water amount is controlled at 0.9L/kg.min, a secondary cooling 1 area is water-cooled, a 2-4 area is gas fog cooled, and a crystallizer adopts non-sinusoidal vibration. Continuously casting into square billet with the size of 280mm x 320 mm.
(4) A heating procedure, wherein the continuous casting blank is heated to 1120 ℃ before rolling, and the temperature is kept for 105 min;
(5) and a rolling step of high-speed wire rod rolling. Descaling a square billet by using high-pressure water, wherein the descaling high-pressure water pressure is not lower than 15MPa, and after surface descaling, carrying out rough rolling, medium rolling, finish rolling and reducing sizing in sequence, wherein the inlet temperature of the reducing sizing is 860 ℃, and the spinning temperature is 895 ℃.
(6) A cooling control procedure, namely, entering a stelmor cooling line after rolling, fully closing the heat-insulating cover and fully closing the fan; the temperature of the wire rod entering the heat preservation cover is 845 ℃, the temperature of the wire rod exiting the heat preservation cover is lower than 550 ℃, and the cooling speed is 0.8 ℃/s.
The hot rolled wire rod with the diameter of 8mm is basically tested to be ferrite and pearlite, the austenite grain size is 10 grade, the core hardness of the wire rod after oil quenching is 45HRC, and the tempering hardness is 29 HRC. A middle rolling process sample is taken for Jominy test, and the result is as follows: j51-1.5, J48-3, J37-5, J33-7, J27-9, J25-11, J24-13, J23-15, J22-20 and J20-25.
Example 4
A wire rod for high-hardenability medium-carbon cold forging steel comprises the chemical components and the mass percentage shown in table 1, and the specification is a hot-rolled wire rod with the diameter of 6.5 mm.
A production process of a wire rod for high-hardenability medium carbon cold heading steel comprises the working procedures of converter smelting, LF refining, continuous casting, heating, rolling and controlled cooling;
(1) a converter smelting process, wherein the molten iron ratio is 970kg/t steel, the lime consumption is 27 kg/ton steel, the light-burned dolomite is 23 kg/ton steel, and the sintered return mine is 18 kg/ton steel; the blowing adopts low-high-low gun position, the working oxygen pressure is 0.8MPa, the end point C is controlled at 0.15%, the end point O is controlled at 200ppm, the alloying deoxidation is carried out after carbon powder is adopted for preliminary deoxidation during the deoxidation, the alloying addition sequence is aluminum deoxidizer-ferrosilicon-ferromanganese-ferrochrome, 700kg of pre-melted slag charge is added for preliminary slagging during the tapping of 3/4.
(2) And in the LF refining process, the addition of slag materials is 8.4kg of lime per ton of steel and 0.6kg of fluorite per ton of steel, ferrosilicon powder is adopted for slag surface deoxidation in the slagging process, the addition of an aluminum wire is calculated according to the aluminum content of steel types and a calculation model and is fed in the initial stage of refining, the aluminum wire is not fed in the later stage, the alkalinity of refining slag is 4.0-5.0, the content of total ferrous oxide is 0.9%, and the nitrogen content of the discharged molten steel is 42 ppm.
(3) The continuous casting process comprises the steps that a steel ladle adopts a whole-process covering process, the superheat degree of molten steel is 50 ℃, the molten steel of a tundish is covered by double-layer slag, argon is blown into the tundish for 2-5 minutes before casting for replacing air in the tundish, the continuous casting tundish adopts an integral submerged nozzle for casting, the insertion depth of the nozzle is automatically adjusted within the range of 70-150mm according to set parameters of a model, the casting speed is controlled at 2.3m/min, the secondary cooling adopts intercooling strength, the specific water amount is controlled at 0.8L/kg.min, a secondary cooling 1 area is water-cooled, a 2-4 area is gas fog cooled, and a crystallizer adopts non-sinusoidal vibration. Continuously casting into square billet with the size of 150mm by 150 mm.
(4) A heating procedure, namely heating the continuous casting slab to 1080 ℃ before rolling, and preserving heat for 110 min;
(5) and a rolling step of high-speed wire rod rolling. Descaling a square billet by using high-pressure water, wherein the descaling high-pressure water pressure is not lower than 15MPa, and after surface descaling, carrying out rough rolling, medium rolling, finish rolling and sizing reduction in sequence, wherein the inlet temperature of the sizing reduction is 855 ℃, and the spinning temperature is 895 ℃.
(6) A cooling control procedure, namely, entering a stelmor cooling line after rolling, fully closing the heat-insulating cover and fully closing the fan; the temperature of the wire rod entering the heat preservation cover is 830 ℃, the temperature of the wire rod exiting the heat preservation cover is lower than 560 ℃, and the cooling speed is 0.6 ℃/s.
The hot rolled wire rod with the diameter of 6.5mm is basically tested to be ferrite and pearlite, the austenite grain size is 10 grade, the core hardness of the wire rod after oil quenching is 46HRC, and the tempering hardness is 28 HRC. A middle rolling process sample is taken for Jominy test, and the result is as follows: j51-1.5, J45-3, J30-5, J26-7, J25-9, J23-11, J22-13, J21-15, J20-20 and J19-25.
Example 5
A wire rod for high-hardenability medium-carbon cold forging steel comprises the chemical components and the mass percentage shown in table 1, and the specification is a hot-rolled wire rod with the diameter of 5.5 mm.
A production process of a wire rod for high-hardenability medium carbon cold heading steel comprises the working procedures of converter smelting, LF refining, continuous casting, heating, rolling and controlled cooling;
(1) a converter smelting process, wherein the molten iron ratio is 880kg/t steel, the lime consumption is 22 kg/ton steel, the light-burned dolomite is 19 kg/ton steel, and the sintered return mine is 24 kg/ton steel; blowing adopts low-high-low gun position, working oxygen pressure is 0.6MPa, end point C is controlled at 0.12%, end point O is controlled at 600ppm, carbon powder is adopted for pre-deoxidation during deoxidation, alloying deoxidation is carried out, aluminum deoxidizer-ferrosilicon-ferromanganese-ferrochrome is added in the sequence of alloying, 650kg of pre-melted slag charge is added during tapping 3/4 for pre-slagging.
(2) In the LF refining process, the addition of slag materials is 7.5kg of lime per ton of steel and 0.6kg of fluorite per ton of steel, ferrosilicon powder is adopted for slag surface deoxidation in the slagging process, the addition of an aluminum wire is calculated according to the aluminum content of steel types and a calculation model and is fed in the initial stage of refining, the aluminum wire is not fed in the later stage, the alkalinity of refining slag is 4.0-5.0, the content of total ferrous oxide is 0.7%, and the nitrogen content of the discharged molten steel is 43 ppm.
(3) The continuous casting process comprises the steps that a steel ladle adopts a whole-process covering process, the superheat degree of molten steel is 40 ℃, the molten steel of a tundish is covered by double-layer slag, argon is blown into the tundish for 2-5 minutes before casting for replacing air in the tundish, the continuous casting tundish adopts an integral submerged nozzle for casting, the insertion depth of the nozzle is automatically adjusted within the range of 70-150mm according to set parameters of a model, the casting speed is controlled at 2.2m/min, the secondary cooling adopts intercooling strength, the specific water amount is controlled at 0.9L/kg.min, a secondary cooling 1 area is water-cooled, a 2-4 area is gas fog cooled, and a crystallizer adopts non-sinusoidal vibration. Continuously casting into square billet with the size of 150mm by 150 mm.
(4) A heating procedure, namely heating the continuous casting blank to 1050 ℃ before rolling, and keeping the temperature for 120 min;
(5) and a rolling step of high-speed wire rod rolling. Descaling a square billet by using high-pressure water, wherein the descaling high-pressure water pressure is not lower than 15MPa, and after surface descaling, carrying out rough rolling, medium rolling, finish rolling and reducing sizing in sequence, wherein the reducing sizing inlet temperature is 850 ℃, and the spinning temperature is 880 ℃.
(6) A cooling control procedure, namely, entering a stelmor cooling line after rolling, fully closing the heat-insulating cover and fully closing the fan; the temperature of the wire rod entering the heat preservation cover is 820 ℃, the temperature of the wire rod exiting the heat preservation cover is lower than 590 ℃, and the cooling speed is 0.7 ℃/s.
The hot rolled wire rod with the diameter of 5.5mm is basically tested to be ferrite and pearlite, the austenite grain size is 10 grade, the core hardness of the wire rod after oil quenching is 49HRC, and the tempering hardness is 30 HRC. A middle rolling process sample is taken for Jominy test, and the result is as follows: j53-1.5, J48-3, J35-5, J28-7, J26-9, J24-11, J23-13, J22-15, J21-20 and J20-25.
TABLE 1 chemical composition and mass percent (wt%) of wire rod for carbon cold heading steels in examples 1 to 5
Figure 37716DEST_PATH_IMAGE001
The balance in table 1 is iron and inevitable impurity elements.
Although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that: modifications and equivalents may be made thereto without departing from the spirit and scope of the invention and it is intended to cover in the claims the invention as defined in the appended claims.

Claims (10)

1. The utility model provides a wire rod for medium carbon cold-heading steel of high hardenability which characterized in that: the wire rod comprises the following chemical components in percentage by mass: c: 0.37% -0.40%, Si: 0.15-0.30%, Mn: 0.70 to 0.90 percent of Cr, 0.10 to 0.20 percent of Cr, less than or equal to 0.020 percent of P, less than or equal to 0.020 percent of S, 0.010 to 0.030 percent of Als, and the balance of iron and inevitable impurity elements; the Jominy test result of the medium carbon cold heading steel with high hardenability is as follows: j51/56-1.5, J45/52-3, J30/37-5, J26/33-7, J25/27-9, J23/25-11, J22/24-13, J21/23-15, J20/22-20 and J18/20-25.
2. The wire rod for medium carbon cold heading steel with high hardenability according to claim 1, wherein: the austenite grain size of the wire rod is more than or equal to grade 9, the critical quenching specification of the oil quenching process of the wire rod is phi 12mm, the core hardness of the wire rod after oil quenching is more than or equal to 45HRC, and the core hardness of the wire rod after tempering is 28-30 HRC.
3. The production process of the wire rod for the high-hardenability medium-carbon cold heading steel according to claim 1 or 2, characterized in that: the production process of the wire rod comprises the working procedures of converter smelting, LF refining, continuous casting, heating, rolling and controlled cooling; in the converter smelting process, the end point C is controlled to be 0.10-0.20%, the end point O is controlled to be 200-600ppm, the alloying deoxidation is carried out after the carbon powder is adopted for pre-deoxidation during the deoxidation, and the alloying addition sequence is aluminum deoxidizer-ferrosilicon-ferromanganese-ferrochrome.
4. The process for producing a wire rod for high-hardenability medium-carbon cold heading steel according to claim 3, wherein: in the LF refining process, the alkalinity of refining slag is 4.0-5.0, the content of total ferrous oxide is less than or equal to 1.0 percent, and the nitrogen content of the outbound molten steel is less than or equal to 50 ppm.
5. The process for producing a wire rod for high-hardenability medium-carbon cold heading steel according to claim 3, wherein: in the continuous casting process, the superheat degree of molten steel is 20-50 ℃, the medium drawing speed is controlled to be 2.0-2.5m/min, the secondary cooling adopts the medium cooling strength, the specific water amount is controlled to be 0.7-0.9L/kg.min, the secondary cooling area 1 is water cooling, and the secondary cooling area 2-4 is gas fog cooling.
6. The process for producing a wire rod for high-hardenability medium-carbon cold heading steel according to claim 3, wherein: in the heating procedure, the continuous casting blank is heated to 1050-1150 ℃ before rolling, and the temperature is kept for 90-120 min; the rolling procedure is high-speed wire rod rolling; descaling a square billet by using high-pressure water, and then sequentially carrying out rough rolling, medium rolling, finish rolling and sizing reduction, wherein the inlet temperature of the sizing reduction is 850-890 ℃, and the spinning temperature is 880-910 ℃.
7. The process for producing a wire rod for high-hardenability medium-carbon cold heading steel according to claim 3, wherein: in the cold control procedure, after rolling, the steel wire enters a stelmor cooling line, the heat-preserving cover is fully closed, the fan is fully closed, the temperature of the steel wire rod entering the heat-preserving cover is 820-.
8. The process for producing a wire rod for a medium carbon cold heading steel with high hardenability according to any one of claims 3 to 7, wherein: in the converter smelting process, the molten iron ratio is 850-; the blowing adopts a low-high-low lance position, the working oxygen pressure is 0.6-0.8MPa, and 500-800kg of premelted slag is added for premelting when 3/4 steel is tapped.
9. The process for producing a wire rod for a medium carbon cold heading steel with high hardenability according to any one of claims 3 to 7, wherein: in the LF refining process, the adding amount of slag materials is 5.7-10.7kg of lime per ton of steel and 0.6kg of fluorite per ton of steel, ferrosilicon powder is adopted for slag surface deoxidation in the slag melting process, the adding amount of an aluminum wire is calculated according to the aluminum content of steel types and a calculation model and is fed in the initial refining stage, and the aluminum wire is not fed in the later stage.
10. The process for producing a wire rod for a medium carbon cold heading steel with high hardenability according to any one of claims 3 to 7, wherein: in the continuous casting process, a steel ladle adopts a full-process covering process, molten steel in a tundish is covered by double-layer slag, argon is blown into the tundish for 2-5 minutes before casting for replacing air in the tundish, the continuous casting tundish adopts an integral submerged nozzle for casting, the insertion depth of the nozzle is automatically adjusted within the range of 70-150mm according to set parameters of a model, and a crystallizer adopts non-sinusoidal vibration; the continuous casting adopts square billet continuous casting; the production process has Mn element yield not less than 95% and Si element yield not less than 93%.
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