CN110106443B - Production method of round steel for ultrahigh-strength bolt - Google Patents
Production method of round steel for ultrahigh-strength bolt Download PDFInfo
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- CN110106443B CN110106443B CN201910465068.XA CN201910465068A CN110106443B CN 110106443 B CN110106443 B CN 110106443B CN 201910465068 A CN201910465068 A CN 201910465068A CN 110106443 B CN110106443 B CN 110106443B
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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
- B22D11/10—Supplying or treating molten metal
- B22D11/11—Treating the molten metal
- B22D11/114—Treating the molten metal by using agitating or vibrating means
- B22D11/115—Treating the molten metal by using agitating or vibrating means by using magnetic fields
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- 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
- C21C7/10—Handling in a vacuum
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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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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- 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
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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Abstract
The invention discloses a method for producing round steel for an ultrahigh-strength bolt, which comprises the following steps: (1) the method comprises the following steps of (1) smelting by using molten iron and waste steel as raw materials and using an ultrahigh-power eccentric bottom type electric furnace, (2) refining the materials by using an LF refining furnace, (3) degassing by using a VD vacuum furnace and feeding core-spun yarns, (4) carrying out continuous casting treatment by using an arc continuous casting machine, (5) rolling, (6) cogging, (7) heating a steel billet by using a steel pushing type heating furnace, (8) stacking and slow cooling, and (9) carrying out heat treatment. The invention adopts a more optimized heat treatment process, so that the mechanical property of the product is exerted more remarkably to meet the requirements of high strength and high toughness of the product.
Description
Technical Field
The invention relates to the technical field of round steel production, in particular to a method for producing round steel for an ultrahigh-strength bolt.
Background
In recent years, with the rapid development of various industries such as automobiles, wind power, machinery, buildings, light industry and the like in China, higher requirements are put forward on materials used for manufacturing parts such as various fasteners (such as bolts, nuts and the like). Higher required strength and better impact toughness. At present, 10.9-grade bolts are commonly used, but the requirement that the tensile strength is only 1000MPa cannot meet the requirements of partial industries, particularly the automobile industry with light weight design and the wind and electricity industry. For this purpose, higher strength products are required, for example tensile strengths of > 1400 MPa. However, the prior art does not relate to the production of round steel with tensile strength requirement of more than 1400MPa and used for 14.9-grade ultrahigh-strength bolts.
Therefore, the development of a novel method for producing round steel for ultra-high strength bolts not only has urgent research value, but also has good economic benefit and industrial application potential, which is the power place and basis for the invention
Disclosure of Invention
The present inventors have conducted intensive studies to overcome the above-identified drawbacks of the prior art, and as a result, have completed the present invention after having made a great deal of creative efforts.
Specifically, the technical problems to be solved by the present invention are: the production method of the round steel for the ultrahigh-strength bolt is provided to improve the performances such as tensile strength of the round steel, particularly the performances such as the tensile strength of the round steel after heat treatment.
In order to solve the technical problems, the technical scheme of the invention is as follows:
a production method of round steel for ultra-high strength bolts comprises the following steps: (1) the method comprises the following steps of (1) smelting by using molten iron and waste steel as raw materials and using an ultrahigh-power eccentric bottom type electric furnace, (2) refining the materials by using an LF refining furnace, (3) degassing by using a VD vacuum furnace and feeding core-spun yarns, (4) carrying out continuous casting treatment by using an arc continuous casting machine, (5) rolling, (6) cogging, (7) heating a steel billet by using a steel pushing type heating furnace, (8) stacking and slow cooling, and (9) carrying out heat treatment.
In the invention, as a preferred technical scheme, the specific process of the step (1) is as follows: in the electric furnace smelting process, the raw material ratio of 50-70% of molten iron and scrap steel is adopted to carry out electric furnace smelting, the C content wt of tapping is controlled to be more than or equal to 0.06%, and the P content wt of tapping is controlled to be less than or equal to 0.010%; adding SiCaBaAl 1.0kg/t and steel core aluminum 2.0kg/t for strong deoxidation when tapping 15-20 t, adding ferroalloy material, carburant (with carbon content more than 90 wt%) and slag material into the ladle, and performing argon strong stirring at the later stage of tapping by adopting 0.3-0.4 MPa to uniform temperature and components and promote the upward floating of deoxidation products.
In the invention, as a preferred technical scheme, the specific process of the step (2) is as follows: the refining furnace is diffused and deoxidized by calcium carbide and silicon carbide in the earlier stage, stable white slag is formed as soon as possible, the binary alkalinity R of the white slag is controlled to be 4.0-6.0, and the design target of chemical components is as follows: C. the Si content wt is controlled according to the lower limits of 0.39-0.43% and 0.23-0.27% respectively; the contents wt of Mn, Cr, Mo and V are controlled according to target values of 0.62%, 1.02%, 0.54% and 0.58%; p, S wt: less than or equal to 0.015 percent; al content wt: less than or equal to 0.015 percent;
the binary alkalinity R2 of the LF refining final slag is more than or equal to 4.5, and the chemical composition wt% of the LF refining final slag is as follows: 50-65% of CaO and SiO27～15％，MgO 0.4～1.2％，Al2O325～30％，S 0.3～0.5％，FeO≤0.50％。
In the invention, as a preferred technical scheme, the specific process of the step (3) is as follows: and keeping the temperature at 1650 +/-10 ℃ and the vacuum degree of less than 67Pa for more than 15min for carrying out VD vacuum degassing treatment, feeding 1.5-2.5 m/t of steel CaSi core-spun yarn after the treatment is finished, and carrying out argon soft stirring for 8-15 min before the bale hanging.
The chemical components of the material in the step (3) are controlled to have target wt percent: 0.41 percent of C, 0.25 percent of Si, 0.62 percent of Mn, 1.02 percent of Cr, 0.54 percent of Mo, 0.28 percent of V, less than or equal to 0.015 percent of S, less than or equal to 0.015 percent of P, and less than or equal to 0.015 percent of Al.
In the invention, as a preferred technical scheme, the specific process of the step (4) is as follows: and an Ar sealing device is used for a ladle long nozzle, argon is blown to protect the ladle steel flow in the whole process, the superheat degree is 20-45 ℃, special carbon protective slag is selected from a rectangular billet of 150mm multiplied by 150mm, the drawing speed is 1.50 +/-0.15 m/min, and a crystallizer is adopted for a continuous casting machine to electromagnetically stir for 3 Hz/480A.
In the invention, as a preferred technical scheme, the specific process of the step (5) is as follows: the steel rolling adopts a 150mm multiplied by 150mm rectangular billet combined dephosphorization method, high-pressure water descaling at 18-22MPa is adopted, and an iron broom descaling device is arranged on a conveying roller way.
In the invention, as a preferred technical scheme, the specific process of the step (6) is as follows: the steel rolling takes a rectangular blank of 150mm multiplied by 150mm as a raw material blank, adopts a phi 550mm cogging mill to produce an intermediate square blank of 88mm multiplied by 88mm, and then rolls the intermediate square blank into a phi 31-phi 40mm steel material; and (3) producing a 68 x 68mm intermediate square billet by using a phi 550mm cogging mill, and rolling the intermediate square billet into a phi 16-phi 30mm steel material.
In the invention, as a preferred technical scheme, the specific process of the step (7) is as follows: the steel billet is heated by a long-time high-temperature heating process, a steel pushing type heating furnace is used for 150mm multiplied by 150mm, the temperature of the heating section I is controlled to be 1050-.
In the invention, as a preferred technical scheme, the specific process of the step (8) is as follows: after the rolling of the steel is finished, a concentrated stacking and slow cooling mode is adopted at the wind sheltering position of more than 350 ℃, and the stress is further removed.
In the invention, as a preferred technical scheme, the specific process of the step (9) is as follows: heating and preserving heat at 900 ℃, quenching by using LT18A rapid bright quenching oil, and tempering at two limit temperatures of 500 ℃ and 600 ℃.
Compared with the prior art, the invention has the following obvious advantages:
the invention is obtained by the inventor through a large number of repeated tests and creative work exploration in long-term practice, the invention is mainly designed after optimizing the hardenability and the impact toughness of the round steel during smelting, the designed product can meet the requirements of tensile strength being more than or equal to 1400MPa, yield strength being more than or equal to 1300MPa, elongation after fracture being more than or equal to 10%, reduction of area being more than or equal to 43%, and AKV being more than or equal to 27J (average value) at minus 20 ℃ through the optimized heat treatment process.
In the invention, the types of elements added into the round steel are strictly screened, and the weight ratio of various elements in the round steel is strictly controlled, wherein Cr belongs to elements in a reduced austenite phase region, the hardenability of the steel can be obviously improved, but the Cr can increase the temper brittleness tendency of the steel, so that other alloy elements are required to compensate the brittleness tendency. In the step (2), the content of Mo is adjusted, wherein the Mo element belongs to an element for reducing an austenite phase region, and is an element for increasing the hardenability of steel, improving the heat strength of a product and preventing temper brittleness. Vanadium is a strong carbide forming element and has similar characteristics with chromium, and the addition content of vanadium is very little and is generally below 0.50 percent; and the crystal grains can be refined, the strength of the steel ingot can be further improved by the vanadium carbonitride precipitated during tempering at higher temperature, and the vanadium carbonitride has stronger trap energy, so that hydrogen can be paved and uniformly dispersed in the crystal grains, the diffusion of the hydrogen is inhibited, and the delayed fracture resistance of the steel is improved. Al element belongs to strong deoxidizer, plays a role in deoxidation and nitrogen determination, and can refine grains. However, since the aluminum element competes with the vanadium element for the nitrogen content in the steel, the Al content in the steel needs to be strictly controlled. According to the calculation of the solubility of Al, if Al in the steel is completely combined with oxygen, the content of Al in the steel is 0.015 percent at most, so the content of Al is required to be 0.015 percent at most in the composition design process, the deoxidation is ensured, meanwhile, the precipitation of AlN is reduced, and the Al and V compete for nitrogen elements in the steel. In the step (2), Al on the slag surface is adopted for diffusion deoxidation to replace Al added in electric furnace tapping, so that the Al content in steel can be reduced, and the deoxidation effect can be ensured. And (3) properly feeding Ti wires and properly adding Ti elements to play a role in enhancing hydrogen traps.
In a word, the round steel provided by the invention is subjected to enhanced hardenability design on main elements such as C, Si, Mn, Cr, Mo, V and the like, is controlled in a narrower range than usual, and has good steel uniformity and reduced product performance fluctuation range. The invention adopts the operation of reserving steel and slag in the electric furnace, and the refining furnace manufactures high-alkalinity slag, thereby realizing the control of low P and low S. And VD vacuum degassing and argon protection pouring are adopted to control the content of H, O, N and other impurities, so that the number of non-metallic inclusions in the steel is reduced, the non-metallic inclusions are finely dispersed, and the low-temperature ductile-brittle transition temperature of the steel is improved. The invention adopts the continuous casting billet produced by the continuous casting process method and applies the electromagnetic stirring technology to effectively improve the compactness and the composition segregation of steel. The invention reduces the generation of AlN precipitation enhanced vanadium carbonitride by controlling the Al content, thereby not only meeting the requirement of grain refinement, but also improving the hydrogen trap, and having less hydrogen-induced cracks and delayed fracture. The invention adopts a more optimized heat treatment process, so that the mechanical property of the product is exerted more remarkably to meet the requirements of high strength and high toughness of the product.
Drawings
FIG. 1 is a schematic representation of a metallographic structure of steel (JNCGQLS) produced in example 2 of the present invention, which is oil quenched at 900 ℃ and heat-preserved, and amplified 500 times at 500 ℃ by heating, heat-preserving and water-cooling;
FIG. 2 is a schematic representation of a metallographic structure of steel (JNCGQLS) produced in example 2 of the present invention, which is oil quenched at 900 ℃ and water-cooled and amplified 500 times at 600 ℃;
FIG. 3 is a schematic diagram of a metallographic structure of conventional steel (42CrMoA) which is subjected to heating, heat preservation and oil quenching at 880 ℃ and is amplified by 500 times through heating, heat preservation and water cooling at 500 ℃;
FIG. 4 is a metallographic structure diagram of conventional steel (42CrMoA) heated at 880 ℃ with oil quenching and heated at 600 ℃ with water cooling amplification by 500 times.
Detailed Description
The invention is further illustrated by the following specific examples. The use and purpose of these exemplary embodiments are to illustrate the present invention, not to limit the actual scope of the present invention in any way, and not to limit the scope of the present invention in any way.
A production method of round steel for ultra-high strength bolts comprises the following steps: (1) the method comprises the following steps of (1) smelting by using molten iron and waste steel as raw materials and using an ultrahigh-power eccentric bottom type electric furnace, (2) refining the materials by using an LF refining furnace, (3) degassing by using a VD vacuum furnace and feeding core-spun yarns, (4) carrying out continuous casting treatment by using an arc continuous casting machine, (5) rolling, (6) cogging, (7) heating a steel billet by using a steel pushing type heating furnace, (8) stacking and slow cooling, and (9) carrying out heat treatment.
Example 1
The rolled material with the diameter of 31mm produced by continuously casting a rectangular billet with the section of 150mm multiplied by 150mm has all the performances meeting the technical requirements. The specific process method comprises the following steps:
(1) adopting 45t molten iron and scrap steel as raw materials, and smelting by using an ultrahigh-power eccentric bottom type electric furnace, wherein 50% of molten iron and scrap steel are adopted in the raw material ratio in the electric furnace smelting process for electric furnace smelting, the content wt of C in steel tapping is controlled to be more than or equal to 0.06%, and the content wt of P in steel tapping is controlled to be less than or equal to 0.010%; adding SiCaBaAl 1.0kg/t and steel core aluminum 1.5kg/t for strong deoxidation when tapping 15t, then adding ferroalloy material, carburant and slag charge into a ladle, and strongly stirring with argon at the later stage of tapping to uniform temperature and components and promote the upward floating of a deoxidation product;
(2) refining the material by using an LF refining furnace; the refining furnace is diffused and deoxidized by calcium carbide and silicon carbide in the earlier stage, stable white slag is formed as soon as possible, the binary alkalinity R of the white slag is controlled at 4.0, and the design target of chemical components is as follows: C. the contents wt of Si, Mn, Cr, Mo and V are respectively controlled according to target values of 0.39-0.43%, 0.23-0.27%, 0.60-0.65%, 1.00-1.05%, 0.53-0.55% and 0.27-0.30%; p, S wt: less than or equal to 0.015 percent; al content wt: less than or equal to 0.015 percent; the binary alkalinity R2 of the LF refining final slag is 4.5, and the chemical composition wt% of the LF refining final slag is as follows: 50-65% of CaO and SiO27～15％，MgO 0.4～1.2％，Al2O325-30%, S0.3-0.5%, FeO less than or equal to 0.50%; the final smelting finished product comprises the following componentsThe other control conditions are as follows:
(3) degassing by using a VD vacuum furnace, and feeding a core-spun yarn: keeping the temperature at 1630 ℃ and the vacuum degree below 67Pa for more than 15min for VD vacuum degassing treatment, feeding 1.5m/t steel CaSi core-spun yarn after the treatment is finished, and carrying out argon soft stirring for 10min before hoisting.
(4) Adopting an arc continuous casting machine to carry out continuous casting treatment: an Ar sealing device is used for a ladle long nozzle, argon is blown to protect the ladle steel flow in the whole process, the superheat degree is at 20 ℃, special carbon protective slag is selected from a rectangular billet of 150mm multiplied by 150mm, the drawing speed is 1.35m/min, and a crystallizer is adopted for a continuous casting machine to electromagnetically stir for 3 Hz/480A;
(5) steel rolling: the steel rolling adopts a 150mm multiplied by 150mm rectangular billet combined dephosphorization method, high-pressure water under 18MPa is adopted for descaling, and an iron broom descaler is arranged on a conveying roller way;
(6) cogging, in the steel rolling, 150mm multiplied by 150mm rectangular billets are used as raw material billets, 88mm multiplied by 88mm intermediate square billets are produced by a phi 550mm cogging mill, and then phi 31mm steel is rolled;
(7) the steel billet is heated by a steel pushing type heating furnace: the steel billet is heated by a long-time high-temperature heating process, a steel pushing type heating furnace is used for heating 150mm multiplied by 150mm, the temperature of a heating section I is controlled to be 950 ℃, the temperature of a heating section II is controlled to be 1180 ℃, the temperature of a soaking section is controlled to be 1200 ℃, and the uniform diffusion of the steel is ensured by the heating process of heating for 180 minutes in total;
(8) stacking and slow cooling: after the rolling of the steel is finished, a 355 ℃ wind shielding position concentrated stacking slow cooling mode is adopted to further remove stress;
(9) and (3) heat treatment: heating and preserving heat at 900 ℃, quenching by using LT18A rapid bright quenching oil, and tempering at two limit temperatures of 500 ℃ and 600 ℃.
The round steel (JNCGQLS) prepared in this example had the following properties:
example 2
The rolled material with the diameter of 34mm produced by the continuous casting rectangular billet with the section of 150mm multiplied by 150mm has all the performances meeting the technical requirements. The specific process method comprises the following steps:
(1) adopting 45t of high-quality molten iron as a main raw material, and smelting by using an ultrahigh-power eccentric bottom type electric furnace, wherein the molten iron is adopted for electric furnace smelting in the electric furnace smelting process, the content wt of C in steel tapping is controlled to be 0.08%, and the content wt of P in steel tapping is less than or equal to 0.010%; adding SiCaBaAl 1.2kg/t and steel core aluminum 2.0kg/t for strong deoxidation when tapping for 18t, then adding iron alloy material, carburant and slag charge into a ladle, and strongly stirring by argon in the later tapping stage to uniform temperature and components and promote the upward floating of a deoxidation product;
(2) refining the material by using an LF refining furnace; the refining furnace is diffused and deoxidized by calcium carbide and silicon carbide in the earlier stage, stable white slag is formed as soon as possible, the good alkalinity and the flowability of the refining slag are ensured, the binary alkalinity R of the white slag is controlled to be 4.8, and the chemical component design target is as follows: C. the contents wt of Si, Mn, Cr, Mo and V are respectively 64.1 percent of CaO, 28.76 percent of SiO28, 0.64 percent of MgO, 0.08 percent of Al2O325, 0.47 percent of S, and the balance of TFe (Mn); the binary alkalinity R2 of the LF refining final slag is 4.5, and the chemical composition wt% of the LF refining final slag is as follows: CaO 58.02%, SiO212.89%, MgO 0.38%, Al2O330.72%, S0.39%, the rest is TFe (Mn); refining tapping C, Si, Mn, Cr, V, Mo, Al, P and S are controlled according to internal control specifications, and finally smelting finished products are respectively controlled by the following components:
(3) degassing by using a VD vacuum furnace, and feeding a core-spun yarn: performing VD vacuum degassing treatment at 1655 deg.C and vacuum degree of less than 67Pa for more than 15min, feeding 2m/t steel CaSi core-spun yarn after the treatment, simultaneously adding carbonized rice husk for protecting molten steel, soft stirring with argon gas for 15min before ladle-lifting, and ladle-lifting temperature of 1560 deg.C;
(4) adopting an arc continuous casting machine to carry out continuous casting treatment: an Ar sealing device is used for a large ladle long nozzle, argon is blown to protect the large ladle steel flow in the whole process, the superheat degree is 35 ℃, carbon special protective slag is selected from a rectangular billet of 150mm multiplied by 150mm, the drawing speed is 1.50m/min, a continuous casting machine adopts a crystallizer to electromagnetically stir for 3Hz/480A, and the solidification segregation tendency of a casting blank is reduced;
(5) steel rolling: the steel rolling adopts a 150mm multiplied by 150mm rectangular billet combined dephosphorization method, high-pressure water under 20MPa is adopted for descaling, and an iron broom descaler is arranged on a conveying roller way;
(6) cogging, in the steel rolling, 150mm multiplied by 150mm rectangular billets are used as raw material billets, 88mm multiplied by 88mm intermediate square billets are produced by a phi 550mm cogging mill, and then phi 34mm steel is rolled;
(7) the steel billet is heated by a steel pushing type heating furnace: the steel billet is heated by a long-time high-temperature heating process, a steel pushing type heating furnace is used for heating 150mm multiplied by 150mm, the temperature of a heating section I is controlled to be 1050 ℃, the temperature of a heating section II is controlled to be 1200 ℃, the temperature of a soaking section is controlled to be 1210 ℃, and the uniform diffusion of the steel is ensured by the heating process of heating for 180 minutes in total;
(8) stacking and slow cooling: after the rolling of the steel is finished, a concentrated stacking and slow cooling mode is adopted at a wind sheltering position of 370 ℃, and the stress is further removed;
(9) and (3) heat treatment: heating and preserving heat at 900 ℃, quenching by using LT18A rapid bright quenching oil, and tempering at two limit temperatures of 500 ℃ and 600 ℃.
The round steel (JNCGQLS) prepared in this example had the following properties:
example 3
The rolled material with the diameter of 38mm produced by continuously casting a rectangular billet with the section of 150mm multiplied by 150mm has all the performances meeting the technical requirements. The specific process method comprises the following steps:
(1) molten iron and scrap steel are used as raw materials, and an ultrahigh-power eccentric bottom type electric furnace is used for smelting, wherein in the electric furnace smelting process, 70% of molten iron and scrap steel are used in a raw material ratio to carry out electric furnace smelting, the content wt of C in tapping is controlled to be more than or equal to 0.06%, and the content wt of P in tapping is controlled to be less than or equal to 0.010%; adding SiCaBaAl 1.0-1.5 kg/t and steel core aluminum 1.5-2.5 kg/t for strong deoxidation when tapping 15-20 t, then adding ferroalloy material, carburant and slag charge into a ladle, and strongly stirring by argon in the later tapping stage to uniform temperature and components and promote the upward floating of a deoxidation product;
(2) refining the material by using an LF refining furnace; the refining furnace is diffused and deoxidized by calcium carbide and silicon carbide in the earlier stage, stable white slag is formed as soon as possible, the binary alkalinity R of the white slag is controlled at 6.0, and the design target of chemical components is as follows: C. the contents wt of Si, Mn, Cr, Mo and V are respectively controlled according to target values of 0.39-0.43%, 0.23-0.27%, 0.60-0.65%, 1.00-1.05%, 0.53-0.55% and 0.27-0.30%; p, S wt: less than or equal to 0.015 percent; al content wt: less than or equal to 0.015 percent; the binary alkalinity R2 of the LF refining final slag is 5.0, and the chemical composition wt% of the LF refining final slag is as follows: 50-65% of CaO and SiO27～15％，MgO 0.4～1.2％，Al2O325-30%, S0.3-0.5%, FeO less than or equal to 0.50%; the final smelting finished product comprises the following components in respective control conditions:
(3) degassing by using a VD vacuum furnace, and feeding a core-spun yarn: keeping the temperature at 1670 ℃ and the vacuum degree below 67Pa for more than 15min for VD vacuum degassing treatment, feeding 2.5m/t steel CaSi core-spun yarn after the treatment is finished, and carrying out argon soft stirring for 25min before hoisting.
(4) Adopting an arc continuous casting machine to carry out continuous casting treatment: an Ar sealing device is used for a ladle long nozzle, argon is blown to protect the ladle steel flow in the whole process, the superheat degree is 45 ℃, special carbon protective slag is selected from a rectangular billet of 150mm multiplied by 150mm, the drawing speed is 1.65m/min, and a crystallizer is adopted for a continuous casting machine to electromagnetically stir for 3 Hz/480A;
(5) steel rolling: the steel rolling adopts a 150mm multiplied by 150mm rectangular billet combined dephosphorization method, 22MPa high-pressure water is adopted for descaling, and an iron broom descaler is arranged on a conveying roller way;
(6) cogging, in the steel rolling, 150mm multiplied by 150mm rectangular billets are used as raw material billets, 88mm multiplied by 88mm intermediate square billets are produced by a phi 550mm cogging mill, and then rolled into phi 31-phi 38mm steel products;
(7) the steel billet is heated by a steel pushing type heating furnace: the steel billet is heated by a long-time high-temperature heating process, a steel pushing type heating furnace is used for heating 150mm multiplied by 150mm, the temperature of a heating section I is controlled to be 950 ℃, the temperature of a heating section II is controlled to be 1240 ℃, the temperature of a soaking section is controlled to be 1220 ℃, and the uniform diffusion of the steel is ensured by the heating process of heating for 200 minutes in total;
(8) stacking and slow cooling: after the rolling of the steel is finished, a concentrated stacking and slow cooling mode is adopted at a wind sheltering position of 400 ℃, and the stress is further removed;
(9) and (3) heat treatment: heating and preserving heat at 900 ℃, quenching by using LT18A rapid bright quenching oil, and tempering at two limit temperatures of 500 ℃ and 600 ℃.
The round steel (JNCGQLS) prepared in this example had the following properties:
after the conventional 42CrMoA steel is subjected to heat treatment, the performance indexes are as follows:
from the data, the tempering temperature of the 42CrMoA is reduced to the lowest in time, and the requirement that the tensile strength is more than 1400MPa cannot be met by adopting a water quenching mode.
Chemical composition of comparative product
As can be seen from the metallographic structures of FIGS. 1 to 4, the structure of JNCGQLS is finer than that of 42CrMoA, so that the strength and toughness of the product are better than those of 42 CrMoA.
It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should also be understood that various alterations, modifications and/or variations can be made to the present invention by those skilled in the art after reading the technical content of the present invention, and all such equivalents fall within the protective scope defined by the claims of the present application.
Claims (6)
1. A production method of round steel for ultra-high strength bolts is characterized by comprising the following steps: the method comprises the following steps: (1) molten iron and scrap steel are used as raw materials, an ultrahigh-power eccentric bottom type electric furnace is used for smelting, and the specific process comprises the following steps: in the electric furnace smelting process, the raw material ratio of 50-70% of molten iron and scrap steel is adopted to carry out electric furnace smelting, the C content wt of tapping is controlled to be more than or equal to 0.06%, and the P content wt of tapping is controlled to be less than or equal to 0.010%; adding SiCaBaAl 1.0kg/t and steel core aluminum 2.0kg/t for strong deoxidation when tapping 15-20 t, adding ferroalloy material, carburant with carbon content more than 90wt% and slag charge into a ladle, and performing argon strong stirring at the later stage of tapping by adopting 0.3-0.4 MPa to uniform temperature and components and promote the upward floating of a deoxidation product; (2) the material is refined by an LF refining furnace, and the specific process comprises the following steps: the refining furnace is diffused and deoxidized by calcium carbide and silicon carbide in the earlier stage, stable white slag is formed as soon as possible, the binary alkalinity R of the white slag is controlled to be 4.0-6.0, and the design target of chemical components is as follows: C. the Si content wt is controlled according to the lower limits of 0.39-0.43% and 0.23-0.27% respectively; the contents wt of Mn, Cr, Mo and V are controlled according to target values of 0.62%, 1.02%, 0.54% and 0.58%; p, S wt: less than or equal to 0.015 percent; al content wt: less than or equal to 0.015 percent; the binary alkalinity R2 of the LF refining final slag is more than or equal to 4.5, and the chemical composition wt% of the LF refining final slag is as follows: 50-65% of CaO and SiO27～15%，MgO 0.4～1.2%，Al2O325-30%, S0.3-0.5%, FeO less than or equal to 0.50%; (3) carrying out VD vacuum degassing treatment by keeping the temperature at 1650 +/-10 ℃ and the vacuum degree below 67Pa for more than 15min, feeding 1.5-2.5 m/t of steel CaSi core-spun yarn after the treatment is finished, carrying out argon soft stirring for 8-15 min before ladle lifting, (4) using an Ar sealing device for a ladle long nozzle, carrying out argon blowing protection on the whole ladle steel flow, controlling the superheat degree at 20-45 ℃, selecting carbon special protective slag in a 150mm multiplied by 150mm rectangular billet, carrying out the pulling speed at 1.50 +/-0.15 m/min, electromagnetically stirring 3Hz/480A by using a crystallizer for a continuous casting machine, realizing the continuous casting treatment by using an arc continuous casting machine, (5) carrying out steel rolling, (6) cogging, (7) pushing a steel heating furnace to carry out billet heating, (8) stacking and slow cooling, and (9) carrying out heat treatment.
2. The method for producing the round steel for the ultra-high strength bolt as claimed in claim 1, wherein: the specific process of the step (5) is as follows: the steel rolling adopts a 150mm multiplied by 150mm rectangular billet combined dephosphorization method, high-pressure water descaling at 18-22MPa is adopted, and an iron broom descaling device is arranged on a conveying roller way.
3. The method for producing the round steel for the ultra-high strength bolt as claimed in claim 1, wherein: the specific process of the step (6) is as follows: the steel rolling takes a rectangular blank of 150mm multiplied by 150mm as a raw material blank, adopts a phi 550mm cogging mill to produce an intermediate square blank of 88mm multiplied by 88mm, and then rolls the intermediate square blank into a phi 31-phi 40mm steel material; and (3) producing a 68 x 68mm intermediate square billet by using a phi 550mm cogging mill, and rolling the intermediate square billet into a phi 16-phi 30mm steel material.
4. The method for producing the round steel for the ultra-high strength bolt as claimed in claim 1, wherein: the specific process of the step (7) is as follows: the steel billet is heated by a long-time high-temperature heating process, a steel pushing type heating furnace is used for 150mm multiplied by 150mm, the temperature of the heating section I is controlled to be 1050-.
5. The method for producing the round steel for the ultra-high strength bolt as claimed in claim 1, wherein: the specific process of the step (8) is as follows: after the rolling of the steel is finished, a concentrated stacking and slow cooling mode is adopted at the wind sheltering position of more than 350 ℃, and the stress is further removed.
6. The method for producing the round steel for the ultra-high strength bolt as claimed in claim 1, wherein: the specific process of the step (9) is as follows: heating and preserving heat at 900 ℃, quenching by using LT18A rapid bright quenching oil, and tempering at two limit temperatures of 500 ℃ and 600 ℃.
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| CN113198989A (en) * | 2021-03-31 | 2021-08-03 | 邯郸钢铁集团有限责任公司 | Method for improving reduction of area of chromium-molybdenum steel high-strength bolt for automobile |
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