CN115233109A

CN115233109A - Narrow-hardenability bearing steel and production process thereof

Info

Publication number: CN115233109A
Application number: CN202211162763.7A
Authority: CN
Inventors: 乔佳川; 王鲁义; 薛伟江
Original assignee: Lianfeng Steel Zhangjiagang Co Ltd
Current assignee: Lianfeng Steel Zhangjiagang Co Ltd
Priority date: 2022-09-23
Filing date: 2022-09-23
Publication date: 2022-10-25
Anticipated expiration: 2042-09-23
Also published as: CN115233109B

Abstract

The invention relates to narrow hardenability bearing steel and a production process thereof, wherein the components of Sn + Sb + As + Pb are controlled to be less than or equal to 0.035%; the process comprises the working procedures of electric furnace smelting, LF refining, VD vacuum, continuous casting, heating, high-pressure water descaling, rolling, spinning and stelmor line cooling, wherein the LF refining adopts C-A-S slag system with proper alkalinity, fluidity and foamability to match with Al + CaC ₂ The method has the advantages of combining deoxidation and desulfurization, absorbing impurities, feeding cerium wires to reduce the content of residual elements, controlling the purity of narrow components, low residual elements and high molten steel, improving austenite grain size, carbide reticulation, carbide banding and carbide liquation through continuous casting, heating, high-pressure water descaling and controlled rolling and cooling, reducing the nucleation rate of pearlite, increasing the transformation incubation period, enabling a C curve to be shifted to the right, reducing the quenching bandwidth, controlling the quenching band to be 1.5-2.5HRC, and improving the dimensional stability and the mechanical property of heat treatment.

Description

Narrow hardenability bearing steel and production process thereof

Technical Field

The invention belongs to the technical field of bearing steel, and particularly relates to narrow-hardenability bearing steel and a production process thereof.

Background

The bearing is subjected to high-frequency variable stress between an inner ring and an outer ring of the bearing and a rolling body, the bearing is subjected to centrifugal force and impact load, the rolling body and the ring are subjected to friction force and the like, fatigue cracks are easily generated at a part with low fatigue resistance, fatigue peeling is formed, and the bearing is damaged and failed and potential safety hazards are caused. The existing bearing steel comprises alloy carburizing steel adopting surface carburizing and hardening treatment and high-carbon chromium bearing steel adopting martensite hardening treatment, the carburizing treatment process of the alloy carburizing steel is complex and long in period, and the martensite of the high-carbon chromium bearing steel is more economical, but the following problems still exist:

(1) Residual elements in pig iron and scrap steel are subjected to solidification segregation in the casting blank process and grain boundary segregation during heat treatment to deteriorate the hot rolling performance of steel, the enriched residual elements are melted into the surface of steel to form an enriched layer instead of a low-melting-point liquid phase, the hot cracking sensitivity is increased, grain boundary embrittlement is caused, the quenching bandwidth is increased, the impact power is reduced, and the anti-seizure capacity and the fatigue performance of a bearing are influenced.

(2) In the continuous casting process, the primary crystal precipitated during alloy solidification has a large specific gravity difference with the rest liquid, the temperature gradient of the surface and the central molten steel is large, the phenomenon of columnar crystal bridging is easily generated, the segregation is caused, the compactness and the uniformity are influenced, the segregation of chemical components at different positions of the carbon element section is large, the fluctuation of the section hardness value is large due to the uneven distribution of non-metallic inclusions, the carbide liquification is serious, the quenching through bandwidth is influenced, and quenching cracks are generated during heat treatment.

(3) The long-time high-temperature diffusion is accompanied with serious billet decarburization, the network carbide structure is enlarged, an equiaxial crystal area and an internal columnar crystal area on the surface are elongated into strips during hot rolling, austenite grains are thick to cause uneven quenching structure, the concentration of solute elements in each area of the cooling speed after rolling is different to cause different transformation concentrations, the inoculation period of transformation caused by uneven austenite components is shortened, a C curve is shifted to the left, the critical cooling speed is increased, the quenching bandwidth is increased, the deformation and cracking tendency of steel are increased, the toughness is reduced, and the fatigue life is influenced.

(4) The cooling speed after austenitizing and the influence of heat between adjacent wire rings can cause austenite grains to be coarsened, the net carbon carbide is precipitated to cause uneven carbide after heat processing, and the banded structure causes non-martensitic structure to be locally generated in the steel during quenching process, thereby increasing the quenching bandwidth, causing the phenomena of uneven hardness distribution and stress concentration, showing obvious anisotropy and intensifying deformation and cracking during heat treatment.

Disclosure of Invention

The invention aims to solve at least one of the technical problems to a certain extent, and provides narrow-hardenability bearing steel and a production process thereof.

The technical scheme adopted by the invention for solving the technical problems is as follows:

the narrow hardenability bearing steel comprises the following components in percentage by mass: c:0.94-0.97%, si:0.46-0.5%, mn:1.52-1.57%, cr: 1.43-1.49%, P: less than or equal to 0.015 percent, S: less than or equal to 0.015 percent, ni: less than or equal to 0.22 percent, cu: less than or equal to 0.22 percent, mo: less than or equal to 0.03%, al:0.008-0.014%, ti:0.005-0.015%, nb:0.021-0.028%, B:0.001-0.0025%, sn: less than or equal to 0.015 percent, sb: less than or equal to 0.01 percent, as: less than or equal to 0.015 percent, pb: less than or equal to 0.002%, ce:0.015 to 0.025%, O: less than or equal to 0.0006 percent, N:0.005-0.012%, and the rest is Fe and inevitable impurities.

The narrow hardenability bearing steel further has the composition that Sn + Sb + As + Pb are less than or equal to 0.035%, the hardenability zone is controlled to be 1.5-2.5HRC, and the narrow hardenability improves the dimensional stability and the mechanical property of heat treatment.

The narrow hardenability bearing steel is based on the following composition design:

(1) Determination of contents of C, mn and Cr: C. mn and Cr are melted into austenite during heating, the nucleation work of the phase A to the phase F + P is increased, the transformation of the phase A to the phase F + P is delayed, the critical cooling temperature is reduced, and the hardenability is increased; c is an important element for ensuring the hardness and the wear resistance of the bearing steel, the increase of the carbon concentration in austenite causes the reduction of the critical cooling speed, so that the C curve is shifted to the right, the hardenability is increased, the hardness of martensite is increased after quenching, but the large carbide liquation is easily generated when the C content is too high, and therefore, the C content range is determined to be 0.94-0.97%; mn is used as a deoxidizing element in the steelmaking process, is dissolved in a solid solution to influence the formation rate of an oxide layer and reduce the diffusion coefficient of carbon, but the tempering brittleness is improved and the toughness is reduced due to the excessively high content of Mn, so that the content range of Mn is determined to be 1.52-1.57 percent; cr is a carbide-forming element and can improve the hardenability, wear resistance and corrosion resistance of steel, but if the Cr content is too high, massive carbides are easily formed, the carbide is decomposed slowly, and a decarburized layer is increased, so that the Cr content of the invention is determined to be 1.43-1.49%.

(2) Determination of Si content: si is a reducing agent and a deoxidizing agent, can strengthen ferrite, and improve the strength, the elastic limit and the hardenability, but the excessive Si content can concentrate in oxide skin to form olivine-shaped compounds, slow down the formation rate of the oxide layer, increase the heat sensitivity, the crack and the decarburization tendency, and bring adverse effects to the fatigue performance, and the range of the Si content is determined to be 0.46-0.5%.

(3) Determining the contents of P, S and O: p causes element segregation when steel is solidified, and is dissolved in ferrite to distort and coarsen crystal grains and increase cold brittleness, so that the range of the P content is determined to be less than or equal to 0.015 percent; s is easy to cause hot brittleness of steel, the ductility and the toughness of the steel are reduced, and the formed sulfide also destroys the continuity of the steel, so the range of the S content is determined to be less than or equal to 0.015 percent; oxide inclusions are easily generated when the O content is too high, and the range of the O content is determined to be less than or equal to 0.0006 percent.

(4) Determination of Ni and Mo contents: ni can reduce the dissolution of carbon in a surface layer, limit outward diffusion, reduce a decarburized layer and improve the oxidation resistance, and the comprehensive effect of Ni and Mo can improve the hardenability, so that the range of the Ni content is determined to be less than or equal to 0.22 percent; mo can refine the crystal grains of the steel and improve the hardenability and the heat strength, but the content of Mo is too high, and ferrite delta phase or other brittle phases are easy to appear to reduce the toughness, so the content range of the Mo in the invention is determined to be less than or equal to 0.03 percent.

(5) Determination of Al, ti, nb and N contents: al and N are combined to form AlN particles dispersed on a crystal boundary, the crystal boundary movement is hindered, austenite grains are prevented from growing to be large, and the purpose of refining the grains is achieved, but the content of Al is too high, and oxide inclusion is increased, so that the content of Al in the invention is determined to be 0.008-0.014%; most of Ti can be melted into austenite during quenching and heating to reduce the critical cooling speed, but too high Ti is easy to form TiN large particles to be unfavorable for fatigue resistance and reduce hardenability, so the range of the Ti content is determined to be 0.005-0.015 percent; nb can trap solid-solution N and refine grains, and the content range of Nb is determined to be 0.021-0.028%; in order to refine the crystal grains and avoid the generation of mixed crystals, the content of N in the invention is determined to be 0.005-0.012%.

(6) Determination of B content: the micro B is taken as a surface active element, is adsorbed on an austenite crystal boundary to be beneficial to forming martensite and improving the hardenability, but the hardenability is obviously influenced by over high B, and the hardenability bandwidth is increased, so the content range of the B is determined to be 0.001-0.0025 percent.

(7) Determination of Cu, sn, sb, as and Pb contents: cu can improve the strength, toughness and corrosion resistance, but is easy to generate heat quenching during hot processing, so the Cu content of the invention is determined to be less than or equal to 0.22 percent; sn, sb, as and Pb can cause the second type of temper brittleness of structural steel, copper brittleness sensitivity is enhanced, a columnar crystal band at the upper part of a casting blank is easy to be positively segregated and gradually increased towards the center, the lower part of the casting blank is negatively segregated, enriched residual elements are melted into the surface of steel to form an enriched layer instead of a low-melting-point liquid phase, as is melted into the steel to obviously reduce the carbon content in ferrite to cause carbide increase, sb and Pb have obvious embrittlement effect, hot cracking sensitivity is increased, grain boundary embrittlement is caused, the quenching bandwidth is increased, and impact power is reduced, so that the invention determines the Sn: less than or equal to 0.015 percent, sb: less than or equal to 0.01%, as: less than or equal to 0.015 percent, pb: less than or equal to 0.002 percent, less than or equal to 0.035 percent of Sn + Sb + As + Pb, and residual elements are controlled, so that segregation embrittlement caused by combined action of metallographic structure and unbalanced grain boundary segregation is avoided.

(8) Determination of the Ce content: ce can react with residual elements Sb, P, sn and As, so As to improve the cast structure, shorten columnar crystals and improve segregation, meanwhile, the phase transformation temperature can be raised by melting austenite, the C curve is shifted to the right, the austenite is promoted to be stable, the pearlite amount is reduced, the banded structure is improved, and the effect of refining grains is achieved, therefore, the content range of the Ce is determined to be 0.015-0.025%.

The production process of the narrow hardenability bearing steel comprises the following steps:

s1, electric furnace smelting: performing KR desulfurization on a steelmaking raw material with the molten iron mass more than or equal to 78 percent through molten iron pretreatment, and smelting by using an oxygen top-blown and double-slag method electric furnace to obtain molten steel, wherein a desulfurizer for the KR desulfurization of the molten iron pretreatment adopts 3-4kg/t of CaO and 0.3-0.4kg/t of fluorite of the molten steel, keeps better fluidity, controls the end point S to be less than or equal to 0.005%, the end point carbon content of tapping to be 0.14-0.22%, the end point P to be less than or equal to 0.013%, the tapping temperature to be 1620-1680 ℃, avoids the high-temperature phosphorus return phenomenon, blocks slag and taps, and sequentially adds 0.6-0.8kg/t of aluminum ingot, 3-5kg/t of ferromanganese alloy (FeMn82C1.5), 2.7-3.6kg/t of lime and 2.5-3.2kg/t of calcium aluminate to the tapping process in the tapping process, strongly deoxidizes and reduces the number of large Si and Mn inclusions;

s2, LF refining: and (2) refining the molten steel in the step (S1) in an LF (ladle furnace) station, adding 1-1.5kg/t of refining slag of the molten steel to prepare white slag, wherein the refining slag comprises the following components in percentage by mass: 46-50%, mgO:10-14% of SiO ₂ ：2-5%、Al ₂ O ₃ ：17-22%、SiC：4-8%、CaF ₂ ：3-5%、BaO：2-5%、Na ₃ AlF ₆ :1-3%, the C-A-S slag system has proper alkalinity R of 3.6-4.5, reduces balanced oxygen and adsorbed inclusion in steel, the refining slag has good fluidity to increase slag steel contact interface and ensure refining effect, and SiO is used for improving the strength of the steel ₂ MgO protects furnace lining, reduces surface tension of slag, promotes deoxidation products to float, improves foaming and desulfurization capacity through BaO and SiC, and passes through CaF ₂ 、Na ₃ The melting point of AlF is reduced, the viscosity of refining slag is adjusted, the white slag time is more than or equal to 20min, the smelting time is more than or equal to 40min, and oxygen and sulfur in molten steel are fully removed through enough white slag time; by using Al + CaC ₂ Adding a small amount of the combined deoxidization Al + CaC for multiple times according to the mass ratio of 1 ₂ The dosage of the low Al-containing molten steel is 0.3-0.5kg/t, the silicon increase caused by over-deep local deoxidation is avoided, the low Al-containing deoxidation is combined with oxygen generated by desulfurization, the desulfurization efficiency is certain, and the CaC ₂ The early-stage foaming of the deoxidation product is realized, the deoxidation and desulfurization capacity is strong, and the products CaO and CO are ₂ Does not pollute molten steel and CO ₂ Can stir molten steel, promote the floating of inclusions, effectively reduce D-type inclusions and reduce xCaO-yAl of bearing steel grade ₂ O ₃ The inclusions are fine and dispersed, so that the deoxidation speed is high, the deoxidation is thorough, the residual Al content is between 0.02 and 0.035 percent, and the mass generation of oxide inclusions in the subsequent process is prevented;

the argon flow in the early stage of refining is 220-250NL/min, and the argon is properly increased and stirred to promote deoxidation and alloying;

low-carbon ferrochrome (FeCr69C1.0), low-carbon ferroboron (FeB16C0.1) and ferroniobium (FeNb 50) are used in the middle stage of refining, the argon flow in the middle stage of refining is 150-180NL/min, the argon strength in the argon is kept for component fine adjustment, recarburization and nitrogen absorption are prevented, the alloy yield and hit rate are improved, and narrow component control is performed;

in the later stage of refining, the argon flow is 60-110NL/min, the rolling and oxidation of the molten steel are avoided, cerium wires of 1.2-1.5m/t of the molten steel are fed at the wire feeding speed of 1-2m/s, sulfides can be controlled, the content of residual elements is reduced, an equiaxed crystal area is enlarged, the segregation is improved, meanwhile, the phase transformation temperature can be increased by melting in austenite, so that a C curve is shifted to the right, and the austenite is promoted to be stable;

s3, VD vacuum: the molten steel in the step S2 is fed into a VD station for VD vacuum degassing treatment, the ultimate vacuum degree is less than or equal to 68Pa, the pressure maintaining time is not less than 20min, slagging and deoxidation are ensured to remove residual elements and inclusions, the soft argon blowing time is not less than 40min, so that the non-metallic inclusions float sufficiently, the content of gas and non-metallic inclusions in the steel is reduced, and after the steel is broken, a ferrotitanium core-spun yarn of 0.5-0.6m/t molten steel is fed at the wire feeding speed of 1-1.5m/S at 1620-1645 ℃, so that the alloy recovery rate and the component uniformity are improved, and higher molten steel purity is obtained;

s4, continuous casting: casting the molten steel in the step S3 in a 150mm-150mm continuous casting machine, controlling the superheat degree to be 15-20 ℃, controlling the low superheat degree to pour and control segregation, controlling the molten steel pouring temperature to be 1565-1610 ℃, adopting a crystallizer to electromagnetically stir, wherein the electromagnetic stirring parameters of the crystallizer are current 200-300A and frequency 2-3Hz, the electromagnetic stirring parameters of the tail end are current 130-150A and frequency 9-10Hz, the specific water amount of a secondary cooling area is 0.19-0.24L/kg, and the pulling speed is 0.85-1.2m/min, so that the dendritic crystal at the solidification front is forcedly broken by convection before solidification, the temperature gradient of core liquid from outside to inside, the specific gravity difference between primary crystal and the rest liquid are reduced, the section equiaxial crystal rate is increased, and alloy segregation elements are uniformly distributed; the soft reduction of the tail end is 8-12 mm, the phenomenon that dendrites at the liquid core are bridged is broken, the center porosity is reduced, the center density is improved, the carbon segregation index of a casting blank is reduced, the carbide liquation is improved, the carbon segregation index is 0.96-1.02, the casting blank is straightened by a straightening machine, cut to length and then put into a pit for slow cooling in time, the temperature of the put-in pit for slow cooling is more than or equal to 640 ℃, the time of slow cooling is more than or equal to 57 hours, and the temperature of the taken-out pit is less than or equal to 210 ℃, so that the casting blank is obtained; the casting blank structure has low-power center porosity, general porosity, ingot type segregation, shrinkage cavity and center segregation which are all less than or equal to 1.0 level, A-type inclusions, B-type inclusions, C-type inclusions and D-type inclusions which are less than or equal to 1.0 level, and Ds-type inclusions which are less than or equal to 1.5 level, so that the quenching through bandwidth is favorably reduced, and quenching cracks are avoided during heat treatment;

s5, heating: the casting blank is heated into a steel billet in a heat accumulating type steel pushing heating furnace, and the furnace temperature is increased in a stepped mode by three sections: the temperature of the preheating section is 850-880 ℃, the heating rate is 2.0-2.5 ℃/min, the preheating and heat preservation time is 50-100min, the thermal stress is reduced, the thermal crack caused by too fast heating is avoided, and the long-time high-temperature decarburization caused by too slow heating is avoided; the temperature of the heating section is 1150-1200 ℃, the heat preservation time of the heating section is 70-120min, the temperature of the soaking section is 1190-1230 ℃, the heat preservation time of the soaking section is 80-150min, and the temperature difference of the section of the billet is less than or equal to 30 ℃; ensuring that the liquated carbide is dissolved in the steel billet, further reducing element segregation through high-temperature diffusion so as to reduce the structure level of the reticular carbide of the wire rod, avoiding overburning and deteriorating the quality of the steel billet caused by overhigh temperature, and avoiding reducing the high-temperature diffusion effect or generating eutectic carbide which is difficult to eliminate caused by overlow temperature;

s6, high-pressure water descaling: controlling the descaling pressure to be more than or equal to 19MPa, the speed of a descaling roller way to be less than or equal to 1.1m/s, and the nozzle impact force to be more than or equal to 0.85N/mm ² The steel billet is accurately centered when entering the descaling ring, and on the basis of controlling heating, the olivine iron scale formed by the steel billet Si and Ni is removed to avoid pressing the steel billet into the surface to generate defects;

s7, rolling: the billet is subjected to 6-pass rough rolling, 6-pass intermediate rolling, 6-pass pre-finish rolling, 8-pass finish rolling and 4-pass diameter reduction and sizing treatment to form a wire, and the initial rolling temperature is controlled to be 1090-1120 ℃; after pre-finish rolling, a water cooling box and a recovery section are adopted for cooling treatment, and the cooling speed of the core part is ensured to be 19-27 ℃/s; the finish rolling temperature is 915-960 ℃, the pressure of a water cooling box at the first water cooling part after finish rolling is 3.0-5.0 bar, the flow rate is 2300-2800 lpm, and low-temperature rolling is adopted to ensure that the austenite crystal grains are fully recrystallized in a near two-phase region, namely austenite plus cementite rolling, so that the fine uniformity of crystal boundaries is improved; reducing the diameter temperature to 870-900 ℃, controlling the pressure of a 1 st section water cooling box at a second water cooling part to be 3.0-4.5bar, the flow rate to 2700-3200lpm, the pressure of a 2 nd section water cooling box at the second water cooling part to be 3.5-4.0bar, and the flow rate to be 1700-2200 lpm, wherein the rapid cooling process can inhibit the growth of ferrite, reduce the nucleation rate of pearlite, increase the transformation incubation period, move the C curve to the right, slow down the critical cooling speed, and reduce the through quenching bandwidth;

the compression ratio of each pass of rough rolling is 1.24-1.35, and the billet core is compressed and the internal defects of the billet are welded; the compression ratio of each pass of finish rolling is 1.12-1.25, so that the phenomenon that the continuity of the structure is damaged due to the movement of carbide among steel structures caused by overlarge finish rolling reduction is avoided; the rough rolling speed is less than or equal to 0.25m/s, the middle rolling speed is less than or equal to 0.5m/s, the pre-finish rolling speed is less than or equal to 4.2m/s, and the secondary finish rolling speed is less than or equal to 8.1m/s, the rolling speed is controlled to be uniformly reduced to avoid the sectional grain size from presenting regional difference, so that the deformed austenite grains are elongated, the grain boundary area, the distortion energy and the recrystallization nucleation part are increased, the grain size is reduced, the uniform dispersion of carbide is promoted, the aggregation of carbide is avoided, the banded carbide is improved, and the quenching bandwidth is reduced;

s8, spinning: the wire rod enters a wire laying machine for laying wires, the tail part of the wire rod is clamped by a V-hole type pinch roll, the torque parameter of the pinch roll before laying wires is set to be 22-28%, the phenomenon that the surface of the wire rod generates indentation, tail trailing, kinking or uneven crystal grains is avoided, the laying temperature is 830-850 ℃, and the phenomenon that the group of crystal grains of the tissue is large due to overhigh temperature is avoided;

s9, stelmor line cooling: the wire enters into a stelmor line, the air quantity of a fan is controlled to be 30-60%, the speed of an initial roller way is 0.14-0.17m/s, a subsequent roller way is increased progressively at the speed of 0.01-0.02m/s, the speed of the roller way is changed to control the overlap distance of coils, the influence of heat between adjacent wire loops is weakened, the corresponding cooling speed is further reduced along with the increase of the speed of the roller way, and the reduction of the tensile strength is restrained; the wire enters a heat-preservation cover at the cooling speed of 2-5 ℃/s, the cover-entering temperature is 675-714 ℃, the cooling speed in the cover is controlled at 0.7-0.9 ℃/s to complete the phase transition at 610-635 ℃, the wire is cooled to be less than or equal to 525 ℃, the wire is taken out of the cover and is controlled to be cooled at 1.5-3 ℃/s, the precipitation of net carbide on the original austenite grain boundary is inhibited, the precipitation of net carbide at too low cooling speed is avoided, the generation of a super-cooling abnormal structure at too high cooling speed is avoided, the wire is collected into a wire rod at the temperature of 250-292 ℃, then the wire rod is air-cooled to room temperature, the surface quality inspection, finishing and sampling are carried out, the austenite grain size in the wire rod structure is more than or equal to 8 grade, the carbide net grade is less than or equal to 1.0 grade, the carbide belt grade is less than or equal to 1.5 grade, and the carbide liquid precipitation grade is less than or equal to 0.5 grade, and the bearing steel wire rod is obtained by packaging.

Compared with the prior art, the invention has the beneficial effects that:

(1) Controlling the contents of S and P in electric furnace smelting, strongly deoxidizing the steel and reducing large-particle inclusions of Si and Mn; the LF refining adopts C-A-S slag system with proper alkalinity, fluidity and foamability to match with Al + CaC ₂ The alloy is combined with deoxidation, desulfurization and impurity adsorption, the yield and hit rate of the alloy are improved by adjusting components in the middle stage of refining, the content of residual elements is reduced by feeding cerium wires, the control of narrow components, low residual elements and high molten steel purity is realized, sn + Sb + As + Pb is controlled to be less than or equal to 0.035%, the solidification segregation of the residual elements in the casting blank process and the grain boundary segregation in the heat treatment process are avoided to cause grain boundary embrittlement, the quenching bandwidth is reduced, and the anti-seizing force and the fatigue performance of the bearing are improved.

(2) Continuous casting adopts low superheat degree pouring, electromagnetic stirring of a crystallizer and electromagnetic stirring of the tail end, temperature gradient of core liquid from outside to inside, specific gravity difference between primary crystals and residual liquid are reduced, section equiaxial crystal rate is increased, a phenomenon that dendritic crystals at a liquid core are broken under light pressure of the tail end to bridge is avoided, carbide liquation is improved, the carbon segregation index of a casting blank is reduced to 0.96-1.02, the general porosity, ingot type segregation, shrinkage cavity and center segregation are all less than or equal to 1.0 level, A type impurities, B type impurities, C type impurities and D type impurities are less than or equal to 1.0 level, ds type impurities are less than or equal to 1.5 level, and the quenching through bandwidth is reduced.

(3) The temperature of the heating furnace is raised in three stages, element segregation is further reduced, carbide liquation is improved or eliminated, decarburization is avoided, controlled rolling and controlled cooling adopt a water cooling box and a recovery section to guarantee the cooling speed of a core, low-temperature rolling is guaranteed to be carried out in a region close to two phases, namely austenite and cementite, the compression ratio and the rolling speed are controlled to be uniform and press down to promote carbide dispersion, strip-shaped carbide is improved, the cooling speed after rolling is controlled to improve the fineness and uniformity of crystal boundaries, the nucleation rate of pearlite is reduced, the transformation incubation period is increased, the C curve is moved to the right, the critical cooling speed is reduced, and the quenching bandwidth is reduced.

(4) Clamping by a pinch roller and low-temperature spinning avoid uneven structure grains or large group, changing the overlap distance of a roller speed control coil, weakening the heat influence between adjacent wire rings, controlling the precipitation and cold abnormal structures of net carbon carbide by stelmor wire cold, wherein the austenite grain size in a wire rod structure is more than or equal to 8, the net grade of the carbide is less than or equal to 1.0, the ribbon grade of the carbide is less than or equal to 1.5, the liquid precipitation grade of the carbide is less than or equal to 0.5, the fine and uniform austenite grain size, the low-grade net, ribbon and liquid precipitation carbide effectively stabilize the tail end hardenability, reduce the hardenability bandwidth, and reduce the deformation and cracking tendency of steel.

Detailed Description

The following detailed description of the embodiments of the invention is intended to be illustrative, and not to be construed as limiting the invention.

Example 1:

the invention relates to a preferable implementation mode of narrow hardenability bearing steel, which comprises the following components in percentage by mass: c:0.95%, si:0.48%, mn:1.53%, cr: 1.46%, P:0.01%, S:0.01%, ni:0.18%, cu:0.13%, mo:0.02%, al:0.012%, ti:0.01%, nb:0.023%, B:0.002%, sn:0.012%, sb:0.008%, as:0.01%, pb:0.001%, ce:0.012%, O:0.0005%, N:0.008% and the balance of Fe and inevitable impurities; sn + Sb + As + Pb =0.031%.

The production process of the narrow hardenability bearing steel has the specification of phi 23mm, and comprises the following steps:

s1, electric furnace smelting: performing KR desulfurization on steelmaking raw materials containing 78 mass percent of molten iron and 22 mass percent of scrap steel through molten iron pretreatment, and smelting the steelmaking raw materials by using oxygen top-blown and double-slag method electric furnaces to obtain molten steel, wherein a desulfurizer for the KR desulfurization through the molten iron pretreatment adopts CaO of 3.2kg/t molten steel and fluorite of 0.32kg/t molten steel, the end point S is controlled to be less than or equal to 0.005 percent, the carbon content at the tapping end point is 0.15 percent, the end point P is controlled to be less than or equal to 0.013 percent, and the tapping temperature is controlled to be 1665 ℃; during slag-stopping and tapping, 0.72kg/t of molten steel aluminum ingot, 4.2kg/t of molten steel ferromanganese (FeMn82C1.5), 2.8kg/t of molten steel lime and 2.9kg/t of molten steel calcium aluminate are sequentially added in the tapping process;

s2, LF refining: and (2) refining the molten steel in the step (S1) in an LF (ladle furnace) station, adding refining slag of 1.3kg/t of molten steel to make white slag, wherein the refining slag comprises the following components in percentage by mass: 49%, mgO:12% SiO ₂ ：3%、Al ₂ O ₃ ：18%、SiC：7%、CaF ₂ ：5%、BaO：3%、Na ₃ AlF ₆ :3 percent, the white slag time is 25min, and the smelting time is 45min; by using Al + CaC ₂ Adding a small amount of the Al + CaC into the mixed solution for multiple times according to the mass ratio of 1 ₂ The using amount of the Al-containing alloy is 0.42kg/t molten steel, and the content of residual Al is 0.026%;

the argon flow in the early stage of refining is 230NL/min; low-carbon ferrochrome (FeCr69C1.0), low-carbon ferroboron (FeB16C0.1) and ferroniobium (FeNb 50) are used in the middle stage of refining, the argon flow rate in the middle stage of refining is 170NL/min, and the argon strength such as argon is kept for component fine adjustment; feeding a cerium wire of 1.3m/t molten steel at a wire feeding speed of 1.3m/s with an argon flow of 80NL/min in the later stage of refining;

s3, VD vacuum: feeding the molten steel in the step S2 into a VD station for VD vacuum degassing treatment, wherein the ultimate vacuum degree is less than or equal to 68Pa, the pressure maintaining time is 25min, the soft argon blowing time is 45min, and feeding a ferrotitanium cored wire of 0.53m/t molten steel at a wire feeding speed of 1.25m/S at 1630 ℃ after vacuum breaking;

s4, continuous casting: casting the molten steel in the step S3 in a 150mm by 150mm continuous casting machine, controlling the superheat degree to be 15-20 ℃, the casting temperature of the molten steel to be 1580 ℃, the electromagnetic stirring parameters of a crystallizer to be 200A and 2Hz, the electromagnetic stirring parameters of the tail end to be 140A and 9Hz, the specific water amount of a secondary cooling area to be 0.23L/kg, the pulling speed to be 0.9m/min, the soft reduction of the tail end to be 11mm, straightening a casting blank by a straightening machine, cutting to length, then timely entering a pit for slow cooling, controlling the temperature of entering the pit for slow cooling to be 650 ℃, controlling the time of slow cooling to be 60h, and controlling the temperature of leaving the pit to be 200 ℃ to obtain the casting blank;

s5, heating: the casting blank is heated into a steel billet in a heat accumulating type steel pushing heating furnace, and the furnace temperature is increased in a stepped mode by three sections: the temperature of the preheating section is 870 ℃, the heating rate is 2.2 ℃/min, and the preheating and heat preservation time is 80min; the temperature of the heating section is 1170 ℃, the time of the heating section is 90min, the heat preservation temperature of the soaking section is 1200 ℃, the heat preservation time of the soaking section is 115min, and the temperature difference of the section of the billet is less than or equal to 30 ℃;

s6, high-pressure water descaling: controlling the descaling pressure to be 20MPa, the speed of a descaling roller way to be 1m/s and the striking force of a nozzle to be 0.9N/mm ² The steel billet is accurately centered when entering the descaling ring;

s7, rolling: the steel billet is rolled into a wire to be made into a wire rod through 6-pass rough rolling, 6-pass intermediate rolling, 6-pass pre-finish rolling, 8-pass finish rolling and 4-pass sizing reduction treatment, and the initial rolling temperature is controlled to be 1100 ℃; after pre-finish rolling, a water cooling box and a recovery section are adopted for cooling treatment, and the cooling speed of the core part is ensured to be 19-20 ℃/s; the precision rolling temperature is 945 ℃, the pressure of a water cooling box at the first water cooling part after precision rolling is 4.0bar, and the flow is 2400pm; reducing the diameter temperature to 880 ℃, controlling the pressure of a 1 st section water cooling box at the second water cooling part to be 3.5bar and the flow rate to 2800lpm, controlling the pressure of a 2 nd section water cooling box at the second water cooling part to be 3.6bar and the flow rate to be 1900lpm;

the compression ratio of each pass of rough rolling is 1.25, 1.27, 1.33, 1.29, 1.27 and 1.25 respectively; the rough rolling speed is 0.23m/s, the medium rolling speed is 0.47m/s, the pre-finish rolling speed is 4.1m/s, and the secondary finish rolling speed is 8m/s; the compression ratios of the finish rolling passes are respectively 1.12, 1.13, 1.14, 1.19, 1.22 and 1.17;

s8, spinning: feeding the wire into a wire laying head for laying wires, clamping the tail of the wire by adopting a V-hole type pinch roll, setting the torque parameter of the pinch roll before laying wires to be 24%, and setting the laying temperature to be 845 ℃;

s9, stelmor line cooling: the wire enters a stelmor line, the initial roller way speed is 0.16m/s, the subsequent roller way is increased progressively at the speed of 0.012m/s, the wire enters a heat-preservation cover at the cooling speed of 2.8 ℃/s, the cover entering temperature is 698 ℃, the cooling speed in the cover is controlled at 0.82 ℃/s to complete the 622 ℃ phase change, the wire is cooled to 515 ℃ and then is discharged from the cover to be controlled to be cooled at the speed of 2.5 ℃/s, the wire rod is collected into a wire rod at the temperature of 270 ℃, then the wire rod is cooled to room temperature, and the wire rod is subjected to surface quality inspection, finishing and sampling, and is packaged to obtain the bearing steel wire rod.

Example 2:

the invention relates to a preferable implementation mode of narrow hardenability bearing steel, which comprises the following components in percentage by mass: c:0.95%, si:0.48%, mn:1.52%, cr: 1.48%, P:0.01%, S:0.008%, ni:0.17%, cu:0.11%, mo:0.01%, al:0.009%, ti:0.009%, nb:0.027%, B:0.0016%, sn:0.011%, sb:0.007%, as:0.011%, pb:0.0015%, ce:0.016%, O:0.0004%, N:0.008% and the balance of Fe and inevitable impurities; sn + Sb + As + Pb =0.0305%.

The production process of the narrow hardenability bearing steel has the specification of phi 20mm, and comprises the following steps:

s1, electric furnace smelting: performing KR desulfurization on steelmaking raw materials containing 78% of molten iron and 22% of scrap steel by weight, performing top blowing with oxygen and smelting in a double-slag method electric furnace to obtain molten steel, wherein a desulfurizer for KR desulfurization in the molten iron pretreatment adopts 3.5kg/t of CaO and 0.34kg/t of fluorite of molten steel, the end point S is controlled to be less than or equal to 0.005%, the carbon content at the end point of tapping is 0.18%, the end point P is controlled to be less than or equal to 0.013%, and the tapping temperature is controlled to be 1672 ℃; during slag-stopping and tapping, 0.71kg/t of molten steel aluminum ingot, 3.7kg/t of molten steel ferromanganese (FeMn82C1.5), 2.9kg/t of molten steel lime and 3.1kg/t of molten steel calcium aluminate are sequentially added in the tapping process;

s2, LF refining: and (2) refining the molten steel in the step (S1) in an LF (ladle furnace) station, adding 1-1.5kg/t of refining slag of the molten steel to prepare white slag, wherein the refining slag comprises the following components in percentage by mass: 47%, mgO:14% SiO ₂ ：4%、Al ₂ O ₃ ：21%、SiC：5%、CaF ₂ ：4%、BaO：4%、Na ₃ AlF ₆ :1%, white slag time is 25min, and smelting time is 25min; by using Al + CaC ₂ Adding a small amount of the combined deoxidization Al + CaC for multiple times according to the mass ratio of 1 ₂ The using amount of the Al-containing alloy is 0.44kg/t molten steel, and the content of residual Al is 0.028%;

the argon flow in the early stage of refining is 230NL/min; low-carbon ferrochrome (FeCr69C1.0), low-carbon ferroboron (FeB16C0.1) and ferroniobium (FeNb 50) are used in the middle stage of refining, the argon flow in the middle stage of refining is 170NL/min, and the argon strength in the argon is kept for component fine adjustment; feeding a cerium wire of 1.4m/t molten steel at a wire feeding speed of 1.2m/s with an argon flow of 100NL/min in the later stage of refining;

s3, VD vacuum: feeding the molten steel in the step S2 into a VD station for VD vacuum degassing treatment, wherein the ultimate vacuum degree is less than or equal to 68Pa, the pressure maintaining time is 25min, the soft argon blowing time is 45min, and feeding a ferrotitanium cored wire of 0.52m/t molten steel at a wire feeding speed of 1.2m/S at 1633 ℃ after vacuum breaking;

s4, continuous casting: casting the molten steel in the step S3 in a 150mm by 150mm continuous casting machine, controlling the superheat degree to be 15-20 ℃, the casting temperature of the molten steel to be 1582 ℃, the electromagnetic stirring parameters of a crystallizer to be 300A and 2Hz, the electromagnetic stirring parameters of the tail end to be 140A and 9Hz, the specific water amount of a secondary cooling area to be 0.22L/kg, the pulling speed to be 1.1m/min, the soft reduction of the tail end to be 10mm, straightening, cutting to length and then timely entering a pit for slow cooling, wherein the temperature of entering the pit for slow cooling is 660 ℃, the time of slow cooling is 63h, and the temperature of leaving the pit is 180 ℃, so as to obtain a casting blank;

s5, heating: the casting blank is heated into a billet by a heat accumulating type steel pushing heating furnace, and the furnace temperature is increased in a stepped way by three sections: the temperature of the preheating section is 870 ℃, the heating rate is 2.4 ℃/min, and the preheating and heat preservation time is 90min; the temperature of the heating section is 1172 ℃, the heat preservation time of the heating section is 95min, the temperature of the soaking section is 1215 ℃, the heat preservation time of the soaking section is 120min, and the temperature difference of the section of the billet is less than or equal to 30 ℃;

s6, high-pressure water descaling: the descaling pressure is controlled to be 20MPa, the speed of a descaling roller way is 0.95m/s, and the striking force of a nozzle is 0.88N/mm ² The steel billet is accurately centered when entering the descaling ring;

s7, rolling: the billet is subjected to wire binding to be made into a wire rod through 6-pass rough rolling, 6-pass intermediate rolling, 6-pass pre-finish rolling, 8-pass finish rolling and 4-pass diameter reduction and sizing treatment, and the initial rolling temperature is controlled to be 1105 ℃; after pre-finish rolling, a water cooling box and a recovery section are adopted for cooling treatment, and the cooling speed of the core part is ensured to be 25-26 ℃/s; the precision rolling temperature is 935 ℃, the pressure of a water cooling box at the first water cooling part after precision rolling is 3.5bar, and the flow rate is 2600lpm; reducing the diameter temperature to be 984 ℃, controlling the pressure of a 1 st section water cooling box at the second water cooling part to be 4.2bar, controlling the flow rate to be 2900lpm, controlling the pressure of a 2 nd section water cooling box at the second water cooling part to be 3.8bar, and controlling the flow rate to be 1900lpm;

the compression ratios of the rough rolling passes are respectively 1.24, 1.29, 1.32, 1.35, 1.27 and 1.25; the rough rolling speed is 0.23m/s, the medium rolling speed is 0.46m/s, the pre-finish rolling speed is 3.9m/s, and the secondary finish rolling speed is 7.8m/s; the compression ratios of the finish rolling passes are respectively 1.12, 1.14, 1.19, 1.23, 1.21 and 1.16;

s8, spinning: feeding the wire rod into a wire laying machine for laying wires, clamping the tail of the wire rod by adopting a V-hole type pinch roll, setting the torque parameter of the pinch roll before laying the wires to be 26%, and setting the laying temperature to be 837 ℃;

s9, stelmor line cooling: the wire enters a stelmor line, the speed of an initial roller way is 0.15m/s, the speed of a subsequent roller way is increased progressively at 0.014m/s, the cooling speed of the wire enters a heat-insulating cover at 4 ℃/s, the cover entering temperature is 690 ℃, the cooling speed in the cover is controlled at 0.76 ℃/s to complete 614 ℃ phase change, the wire is cooled to 510 ℃ and then is discharged from the cover and is controlled to be cooled according to 2 ℃/s, the wire rod is collected into a wire rod at 275 ℃, then the wire rod is air-cooled to room temperature, and the wire rod is subjected to surface quality inspection, finishing, sampling and packaging to obtain the bearing steel wire rod.

Example 3:

the invention relates to a preferable implementation mode of narrow hardenability bearing steel, which comprises the following components in percentage by mass: c:0.94%, si:0.49%, mn:1.55%, cr: 1.47%, P:0.012%, S:0.011%, ni:0.08%, cu:0.07%, mo:0.015%, al:0.009%, ti:0.011%, nb:0.027%, B:0.018%, sn: less than or equal to 0.013%, sb:0.008%, as:0.008%, pb:0.002%, ce:0.019%, O:0.005%, N:0.008% and the balance of Fe and inevitable impurities; sn + Sb + As + Pb =0.031%.

s1, electric furnace smelting: performing KR desulfurization on steelmaking raw materials containing 78% of molten iron and 22% of scrap steel by mass, and smelting the steelmaking raw materials by using oxygen top-blown and double-slag method electric furnaces to obtain molten steel, wherein a desulfurizer for the KR desulfurization in the molten iron pretreatment adopts CaO of 3.4kg/t of the molten steel and fluorite of 0.35kg/t of the molten steel, the end point S is controlled to be less than or equal to 0.005%, the carbon content at the tapping end point is 0.17%, the end point P is controlled to be less than or equal to 0.013%, and the tapping temperature is controlled to 1638 ℃; during slag-stopping and tapping, 0.64kg/t of molten steel aluminum ingot, 4.4kg/t of molten steel ferromanganese (FeMn82C1.5), 3.4kg/t of molten steel lime and 2.6kg/t of molten steel calcium aluminate are sequentially added in the tapping process;

s2, LF refining: and (2) refining the molten steel in the step (S1) in an LF (ladle furnace) station, adding 1.3kg/t of molten steel into the molten steel, and making white slag, wherein the refining slag comprises the following components in percentage by mass: 48%, mgO:11% SiO ₂ ：4%、Al ₂ O ₃ ：20%、SiC：6%、CaF ₂ ：5%、BaO：3%、Na ₃ AlF ₆ :3 percent, the white slag time is 25min, and the smelting time is 45min; by using Al + CaC ₂ Adding a small amount of the Al + CaC into the mixed solution for multiple times according to the mass ratio of 1 ₂ The dosage of the Al-Al alloy is 0.3-0.5kg/t molten steel, and the content of residual Al is 0.02% -0.035%;

the argon flow in the early stage of refining is 245NL/min; low-carbon ferrochrome (FeCr69C1.0), low-carbon ferroboron (FeB16C0.1) and ferroniobium (FeNb 50) are used in the middle stage of refining, the argon flow in the middle stage of refining is 175NL/min, and the argon strength in the argon is kept for component fine adjustment; feeding a cerium wire of 1.3m/t molten steel at a wire feeding speed of 1.6m/s by using argon flow of 92NL/min in the later stage of refining;

s3, VD vacuum: feeding the molten steel in the step S2 into a VD station for VD vacuum degassing treatment, wherein the ultimate vacuum degree is less than or equal to 68Pa, the pressure maintaining time is 25min, the soft argon blowing time is 45min, and feeding a ferrotitanium cored wire of 0.53m/t molten steel at a wire feeding speed of 1.2m/S at 1630 ℃ after vacuum breaking;

s4, continuous casting: casting the molten steel in the step S3 in a 150mm by 150mm continuous casting machine, controlling the superheat degree to be 15-20 ℃, the casting temperature of the molten steel to be 1585 ℃, the electromagnetic stirring parameters of a crystallizer to be 300A and 3Hz, the electromagnetic stirring parameters of the tail end to be 150A and 10Hz, the specific water amount of a secondary cooling area to be 0.2L/kg, the pulling speed to be 1.1m/min, the soft reduction of the tail end to be 12mm, straightening a casting blank by a straightening machine, cutting to length, then timely entering a pit for slow cooling, controlling the temperature of entering the pit for slow cooling to be 650 ℃, controlling the time of slow cooling to be 60h, and controlling the temperature of leaving the pit to be 200 ℃ to obtain the casting blank;

s5, heating: the casting blank is heated into a steel billet in a heat accumulating type steel pushing heating furnace, and the furnace temperature is increased in a stepped mode by three sections: the temperature of the preheating section is 880 ℃, the temperature rising speed is 2.4 ℃/min, and the preheating and heat preservation time is 70min; the temperature of the heating section is 1175 ℃, the heat preservation time of the heating section is 80min, the temperature of the soaking section is 1220 ℃, the heat preservation time of the soaking section is 95min, and the temperature difference of the section of the steel billet is less than or equal to 30 ℃;

s6, high-pressure water descaling: controlling the descaling pressure to be 20MPa, the speed of a descaling roller way to be 1.0m/s and the nozzle striking force to be 0.85N/mm ² The centering is accurate when the billet enters the descaling ring;

s7, rolling: the steel billet is rolled into a wire to be made into a wire rod through 6-pass rough rolling, 6-pass intermediate rolling, 6-pass pre-finish rolling, 8-pass finish rolling and 4-pass sizing reduction treatment, and the initial rolling temperature is controlled to be 1110 ℃; after pre-finish rolling, adopting a water cooling box and a recovery section for cooling treatment to ensure that the cooling speed of a core part is 22 ℃/s-23 ℃/s; the precision rolling temperature is 925 ℃, the pressure of a water cooling box at the first water cooling part after precision rolling is 4.0bar, and the flow rate is 2600lpm; reducing the diameter temperature to 890 ℃, controlling the pressure of a 1 st section water cooling box at a second water cooling part to be 4.0bar and the flow rate to be 3000lpm, controlling the pressure of a 2 nd section water cooling box at the second water cooling part to be 3.8bar and the flow rate to be 1800lpm;

the compression ratios of the rough rolling passes are respectively 1.24, 1.29, 1.34, 1.29, 1.26 and 1.25; the rough rolling speed is 0.22m/s, the medium rolling speed is 0.48m/s, the pre-finish rolling speed is 3.8m/s, and the secondary finish rolling speed is 7.7m/s; the compression ratios of the finish rolling passes are respectively 1.12, 1.15, 1.19, 1.23, 1.20 and 1.16;

s8, spinning: feeding the wire rod into a wire laying machine for laying wires, clamping the tail of the wire rod by adopting a V-hole type pinch roll, setting the torque parameter of the pinch roll before laying wires to be 24%, and setting the laying temperature to be 844 ℃;

s9, stelmor line cooling: the wire enters a stelmor line, the initial roller way speed is 0.16m/s, the subsequent roller way is increased progressively at the speed of 0.018m/s, the wire enters a heat-insulating cover at the cooling speed of 2.7 ℃/s, the cover entering temperature is 704 ℃, the cooling speed in the cover is controlled at 0.78 ℃/s to complete the phase change at the temperature of 625 ℃, the wire is cooled to 512 ℃, then the wire is taken out of the cover and is controlled to be cooled at the temperature of 275 ℃, the wire is collected into a wire rod, then the wire rod is cooled to the room temperature by air, and the surface quality inspection, finishing and sampling are carried out, and the bearing steel wire rod is obtained by packaging.

Example 4:

the invention relates to a preferable implementation mode of narrow hardenability bearing steel, which comprises the following components in percentage by mass: c:0.97%, si:0.48%, mn:1.54%, cr: 1.44%, P:0.012%, S:0.009%, ni:0.18%, cu:0.11%, mo:0.02%, al:0.012%, ti:0.007%, nb:0.024%, B:0.0017%, sn:0.009%, sb:0.007%, as:0.014%, pb:0.002%, ce:0.021%, O:0.004%, N:0.009%, the balance being Fe and inevitable impurities; sn + Sb + As + Pb =0.032%.

s1, electric furnace smelting: performing KR desulfurization on steelmaking raw materials containing 78% of molten iron and 22% of scrap steel by mass, performing top blowing with oxygen and smelting in a double-slag method electric furnace to obtain molten steel, wherein a desulfurizer for KR desulfurization in the molten iron pretreatment adopts 3.5kg/t of CaO and 0.38kg/t of fluorite of molten steel, the end point S is controlled to be less than or equal to 0.005%, the carbon content at the end point of tapping is 0.19%, the end point P is controlled to be less than or equal to 0.013%, and the tapping temperature is controlled to be 1665 ℃; during the slag-stopping and tapping process, 0.68kg/t of aluminum ingot of molten steel, 3.6kg/t of ferromanganese (FeMn82C1.5) of molten steel, 2.8kg/t of lime of molten steel and 2.9kg/t of calcium aluminate of molten steel are added in sequence;

s2, LF refining: and (2) refining the molten steel in the step (S1) in an LF (ladle furnace) station, adding 1.3kg/t of molten steel into the molten steel, and making white slag, wherein the refining slag comprises the following components in percentage by mass: 50%, mgO:13% SiO ₂ ：5%、Al ₂ O ₃ ：19%、SiC：4%、CaF ₂ ：5%、BaO：2%、Na ₃ AlF ₆ :2%, white slag time is 25min, and smelting time is 45min; by using Al + CaC ₂ Adding a small amount of the Al + CaC into the mixed solution for multiple times according to the mass ratio of 1 ₂ The using amount of the Al-containing slag is 0.36kg/t molten steel, and the residual Al content is 0.024%;

the argon flow in the early stage of refining is 240NL/min; low-carbon ferrochrome (FeCr69C1.0), low-carbon ferroboron (FeB16C0.1) and ferroniobium (FeNb 50) are used in the middle stage of refining, the argon flow in the middle stage of refining is 170NL/min, and the argon strength in the argon is kept for component fine adjustment; feeding a cerium wire of 1.4m/t molten steel at a wire feeding speed of 1-2m/s with argon flow of 100NL/min in the later stage of refining;

s3, VD vacuum: feeding the molten steel in the step S2 into a VD station for VD vacuum degassing treatment, wherein the ultimate vacuum degree is less than or equal to 68Pa, the pressure maintaining time is 25min, the soft argon blowing time is 45min, and feeding a ferrotitanium core-spun yarn of 0.52m/t molten steel at a wire feeding speed of 1m/S at 1630 ℃ after the vacuum breaking;

s4, continuous casting: casting the molten steel in the step S3 in a 150mm-150mm continuous casting machine, controlling the superheat degree to be 15-20 ℃, the molten steel casting temperature to be 1602 ℃, the electromagnetic stirring parameters of a crystallizer to be 300A and 2Hz, the electromagnetic stirring parameters of the tail end to be 140A and 9Hz, the specific water amount of a secondary cooling area to be 0.22L/kg, the pulling speed to be 0.9m/min, the soft reduction of the tail end to be 10mm, straightening a casting blank by a straightening machine, cutting to length, then timely entering a pit for slow cooling, controlling the temperature of entering the pit for slow cooling to be 645 ℃, controlling the slow cooling time to be 58h, and controlling the temperature of leaving the pit to be 200 ℃ to obtain the casting blank;

s5, heating: the casting blank is heated into a steel billet in a heat accumulating type steel pushing heating furnace, and the furnace temperature is increased in a stepped mode by three sections: the temperature of the preheating section is 860 ℃, the temperature rising speed is 2.3 ℃/min, and the preheating and heat preservation time is 68min; the temperature of the heating section is 1160 ℃, the heat preservation time of the heating section is 110min, the temperature of the soaking section is 1195 ℃, the heat preservation time of the soaking section is 120min, and the temperature difference of the section of the billet is less than or equal to 30 ℃;

s6, high-pressure water descaling: controlling the descaling pressure to be 22MPa, the speed of a descaling roller way to be 1.0m/s and the nozzle striking force to be 0.9N/mm ² The centering is accurate when the billet enters the descaling ring;

s7, rolling: the steel billet is rolled into a wire to be made into a wire rod through 6-pass rough rolling, 6-pass intermediate rolling, 6-pass pre-finish rolling, 8-pass finish rolling and 4-pass sizing reduction treatment, and the initial rolling temperature is controlled to be 1112 ℃; after pre-finish rolling, a water cooling box and a recovery section are adopted for cooling treatment, and the cooling speed of the core part is ensured to be 22-23 ℃/s; the precision rolling temperature is 952 ℃, the pressure of a water cooling box at the first water cooling part after precision rolling is 4.0bar, and the flow rate is 2600pm; reducing the diameter temperature to 885 ℃, controlling the pressure of a 1 st section water cooling box at the second water cooling part to be 3.5bar, controlling the flow rate to be 3000lpm, controlling the pressure of a 2 nd section water cooling box at the second water cooling part to be 3.8bar, and controlling the flow rate to be 2000lpm;

the compression ratios of the rough rolling passes are respectively 1.25, 1.28, 1.34, 1.29, 1.27 and 1.25; the rough rolling speed is 0.24m/s, the medium rolling speed is 0.5m/s, the pre-finish rolling speed is 4m/s, and the secondary finish rolling speed is 7.5m/s; the compression ratios of the finish rolling passes are 1.12, 1.14, 1.19, 1.22, 1.17 and 1.17 respectively;

s8, spinning: feeding the wire rod into a wire laying machine for laying wires, clamping the tail of the wire rod by adopting a V-hole type pinch roll, setting the torque parameter of the pinch roll before laying wires to be 26%, and setting the laying temperature to be 835 ℃;

s9, stelmor line cooling: the wire enters a stelmor line, the speed of an initial roller way is 0.16m/s, the speed of a subsequent roller way is increased progressively at 0.011m/s, the cooling speed of the wire enters a heat-preservation cover at 4 ℃/s, the cover entering temperature is 688 ℃, the cooling speed in the cover is controlled at 0.85 ℃/s to complete the phase change at 616 ℃, the wire is cooled to 510 ℃ and then is discharged from the cover and is controlled to be cooled at 2.3 ℃/s, the wire rod is collected as a wire rod at the temperature of 267 ℃, then the wire rod is cooled to room temperature by air, and the surface quality inspection, finishing and sampling are carried out, and the bearing steel wire rod is obtained by packaging.

The non-roundness, the size and the allowable deviation of the steel wire rods of the embodiments 1 to 4 conform to the C-grade precision regulation in GB/T14981-2009 standard, and the surface part has other defects harmful to the use, such as cracks, folds, pulling cracks, scabs, inclusions and the like.

Comparative example 1:

the bearing steel comprises the following components in percentage by mass: c:1.02%, si:0.22%, mn:0.31%, cr: 1.42%, P:0.02%, S:0.022%, ni:0.05%, cu:0.15%, mo:0.01%, al:0.02%, ti:0.03%, sn:0.017%, sb:0.026%, as:0.02%, pb:0.014%, O:0.009%, N:0.009%, the balance being Fe and inevitable impurities; sn + Sb + As + Pb =0.077%.

The production process of the bearing steel has the specification of phi 23mm, and the production process is different from the production process of the embodiment 1 in the following steps:

s1, electric furnace smelting: performing KR desulfurization on a steelmaking raw material containing 75% of molten iron and 25% of scrap steel by molten iron pretreatment, performing top-blown oxygen and electric furnace smelting by a double-slag method to obtain molten steel, controlling the end point S to be less than or equal to 0.015%, controlling the carbon content at the end point of tapping to be 0.08%, controlling the end point P to be less than or equal to 0.02%, and adding 4.3kg/t of aluminum ingot of molten steel and 4.5kg/t of lime of molten steel in the tapping process;

s2, LF refining: and (2) refining the molten steel in the step (S1) in an LF (ladle furnace) station, adding refining slag of 2.2kg/t of molten steel to make white slag, wherein the refining slag comprises the following components in percentage by mass: 55% of SiO ₂ ：6.5％、MgO：7.8％、 Al ₂ O ₃ :30.7 percent of the mixture, and 1.5kg/t of molten steel silicon carbide is added for diffusion deoxidation; feeding an aluminum wire of 1.8m/t molten steel at a wire feeding speed of 1.5m/s in the later stage of refining;

s3, LF refining: the treatment of feeding ferrotitanium core-spun yarn is not carried out;

s4, continuous casting: controlling the superheat degree to be 25-35 ℃, the pouring temperature of the molten steel to be 1644 ℃, not adopting tail end electromagnetic stirring, controlling the specific water amount of a secondary cooling zone to be 0.27L/kg, and controlling the drawing speed to be 1.3m/min;

s5, heating: the temperature of the preheating section is 840 ℃, the temperature rise speed is 1.8 ℃/min, and the preheating and heat preservation time is 110min; the temperature of the heating section is 1210 ℃, the heat preservation time of the heating section is 60min, the temperature of the soaking section is 1260 ℃, and the heat preservation time of the soaking section is 75min;

s6, high-pressure water descaling: controlling the descaling pressure to be 18MPa and the speed of a descaling roller way to be 1.2m/s;

s7, rolling: the steel billet is rolled into a wire to be made into a wire rod through 6-pass rough rolling, 6-pass intermediate rolling, 6-pass pre-finish rolling, 8-pass finish rolling and 4-pass sizing reduction treatment, and the initial rolling temperature is controlled to be 1180 ℃; pre-finish rolling and then adopting water-through cooling treatment; the precision rolling temperature is 1010 ℃, the pressure of a water cooling box at the first water cooling part after precision rolling is 2.7bar, and the flow is 2600pm; reducing the diameter temperature to 950 ℃, controlling the pressure of a 2 nd section water cooling box at a second water cooling part to be 2.6bar, and controlling the flow rate to be 1300lpm;

the compression ratios of the rough rolling passes are respectively 1.15, 1.22, 1.26, 1.21, 1.32 and 1.42; the rough rolling speed is 0.35m/s, the medium rolling speed is 0.45m/s, the pre-finish rolling speed is 6m/s, and the secondary finish rolling speed is 8.6m/s; the compression ratios of the finish rolling passes are respectively 1.21, 1.23, 1.24, 1.26, 1.28 and 1.29;

s8, spinning: setting the torque parameter of a pinch roll before spinning to be 18 percent, and setting the spinning temperature to be 905 ℃;

s9, stelmor line cooling: and (3) feeding the wire into a stelmor line, feeding the wire into a heat-preserving cover at the cooling speed of 1.5 ℃/s, controlling the temperature of the cover to be 740 ℃, controlling the cooling speed in the cover to be 1.5 ℃/s to finish the phase change at 662 ℃, cooling to 550 ℃, then taking out the cover for air cooling, and packaging to obtain the bearing steel wire rod.

Comparative example 2:

the bearing steel comprises the following components in percentage by mass: c:1.04%, si:0.21%, mn:0.32%, cr: 1.45%, P:0.015%, S:0.02%, ni:0.08%, cu:0.12%, mo:0.03%, al:0.25%, ti:0.09%, sn:0.022%, sb:0.023%, as:0.024%, pb:0.008%, O:0.009%, N:0.009%, and the balance of Fe and inevitable impurities; sn + Sb + As + Pb =0.077%.

The production process of the bearing steel has the specification of phi 23mm, and the production process is different from the production process of the embodiment 4 in the following steps:

s2, LF refining: the argon flow in the early stage of refining is 105NL/min, the argon flow in the middle stage of refining is 300NL/min, the argon flow in the later stage of refining is 160NL/min, and an aluminum wire of 2m/t molten steel is fed at the wire feeding speed of 1.5m/s in the later stage of refining;

s3, LF refining: feeding ferrotitanium core-spun yarn is not carried out;

s4, continuous casting: controlling the superheat degree to be 25-35 ℃, the pouring temperature of the molten steel to be 1650 ℃, not adopting end electromagnetic stirring, controlling the specific water amount of a secondary cooling zone to be 0.28L/kg, and controlling the drawing speed to be 1.4m/min;

s5, heating: the temperature of the preheating section is 840 ℃, the temperature rise speed is 3.5 ℃/min, and the preheating and heat preservation time is 60min; the temperature of the heating section is 985 ℃, the heat preservation time of the heating section is 120min, the temperature of the soaking section is 1028 ℃, and the heat preservation time of the soaking section is 120min;

s7, rolling: the billet is subjected to 6-pass rough rolling, 6-pass intermediate rolling, 6-pass pre-finish rolling, 8-pass finish rolling and 4-pass diameter reduction and sizing treatment to prepare a wire rod, and the initial rolling temperature is controlled to be 1000 ℃; pre-finish rolling and then adopting water-through cooling treatment; the precision rolling temperature is 935 ℃, the pressure of a water cooling box at the first water cooling part after precision rolling is 2.5bar, and the flow rate is 2500pm; reducing the diameter temperature to 865 ℃, controlling the pressure of a 2 nd section water cooling box at the second water cooling part to be 2.7bar, and controlling the flow to be 1500lpm;

s8, spinning: setting the torque parameter of a pinch roll before spinning to be 12 percent and the spinning temperature to be 820 ℃;

s9, stelmor line cooling: and (3) feeding the wire into a stelmor line, wherein the initial roller way speed is 0.16m/s, the subsequent roller way roller speed is 0.22m/s, the wire enters a heat-preservation cover at the cooling speed of 6.2 ℃/s, the cover-entering temperature is 660 ℃, the in-cover cooling speed is controlled at 1 ℃/s to complete the phase change at 598 ℃, the wire is taken out of the cover for air cooling after being cooled to 492 ℃, and the wire is packaged to obtain the bearing steel wire rod.

The air volume of the fans of examples 1 to 4, comparative examples 1 and 2 is shown in the following table 1, and the air volume of each fan is 20 ten thousand meters ³ /h：

TABLE 1

As can be seen from Table 1, the air volume of the fan is controlled to be 30-60%, the speed of the initial roller way is 0.14-0.17m/s, the follow-up roller way is gradually increased at the speed of 0.01-0.02m/s, the overlap distance of the speed control coils of the roller way is changed, the heat influence between adjacent wire loops is weakened, the corresponding cooling speed is further reduced along with the increase of the speed of the roller way, and the Stelmor wire controlled cooling is achieved.

The slabs of examples 1 to 4, comparative example 1 and comparative example 2 were subjected to a non-metallic inclusion test according to test standard GB/T10561, and the results are shown in Table 2 below:

TABLE 2

As can be seen from Table 2, the contents of S and P are controlled by electric furnace smelting, the steel is strongly deoxidized and large-particle inclusions of Si and Mn are reduced; the LF refining adopts C-A-S slag system with proper alkalinity, fluidity and foamability to match with Al + CaC ₂ The alloy is combined with deoxidation, desulfurization and inclusion adsorption, the yield and hit rate of the alloy are improved by adjusting the components in the middle refining period, the content of residual elements is reduced by feeding cerium wires, the flow of refining argon is controlled, the control of the purity of narrow components, low residual elements and high molten steel is realized, sn + Sb + As + Pb is controlled to be less than or equal to 0.035%, A-type inclusions, B-type inclusions, C-type inclusions and D-type inclusions are controlled to be less than or equal to 1.0 level, and Ds-type inclusions are controlled to be less than or equal to 1.5 level, so that the grain boundary embrittlement caused by solidification segregation and grain boundary segregation during heat treatment of the residual elements in the casting blank process is avoided, the quenching bandwidth is reduced, and the anti-seizure force and fatigue performance of a bearing are improved.

Macrostructure inspection was performed on the cast slabs of examples 1 to 4, comparative example 1 and comparative example 2 in accordance with test standard GB/T226, and the results are shown in Table 3;

TABLE 3

As can be seen from Table 3, the continuous casting of the invention adopts low superheat degree casting at 15-20 ℃, electromagnetic stirring of a crystallizer is matched with electromagnetic stirring at the tail end, the temperature gradient of core liquid from outside to inside and the specific gravity difference between primary crystals and the rest liquid are reduced, the equiaxed crystal rate of the section is increased, the phenomenon that dendritic crystals at the liquid core are bridged is broken under the light pressure at the tail end, the liquation of carbide is improved, the carbon segregation index of a casting blank is reduced to 0.96-1.02, the carbon segregation index of the casting blank is generally loose, ingot type segregation, shrinkage cavity and central segregation are all less than or equal to 1.0 grade, the quenching bandwidth is reduced, and quenching cracks are avoided during heat treatment.

The steel wire rods of examples 1 to 4, comparative example 1 and comparative example 2 were subjected to tensile test in accordance with test standard GB/T228.1, grain size test in accordance with GB/T6394, microstructure test in accordance with GB/T18254, carbide reticulation, carbide banding and carbide liquation rating, and hardenability test of steel in accordance with GB/T225, the results of which are shown in Table 4;

TABLE 4

As can be seen from Table 4, the heating furnace temperature of the invention is increased in three steps, element segregation is further reduced by high-temperature diffusion, carbide liquation is improved or eliminated, decarburization is avoided, overburning and billet quality deterioration caused by overhigh temperature are avoided, reduction of high-temperature diffusion effect or generation of eutectic carbide which is difficult to eliminate caused by overlow temperature is avoided, controlled rolling and controlled cooling adopts a water cooling box and a recovery section to ensure that the core cooling speed is 19 ℃/s-27 ℃/s, the finish rolling temperature is 915-960 ℃, the sizing temperature is 870-900 ℃, low-temperature rolling is ensured to be close to a two-phase region, namely austenite + cementite rolling, rapid cooling inhibits growth of ferrite, the compression ratio of each rough rolling pass is 1.24-1.35, the compression ratio of each finish rolling pass is 1.12-1.25, the rolling speed is controlled to uniformly press down to promote carbide dispersion, banded carbide is improved, the cooling speed after rolling is controlled to improve grain boundary fineness uniformity, the pearlite nucleation rate is reduced, the transformation incubation period is increased, the C curve is shifted to the right, the critical cooling speed is reduced, and the quenching bandwidth is reduced.

Clamping by a pinch roll, low-temperature spinning avoids uneven structure crystal grains or large group, the overlap distance of a control coil of the speed of a roller way is changed, the heat influence between adjacent wire loops is weakened, the Stelmor wire cooling speed enters a heat-preservation cover at 2-5 ℃/s, the cover entering temperature is 675-714 ℃, the cooling speed in the cover is controlled at 0.7-0.9 ℃/s to complete the phase change at 610-635 ℃, the cover is cooled to be less than or equal to 525 ℃, the separation of the net carbon carbide on the original austenite crystal boundary is inhibited, the net carbide is prevented from being separated out due to the low cooling speed, the supercooled abnormal structure caused by the overhigh cooling speed is avoided, the austenite crystal grain size in the wire rod structure is more than or equal to 8 grade, the carbide net grade is less than or equal to 1.0 grade, the carbide strip grade is less than or equal to 1.5 grade, the carbide liquid precipitation grade is less than or equal to 0.5 grade, the fine and uniform austenite crystal grain size, the low grade net, the strip-shaped and liquid precipitation carbide effectively stabilizes the tail end hardenability, reduces the quenching bandwidth, and reduces the deformation and cracking tendency of steel.

The above-listed detailed description is only a specific description of a possible embodiment of the present invention, and they are not intended to limit the scope of the present invention, and equivalent embodiments or modifications made without departing from the technical spirit of the present invention should be included in the scope of the present invention.

Claims

1. The narrow hardenability bearing steel is characterized by comprising the following components in percentage by mass: c:0.94-0.97%, si:0.46-0.5%, mn:1.52-1.57%, cr: 1.43-1.49%, P: less than or equal to 0.015 percent, S: less than or equal to 0.015 percent, ni: less than or equal to 0.22 percent, cu: less than or equal to 0.22 percent, mo: less than or equal to 0.03%, al:0.008-0.014%, ti:0.005-0.015%, nb:0.021-0.028%, B:0.001-0.0025%, sn: less than or equal to 0.015 percent, sb: less than or equal to 0.01 percent, as: less than or equal to 0.015 percent, pb: less than or equal to 0.002%, ce:0.015 to 0.025%, O: less than or equal to 0.0006 percent, N:0.005-0.012%, and the balance of Fe and inevitable impurities.

2. The narrow hardenability bearing steel according to claim 1, wherein the composition of the bearing steel is Sn + Sb + As + Pb < 0.035%, the austenite grain size in the wire rod structure of the bearing steel is greater than or equal to 8 grade, the carbide net grade is less than or equal to 1.0 grade, the carbide belt grade is less than or equal to 1.5 grade, the carbide liquid precipitation grade is less than or equal to 0.5 grade, and the hardenability zone of the bearing steel is controlled at 1.5-2.5HRC.

3. A process for producing a narrow hardenability bearing steel according to claim 1 or 2, comprising the steps of electric furnace smelting, LF refining, VD vacuum, continuous casting, heating, high pressure water descaling, rolling, spinning and stelmor line cooling;

in the electric furnace smelting process, the end point S is controlled to be less than or equal to 0.005 percent, the end point P is controlled to be less than or equal to 0.013 percent, and aluminum ingots, ferromanganese, lime and calcium aluminate are added in the tapping process;

in the LF refining process, refining slag is added to produce white slag; by using Al + CaC ₂ Joint deoxidation; extract of Chinese medicinal materialsAdjusting components in the middle of refining; feeding a cerium wire in the later stage of refining;

after the VD vacuum process is broken, feeding ferrotitanium cored wires;

in the continuous casting process, the superheat degree is controlled to be 15-20 ℃, and crystallizer electromagnetic stirring and tail end electromagnetic stirring are adopted;

the furnace temperature of the heating procedure is increased in three stages in a stepped manner, and the temperature difference of the section of the billet is controlled to be less than or equal to 30 ℃;

in the rolling process, the initial rolling temperature is controlled to be 1090-1120 ℃, the cooling speed of the core part after pre-finish rolling is 19 ℃/s-27 ℃/s, and the finish rolling temperature is 915-960 ℃;

the spinning temperature is controlled to be 830-850 ℃ in the spinning procedure;

the stelmor line cooling process controls the cooling speed of the wire rod in the cover to be controlled at 0.7-0.9 ℃/s to complete the phase change.

4. The production process of the narrow hardenability bearing steel according to claim 3, wherein CaO and fluorite are adopted in the electric furnace smelting process for KR desulfurization, the carbon content at the end point of tapping is 0.14-0.22%, and 0.6-0.8kg/t of molten steel of aluminum ingots, 3-5kg/t of ferromanganese alloy, 2.7-3.6kg/t of molten steel of lime and 2.5-3.2kg/t of molten steel of calcium aluminate are sequentially added in the tapping process.

5. The production process of the narrow hardenability bearing steel according to claim 3, wherein the refining slag comprises the following components by mass percent: 46-50%, mgO:10-14% of SiO ₂ ：2-5%、Al ₂ O ₃ ：17-22%、SiC：4-8%、CaF ₂ ：3-5%、BaO：2-5%、Na ₃ AlF ₆ :1-3%, the white slag time is more than or equal to 20min, and the smelting time is more than or equal to 40min; al + CaC ₂ The dosage of the combined deoxidation is 0.3-0.5kg/t molten steel according to the mass ratio of 1.

6. The production process of the narrow hardenability bearing steel according to claim 3, wherein the argon flow at the early stage of LF refining is 220-250NL/min; low-carbon ferrochromium, low-carbon ferroboron and ferroniobium are used in the middle stage of LF refining, and the flow rate of argon gas in the middle stage of LF refining is 150-180NL/min; feeding a cerium wire of molten steel at a flow rate of 1.2-1.5m/t at a wire feeding speed of 1-2m/s with an argon flow rate of 60-110NL/min in the later stage of LF refining; in the VD vacuum process, the ferrotitanium core-spun yarn of molten steel of 0.5-0.6m/t is fed at the wire feeding speed of 1-1.5m/s at 1620-1645 ℃ after being broken.

7. The production process of the narrow hardenability bearing steel according to claim 3, wherein the casting temperature of molten steel in the continuous casting process is 1565-1610 ℃, the electromagnetic stirring parameters of a crystallizer are 200-300A and 2-3Hz, the electromagnetic stirring parameters of a tail end are 130-150A and 9-10Hz, the specific water amount of a secondary cooling zone is 0.19-0.24L/kg, the pulling rate is 0.85-1.2m/min, the terminal pressing amount is 8-12 mm, the carbon segregation index is 0.96-1.02, the pit entering slow cooling temperature is greater than or equal to 640 ℃, the slow cooling time is greater than or equal to 57h, and the pit outlet temperature is less than or equal to 210 ℃.

8. The production process of the narrow hardenability bearing steel according to claim 3, wherein the furnace temperature of the heating process is increased in three stages: the temperature of the preheating section is 850-880 ℃, the heating rate is 2.0-2.5 ℃/min, the preheating and heat preservation time is 50-100min, the temperature of the heating section is 1150-1200 ℃, the heat preservation time of the heating section is 70-120min, the temperature of the soaking section is 1190-1230 ℃, and the heat preservation time of the soaking section is 80-150min; the descaling pressure of the high-pressure water descaling procedure is more than or equal to 19MPa, the speed of a descaling roller way is less than or equal to 1.1m/s, and the impact force of a nozzle is more than or equal to 0.85N/mm ² 。

9. The production process of the narrow hardenability bearing steel according to claim 3, wherein the rolling process comprises 6-pass rough rolling, 6-pass intermediate rolling, 6-pass pre-finish rolling, 8-pass finish rolling and 4-pass reducing and sizing treatment, the compression ratio of each pass of rough rolling is 1.24-1.35, a water cooling box and a recovery section are adopted for cooling after the pre-finish rolling, the compression ratio of each pass of finish rolling is 1.12-1.25, the rough rolling speed is less than or equal to 0.25m/s, the intermediate rolling speed is less than or equal to 0.5m/s, the pre-finish rolling speed is less than or equal to 4.2m/s, the secondary finish rolling speed is less than or equal to 8.1m/s, the spinning process is clamped by V-shaped pinch rolls, and the torque parameter of pinch rolls before spinning is set to be 22-28%.

10. The production process of the narrow hardenability bearing steel according to claim 3, wherein the stelmor line cooling process controls the air volume of a fan to be 30-60%, the speed of an initial roller way is 0.14-0.17m/s, the speed of a subsequent roller way is increased progressively at 0.01-0.02m/s, the cooling speed of a wire rod enters a heat-preserving cover at 2-5 ℃/s, the temperature of the wire rod entering the heat-preserving cover is 675-714 ℃, and the wire rod is cooled to be less than or equal to 525 ℃ and then is taken out of the heat-preserving cover and the cooling is controlled according to 1.5-3 ℃/s.