CN116815055A - Low-cost long-life bearing steel and production method and heat treatment method thereof - Google Patents
Low-cost long-life bearing steel and production method and heat treatment method thereof Download PDFInfo
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- 229910052782 aluminium Inorganic materials 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
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- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
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- 229910000859 α-Fe Inorganic materials 0.000 description 1
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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Abstract
The invention provides low-cost long-life bearing steel, a production method and a heat treatment method thereof, which comprise the following components: 0.95 to 1.05 percent of C, 0.32 to 0.42 percent of Si, 0.38 to 0.58 percent of Mn, 1.7 to 1.9 percent of Cr, 0.4 to 0.7 percent of Mo, 0.05 to 0.07 percent of Nb, 0.015 to 0.025 percent of V, less than or equal to 0.0015 percent of Ti, 0.015 to 0.025 percent of Alt, less than or equal to 0.010 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.0015 percent of T.O, less than or equal to 0.0065 percent of N, and the balance of Fe and other unavoidable impurities; compared with the prior art, the product produced by the components, the production method and the heat treatment method has high wear resistance, high impact toughness and high fatigue resistance.
Description
Technical Field
The invention belongs to the technical field of bearing steel, and particularly relates to low-cost long-life bearing steel, a production method thereof and a heat treatment method thereof.
Background
The bearing is an important and key basic part in the equipment manufacturing industry, and the bearing steel is widely applied to the fields of important equipment, wind power generation, high-speed rail motor cars, aerospace and other emerging industries by virtue of the advantages of good fatigue resistance, wear resistance, cold and hot workability and the like.
In recent years, with the rapid development of industries such as automobiles and high-end manufacturing, the requirements on bearings are increasing. Not only high strength, good plasticity and ultra-long service life are required, but also high and uniform surface layer strength and low and uniform core hardness are required after heat treatment, and the heat-treated steel can bear load and alternating load; meanwhile, the paint has good corrosion resistance, and does not rust or corrode in the atmosphere.
The patent with publication number CN114015927A published in 2 month 8 of 2022 is named as providing a rare earth-containing high-carbon chromium bearing steel and a preparation method thereof, wherein the disclosed rare earth-containing high-carbon chromium bearing steel comprises, by weight, 0.95-1.05% of C, 0.15-0.30% of Si, 0.25-0.40% of Mn, less than or equal to 0.010% of P, less than or equal to 0.010% of S, 1.50-1.75% of C, 0.015-0.035% of RE, 3-5ppm of O, and the balance of iron and unavoidable impurities, and is prepared by the steps of blast furnace iron making, molten iron pretreatment, converter steelmaking, LF refining and RH refining and continuous casting, wherein rare earth alloy is added in two parts after converter tapping and RH breaking respectively, and can obtain better effect after being matched with an electroslag remelting process, and the contact fatigue life L10 is more than or equal to 6.1×10 7 And twice. However, rare earth elements are required to be added, so that the cost is high, and the method is not suitable for mass industrial production.
The patent with publication number CN114318173A published in 2/8/2022 discloses a bearing steel and a production method thereof, wherein the bearing steel comprises the following components in percentage by weight: 0.50 to 0.60% carbon, 0.30 to 0.40% silicon, 2.20 to 2.50% chromium, 1.00 to 1.20% nickel, 0.80 to 1.00% cobalt, 1.10 to 1.30% tungsten, 0.010 to 0.025% lanthanum, 0.010 to 0.025% yttrium, trace amounts to 0.015% sulfur, 0.005% or less titanium, 0.0015% or less oxygen, the balance being Fe and other unavoidable impurities. The invention fully utilizes the impurity modification effect and corrosion resistance effect of La and Y, and simultaneously ensures that the corrosion resistance coefficient I value is more than or equal to 2.40, the corrosion resistance of the steel reaches more than 2.5 times of that of general bearing steel GCr15, and the yield strength Rp0.2 is more than or equal to 1400MPa at 500 ℃. The rare earth elements La and Y are required to be added, so that the cost is high, and the method is not suitable for mass industrial production.
Disclosure of Invention
The invention aims to provide low-cost long-life bearing steel, a production method and a heat treatment method thereof, and the hardness of the obtained product is 61-63HR and room temperature impact power KV through composition and process design and heat treatment 2 The austenite grain size of the steel is more than or equal to 10.0 level, the level of the reticular carbide of the core is controlled within 1.5 level, and the steel has high wear resistance, high impact toughness and high fatigue resistance.
The specific technical scheme of the invention is as follows:
the bearing steel with low cost and long service life comprises the following components in percentage by mass:
0.95 to 1.05 percent of C, 0.32 to 0.42 percent of Si, 0.38 to 0.58 percent of Mn, 1.7 to 1.9 percent of Cr, 0.4 to 0.7 percent of Mo, 0.05 to 0.07 percent of Nb, 0.015 to 0.025 percent of V, less than or equal to 0.0015 percent of Ti, 0.015 to 0.025 percent of Alt, less than or equal to 0.010 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.0015 percent of T.O, less than or equal to 0.0065 percent of N, and the balance of Fe and other unavoidable impurities.
The components of the low-cost long-life bearing steel meet the following conditions: the A value is more than or equal to 1.40 and less than or equal to 1.70; a value = [ C ] + [ Mo ];
the components of the low-cost long-life bearing steel meet the following conditions: b value is more than or equal to 3.5 and less than or equal to 6.0; the B value= ([ V ] + [ Nb ])/[ Alt ].
The invention provides a production method of low-cost long-life bearing steel, which comprises the following process flows: electric furnace smelting, LF furnace refining, RH vacuum refining, 380X 450 billet continuous casting, 250 billet rolling, flaw detection, grinding, excellent rod heating, controlled rolling and cooling, round steel finished product packaging and warehousing.
The electric furnace smelting comprises the following steps: the end point C of the electric furnace is controlled to be 0.15-0.25%, and P is less than or equal to 0.010%; adding refining slag and lime when tapping 1/5-1/4 molten steel, adding deoxidizer and alloy when tapping 1/4-1/3, and uniformly throwing a proper amount of aluminum particles to the steel slag surface according to the slag discharging amount after tapping.
Refining in the LF furnace: argon is blown to the bottom of the whole ladle, and the argon flow is based on the condition that molten steel does not splash the ladle; adding premelted refining slag and lime for slagging, wherein the alkalinity is R3-6, the white slag time is more than or equal to 20 minutes, and adding alloy to adjust the Si, mn, cr, mo, nb content before and during refining according to the analysis result of the components before entering an LF furnace.
The RH vacuum degassing: in the early stage of vacuum, if the vacuum degree is less than or equal to 100 Pa, the vacuum holding time is more than or equal to 10 minutes, and if the vacuum degree is less than or equal to 200 Pa, the vacuum holding time is more than or equal to 15 minutes; the holding time of the vacuum later period is more than or equal to 10 minutes. According to the result of the vacuum early-stage component analysis, if component adjustment is required in the middle stage, a vacuum holding time of 5 minutes or more is required after the adjustment. And (5) carrying out soft argon blowing treatment before the station is out, wherein the soft argon blowing time is more than or equal to 20min.
The 380X 450 billet continuous casting: because the contents of alloy elements such as Cr, mo and the like are higher, in order to obtain the bearing steel with high fatigue life, a bloom continuous casting and cogging two-fire forming process is adopted, grains are refined, and the uniformity of a structure is ensured. The whole-process protection casting is adopted, a protection sleeve and argon seal are adopted between a ladle and a tundish, the tundish is protected by using a molten steel covering agent and argon blowing, a submerged nozzle is adopted between the tundish and a crystallizer, and secondary cooling, end electromagnetic stirring and light and heavy reduction are combined to eliminate center segregation of a casting blank, wherein the primary cooling water pressure is 5.0-9.0 bar, the secondary cooling water pressure is 9.0-15.0 bar, the light and heavy reduction is less than or equal to 35mm, and the liquid level, the drawing speed and the superheat degree are stable in the casting process, so that a defect-free casting blank is obtained.
And rolling the 250 square billets: the soaking section temperature of the heating furnace is controlled at 1200-1300 ℃, the total heating time is controlled at 250-350 min, the initial rolling temperature is controlled at 1100+/-50 ℃, the stack cooling temperature after rolling is more than or equal to 400 ℃, the surface and end part polishing treatment is carried out on the 250-direction after rolling, good surface quality is provided for subsequent excellent rod rolling, and the surface decarburization sensitivity of excellent rods is reduced.
Heating by a excellent heating furnace: according to the invention, excellent bar rolling with phi of 41-80mm can be realized, in order to enable C, cr, mo and V elements to be in solid solution in austenite, the heating temperature is controlled to be 1050-1150 ℃, the heating is performed slowly, the heating rate is not more than 20 ℃/min, cracking in the heating process is prevented, the soaking time is more than 35min, the Cr, mo and V elements are ensured to be in full solid solution, and meanwhile, in order to prevent decarburization sensitivity, the heating temperature cannot be more than 1150 ℃.
The rolling and cooling control method comprises the following steps: the heated casting blank is descaled by high-pressure water and then enters a continuous rolling unit for rolling, the initial rolling temperature is 950-980 ℃, the final rolling temperature is 750-800 ℃, the lower final rolling temperature ensures that more dispersed and precipitated nucleation points and fine crystals are formed, and the rapid water cooling after rolling is adopted, and the highest reddening temperature is less than or equal to 680 ℃, so that the retained austenite in the structure after phase transformation is uniformly distributed.
The invention provides a heat treatment method of bearing steel with low cost and long service life, which comprises the following process flows: spheroidizing annealing, blanking, forging, isothermal quenching treatment and tempering, surface treatment and bearing.
The spheroidizing annealing: heating to 780-820 ℃ and preserving heat for 8-10 hours, cooling to 680-720 ℃ at the speed of 1.5 ℃/min-2.5 ℃/min and preserving heat for 4-6 hours, cooling to 650 ℃ along with a furnace, discharging from the furnace and air cooling to room temperature to form a spheroidizing annealing structure of the high-carbon bearing steel, wherein the spheroidizing grade is 2-4.
Because the segregation of the core part of the bearing steel exists, the phenomena of overheating or overburning and the like of the core part of the round steel are easier to occur than the surface during heating, the high-temperature plasticity is influenced, and the large-specification bearing steel is more obvious, so that the high-temperature plasticity of the core part is ensured by adopting an induction heating method, the forging heating temperature is less than or equal to 1180 ℃, the defects of microscopic holes and the like generated by overburning are prevented, meanwhile, crystal grains are refined by adopting multidirectional forging, and carbide is changed from a thick fishbone shape into a tiny three-dimensional net shape in dispersion distribution, so that the fatigue life and the wear resistance of the round steel are obviously improved;
the isothermal quenching treatment comprises the following steps: in order to obtain high contact fatigue life, high residual austenite content is obtained as much as possible, and the initiation and the extension of fatigue cracks are restrained, so an isothermal quenching process is adopted, meanwhile, the content of alloy elements such as Cr, mo, V and the like is considered to be higher, in order to obtain uniform carbide, the fatigue strength of a final finished product is ensured, and a double quenching process is adopted, specifically: heating to 870+ -10deg.C, and maintaining for 40-60min, preferably 50min; then cooling to 210+/-10 ℃ and preserving heat in a salt bath furnace for 170-185min, preferably 180min, and then air-cooling; heating to 830+ -10deg.C, maintaining for 40-60min, preferably 50min, cooling to 180deg.C+ -10deg.C, maintaining in salt bath furnace for 140-155min, preferably 150min, and air cooling to room temperature. The specific process is shown in figure 1, the microstructure after quenching is bainite, martensite, carbide and residual austenite, and the content of the residual austenite is more than or equal to 20%;
the tempering: the temperature is 180+/-10 ℃, the temperature is kept for 120+/-10 min, the air cooling is carried out to the room temperature, the microstructure is tempered bainite, tempered martensite, carbide and retained austenite, and the retained austenite content is more than or equal to 20 percent.
After heat treatment, the austenite grain size of the product is more than or equal to 10.0 level, and the level of the core network carbide is controlled within 1.5 level; product hardness is 61-63HR, room temperature impact power KV 2 Not less than 20J, yield strength not less than 1500MPa, tensile strength R m Not less than 2300MPa, and the elongation after break A is not less than 12%; the contact fatigue life L10 is more than or equal to 5.1X10 7 And the weight loss after 30min of abrasion at room temperature is less than 0.005g, and the weight loss after 30min of abrasion at 350 ℃ is less than 0.008g.
The design idea of the invention is as follows:
c: the C element is necessary for obtaining high strength and hardness. In order to obtain the high strength required for bearing steel, the C content is required to be more than 0.95%, but too high C content causes the aggregation phenomenon of carbide to be increased, the heat strength performance of the steel is obviously reduced, meanwhile, the brittleness is increased, and the fatigue resistance and the processing performance of the steel are deteriorated, so that the C content is preferably controlled to be 0.95% -1.05%.
Si: si is a main deoxidizing element in steel, and as a solid solution hardening element contributes to improvement of strength, and can significantly improve deformation resistance of steel. However, too high Si content will decrease the plasticity and toughness of the steel, and increase the activity of C, promote decarburization and graphitization tendency of the steel during rolling and forging heating, and make smelting difficult and inclusion formation easy, deteriorating the fatigue resistance of the steel. Therefore, the Si content is controlled to be 0.32-0.42%.
Mn: mn is an effective element for deoxidation and desulfurization, and can also improve the hardenability and strength of steel. When the content is less than 0.3%, the above-mentioned effect is hardly achieved. However, when the Mn content is too high and quenched steel is tempered, mn and P have strong tendency of grain boundary co-segregation, so that tempering brittleness is promoted, and toughness of the steel is deteriorated. Thus controlling Mn content to be 0.38% -0.58%.
Cr: cr can effectively improve the hardenability of steel and has the function of secondary hardening, is one of main elements for bearing steel to obtain high strength, and improves the strength, hardness and wear resistance without embrittling the steel; at the same time, cr can reduce the activity of C, reduce the decarburization tendency of the steel surface during heating, rolling and heat treatment, and obtain high fatigue resistance by utilization, but the too high content can deteriorate the toughness and cold workability of the steel, so the Cr content is controlled to be 1.70-1.90%.
Mo: mo is a stronger carbide forming element, can effectively improve the hardenability of steel, improve the tempering resistance or tempering stability of steel, and is combined with carbon to form stable small-size carbide after heat treatment, so that the hardness of the steel is improved and certain wear resistance is maintained. However, excessive Mo tends to develop ferrite and lower the martensitic transformation point, making the steel difficult to harden. Therefore, the content of Mo to be added should be 0.40 to 0.70%.
Nb: nb element can obviously refine grains, and the invention aims to improve the network carbide of the core part of the large-size bearing steel, and Nb is added to refine the size of the network carbide, and meanwhile, the toughness of the steel is improved, and the low-temperature performance of the steel is improved. Meanwhile, the crystal grains are finer, so that the corrosion resistance can be improved. The range of Nb can be controlled between 0.05% and 0.07%.
V: the V element can obviously refine grains, and the grain refinement not only can improve the toughness of the steel, but also can improve the low-temperature performance of the steel. Meanwhile, the crystal grains are finer, so that the corrosion resistance can be improved. The V content is too high, the cost is high, and the V range can be controlled to be 0.015-0.025%.
Ti: titanium is easy to form titanium inclusion with nitrogen in high-carbon steel, and the fatigue life of bearing steel after being made into a bearing is reduced, so that the content of Ti is strictly controlled, and the Ti is required to be less than or equal to 0.0015 percent.
Alt: alt is a stronger deoxidizing element, improves the oxidation resistance of steel, and refines austenite grains. In addition, alt element and nitrogen are combined to form AlN, so that the pinning effect of dislocation is reduced, the blue embrittlement tendency is remarkably reduced, and meanwhile, the impact toughness is improved, but the Alt content is too high, coarse carbonitride is formed to cause the brittle inclusion content to be too high, and the fatigue life is influenced. The Alt content is controlled to be 0.015-0.025%.
S and P: impurity elements such as S, P are aggregated at grain boundaries, so that the delayed fracture resistance is greatly reduced. The P element can form micro segregation when molten steel is solidified, and then the P element is biased to a grain boundary when heated at an austenitizing temperature, so that the brittleness of the steel is obviously increased, and the delayed fracture sensitivity of the steel is increased; the S element forms Mn S inclusion and segregation in grain boundary, so that the delayed fracture sensitivity of the steel is increased, and therefore, the content of P, S is controlled to be less than or equal to 0.010 percent of P and less than or equal to 0.010 percent of S.
T.o and N: oxygen forms various oxide inclusions in the steel. Under the action of stress, stress concentration is easy to occur at the oxide inclusions, so that microcrack initiation is caused, and the mechanical properties, particularly toughness and fatigue resistance, of the steel are deteriorated. Therefore, in the metallurgical production, measures are taken to reduce the content of the T.O as much as possible and control the content of the T.O to be less than or equal to 0.0015 percent; n precipitates Fe4N in steel, the diffusion speed is low, the steel generates timeliness, meanwhile, the cold processing performance of the steel is reduced, and the N is controlled to be less than or equal to 0.0065%.
In order to meet the strength and the toughness of the large-size bearing steel, the invention carries out optimization design (1) on chemical components again to properly improve the contents of Cr and Mo elements, on one hand, improves the hardenability, can be used for producing the large-size bearing steel, and simultaneously ensures that the strength chemical components of the large-size bearing steel need to meet the requirement that A= [ C ] + [ Mo ] -1.70 is more than or equal to 1.40; (2) Mo element is added, the carbide of Mo is utilized to improve the heat resistance of the bearing steel, good red hardness is obtained, in addition, the Mo element can also reduce the hydrogen amount invaded by the steel surface, inhibit the generation of corrosion pits and improve the corrosion resistance; (3) In order to improve the non-uniformity of the network carbide of the large-size bearing steel, the Nb content is increased to 0.05-0.07%, grains are refined, so that the precipitation of secondary cementite is ensured to have more nucleation points, so that the secondary cementite is more dispersed and precipitated and is discontinuous, and the network carbide grade of the core part of the bearing steel is controlled within 1.5 grade; (4) The V element and Alt element are added in proper amount to refine the size of the prior austenite crystal grain, so that the strength is improved, the toughness is improved, and the high contact fatigue strength is obtained, in addition, the corrosion resistance of the fine crystal grain is improved, and the chemical composition is required to meet the requirement that B= ([ V ] + [ Nb ])/[ Alt ] < 6.0.
Compared with the prior art, the product produced by the components, the production method and the heat treatment method has the hardness of 61-63HR, the room temperature impact energy KV2 is more than or equal to 20J, the austenite grain size of steel is more than or equal to 10.0 level, the core netlike carbide level is controlled within 1.5 level, and the product has high wear resistance, high impact toughness, high fatigue resistance and contact fatigue life L 10 Can reach 5.1X10 times 7 The wear-resistant rubber has good wear resistance, the weight loss after 30min of room temperature wear is less than 0.005g, and the weight loss after 30min of 350 ℃ high temperature wear is less than 0.008g.
Drawings
FIG. 1 is a schematic diagram of a dual quenching process according to the present invention.
Detailed Description
Example 1 to example 5
The bearing steel with low cost and long service life comprises the following components in percentage by mass: as shown in table 1, the balance not shown in table 1 is Fe and unavoidable impurities.
Comparative example 1-comparative example 3
The bearing steel with low cost and long service life comprises the following components in percentage by mass: as shown in table 1, the balance not shown in table 1 is Fe and unavoidable impurities.
Table 1 chemical composition (wt%) of each of examples and comparative examples
| Case (B) | C | Si | Mn | Cr | Mo | Nb | V | Ti | Alt | P | S | T.O | N | A value | B value |
| Example 1 | 0.95 | 0.42 | 0.58 | 1.80 | 0.65 | 0.050 | 0.015 | 0.0009 | 0.015 | 0.005 | 0.005 | 0.0009 | 0.0045 | 1.60 | 4.33 |
| Example 2 | 1.00 | 0.35 | 0.38 | 1.70 | 0.70 | 0.063 | 0.018 | 0.0008 | 0.020 | 0.006 | 0.006 | 0.0008 | 0.0038 | 1.70 | 4.05 |
| Example 3 | 1.05 | 0.36 | 0.55 | 1.82 | 0.40 | 0.062 | 0.015 | 0.0007 | 0.020 | 0.006 | 0.005 | 0.0010 | 0.0043 | 1.45 | 3.85 |
| Example 4 | 1.05 | 0.32 | 0.45 | 1.90 | 0.58 | 0.070 | 0.020 | 0.0007 | 0.025 | 0.008 | 0.005 | 0.0010 | 0.0050 | 1.63 | 3.60 |
| Example 5 | 1.03 | 0.40 | 0.53 | 1.85 | 0.63 | 0.058 | 0.025 | 0.0008 | 0.018 | 0.010 | 0.006 | 0.0009 | 0.0046 | 1.66 | 4.61 |
| Comparative example 1 | 0.95 | 0.38 | 0.38 | 1.78 | 0.40 | 0.068 | 0.025 | 0.0006 | 0.023 | 0.007 | 0.007 | 0.0010 | 0.0043 | 1.35 | 4.04 |
| Comparative example 2 | 1.02 | 0.39 | 0.47 | 1.75 | 0.59 | 0.056 | 0.020 | 0.0010 | 0.023 | 0.007 | 0.006 | 0.0011 | 0.0045 | 1.61 | 3.30 |
| Comparative example 3 | 0.95 | 0.42 | 0.58 | 1.80 | 0.65 | 0.050 | 0.015 | 0.0009 | 0.015 | 0.005 | 0.005 | 0.0009 | 0.0045 | 1.60 | 4.33 |
The production method of the low-cost long-life bearing steel in the above examples and comparative examples comprises the following process flows: electric furnace smelting, LF furnace refining, RH vacuum refining, 380X 450 billet continuous casting, 250 billet rolling, flaw detection, grinding, excellent rod heating, controlled rolling and cooling, round steel finished product packaging and warehousing.
The electric furnace smelting comprises the following steps: the end point C of the electric furnace is controlled to be 0.15-0.25%, and P is less than or equal to 0.010%; adding refining slag and lime when tapping 1/5-1/4 molten steel, adding deoxidizer and alloy when tapping 1/4-1/3, and uniformly throwing a proper amount of aluminum particles to the steel slag surface according to the slag discharging amount after tapping.
Refining in the LF furnace: argon is blown to the bottom of the whole ladle, and the argon flow is based on the condition that molten steel does not splash the ladle; adding premelted refining slag and lime for slagging, wherein the alkalinity is R3-6, the white slag time is more than or equal to 20 minutes, and adding alloy to adjust the Si, mn, cr, mo, nb content before and during refining according to the analysis result of the components before entering an LF furnace.
The RH vacuum degassing: in the early stage of vacuum, if the vacuum degree is less than or equal to 100 Pa, the vacuum holding time is more than or equal to 10 minutes, and if the vacuum degree is less than or equal to 200 Pa, the vacuum holding time is more than or equal to 15 minutes; the holding time of the vacuum later period is more than or equal to 10 minutes. According to the result of the vacuum early-stage component analysis, if component adjustment is required in the middle stage, a vacuum holding time of 5 minutes or more is required after the adjustment. And (5) carrying out soft argon blowing treatment before the station is out, wherein the soft argon blowing time is more than or equal to 20min.
The 380X 450 billet continuous casting: because the contents of alloy elements such as Cr, mo and the like are higher, in order to obtain the bearing steel with high fatigue life, a bloom continuous casting and cogging two-fire forming process is adopted, grains are refined, and the uniformity of a structure is ensured. The whole-process protection casting is adopted, a protection sleeve and argon seal are adopted between a ladle and a tundish, the tundish is protected by using a molten steel covering agent and argon blowing, a submerged nozzle is adopted between the tundish and a crystallizer, and secondary cooling, end electromagnetic stirring and light and heavy reduction are combined to eliminate center segregation of a casting blank, wherein the primary cooling water pressure is 5.0-9.0 bar, the secondary cooling water pressure is 9.0-15.0 bar, the light and heavy reduction is less than or equal to 35mm, and the liquid level, the drawing speed and the superheat degree are stable in the casting process, so that a defect-free casting blank is obtained.
And rolling the 250 square billets: the soaking section temperature of the heating furnace is controlled at 1200-1300 ℃, the total heating time is controlled at 250-350 min, the initial rolling temperature is controlled at 1100+/-50 ℃, the stack cooling temperature after rolling is more than or equal to 400 ℃, the surface and end part polishing treatment is carried out on the 250-direction after rolling, good surface quality is provided for subsequent excellent rod rolling, and the surface decarburization sensitivity of excellent rods is reduced.
Heating by a excellent heating furnace: according to the invention, excellent bar rolling with phi of 41-80mm can be realized, in order to enable C, cr, mo and V elements to be in solid solution in austenite, the heating temperature is controlled to be 1050-1150 ℃, the heating is performed slowly, the heating rate is not more than 20 ℃/min, cracking in the heating process is prevented, the soaking time is more than 35min, the Cr, mo and V elements are ensured to be in full solid solution, and meanwhile, in order to prevent decarburization sensitivity, the heating temperature cannot be more than 1150 ℃.
The rolling and cooling control method comprises the following steps: the heated casting blank is descaled by high-pressure water and then enters a continuous rolling unit for rolling, the initial rolling temperature is 950-980 ℃, the final rolling temperature is 750-800 ℃, the lower final rolling temperature ensures that more dispersed and precipitated nucleation points and fine crystals are formed, and the rapid water cooling after rolling is adopted, and the highest reddening temperature is less than or equal to 680 ℃, so that the retained austenite in the structure after phase transformation is uniformly distributed.
The specific production process parameters of each example and comparative example are shown in table 2.
Table 2 specific production process parameters for each of the examples and comparative examples
The bearing steel with low cost and long service life produced by the method is subjected to heat treatment, and the process flow is as follows: spheroidizing annealing, blanking, forging, isothermal quenching treatment and tempering, surface treatment, and bearing control as follows:
1) Spheroidizing annealing process: heat preservation is carried out for 8-10 hours at 780-820 ℃, then cooling is carried out to 680-720 ℃ at the speed of 1.5 ℃/min-2.5 ℃/min for 4-6 hours, cooling is carried out along with furnace cooling to 650 ℃, and then furnace discharging air cooling is carried out to room temperature, thus forming the spheroidizing annealing structure of the high-carbon bearing steel, and the spheroidizing grade is 2-4. 2) Because the segregation of the core part of the bearing steel exists, the phenomena of overheating or overburning and the like of the core part of the round steel are easier to occur than the surface during heating, the high-temperature plasticity is influenced, and the large-specification bearing steel is more obvious, so that the high-temperature plasticity of the core part is ensured by adopting an induction heating method, the forging heating temperature is less than or equal to 1180 ℃, the defects of microscopic holes and the like generated by overburning are prevented, meanwhile, crystal grains are refined by adopting multidirectional forging, and carbide is changed from a thick fishbone shape into a tiny three-dimensional net shape in dispersion distribution, so that the fatigue life and the wear resistance of the round steel are obviously improved; 3) Isothermal quenching: in order to obtain high contact fatigue life, high residual austenite content is obtained as much as possible, and the initiation and the expansion of fatigue cracks are restrained, so an isothermal quenching process is adopted, meanwhile, the content of alloy elements such as Cr, mo, V and the like is considered to be higher, in order to obtain uniform carbide, the fatigue strength of a final finished product is ensured, a double quenching process is adopted, and the temperature is firstly kept for 40-60min, preferably 50min, after heating to 870+/-10 ℃; then cooling to 210+/-10 ℃ and preserving heat in a salt bath furnace for 170-185min, preferably 180min, and then air-cooling; heating to 830+/-10 ℃ and preserving heat for 40-60min, preferably 50min, then cooling to 180+/-10 ℃ and preserving heat for 140-155min, preferably 150min, and then cooling to room temperature in an air-cooling manner, wherein the specific process is shown in figure 1, the microstructure after quenching is bainite+martensite+carbide+retained austenite, the retained austenite content is more than or equal to 20%, 4) tempering is carried out, the temperature is 180-200 ℃, the heat is preserved for 120+/-10 min, air-cooling is carried out, the microstructure is tempered bainite+tempered martensite+carbide+retained austenite, and the retained austenite content is more than or equal to 20%.
The heat treatment process parameters of each example and comparative example are shown in table 3.
Table 3 heat treatment parameters for each of the examples and comparative examples
The test sample is subjected to wear resistance test after heat treatment, the wear resistance test is carried out on an MM200 wear testing machine, and the test conditions are as follows: the load was 50N, the linear velocity was 0.40m/s, the friction was dried for 30 minutes, and then the amount of material loss was measured with a balance. And (3) carrying out quality abrasion assessment on the abrasion resistance test result of the material of the MM-200 abrasion tester by a weighing method according to GB/T12444-2006 standard of a test ring-test block sliding abrasion test of a metal material abrasion test method, wherein compared with a comparative example, the weight loss of the material is less than 0.005g after 30min of abrasion at room temperature and less than 0.008g after 30min of abrasion at a high temperature of 350 ℃. Performance tests were performed according to the GB/T228.1-2010 metallic material room temperature tensile test method, and the results are shown in table 4.
TABLE 4 Properties after Heat treatment of the inventive examples
Comparative example 1 is that the A value is not within the invention, the hardenability is insufficient, and the production of large-size bearing steel cannot be satisfied; comparative example 2 is that the B value is not within the present invention, and the fatigue strength and wear resistance do not meet the design requirements. Comparative example 2 the heat treatment process meeting the requirements of the present invention was used with a lower retained austenite content. Comparative example 3 is a composition of example 1 with a conventional quench tempering process (i.e., without salt bath furnace incubation) where the microstructure is predominantly martensitic and the fatigue life is significantly lower than in the examples.
Claims (10)
1. The low-cost long-life bearing steel is characterized by comprising the following components in percentage by mass:
0.95 to 1.05 percent of C, 0.32 to 0.42 percent of Si, 0.38 to 0.58 percent of Mn, 1.7 to 1.9 percent of Cr, 0.4 to 0.7 percent of Mo, 0.05 to 0.07 percent of Nb, 0.015 to 0.025 percent of V, less than or equal to 0.0015 percent of Ti, 0.015 to 0.025 percent of Alt, less than or equal to 0.010 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.0015 percent of T.O, less than or equal to 0.0065 percent of N, and the balance of Fe and other unavoidable impurities.
2. The low cost long life bearing steel of claim 1, wherein the composition of said low cost long life bearing steel meets: the A value is more than or equal to 1.40 and less than or equal to 1.70; a value= [ C ] + [ Mo ].
3. The low cost long life bearing steel according to claim 1 or 2, wherein the composition of the low cost long life bearing steel satisfies: b value is more than or equal to 3.5 and less than or equal to 6.0; the B value= ([ V ] + [ Nb ])/[ Alt ].
4. A method for producing a low cost long life bearing steel according to any of claims 1-3, characterized in that the method comprises the following process steps: electric furnace smelting, LF furnace refining, RH vacuum refining, 380X 450 billet continuous casting, 250 billet rolling, flaw detection, grinding, excellent rod heating, controlled rolling and cooling, round steel finished product packaging and warehousing.
5. The method according to claim 4, wherein the 380 x 450 billet is continuously cast: the whole-process protection casting is adopted, a protection sleeve and argon seal are adopted between a ladle and a tundish, the tundish is protected by using a molten steel covering agent and argon blowing, a submerged nozzle is adopted between the tundish and a crystallizer, and a mode of secondary cooling, end electromagnetic stirring and light-weight pressing are adopted, wherein the pressure of primary cooling water is 5.0-9.0 bar, the pressure of secondary cooling water is 9.0-15.0 bar, and the light-weight pressing weight is less than or equal to 35mm.
6. The method of claim 4, wherein the 250 billets are rolled: the soaking section temperature of the heating furnace is controlled at 1200-1300 ℃, the total heating time is controlled at 250-350 min, the initial rolling temperature is controlled at 1100+/-50 ℃, and the stack cooling temperature after rolling is more than or equal to 400 ℃.
7. The method of claim 4, wherein the excellent heater heats: the heating temperature is controlled at 1050-1150 ℃ and the soaking time is more than 35min; the rolling and cooling control method comprises the following steps: the initial rolling temperature is 950-980 ℃, the final rolling temperature is 750-800 ℃, and the maximum reddening temperature is less than or equal to 680 ℃.
8. A method for heat treatment of low cost long life bearing steel according to any of claims 1-3, wherein the heat treatment process flow is: spheroidizing annealing, blanking, forging, isothermal quenching treatment and tempering, surface treatment and bearing.
9. The heat treatment method according to claim 8, wherein the spheroidizing annealing: heating to 780-820 ℃, preserving heat for 8-10 hours, cooling to 680-720 ℃ and preserving heat for 4-6 hours, cooling to 650 ℃ along with the furnace, discharging from the furnace, and cooling to room temperature by air cooling.
10. The heat treatment method according to claim 8 or 9, wherein the austempering treatment: adopts a double quenching process, which comprises the following steps: heating to 870+/-10 ℃ for heat preservation for 40-60min, then cooling to 210+/-10 ℃ for heat preservation for 170-185min in a salt bath furnace, and then air cooling; heating to 830+ -10deg.C, maintaining for 40-60min, cooling to 180deg.C+ -10deg.C, maintaining in salt bath furnace for 140-155min, and air cooling to room temperature.
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