CN113337693B - Heat treatment method for reducing grade of large-size bearing steel net-shaped carbide - Google Patents
Heat treatment method for reducing grade of large-size bearing steel net-shaped carbide Download PDFInfo
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- C21D1/18—Hardening; Quenching with or without subsequent tempering
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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- C21D6/00—Heat treatment of ferrous alloys
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
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Abstract
The invention relates to a heat treatment method for reducing the grade of large-size bearing steel net-shaped carbide, and belongs to the technical field of bearing steel heat treatment. The invention provides a heat treatment method for reducing the level of the net-shaped carbide of large-size bearing steel, which aims to solve the problem that the net-shaped carbide of the large-size bearing steel is too high due to no online cooling control means, and comprises the steps of bearing steel quenching treatment, water cooling treatment, isothermal spheroidizing annealing treatment, furnace cooling treatment, wherein the specific quenching temperature is 930+/-10 ℃, water cooling is carried out for 2-3 min after quenching and heat preservation are completed, and the steel temperature is controlled to 600-650 ℃ after water cooling; the isothermal spheroidizing annealing treatment is carried out by heating to 800+/-10 ℃ for 13 hours, cooling to 700+/-10 ℃ for 5 hours. The invention can effectively control the distribution form of the netlike carbide of the large-specification bearing steel core, the grade of the netlike carbide of the large-specification bearing steel is less than or equal to 2.5, and the product requirement of the cold-working bearing steel for the large-specification rolling body is met.
Description
Technical Field
The invention belongs to the technical field of heat treatment of bearing steel, and particularly relates to a heat treatment method for reducing the grade of large-size bearing steel net-shaped carbide.
Background
The cold-working bearing steel for large-sized rolling bodies of large-sized high-end equipment bearings such as high-power wind power and shield machines adopts the production process of secondary forging forming and spheroidizing annealing of forging materials, and has the outstanding problems of long production period, low efficiency, serious internal netlike carbide and the like. The structural uniformity of high-carbon chromium bearing steel, especially the carbide state, has important influence on the performance and service life of the bearing rolling bodies. The main bearing of the domestic high-end equipment adopts imported products in 100 percent, and the domestic process of the main bearing is mainly limited by the quality of the domestic high-quality bearing steel material.
The large-section bar and the small-section bar have great difference in the rolling production process. The small-section bearing steel with the diameter of the rolled material smaller than 40mm can utilize online control cooling to inhibit the network carbide, so that the grade of the network carbide is not more than 2.0 grade; and the large-section bearing steel with the diameter of the rolled material being larger than 40mm does not have an on-line cooling control means, and the net carbide in the rolled material can reach 3.0 grade or even higher. The size of the main bearing rolling body of the large shield machine is above 90mm, the rolled material is directly subjected to heat treatment without secondary processing, the net-shaped carbide after the heat treatment is required to be less than 2.5 grades, and the lower the grade is, the better the quality is. Conventional heat treatment can only slightly improve the state of the network carbide, and cannot fundamentally eliminate the influence of the network carbide.
Disclosure of Invention
The invention provides a heat treatment method for reducing the mesh carbide grade of large-size bearing steel, which aims to solve the problem that the mesh carbide grade of the large-size bearing steel is too high because no online cooling control means are available.
The technical scheme of the invention is as follows:
a heat treatment method for reducing the level of the net-shaped carbide of large-size bearing steel comprises the steps of bearing steel quenching treatment, water cooling treatment, isothermal spheroidizing annealing treatment and furnace cooling treatment, wherein the quenching temperature is 930+/-10 ℃, water cooling is carried out for 2-3 min after quenching heat preservation is finished, and the steel temperature is controlled to be 600-650 ℃ after water cooling; the isothermal spheroidizing annealing treatment firstly increases the temperature to 800+/-10 ℃ for 13 hours, and then decreases the temperature to 700+/-10 ℃ for 5 hours.
Further, the section diameter of the large-size bearing steel is not less than 40mm.
Further, the quenching treatment heat preservation time is 8 hours.
Further, the temperature reduction speed from 800+/-10 ℃ to 700+/-10 ℃ in the isothermal spheroidizing annealing treatment process is 10-15 ℃/h.
Further, the furnace cooling treatment is to cool to 600 ℃ at a cooling speed of 20 ℃/h and then air-cool.
Further, the bearing steel comprises the following chemical components in percentage by weight: c: 0.96-0.97%, si:0.21 to 0.24 percent of Mn:0.28 to 0.29 percent, P:0.007 to 0.014%, S:0.001 to 0.006 percent, als: 0.009-0.013%, alt: 0.011-0.015%, cr:1.43%, ni:0.02%, mo: 0.001-0.006%, V: 0.002-0.003%, ti:0.0010% of Fe and the balance of unavoidable impurities.
The invention has the beneficial effects that:
the heat treatment method for the large-size bearing steel can effectively control the distribution form of the network carbide of the large-size bearing steel, is applicable to rolling or forging bearing steel products, and solves the problem that the network carbide grade of the large-section bearing steel is too high due to no online cooling control means.
The invention solves the problem that the conventional heat treatment can only slightly improve the state of the network carbide and can not fundamentally eliminate the influence of the network carbide. The isothermal spheroidizing annealing is adopted, the isothermal annealing process has short period, is more uniform and consistent along the section structure, has simple operation and convenient control compared with the repeated spheroidizing annealing,
the grade of 1/2R and the grade of the meshed carbide in the core are less than or equal to 2.5, the hardness can be stably controlled at 180-190 HBW, the microstructure is 2.0, and the microstructure is uniform and stable. The maximum specification of the bearing steel suitable for the heat treatment method provided by the invention can reach 150mm, and the product requirement of the cold-working bearing steel for large-scale rolling bodies of large-scale high-end equipment bearings such as high-power wind power and shield machines can be met.
Drawings
FIG. 1 is a network carbide distribution diagram of a phi 90mm bearing steel stock in the hot rolled state of example 1;
FIG. 2 is a network carbide distribution diagram of a phi 110mm bearing steel feedstock in the hot rolled state of example 2;
FIG. 3 is a network carbide distribution diagram of a 150mm diameter bearing steel feedstock in the hot rolled state of example 3;
FIG. 4 is a graph of the network carbide distribution at the edge of the 90mm diameter bearing steel after heat treatment of example 1;
FIG. 5 is a graph of network carbide distribution at the 1/2R position of a 90mm phi bearing steel after heat treatment of example 1;
FIG. 6 is a graph showing the distribution of network carbides at the position of the steel core of a 90mm phi bearing after heat treatment in example 1;
FIG. 7 is a graph of network carbide distribution at the edge of a phi 110mm bearing steel after heat treatment of example 2;
FIG. 8 is a graph of network carbide distribution at the 1/2R position of a phi 110mm bearing steel after heat treatment of example 2;
FIG. 9 is a graph showing the distribution of network carbides at the position of the steel core of a phi 110mm bearing after heat treatment in example 2;
FIG. 10 is a graph of network carbide distribution at the edge of 150mm bearing steel after heat treatment in example 3;
FIG. 11 is a graph of network carbide distribution at the 1/2R position of 150mm bearing steel after heat treatment in example 3;
FIG. 12 is a graph showing the distribution of network carbides at the position of the steel core of a 150mm bearing after heat treatment in example 3;
FIG. 13 is a graph showing the distribution of network carbides at 5mm of the edge of 150mm bearing steel after heat treatment in example 3;
FIG. 14 is a graph showing the distribution of network carbides at 10mm of the edge of 150mm bearing steel after heat treatment in example 3;
FIG. 15 is a graph showing the distribution of network carbides at 15mm from the edge of 150mm bearing steel after heat treatment in example 3;
FIG. 16 is a graph showing the distribution of network carbides at 20mm of the edge of 150mm bearing steel after heat treatment in example 3;
FIG. 17 is a graph showing the distribution of network carbides at 25mm of the edge of 150mm bearing steel after heat treatment in example 3;
FIG. 18 is a graph showing the distribution of network carbides at 30mm from the edge of 150mm bearing steel after heat treatment in example 3;
FIG. 19 is a graph showing the distribution of network carbides at 40mm from the edge of 150mm bearing steel after heat treatment in example 3;
FIG. 20 is a graph showing the distribution of network carbides at 45mm of the edge of 150mm bearing steel after heat treatment in example 3;
FIG. 21 is a graph showing the distribution of network carbides at 50mm of the edge of 150mm bearing steel after heat treatment in example 3;
FIG. 22 is a graph showing the distribution of network carbides at 55mm of the edge of 150mm bearing steel after heat treatment in example 3;
FIG. 23 is a graph showing the distribution of network carbides at 65mm of the edge of 150mm bearing steel after heat treatment in example 3;
FIG. 24 is a graph showing the distribution of network carbides at 70mm of the edge of 150mm bearing steel after heat treatment in example 3;
FIG. 25 is a graph showing the distribution of network carbides at 75mm of the edge of 150mm bearing steel after heat treatment in example 3;
FIG. 26 is a photograph of a microstructure of a portion of the edge of a 150mm diameter bearing steel section after heat treatment in example 3;
FIG. 27 is a photograph of a microstructure of a 1/2R position of a cross-section of 150mm bearing steel after heat treatment in example 3;
FIG. 28 is a photograph of microstructure of a core portion of a 150mm diameter bearing steel section after heat treatment in example 3.
Detailed Description
The following embodiments are used for further illustrating the technical scheme of the present invention, but not limited thereto, and all modifications and equivalents of the technical scheme of the present invention are included in the scope of the present invention without departing from the spirit and scope of the technical scheme of the present invention. The process equipment or apparatus not specifically noted in the following examples are all conventional equipment or apparatus in the art, and the raw materials and the like used in the examples of the present invention are commercially available unless otherwise specified; unless specifically indicated, the technical means used in the embodiments of the present invention are conventional means well known to those skilled in the art.
Example 1
The embodiment provides a heat treatment method for large-size bearing steel with a section diameter of 90 mm.
The raw materials are bearing steel hot rolled materials with the section diameter of 90mm, and the chemical components of the bearing steel comprise the following components in percentage by weight: c:0.97%, si:0.24%, mn:0.28%, P:0.009%, S:0.002%, als:0.011%, alt:0.013%, cr:1.43%, ni:0.02%, mo:0.001%, V:0.002%, ti:0.0010% of Fe and the balance of unavoidable impurities.
Because the high-carbon chromium bearing steel bar with a large section is difficult to effectively control and cool in the production process, more serious reticular carbide exists at the section of the high-carbon chromium bearing steel bar.
When the high-carbon chromium bearing steel is slowly cooled, the defects are more due to irregular atomic arrangement at the grain boundary, and the high-carbon chromium bearing steel is a rapid channel for element diffusion. Therefore, carbide-forming elements such as C, cr, mn and the like have a relatively sufficient time to diffuse into the grain boundaries and accumulate and grow at the grain boundaries, and Cr, mn elements are substituted for part of Fe atoms to form (Fe. Mn) 3 C、(Fe·Mn) 3 C、Cr 7 C 3 、M 23 C 6 And the like, which are like bones and form network carbides along the prior austenite grain boundaries. With the increase of the cooling speed, on one hand, the diffusion rate of C, cr and Mn elements is reduced, and on the other hand, austenite rapidly passes through a carbide precipitated phase region and stays for a short time, so that the diffusion time of the austenite in a high-temperature region is shortened. Therefore, the contents of C, cr and Mn elements at the grain boundary are reduced, thereby limiting the precipitation conditions of secondary carbides and effectively inhibiting the quantity and thickness of network carbides.
"quenching" is a heat treatment process that ultimately determines the performance of the bearing steel. The quenching heating temperature will affect the solid solution amount of carbon in the austenite, and thus the content of the retained austenite and the morphology of the martensite.
Spheroidizing annealing is annealing performed to spheroidize carbide in steel to obtain a structure of spherical or granular carbide uniformly distributed on a ferrite matrix to obtain a spheroidized structure resembling granular pearlite, thereby reducing hardness and improving machinability.
The heat treatment method comprises the steps of quenching treatment, water cooling treatment, isothermal spheroidizing annealing treatment and furnace cooling treatment of the bearing steel hot rolled material.
The quenching temperature of the bearing steel hot rolled material is 930 ℃, and the heat preservation time is 8 hours, so that carbide is further dissolved and diffused. After quenching and heat preservation are completed, water cooling is carried out for 2-3 min, so that the steel can quickly pass through the temperature range of 700-850 ℃, the precipitation of carbide is strongly inhibited, and the proportion of cementite in pearlite is increased. Meanwhile, the temperature of the bar after water cooling is controlled between 600 ℃ and 650 ℃, so that a bainite or martensite structure is avoided being generated, and the formation of bearing steel net-shaped carbide and strip-shaped carbide is reduced.
The bearing steel has extremely high hardness after quenching and is difficult to cut and process. And controlling the hardness of the bearing steel through isothermal spheroidizing annealing after quenching. Firstly, the temperature is raised to 800 ℃ for heat preservation for 13 hours, so that the temperature difference of the section between the central part and the surface of the large-specification bearing steel in the heat treatment process is solved, the disappearance of lamellar pearlite can be ensured, part of carbide which is not completely dissolved in austenite can be reserved as a spheroidizing core, and the normal spheroidizing structure of coarser granular carbide is finally formed.
Cooling to 700 ℃ with a cooling speed of 10-15 ℃/h, and preserving heat for 5h, wherein the transformation of the structure is completed, and the structure of spherical or granular carbide uniformly distributed on the ferrite matrix is obtained. Cooling to 600 ℃ along with the furnace at a cooling rate of 20 ℃/h, and then air cooling.
Example 2
The embodiment provides a heat treatment method for large-size bearing steel with a section diameter of 110 mm.
The raw materials are bearing steel hot rolled materials with the section diameter of 110mm, and the chemical components of the bearing steel comprise the following components in percentage by weight: c:0.96%, si:0.23%, mn:0.29%, P:0.007%, S:0.006%, als:0.013%, alt:0.015%, cr:1.43%, ni:0.02%, mo:0.006%, V:0.002%, ti:0.0010% of Fe and the balance of unavoidable impurities.
The heat treatment method comprises the steps of quenching treatment, water cooling treatment, isothermal spheroidizing annealing treatment and furnace cooling treatment of the bearing steel hot rolled material.
The quenching temperature of the bearing steel hot rolled material is 920 ℃, and the heat preservation time is 8 hours, so that carbide is further dissolved and diffused. And (3) water cooling for 2-3 min after quenching and heat preservation are finished, and controlling the temperature of the bar material between 600 and 650 ℃ after water cooling. The temperature is raised to 790 ℃ and kept for 13 hours, and the mixture is cooled to 690 ℃ along with the furnace at the cooling speed of 10-15 ℃/h and kept for 5 hours, thus finishing the transformation of the structure and obtaining the structure of spherical or granular carbide evenly distributed on the ferrite matrix. Cooling to 600 ℃ along with the furnace at a cooling rate of 20 ℃/h, and then air cooling.
Example 3
The embodiment provides a heat treatment method for large-size bearing steel with a section diameter of 150 mm.
The raw materials are bearing steel hot rolled materials with the section diameter of 150mm, and the chemical components of the bearing steel comprise the following components in percentage by weight: c:0.97%, si:0.21%, mn:0.28%, P:0.014%, S:0.001%, als:0.009%, alt:0.011%, cr:1.43%, ni:0.02%, mo:0.004%, V:0.003%, ti:0.0010% of Fe and the balance of unavoidable impurities.
The heat treatment method comprises the steps of quenching treatment, water cooling treatment, isothermal spheroidizing annealing treatment and furnace cooling treatment of the bearing steel hot rolled material.
The quenching temperature of the bearing steel hot rolled material is 940 ℃, and the heat preservation time is 8 hours, so that carbide is further dissolved and diffused. After quenching and heat preservation are completed, water cooling is carried out for 2-3 min, the temperature of the bar is controlled between 600-650 ℃, the bar is heated to 810 ℃ and is preserved for 13h, and the bar is cooled to 710 ℃ along with a furnace at a cooling speed of 10-15 ℃/h and is preserved for 5h, thus obtaining the structure of spherical or granular carbide uniformly distributed on a ferrite matrix. Cooling to 600 ℃ along with the furnace at a cooling rate of 20 ℃/h, and then air cooling.
The distribution of network carbides of the bearing steel raw material in the hot rolled state of examples 1-3 was examined according to GB/T18254-2016, and as shown in FIGS. 1-3, the network carbide grades of the core portions of the hot rolled bearing steel raw materials of phi 90mm, phi 110mm and phi 150mm were all greater than grade 3.
The distribution of the steel mesh carbides of the bearings after heat treatment of examples 1 to 3 was examined according to GB/T18254-2016, and the results are shown in FIGS. 4 to 12 and Table 1.
TABLE 1
As can be seen from the comparison of the distribution situation of the network carbide shown in fig. 4-12 and the network carbide grade shown in table 1, the heat treatment method provided by the invention can effectively control the distribution form of the network carbide in the steel core of the large-size bearing and reduce the network carbide grade of the large-size bearing.
The full-section net-like carbide test was performed every 5mm on the phi 150mm bearing steel after the heat treatment of example 3, and the results are shown in fig. 13-25 and table 2.
TABLE 2
From the distribution of network carbides shown in FIGS. 13 to 25 and the network carbide grades shown in Table 2, it can be seen that network carbides begin to appear at the 1/2R radius, with the network carbide grades being 1-2 grades and the network carbide grade being up to 2.5 grades at the center.
The hardness of the bearing steel after heat treatment of examples 1 to 3 was examined, and the results are shown in Table 3.
TABLE 3 Table 3
As shown in the data of Table 3, the hardness of the bearing steel after heat treatment can be stably controlled to be 180-190 HBW, the hardness standard 179-207 HBW of the GB/T18254 standard after spheroidizing annealing is met, and the problems that the bearing steel after quenching has high hardness and is difficult to cut and process are solved.
The microstructure of the phi 150mm bearing steel section edge, 1/2R and core after heat treatment of example 3 was observed, and as shown in FIGS. 26 to 28, the microstructure of the section edge, 1/2R and core were all granular pearlite, and the rating was 2.0 grade. Therefore, the bearing steel microstructure obtained by the heat treatment process is uniform and stable.
The maximum specification of the bearing steel suitable for the heat treatment method provided by the invention can reach 150mm, and the product requirement of the cold-working bearing steel for large-scale rolling bodies of large-scale high-end equipment bearings such as high-power wind power and shield machines can be met.
Example 4
The embodiment provides a heat treatment method for large-size bearing steel with a section diameter of 100 mm.
The raw materials are bearing steel hot rolled materials with the section diameter of 100mm, and the chemical components of the bearing steel comprise the following components in percentage by weight: c:0.96%, si:0.23%, mn:0.29%, P:0.007%, S:0.006%, als:0.013%, alt:0.015%, cr:1.43%, ni:0.02%, mo:0.006%, V:0.002%, ti:0.0010% of Fe and the balance of unavoidable impurities.
The heat treatment method comprises the steps of quenching treatment, water cooling treatment, isothermal spheroidizing annealing treatment and furnace cooling treatment of the bearing steel hot rolled material.
The quenching temperature of the bearing steel hot rolled material is 935 ℃, and the heat preservation time is 8 hours, so that carbide is further dissolved and diffused. And (3) after quenching heat preservation is finished, water cooling is carried out for 2-3 min, the temperature of the bar is controlled between 600-650 ℃, the bar is heated to 805 ℃ for heat preservation for 13h, and the bar is cooled to 705 ℃ along with a furnace at a cooling speed of 10-15 ℃/h for heat preservation for 5h, so that the structure transformation is finished, and the structure of spherical or granular carbide uniformly distributed on a ferrite matrix is obtained. Cooling to 600 ℃ along with the furnace at a cooling rate of 20 ℃/h, and then air cooling.
Claims (2)
1. The heat treatment method for reducing the level of the large-size bearing steel net-shaped carbide is characterized by comprising the steps of bearing steel quenching treatment, water cooling treatment, isothermal spheroidizing annealing treatment and furnace cooling treatment, wherein the quenching temperature is 930+/-10 ℃, the quenching treatment heat preservation time is 8 hours, the water cooling is carried out for 2-3 min after the quenching heat preservation is finished, and the steel temperature is controlled to be 600-650 ℃ after the water cooling; the isothermal spheroidizing annealing treatment firstly increases the temperature to 800+/-10 ℃ for 13 hours, then decreases the temperature to 700+/-10 ℃ for 5 hours, the diameter of the section of the large-specification bearing steel is not less than 40mm, and the cooling speed from 800+/-10 ℃ to 700+/-10 ℃ in the isothermal spheroidizing annealing treatment process is 10-15 ℃/h;
the bearing steel comprises the following chemical components in percentage by weight: c: 0.96-0.97%, si:0.21 to 0.24 percent of Mn:0.28 to 0.29 percent, P:0.007 to 0.014%, S:0.001 to 0.006 percent, als: 0.009-0.013%, alt: 0.011-0.015%, cr:1.43%, ni:0.02%, mo: 0.001-0.006%, V: 0.002-0.003%, ti:0.0010% of Fe and the balance of unavoidable impurities.
2. The heat treatment method for reducing the grade of the large-sized bearing steel net-shaped carbide according to claim 1, wherein the furnace-following cooling treatment is air cooling after cooling to 600 ℃ at a cooling rate of 20 ℃/h.
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| CN108486468A (en) * | 2018-05-02 | 2018-09-04 | 本钢板材股份有限公司 | A kind of high-carbon low-alloy bearing steel ring and its heat-treatment technology method |
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