Rare earth modified bainite bearing steel and preparation method thereof

Abstract

The invention discloses rare earth modified bainite bearing steel which comprises the following chemical components in percentage by weight (wt%): 0.9 to 1.2 percent of C, 0.15 to 0.35 percent of Si, 0.25 to 0.45 percent of Mn, 1.3 to 1.5 percent of Cr, 0.35 to 0.70 percent of Mo, 0.003 to 0.015 percent of La + Ce, 0.005 to 0.015 percent of Sc and the balance of Fe. The invention further provides a method for preparing the rare earth modified bainite bearing steel. The method comprises the steps that S1, the alloy raw materials composed of all the chemical components are prepared; s2, the main raw materials are placed in an electric arc furnace for smelting treatment, rare earth raw materials are added in the smelting treatment process for modification treatment, and to-be-cast liquid is obtained; discharging the to-be-cast liquid out of the furnace and pouring to obtain a cast ingot; and S3, the cast ingot is heated to 840-920 DEG C for austenitizing, the cast ingot is subjected to hot rolling to form a bar, the bar is subjected to heat preservation treatment and then subjected to oil cooling to 200-300 DEG C for isothermal quenching, and the rare earth modified bainite bearing steel is obtained. Rare earth elements with a specific content are added into a bainite structure, so that rare earth compound reinforced superfine bainite is formed in the bearing steel, and the wear resistance of the bearing steel is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and in particular to a rare earth modified bainite bearing steel and a preparation method thereof. Background Art

[0002] Bearing steel is a key material in the manufacture of rolling bearings. It must possess both excellent wear resistance and high resistance to contact fatigue. The quality of bearing steel is directly related to the service life of the entire equipment. Traditional bearing steel often uses a tempered martensite structure, but its high hardness and insufficient toughness can easily lead to brittle wear. Bainitic steel, due to its combination of high strength and toughness, has become an alternative. Due to its excellent strength, toughness, fatigue resistance, and cost-effectiveness, it is widely used in bearing steel components in mechanical equipment, rail transportation, wind power equipment, and other fields.

[0003] Traditional bainitic steels primarily optimize their performance by adjusting their carbon content and adding alloying elements such as chromium (Cr), molybdenum (Mo), and manganese (Mn). However, these technologies still face the following bottlenecks: Conventional bainitic steels tend to form coarse grains during heat treatment, and their carbide distribution is uneven, leading to internal stress concentration and reduced fatigue life and wear resistance. Under high loads or poor lubrication, conventional bainitic steels are prone to adhesive wear or spalling, making them difficult to meet the demands of extreme operating conditions. Improving performance through the addition of large amounts of precious metals (such as nickel and cobalt) or complex heat treatment processes significantly increases manufacturing costs, and the narrow process window makes large-scale production difficult. Furthermore, the wear resistance of single bainitic steels is still limited by microstructure coarsening and crack propagation caused by inclusions. In recent years, the application of rare earth elements in steel has attracted considerable attention. Rare earth elements have the function of purifying grain boundaries and refining grains in steel, but existing research on the synergistic improvement of wear performance by the application of rare earth elements in bainitic microstructures is limited. Therefore, research on rare earth-modified bainitic bearing steels and methods for optimizing their wear performance is necessary. Summary of the Invention

[0004] This invention discloses a rare-earth-modified bainitic bearing steel and its preparation method. By adding specific rare-earth elements (La, Ce, and Sc) to the bainite structure, a rare-earth compound-reinforced ultrafine bainite / retained austenite composite structure is formed in the bearing steel, thereby improving the bearing steel's wear resistance. To achieve this objective, the present invention provides the following technical solutions.

[0005] The first object of the present invention is to provide a rare earth modified bainitic bearing steel, characterized in that, calculated by weight percentage (wt%), the chemical composition of the bearing steel is as follows: C: 0.9~1.2%, Si: 0.15~0.35%, Mn: 0.25~0.45%, Cr: 1.3~1.5%, Mo: 0.35~0.70%, La+Ce: 0.003~0.015%, Sc: 0.005~0.015%, and the rest is Fe.

[0006] The second object of the present invention is to provide a method for preparing the rare earth modified bainitic bearing steel described above, the method comprising:

[0007] S1 prepares an alloy raw material with the following chemical components according to the following weight percentages: C: 0.9-1.2%, Si: 0.15-0.35%, Mn: 0.25-0.45%, Cr: 1.3-1.5%, Mo: 0.35-0.70%, La+Ce: 0.003-0.015%, Sc: 0.005-0.015%, and the remainder is Fe; wherein C, Si, Mn, Cr, Mo, and Fe are used as main raw materials in the alloy raw material, and La+Ce and Sc are used as rare earth raw materials in the alloy raw material;

[0008] S2: placing the main raw materials in an electric arc furnace for smelting, adding rare earth raw materials during the smelting process, stirring evenly and then performing modification treatment to obtain a casting liquid; taking the casting liquid out of the furnace for pouring, and after the casting liquid is cooled and solidified, removing it from the mold to obtain an ingot;

[0009] S3 heats the ingot to 840-920°C for austenitization, and uses a reversible hot rolling mill to hot-roll the ingot into bars with a diameter of 16-30 cm. After the bar is heat-insulated, it is oil-cooled to 200-300°C for isothermal quenching to trigger the bainite phase transformation. Finally, it is taken out of the furnace and air-cooled to obtain rare earth modified bainite bearing steel.

[0010] Specifically, the temperature of the smelting treatment in step S2 is 1400-1500°C, preferably 1450-1480°C.

[0011] Specifically, the heat preservation treatment time in step S3 is 20 to 45 minutes, preferably 30 minutes.

[0012] Specifically, in step S3, the temperature is heated to 840-920° C. at a heating rate of 5-10° C. / min.

[0013] Specifically, in step S3, the temperature is oil-cooled to 200-300° C. at a cooling rate greater than 20° C. / s.

[0014] Specifically, the time for isothermal quenching in step S3 is 120-240 min, preferably 160 min.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects:

[0016] (1) The present invention significantly improves the wear resistance of bainitic bearing steel by adding specific contents of rare earth elements La+Ce and Sc to the bainite structure. Rare earth elements can refine the grains, enhance the hardness and toughness of the material, thereby reducing wear and extending the service life of the bearing steel.

[0017] (2) The present invention combines a heat treatment process to purify the molten steel with rare earths and adsorb them onto austenite grain boundaries, inhibiting the coarsening of bainite laths and reducing their average width. The rare earths, combined with carbon and nitrogen, form rare earth compound particles that are dispersed between the bainite laths, increasing hardness and reducing wear caused by plastic deformation by hindering dislocation movement, ultimately reducing the wear rate of the bearing steel by 20-30%. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a heat treatment process diagram of the rare earth modified bainite bearing steel prepared in Example 1 of the present invention;

[0019] Figure 2 This is a metallographic structure diagram of the hot-rolled bar of Example 1 of the present invention;

[0020] Figure 3 This is the metallographic structure diagram of the rare earth modified bainite bearing steel prepared in Example 1 of the present invention;

[0021] Figure 4 These are electron microscope images of cutting marks on the wear surfaces of the bainitic bearing steels prepared in Examples 1-4 of the present invention and Comparative Examples 1-2. Specific implementation plan

[0022] The following will be combined with the contents of the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0023] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as those commonly understood by those skilled in the art to which the present invention pertains. The terms used in this specification are intended only to describe specific embodiments and are not intended to limit the present invention. The term "and / or" as used in this specification includes any and all combinations of one or more of the listed items. It should be understood that, unless otherwise specified, the various raw materials in the present invention may be commercially available.

[0024] Example 1

[0025] S1: Alloy raw materials (main raw materials + rare earth raw materials) with the following chemical composition percentages by weight: C: 0.9%, Si: 0.15%, Mn: 0.25%, Cr: 1.3%, Mo: 0.35%, La+Ce: 0.003%, Sc: 0.005%, and the rest is Fe.

[0026] S2: placing the above-mentioned weight percentages of C, Si, Mn, Cr, Mo and Fe in an electric arc furnace at 1400° C. for smelting, adding rare earth raw materials La+Ce and Sc during the smelting process, stirring evenly and then performing a modification treatment to obtain a liquid a to be cast; taking the liquid a to be cast out of the furnace for pouring, and after the liquid a to be cast is cooled and solidified, removing it from the mold to obtain an ingot a;

[0027] See also Figure 1 , Figure 1 This is a heat treatment process diagram for preparing rare earth modified bainite bearing steel according to Example 1 of the present invention, specifically the following steps:

[0028] S3 heats the ingot a to 840°C at a heating rate of 5°C / min for austenitization, and uses a reversible hot rolling mill to hot-roll the ingot into a rod a with a diameter of 16 cm. After the rod is kept warm for 20 minutes, it is oil-cooled to 200°C at a cooling rate of 30°C / s for isothermal quenching for 120 minutes to trigger the bainite phase transformation. Finally, it is taken out of the furnace and air-cooled to obtain rare earth modified bainitic bearing steel a.

[0029] See also Figure 2 and 3 , Figure 2 This is a metallographic structure diagram of the hot-rolled bar of Example 1 of the present invention; Figure 3 This is the metallographic structure diagram of the rare earth modified bainite bearing steel prepared in Example 1 of the present invention; Figure 2 In the hot-rolled bearing steel, lamellar pearlite is the main component, accompanied by a small amount of network ferrite; Figure 3 The rare earth-modified bainitic bearing steel is primarily composed of fine bainite, accompanied by a small amount of retained austenite. The metallographic images show that the metallographic structure of Example 1 is dense, with the bainite and retained austenite evenly fused, and a small amount of needle-shaped retained austenite present. The surface wear resistance of the bearing steel meets the requirements.

[0030] Example 2

[0031] S1: Alloy raw materials (main raw materials + rare earth raw materials) with the following chemical composition percentages by weight: C: 1.2%, Si: 0.35%, Mn: 0.45%, Cr: 1.5%, Mo: 0.7%, La+Ce: 0.015%, Sc: 0.015%, and the rest is Fe.

[0032] S2: placing the above-mentioned weight percentages of C, Si, Mn, Cr, Mo and Fe in an electric arc furnace at 1500° C. for smelting, adding rare earth raw materials La+Ce and Sc during the smelting process, stirring evenly and then performing a modification treatment to obtain a liquid to be cast b; taking the liquid to be cast b out of the furnace for pouring, and after the liquid to be cast b is cooled and solidified, removing it from the mold to obtain an ingot b;

[0033] S3 heats the ingot b to 920°C at a heating rate of 10°C / min for austenitization, and uses a reversible hot rolling mill to hot-roll the ingot into a rod b with a diameter of 30 cm. After the rod is kept warm for 45 minutes, it is oil-cooled to 300°C at a cooling rate of 40°C / s for isothermal quenching for 240 minutes to trigger the bainite phase transformation. Finally, it is taken out of the furnace and air-cooled to obtain rare earth modified bainitic bearing steel b.

[0034] Example 3

[0035] S1: Alloy raw materials (main raw materials + rare earth raw materials) with the following chemical composition percentages by weight: C: 1%, Si: 0.2%, Mn: 0.3%, Cr: 1.4%, Mo: 0.5%, La+Ce: 0.01%, Sc: 0.01%, and the rest is Fe.

[0036] S2: placing the above-mentioned weight percentages of C, Si, Mn, Cr, Mo and Fe in an electric arc furnace at 1450° C. for smelting, adding rare earth raw materials La+Ce and Sc during the smelting process, stirring evenly and then performing a modification treatment to obtain a liquid to be cast c; taking the liquid to be cast c out of the furnace for pouring, and after the liquid to be cast c cools and solidifies, removing it from the mold to obtain an ingot c;

[0037] S3 heats the ingot c to 880°C at a heating rate of 8°C / min for austenitization, and uses a reversible hot rolling mill to hot-roll the ingot into a bar c with a diameter of 20 cm. After the bar is kept warm for 30 minutes, it is oil-cooled to 250°C at a cooling rate of 50°C / s for isothermal quenching for 160 minutes to trigger the bainite phase transformation. Finally, it is taken out of the furnace and air-cooled to obtain rare earth modified bainitic bearing steel c.

[0038] Example 4

[0039] S1: Alloy raw materials (main raw materials + rare earth raw materials) with the following chemical composition percentages by weight: C: 1.1%, Si: 0.25%, Mn: 0.35%, Cr: 1.35%, Mo: 0.6%, La+Ce: 0.008%, Sc: 0.006%, and the rest is Fe.

[0040] S2: placing the above-mentioned weight percentages of C, Si, Mn, Cr, Mo and Fe in an electric arc furnace at 1480° C. for smelting, adding rare earth raw materials La+Ce and Sc during the smelting process, stirring evenly and then performing a modification treatment to obtain a liquid to be cast d; taking the liquid to be cast d out of the furnace for pouring, and after the liquid to be cast d is cooled and solidified, removing it from the mold to obtain an ingot d;

[0041] S3 heated the ingot d to 850°C at a heating rate of 7°C / min for austenitization, and then hot-rolled the ingot into a rod d with a diameter of 25 cm using a reversible hot rolling mill. The rod was kept warm for 40 minutes and then oil-cooled to 250°C at a cooling rate of 25°C / s for austempering for 200 minutes to trigger a bainite phase transformation. Finally, the rod was taken out of the furnace and air-cooled to obtain rare earth modified bainitic bearing steel d.

[0042] Comparative Example 1

[0043] S1: placing conventional GCr15 bearing steel in an electric arc furnace at 1480°C for smelting to obtain a liquid to be cast A; taking the liquid to be cast A out of the furnace for pouring, and after the liquid to be cast A is cooled and solidified, removing it from the mold to obtain an ingot A;

[0044] S2 heats ingot A to 860°C at a heating rate of 10°C / min for austenitization, and uses a reversible hot rolling mill to hot-roll the ingot into a bar A with a diameter of 25 cm. The bar is kept warm for 30 minutes and then oil-cooled to 210°C at a cooling rate of 25°C / s for isothermal quenching for 240 minutes to trigger bainite phase transformation. Finally, it is taken out of the furnace and air-cooled to obtain bainitic bearing steel A.

[0045] Comparative Example 2

[0046] S1: placing conventional GCr15 bearing steel in an electric arc furnace at 1450°C for smelting to obtain a liquid B to be cast; taking the liquid B out of the furnace and pouring it, and after the liquid B is cooled and solidified, removing it from the mold to obtain an ingot B;

[0047] S2 heats ingot B to 860°C at a heating rate of 10°C / min for austenitization, and uses a reversible hot rolling mill to hot-roll the ingot into a bar B with a diameter of 25 cm. After the bar is kept warm for 30 minutes, it is oil-cooled to 250°C at a cooling rate of 25°C / s for isothermal quenching for 240 minutes to trigger the bainite phase transformation. Finally, it is taken out of the furnace and air-cooled to obtain bainitic bearing steel B.

[0048] Performance Testing

[0049] The impact abrasive wear test was carried out on an MLD-10 dynamic load abrasive wear tester. The wear impact energy was 3J, the impact frequency was 100 times per minute, the lower sample was 45# steel, the rotation speed was 100 revolutions per minute, the abrasive used in the test was quartz sand with a particle size between 60 and 80 meshes, and the flow rate of the abrasive was controlled at about 50 kg per hour. The samples prepared in the examples and comparative examples were divided into three groups to calculate the average weight loss rate. They were pre-ground for 30 minutes before the test. During the impact wear process, the weight loss was measured once with 30 minutes as a wear cycle, and a total of four cycles were carried out for a total of 2 hours; the test results are shown in Table 1:

[0050] Table 1 Performance test of cast steel

[0051]

[0052] Table 1 shows the matrix structure, V-notch impact value, and impact abrasive wear weight loss of the rare earth-modified bainitic bearing steel. The hardness is the average of ten values, and the V-notch impact value is the average of three values. Table 1 shows that the highly wear-hardening bainitic wear-resistant cast steel produced by the present invention has a V-notch impact absorption energy of up to 37 J, a matrix hardness of 904.24 HV, and a hardness of 941.75 HV on the wear surface after impact wear. This indicates high hardening capacity and excellent impact toughness, resulting in the bainitic steel having good abrasive wear resistance under medium to high stresses and significant wear resistance.

[0053] See also Figure 4 , Figure 4 These are electron microscope images of cutting marks on the wear surfaces of the bainitic bearing steels prepared in Examples 1-4 of the present invention and Comparative Examples 1-2. Figure 4 (a) is the bainite bearing steel prepared in Comparative Example 1, Figure 4 (b) is the bainite bearing steel prepared in Example 1, Figure 4 (c) is a picture of the bainite bearing steel prepared in Example 2, 4(d) is a picture of the bainite bearing steel prepared in Comparative Example 2, 4(e) is a picture of the bainite bearing steel prepared in Example 3, and 4(f) is an electron microscope picture of the cutting marks on the wear surface of the bainite bearing steel prepared in Example 3. Figure 4 It can be seen that the wear scar surface of the rare earth modified bainitic bearing steel looks smoother and has less wear scar area. Figure 4 The tribofilm on the wear scar surface of specimens (c) and 4(f) is relatively sparse, with only shallow abrasive scratches remaining on the surface. However, the tribofilm on the wear scar surface of specimens 4(a) and 4(d) is relatively dense.

[0054] It can be seen that the present invention significantly improves the wear resistance of bainitic bearing steel by adding specific contents of rare earth elements La+Ce and Sc to the bainite structure. Rare earth elements can refine the grains, enhance the hardness and toughness of the material, thereby reducing wear, reducing the wear rate of the bearing steel by 20-30%, and extending the service life of the bearing steel.

[0055] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A rare earth modified bainitic bearing steel, characterized in that: Calculated by weight percentage (wt%), the chemical composition of the bearing steel is as follows: C: 0.9-1.2%, Si: 0.15-0.35%, Mn: 0.25-0.45%, Cr: 1.3-1.5%, Mo: 0.35-0.70%, La+Ce: 0.003-0.015%, Sc: 0.005-0.015%, and the rest is Fe.

2. A method for preparing the rare earth modified bainite bearing steel according to claim 1, characterized in that: The preparation method comprises: S1 prepares an alloy raw material with the following chemical components according to the following weight percentages: C: 0.9-1.2%, Si: 0.15-0.35%, Mn: 0.25-0.45%, Cr: 1.3-1.5%, Mo: 0.35-0.70%, La+Ce: 0.003-0.015%, Sc: 0.005-0.015%, and the remainder is Fe; wherein C, Si, Mn, Cr, Mo, and Fe are used as main raw materials in the alloy raw material, and La+Ce and Sc are used as rare earth raw materials in the alloy raw material; S2: placing the main raw materials in an electric arc furnace for smelting, adding rare earth raw materials during the smelting process, stirring evenly and then performing modification treatment to obtain a casting liquid; taking the casting liquid out of the furnace for pouring, and after the casting liquid is cooled and solidified, removing it from the mold to obtain an ingot; S3 heats the ingot to 840-920°C for austenitization, and uses a reversible hot rolling mill to hot-roll the ingot into bars with a diameter of 16-30 cm. After the bar is heat-insulated, it is oil-cooled to 200-300°C for isothermal quenching to trigger the bainite phase transformation. Finally, it is taken out of the furnace and air-cooled to obtain rare earth modified bainite bearing steel.

3. The preparation method according to claim 2, characterized in that The temperature of the smelting treatment in step S2 is 1400-1500°C, preferably 1450-1480°C.

4. The preparation method according to claim 2, characterized in that The heat preservation treatment time in step S3 is 20 to 45 minutes, preferably 30 minutes.

5. The preparation method according to claim 2, characterized in that In step S3, the temperature is heated to 840-920° C. at a heating rate of 5-10° C. / min.

6. The preparation method according to claim 2, characterized in that In step S3, the temperature is cooled to 200-300°C at a cooling rate greater than 20°C / s.

7. The preparation method according to claim 2, characterized in that The time for isothermal quenching in step S3 is 120-240 min, preferably 160 min.

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