CN116377333B - Microalloyed bearing steel casting blank with fine and homogenized structure - Google Patents

Abstract

A microalloyed bearing steel ingot with refined and homogenized structure belongs to the technical field of structural performance regulation of steel materials. The composition is C: 0.93%-1.05%, Si: 0.20-0.50%, Mn: 0.20%-0.50%, Cr: 1.30-1.6%, S: ≤0.01%, P: ≤0.02%, Cu: ≤0.25%, Mo: ≤0.30%, Nb: ≤0.30%, V: ≤0.30%, Zr: 0-0.30% and Al≤0.05%. On this basis, rare earth (Ce, La): ≤0.05%, Ni: ≤1.0%; the balance is Fe. The advantage is that the original austenite size of the ingot is refined by more than 5 times, which can greatly improve the wear resistance, fatigue life and toughness of the bearing steel; it can be applied not only to bearing steel, gear steel and mold steel, but also to the structural regulation of other steel materials.

Description

A microalloyed bearing steel ingot with refined and homogenized structure

Technical Field

The present invention belongs to the technical field of regulating and controlling the microstructure and properties of steel materials, and specifically provides a microalloyed bearing steel ingot with microstructure refinement and homogenization; it relates to the alloying design of the microstructure refinement and homogenization of the ingot of steel materials. The microstructure refinement technology of the bearing steel ingot described in the present invention refines the original austenite size of the ingot by more than 5 times, provides a simple and easy control technology for the refinement, homogenization and stabilization of the microstructure and properties of the bearing steel product, and can greatly improve the wear resistance, fatigue life and toughness of the bearing steel. The present invention can be applied not only to bearing steel, gear steel and mold steel, but also to the microstructure regulation of other steel materials.

Background technique

High contact fatigue life, high wear resistance and high toughness are the future development direction of high-performance bearing steel. The refinement, homogenization and high strengthening of bearing steel are important ways to achieve high performance of bearing steel. In order to achieve this goal, traditional bearing steel uses large-section billets to achieve grain size and carbide refinement in bearing steel, without paying attention to the refinement and homogenization of the structure of bearing steel billets, resulting in the development of bearing steel billets towards larger sizes. However, the large-scale size of bearing steel billets further limits the refinement and homogenization of bearing steel products, resulting in a decrease in the toughness, fatigue life and wear resistance of bearing steel products. How to solve the refinement and homogenization of bearing steel has become a key scientific and technological issue for bearing steel. At the same time, with the development demand for large-scale bearings such as wind power and shield tunneling, the refinement and homogenization of large billets has also become an important development direction for bearing steel. Therefore, solving the homogenization and refinement of bearing steel billets has become the future development direction for high-performance bearing steel and large-section bearing steel billets.

Studies have shown that the dual refinement of the original austenite and carbide of bearing steel can greatly improve the strength, toughness, fatigue life and wear resistance of bearing steel. By performing dual refinement heat treatment on GCr15 bearing steel products, the grain size of the bearing steel is refined from 15-20 microns to 5-10 microns, which can not only increase the strength of the bearing steel GCr15 from 2000MPa to 2500MPa, but also increase the fatigue life of the bearing steel from L ₁₀ ≥1.0x10 ⁷ times to L ₁₀ ≥5.0x10 ⁷ times. At the same time, due to the refinement of the structure, the wear resistance of the bearing steel is also greatly improved. Therefore, the refinement and homogenization of the bearing steel structure not only improves the strength and toughness of the bearing steel, but also greatly improves the fatigue life and wear resistance of the bearing steel. However, due to the inheritance of the bearing steel structure, the coarse cast structure cannot achieve sufficient structure refinement and homogenization through subsequent limited deformation. In addition, traditional bearing steel production requires long-term high-temperature homogenization to reduce the segregation of the ingot and achieve the uniformity of the bearing steel composition, which leads to severe coarsening of the bearing steel ingot structure and coarse and uneven structure of the final bearing steel product. In order to achieve the refinement and homogenization of the bearing steel structure, domestic and foreign countries have proposed a manufacturing technology route for producing high-performance bearing steel products with ultra-large-sized ingots. Domestic bearing steel production has also developed from the initial 180mmx220mm small square billet continuous casting to the current 480mmx520mm large square billet, which has brought huge challenges to the casting and controlled rolling and controlled cooling equipment capabilities of bearing steel, and has not effectively solved the refinement, homogenization and high strengthening of the matrix structure and carbides of bearing steel products. In the future, improvements need to be made in the composition design and process flow of bearing steel to achieve the dual refinement of the matrix structure and carbides of bearing steel products, on the one hand to reduce the excessive requirements of the large-scale ingot section and large deformation in the rolling process on the bearing steel production equipment. On the other hand, large-scale equipment such as high-power and long-life wind power has a demand for 1000mm diameter bearing steel ingots, which is much larger than the diameter specification of traditional bearing steel bar products. It is also necessary to solve the problem of fine-grained and homogenized large-size bearing steel through the alloying design and process improvement of bearing steel.

Summary of the invention

The purpose of the present invention is to provide a micro-alloyed bearing steel ingot with refined and homogenized structure, which solves the problem of refinement and homogenization of large-sized bearing steel. Through the alloying design of refined and homogenized structure of the bearing steel ingot, the matrix structure (original austenite grain size) of the bearing steel ingot can be refined from millimeter level to hundreds of micrometer level (refined by more than 5 times), providing high-quality casting for the manufacture of high-strength, high-fatigue and wear-resistant bearing steel.

The present invention can realize a new alloying design for refining the original austenite grains and carbides in the bearing steel ingot. By alloying the Nb, Mo and V, the ingot structure is greatly refined, providing high-quality ingots for subsequent thermal deformation and heat treatment, thereby ensuring the toughness, high contact fatigue performance and wear resistance of the bearing steel.

1. Chemical composition design

The composition of the microalloyed bearing steel ingot with refined and homogenized structure of the present invention is C: 0.93%-1.05%, Si: 0.20-0.50%, Mn: 0.20%-0.50%, Cr: 1.30-1.6%, S: ≤0.01%, P: ≤0.02%, Cu: ≤0.25%, Mo: ≤0.30%, Nb: ≤0.30%, V: ≤0.30%, Zr: 0-0.30% and Al≤0.05%. On this basis, rare earth (Ce, La): ≤0.05%, Ni: ≤1.0% can be added; the balance is Fe.

The functions and bases of the elements in the present invention are mainly two points. First, the basic performance of the bearing steel GCr15 is ensured by using C, Si, Mn, Cr and Fe as the main alloying elements of the bearing steel, and second, the organization is refined and regulated by alloying Mo, Nb, V and Zr to improve the strength, toughness, fatigue performance and wear resistance.

2. Manufacturing process and conditions

The bearing steel ingot designed by the present invention can be smelted by vacuum induction, electric furnace or converter, and then formed into ingot by mold casting or continuous casting. The grain size of the original austenite on the surface is ≤150um, and the grain size of the original austenite at the center and 1/2 of the radius is ≤250 microns.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a casting microstructure diagram of a billet without Mo/Nb/V/Zr alloying at a radius of 1/2, showing a prior austenite grain size of about 1000 microns.

Figure 2 is a casting microstructure diagram of a Mo/Nb/V/Zr ingot with a total addition of 0.05 at a radius of 1/2, showing a prior austenite grain size of about 700 microns.

FIG3 is a casting microstructure diagram of a Mo/Nb/V/Zr ingot with a total addition of 0.10 at a radius of 1/2, showing a prior austenite grain size of about 500 μm.

FIG. 4 is a casting microstructure diagram of a Mo/Nb/V/Zr ingot with a total addition of 0.30% at a radius of 1/2, showing a prior austenite grain size of about 130 μm.

Figure 5 is an analysis of the change trend of the original austenite grain size in the ingot with the total amount of Mo/Nb/V/Zr, showing the different change behaviors of the ingot surface, radius 1/2 and center and the ingot structure refinement effect of alloying.

Detailed ways

Through composition design, bearing steels with different chemical compositions of 1-4# were prepared by vacuum induction smelting in the laboratory. The specific compositions are shown in Table 1. The smelting and die casting were carried out in a 50 kg induction furnace in the laboratory to simulate the industrial die casting or continuous casting of bearing steel, and an ingot with a diameter of 120 mm was obtained.

Table 1 Invention steel example composition design (wt.%), the balance is Fe

C Si Mn Cr Mo+Nb+V+Zr Other Elements GCr15-0.00 1.01 0.28 0.50 1.30 0.00 Ni: 1.0% GCr15-0.05 1.01 0.28 0.50 1.40 0.05 Ni: 1.0% GCr15-0.10 0.93 0.23 0.50 1.45 0.10 Ni: 1.0% GCr15-0.30 1.05 0.30 0.35 1.60 0.30 La+Ce:0.05%

The microstructures of the four ingots were analyzed by optical microscopy. In the future, the influence of alloying on the microstructure of the ingot was studied, and the microstructure characterization of the ingot surface, the 1/2 radius of the ingot and the core of the ingot was carried out.

Figure 1 shows the microstructure of the ingot at the radius 1/2 without Mo/Nb/V/Zr. It can be seen that the average size of the original austenite grains is 850 μm;

Figure 2 shows the microstructure of the ingot at the radius 1/2 of the ingot with a total amount of Mo/Nb/V/Zr of 0.05%. It can be seen that the average size of the original austenite grains is 700 μm;

Figure 3 shows the microstructure of the ingot at the radius 1/2 of the ingot with a total amount of Mo/Nb/V/Zr of 0.10%. It can be seen that the average size of the original austenite grains is 500 μm;

Figure 4 shows the microstructure of the ingot at the radius 1/2 of the ingot with a total amount of Mo/Nb/V/Zr of 0.30%. It can be seen that the average size of the original austenite grains is 130 μm;

Figure 5 shows the variation of the original austenite size on the billet surface, at 1/2 radius and in the billet core with the addition of Mo/Nb/V/Zr. It can be seen that with the increase of Mo/Nb/V/Zr addition, the original austenite grains in the billet are gradually refined, showing the refinement effect of Mo/Nb/V/Zr addition on the billet structure. Specifically, without the addition of Mo/Nb/V/Zr, the original austenite grain size on the billet surface, at 1/2 radius and in the billet core is 800-1000 microns; after adding 0.05% of the total amount of Mo/Nb/V/Zr, the original austenite size on the surface is rapidly refined to 350 microns, but the original austenite grain size in the core and at 1/2 radius is 600-700 microns, indicating that under the condition of die casting, the addition of 0.05% of Mo/Nb/V/Zr is not enough to achieve the refinement and homogenization of the billet structure; after adding 0.10% of the total amount of Mo/Nb/V/Zr, the surface The size of the original austenite rapidly refined to 190 microns, but the size of the original austenite grains at the center and 1/2 of the radius was about 500 microns, indicating that the addition of 0.10% Mo/Nb/V/Zr under die casting conditions was not enough to achieve the refinement and homogenization of the ingot structure; after adding a total of 0.30% Mo/Nb/V/Zr, the size of the original austenite at the surface and 1/2 of the radius rapidly refined to 130 microns, and the size of the original austenite grains at the center was 200 microns, showing that the addition of 0.30% Mo/Nb/V/Zr under die casting conditions has achieved the refinement and homogenization of the ingot structure.

Considering the low cooling rate of the simulated ingot in the laboratory, it can be predicted that industrial continuous casting can achieve a faster cooling rate, thereby achieving sufficient refinement of the ingot structure without adding a large amount of Mo/Nb/V/Zr. It is recommended to add 0.10% Mo/Nb/V/Zr to the alloying of large-section ingots at a higher cooling rate in industrial continuous casting.

Claims (1)

1. A micro-alloyed bearing steel casting blank with fine and homogenized structure: it is characterized in that ,C:0.93％–1.05％,Si：0.20-0.50％,Mn：0.20％-0.50％,Cr：1.30-1.6％,S：≤0.01％,P：≤0.02％,Cu：≤0.25％,Mo:≤0.30％,Nb：≤0.30％,V：≤0.30％,Zr：0-0.30％ and Al are less than or equal to 0.05 percent; ce and La: less than or equal to 0.05 percent, ni: less than or equal to 1.0 percent; nb+Mo+V+Zr is 0.3%, and the balance is Fe;

Smelting by a vacuum induction furnace or a converter, and then forming a casting blank by die casting or continuous casting, wherein the grain size of the prior austenite on the surface is less than or equal to 150 mu m, and the grain size of the prior austenite at the positions of the core and the radius 1/2 is less than or equal to 250 mu m.