A method for preparing a gcr15 bearing steel by electric field assisted large heterostructure

Abstract

The application discloses a kind of GCr15 bearing steel's electric field auxiliary large heterogeneous organization preparation method;Method includes: rare earth GCr15 bearing steel is heated to 800~950 DEG C, and keeps warm;Subsequently, hot billet is mechanically deformed, and dislocation is generated at the interface of matrix and non-metallic inclusion;Pulse electric field is applied to the billet after deformation, and the gathering effect of electric current is used to generate local joule heat near dislocation, so that the temperature of interface micro area is instantaneously increased to above recrystallization temperature, while the whole matrix keeps lower temperature;Under the action of joule heat, the interface region where dislocation is dense occurs dynamic or static recrystallization, forms fine equiaxed crystal layer, and the fine equiaxed crystal layer can effectively relax stress concentration at the interface, inhibit crack initiation;Cool to room temperature, obtain bearing steel material.The application realizes the active regulation of large heterogeneous structure interface by alloy design and preparation process optimization, and is suitable for the industrialization production of high reliability bearing steel.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing and microstructure control technology, specifically relating to a synergistic treatment technology of plastic deformation and pulsed electric field for GCr15 bearing steel with large heterogeneous local microstructure, which is used to improve the stress state and crack propagation resistance at the interface between the matrix and inclusions / precipitates. Background Technology

[0002] GCr15 bearing steel is the core material for manufacturing rolling bearings, requiring extremely high contact fatigue life and wear resistance. However, non-metallic inclusions (such as Al2O3, TiN, etc.) are inevitably formed during the smelting and solidification process. These inclusions have significant differences in mechanical properties and thermal expansion coefficients compared to the matrix, becoming the preferred sites for fatigue crack initiation.

[0003] Traditional methods, such as grain refinement and improved purity, have limited effectiveness in improving large-sized heterogeneous interfaces. In recent years, solid-state forming technology has introduced dislocation structures between the matrix and inclusions, but it struggles to achieve precise recrystallization control of localized structures. While conventional electric field treatment can be used for metal recrystallization, the overall heating method cannot selectively target the interface. Therefore, a new technology is urgently needed that can specifically control the microstructure of the matrix-inclusion interface and reduce stress concentration. Summary of the Invention

[0004] The purpose of this invention is to provide an electric field-assisted method for preparing large heterogeneous structures of GCr15 bearing steel. By introducing dislocations at the interface between the matrix and inclusions and utilizing local Joule heating induced by the electric field to achieve interface recrystallization, fine structures are formed, thereby reducing stress concentration, delaying crack propagation, and improving the overall performance of the material.

[0005] To achieve the above objectives, the present invention provides the following technical solution: Step 1: Rare Earth Smelting Commercially available GCr15 bearing steel (C 1.00, Cr 1.50, Mn 0.35, Si 0.25, P≤0.025, S≤0.015, Al 0.02, balance Fe, wt.%) was selected. La / Ce rare earth oxidation treatment was performed in a vacuum induction furnace at an addition rate of 0.0010–0.0015 wt.%, with a La / Ce mass ratio of 1:2. The total oxygen content of the molten steel was below 5 ppm at the time of addition. This treatment resulted in rare earth-modified inclusions such as Al2O3 and TiN, reducing inclusion size and improving conductivity. This approach both reduces inclusion size and alters their conductivity, thus providing conditions for the localized heterogeneous microstructure of subsequent products.

[0006] Step 2: Solid billet preparation Rare earth-modified GCr15 bearing steel was heated to 800℃~950℃ and held for 30~60 min, followed by rolling deformation with a strain of 0.1~0.5. Due to the different physical properties of the matrix and inclusions, a large number of geometrically necessary dislocations and thermally mismatched dislocations were generated at the interface between them.

[0007] Step 3: Applying a pulsed electric field and the Joule heating effect During thermoplastic deformation, a pulsed electric field is applied. Because the resistivity at dislocations is higher than that of the intact lattice, current preferentially accumulates near the dislocation lines, generating localized Joule heating. This causes the temperature of the interface micro-regions to instantaneously rise above the recrystallization temperature (e.g., localized heating can reach 200–500°C), while the matrix as a whole remains at a lower temperature. Unlike conventional addition of an electric field, the material in this patented invention has undergone rare-earth modification, giving the inclusions a certain degree of conductivity. This avoids uneven electric field distribution near the inclusions, preventing localized overheating and damage to the material's properties. Furthermore, the electric field can also optimize the morphology of the inclusions, reducing the probability of crack formation.

[0008] Step 4: Local Recrystallization of the Interface Under Joule heating, dynamic or static recrystallization occurs in the dislocation-dense interface region, forming a fine equiaxed crystal layer of 0.01–2 μm, which effectively relaxes the stress concentration at the interface and inhibits crack initiation.

[0009] Step 5: Cooling By air or slow cooling to room temperature, a structurally stable bearing steel is obtained.

[0010] The beneficial effects of this invention are: (1) By taking advantage of the characteristics of rare earth and electric field, special process parameters are coupled to achieve a clever combination of composition, process and performance.

[0011] (2) Local precise control: By utilizing the current accumulation effect of dislocations, Joule heating is confined to the micro-region at the matrix / inclusion interface, avoiding overall heating that leads to coarsening of the tissue.

[0012] (3) Significantly reduces stress concentration: The recrystallization layer at the interface can effectively relax thermal mismatch stress and external stress, delaying crack initiation and propagation.

[0013] (4) Improved fatigue performance: The GCr15 bearing steel treated by this invention has a rotational bending fatigue limit increased by more than 30% and a contact fatigue life increased by 50% to 100%.

[0014] (5) Strong process compatibility: It can be integrated into existing plastic forming or hot processing production lines without the need for complex equipment modification.

[0015] (6) Applicable to large heterogeneous structures: Specifically designed for the interface problem between large inclusions (>5μm) and the matrix, solving the problem of local failure that is difficult to improve with traditional homogenization treatment. Attached Figure Description

[0016] Figure 1 : Schematic diagram of dislocation distribution at the interface between the matrix and inclusions / precipitates after plastic deformation (dislocations are entangled around the inclusions); Figure 2 Comparison of the fine-grained structure of the matrix and inclusion / precipitate interface before and after treatment. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention. Example 1

[0018] Commercially available GCr15 bearing steel was selected, with the following chemical composition (wt.%): C 1.00, Cr 1.50, Mn 0.35, Si 0.25, P≤0.025, S≤0.015, Al 0.02, La 0.00033, Ce 0.00066, with the remainder being Fe. Inclusions are mainly Al2O3 and TiN, with a size of 2–15 μm.

[0019] The sample was heated to 950℃ and held for 30 min. Uniaxial compression deformation was then performed with a strain of 0.1 and a strain rate of 0.1 s⁻¹. This resulted in a large number of dislocation tangles (…). Figure 1 ).

[0020] Immediately after deformation, a pulsed electric field was applied: current density 50 A / mm², pulse width 100 μs, frequency 200 Hz, and processing time 10 min. The mixture was then air-cooled to room temperature.

[0021] Results: TEM observation showed that a fine recrystallized layer with a thickness of approximately 0.01–1.5 μm was formed at the interface. Figure 2 The grain size is approximately 0.3 μm. Compared to the untreated sample, the microhardness gradient at the interface is more gradual, and the crack propagation rate is reduced by approximately 60% at ΔK = 15 MPa·m¹ / ². Example 2

[0022] Commercially available GCr15 bearing steel was selected, with the following chemical composition (wt.%): C 1.00, Cr 1.50, Mn 0.35, Si 0.25, P≤0.025, S≤0.015, Al 0.02, La 0.0005, Ce 0.001, and the remainder being Fe. Inclusions are mainly Al2O3 and TiN, with a size of 2–15 μm.

[0023] Heat the sample to 800℃ and hold for 60 min.

[0024] The deformation method was multi-pass rolling (total strain 0.5), and the electric field parameters were: current density 80 A / mm², pulse width 50 μs, frequency 500 Hz, and processing time 30 min.

[0025] Results: Fatigue life tests (R=0.1, maximum stress 1500 MPa) showed that the average life of the samples treated according to this invention was 3.2 × 10⁻⁶ MPa. 6 Number of cycles, compared to conventional semi-solid forming (1.4 × 10⁻⁶). 6 (Weekly) increased by 128%. Fracture analysis showed that the recrystallization layer in the crack initiation zone effectively prevented crack initiation at the inclusion tips.

[0026] Comparative Example Using GCr15 bearing steel with the same composition, only thermoplastic deformation was performed (without applying a pulsed electric field). The results showed that the interface had dense dislocations but no recrystallization occurred, stress concentration was obvious, and fatigue cracks easily propagated rapidly along the interface.

[0027] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a large heterogeneous microstructure of GCr15 bearing steel using an electric field assisted process, characterized in that, Includes the following steps: (1) Smelting Commercially available GCr15 bearing steel was selected and subjected to La / Ce rare earth treatment in a vacuum induction furnace, ultimately producing La / Ce rare earth modified inclusions. (2) Preparation of solid billet Rare earth-modified GCr15 bearing steel is heated to 800℃~950℃ and held for 30~60 min, with the billet thickness controlled at 30~50mm; then the hot billet is mechanically deformed to generate dislocations at the interface between the matrix and non-metallic inclusions. (3) Pulsed electric field application and Joule heating effect A pulsed electric field is applied to the deformed billet, and local Joule heating is generated by the accumulation effect of current near dislocations, so that the temperature of the interface micro-region rises instantaneously to above the recrystallization temperature, while the matrix as a whole remains at a low temperature. (4) Local recrystallization of the interface Under Joule heating, dynamic or static recrystallization occurs in the interface region with dense dislocations, forming a fine equiaxed crystal layer. The fine equiaxed crystal layer can effectively relax the stress concentration at the interface and inhibit crack initiation. (5) Cool to room temperature to obtain bearing steel material with microscopic local heterogeneity and reduced interfacial stress concentration.

2. The method for preparing a large heterogeneous microstructure of GCr15 bearing steel assisted by electric field as described in claim 1, characterized in that, The amount of La / Ce added is 0.0010 to 0.0015 wt.%, the mass ratio of La / Ce is 1:2, and the total oxygen content of the molten steel is less than 5 ppm when added.

3. The method for preparing a large heterogeneous microstructure of GCr15 bearing steel assisted by electric field as described in claim 1, characterized in that, The inclusions in step (1) are Al2O3 and TiN, with a size of 1 to 20 μm.

4. The method for preparing a large heterogeneous microstructure of GCr15 bearing steel assisted by electric field as described in claim 1, characterized in that, In step (2), the mechanical deformation is rolling, and the strain is 0.1 to 0.

5.

5. The method for preparing a large heterogeneous microstructure of GCr15 bearing steel assisted by electric field as described in claim 1, characterized in that, The parameters of the pulsed electric field in step (3) are: current density 10-100 A / mm², pulse width 10-500 μs, frequency 10-1000 Hz, and processing time 10-30 min.

6. The method for preparing a large heterogeneous microstructure of GCr15 bearing steel assisted by electric field according to claim 1, characterized in that, The grain size of the local recrystallization region at the interface in step (4) is 0.01 to 2 μm, forming a fine equiaxed crystal structure with a local diameter range of 30 to 50 μm.

7. The high-performance GCr15 bearing steel prepared by the method according to any one of claims 1-6, characterized in that, The matrix and the interface between inclusions / precipitates have no continuous cracks, and there is a nanoscale recrystallization layer near the interface, which improves fatigue life by more than 50%.

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