| SHI Bicong,WANG Xinyu,WU Haoxuan,WU Xiaochun.Effect of Shot Peening on Microstructure and Properties of 4Cr5Mo2V Steel Plasma Nitriding Layer[J],54(9):239-247 |
| Effect of Shot Peening on Microstructure and Properties of 4Cr5Mo2V Steel Plasma Nitriding Layer |
| Received:August 26, 2024 Revised:December 18, 2024 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2025.09.020 |
| KeyWord:4Cr5Mo2V steel shot peening plasma nitriding phase constituent nitriding layer |
| Author | Institution |
| SHI Bicong |
School of Materials and Science Engineering,State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai , China |
| WANG Xinyu |
School of Materials and Science Engineering,State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai , China |
| WU Haoxuan |
School of Materials and Science Engineering,State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai , China |
| WU Xiaochun |
School of Materials and Science Engineering,State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai , China |
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| Abstract: |
| During the hot stamping process, the primary failure modes of hot stamping dies are high-temperature wear and stress corrosion. Importantly, these failures usually result in significant economic losses. In order to enhance the service performance, the industrial sector often adopts plasma nitriding for surface treatment. Although a nitriding layer without a compound layer exhibits higher toughness, averting brittle spalling, its lower surface hardness can undermine the wear resistance of the material. Thus, there is a need to develop a method that can not only increase the thickness and hardness of the compound layer, but also prevent the early failure of the die caused by brittle fracture. The work aims to regulate the structure and properties of the plasma nitriding layer, achieve a plasma nitriding layer with favorable toughness and porosity, and increase the thickness of the compound layer and the effective hardened layer. Prior to plasma nitriding (PN) of 4Cr5Mo2V steel at 520 ℃ for 10 h, shot peening treatment (SP) under different process conditions was carried out. The effect of shot peening on the structure and properties of nitriding layer was investigated by adjusting the experimental parameters. The microstructure, phase constituents, microhardness gradient, effective thickness, porosity, surface hardness and surface morphology of plasma nitrided 4Cr5Mo2V steel coupled with TSP processing were tested and analyzed by optical microscopy, scanning electron microscope (SEM), X-ray diffraction (XRD), optical profilometer and microhardness tester. The results showed that under different SP treatment conditions, a large number of dislocations, as well as dislocation cells and nanocrystals composed of high-density dislocations were observed in 4Cr5Mo2V steel. In the plasma nitriding layer, ε-Fe2-3N phase was a hard and brittle phase, while γ′-Fe4N phase had good toughness and a certain hardness. XRD analysis revealed that, compared with the PN sample, the surface of the PN samples after SP treatment had the different contents of γ'-Fe4N and ε-Fe2-3N phase, indicating that shot peening could evidently regulate the phase structure of the nitriding layer. Optical microscopy results showed that, compared with PN treatment, after TSP3 (0.4 mm+0.11 mm+0.11 mm)+PN treatment, the roughness of the sample was 1.12 μm, and the thickness of the compound layer and the effective hardened layer increased by 13.9% and 5.4%, respectively. After TSP2 (0.4 mm+0.19 mm+0.11 mm)+PN treatment, the roughness was 1.21 μm, the content of the ε-Fe2-3N phase decreased, the γ′ phase increased significantly, and the thickness of compound layer and effective hardened layer increased by 37.5% and 10.7%, respectively, with the best toughness and porosity. After TSP1 (0.4 mm+0.28 mm+0.11 mm)+PN treatment, the roughness was 1.46 μm and the thickness of compound layer and effective hardened layer increased by only 1.1% and 1.8%, respectively, with severe damage on the surface. This could be attributed to an increase in dislocation density, crystal refinement, and high strain of carbides and slip bands. However, when the shot peening intensity increases, the sample roughness also increases, which will inhibit the effect of shot peening and affect the efficiency of plasma nitriding. The plasma nitriding layer of 4Cr5Mo2V steel after TSP2 treatment has the best quality, and the surface hardness and thickness are the greatest with values of 980HV0.3 and 310 µm. |
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