Microstructure And Properties Of 17-4PH Stainless Steel Strengthened By Shot Peening And Ion Nitriding

Ion nitriding,as a widely used chemical heat treatment method,can form a nitrided layer of a certain thickness on the surface of materials,effectively improving their hardness and wear resistance.Ion nitriding technology has the advantages of low cost,high efficiency,and environmental friendliness.Relevant studies have shown that surface deformation treatments such as shot peening and mechanical grinding before nitriding can effectively promote the nitriding process,increase the thickness of the nitrided layer,and further improve the performance.17-4PH stainless steel has high strength,hardness and corrosion resistance,but it still needs to be surface strengthened in some extreme working environments.Therefore,this article takes 17-4PH stainless steel as the research object,and uses a combination of shot peening and ion nitriding to modify its surface,and investigates the effect of this combined strengthening process on the microstructure and properties of 17-4PH stainless steel.In this paper,the 17-4PH stainless steel was subjected to 8h ion nitriding at different temperatures,and the metallographic observation,phase composition analysis,mechanical property testing and corrosion resistance testing were carried out through the corresponding tests.Then,the effect of shot peening on the microstructure and properties of 17-4PH stainless steel was studied by different strengths of shot peening.Finally,17-4PH stainless steel after shot peening at different intensities undergoes ion nitriding tests under the same process,studying the influence of composite reinforcement of shot peening and ion nitriding on the microstructure and properties of 17-4PH stainless steel,and selecting the best shot peening and ion nitriding composite reinforcement process.The main conclusions are as follows:(1)The best comprehensive performance of the nitrided layer on 17-4PH stainless steel is obtained by ion nitriding at 550°C for 8 hours.The average thickness of the nitrided layer is66.8 μm,and the surface phase is composed of ε and γ′ phases.The average surface hardness is 1151.1 HV,and the nitrided layer is uniform.(2)After being treated with three different intensities of shot peening,0.2 mm A,0.4mm A,and 0.5 mm A,a residual compressive stress layer was formed on the surface of 17-4PH stainless steel.Among the three types of samples,the 0.2 mm A shot peened sample had the greatest surface residual stress of-894 MPa,while the 0.4 mm A and 0.5 mm A shot peened samples had the highest hardness of around 574 HV.Moreover,analysis of the half-width of the diffraction peak for the three samples showed that the surface structure refinement was most significant in the 0.4 mm A and 0.5 mm A shot peened samples.(3)After shot peening and ion nitriding composite strengthening,the hardness of the nitrided layer of 17-4PH stainless steel was increased by about 120 HV compared to the single ion nitriding sample.In addition,the wear resistance and corrosion resistance were improved.More γ′ phases were generated on the surface of the 0.4 mm A and 0.5 mm A shot peened samples.However,the nitrided layer thickness of the 0.5 mm A shot peened sample decreased,with an average thickness of 61.2 μm.(4)The optimal composite strengthening process for 17-4PH stainless steel in this study is the combination of 0.4 mm A shot peening and ion nitriding at 550℃.The sample treated with this process has the thickest nitrided layer,measuring 80.3 μm,and the highest average hardness of the nitrided layer,measuring 1273.3 HV.Its wear resistance is almost the same as that of the other two composite-treated samples,and it has the best corrosion resistance.