The Influence Of Inclusions In 15-5PH Stainless Steel Of Different Smelting Methods On Fatigue Performance

15-5PH is a kind of precipitation hardening stainless steel with good strength and toughness matching and excellent corrosion resistance.It is widely used in aviation,aerospace and shipbuilding.At present,the domestic smelting process mostly are VIM+VAR,which has higher production cost and smaller output,which limits the promotion of the steel in the civilian field.In order to reduce the smelting cost of 15-5PH high-strength stainless steel and make it more widely used,it is urgent to introduce the smelt ing process of EAF+VOD+VAR with lower smelt ing cost,and these two kinds of smelting processes will have a great influence on the mechanical properties,high and low magnification structure,fatigue performance of 15-5PH precipitation hardening stainless steel.In this paper,the mechanical properties,the particle size distribut ion of inclusions of 15-5PH stainless steel bars which were divided into Φ150mm and Φ350mm 2 kinds of specifications,a total of 4 kinds steel,fatigue properties and hydrogen embrittlement sensitivity of these two smelting processes were compared and analyzed by means of OM,Aspex,SEM,TEM,XRD,TDS,etc.The microstructure and fracture morphology of the test steel were analyzed.The relationship between the non-metallic inclusions in steel and the impact toughness,fracture toughness and fatigue properties of 15-5PH stainless steel was established.The hydrogen embritt lement sensitivity of 15-5PH stainless steel was compared.The main conclusions are as follows:After heat treatment,for the test steel bar with Φ150mm,the strength of the VIM+VAR test steel is slightly lower than that of the EAF+VOD+VAR test steel,and the plastic toughness is equivalent,but the impact toughness and fracture toughness of the VIM+VAR test steel are higher than that of the single vacuum test steel.For the test steel of Φ350mm,the strength and plasticity of the two test steels of VIM+VAR and EAF+VOD+VAR are not much different.The impact toughness of the single vacuum test steel is low.The specifications of the test steel became larger,the strength and plasticity changed little,and the impact toughness decreased.The type,composition,shape and particle size distribution of the inclusions in the test steel of the two smelting processes were compared by the automatic detection of Aspexinclusions.For Φ150mm test steel,the inclusions in VIM+VAR test steel are MnS,Al₂O₃ and a small amount of Al-Mg inclusions.The inclusions of EAF+VOD+VAR test steel mainly include Al₂O₃,CaO and a small amount of MnS and Al-Mg inclusions.The vacuum smelting process has better control on the type,quantity,shape and size of 15-5PH stainless steel inclusions.For Φ350mm test steel,the inclusions in VIM+VAR test steel are MnS,Al₂O₃,etc.,EAF+VOD+VAR test steel.The inclusions are mainly Al₂O₃ and a small amount of MnS.The test steel size has little effect on inclusions.After electrochemical hydrogenat ion,the 15-5PH stainless steels（1#and 2#） of the two smelting processes introduce a certain a mount of diffusible hydrogen;the diffusible hydrogens charged by the two 15-5PH experimental steels are located at the grain boundary and position.Under the action of stress,the movable dislocation hydrogen transports to the grain boundary and the martensite lath boundary,which easily causes the crack to nucleate,expand and cause cracking.Reasonable forging,heat treatment process and microalloying make the grain and microstructure refine,which can reduce the hydrogen embritt lement sensitivity of 15-5PH stainless steel to a limited extent.Among the 15-5PH stainless steels of the two smelting processes,the austenite content of the 1# test steel is about twice that of the 2# test steel.Due to the greater so lubility of hydrogen in austenite and lower diffusion rates,1# experimental steel has lower hydrogen embrittlement sensitivity.After hydrogenation,the binding energy at the grain boundary reduced,and the surface of the sample is broken along the crystal.Comparing the microstructure and properties of the 15-5PH test steel of the two smelting processes,the fatigue performance of the single vacuum test steel is only 30-40 MPa lower than that of the double vacuum test steel,while the mechanical properties are not much different and the microstructure is stable.The production cost is reduced by the range;the15-5PH stainless steel is produced by the EAF+VOD+VAR smelting process,which effectively reduces the production cost and can be widely applied and popularized in engineering.