Study On Microstructure And Properties Of Martensitic Precipitation-hardening Stainless Steel And Precipitate Simulation Prediction

Martensitic precipitation-hardening stainless steel can meet the requirements of heat resistance,corrosion resistance and ultra-high strength of some parts in aerospace industry because of its high tensile strength and fine corrosion resistance.In this paper,the relationship between chemical composition,heat treatment process,microstructure and mechanical properties of 15-5 PH martensitic precipitation-hardening stainless steel were studied by numerical simulation and experimental research.The equilibrium microstructure and precipitates,growth behavior of copper-rich phase in the newly Cocontained martensitic hardening stainless steel were predicted.The results of Thermo-Calc showed that only austenite exists between 950 ?~1288 ?;cooper-rich phase,precipitated phase rich in Nb,C,carbides and reverted austenite were observed after aging treatment;the size of copper rich phase increased with the aging temperature,and grow immediately when the temperature increased to 540?;reverted austenite emerged at 450?.The results of mechanical properties demonstrated that the optimum heat treatment of 15-5 martensitic precipitation-hardening stainless steel was solid solution at 1040? for 30 min,air cooling and aging for 2 h at 480?,air cooling.The mechanical properties of 15-5 PH martensitic precipitating hardening stainless steel under this condition were: tensile strength: 1420 MPa,yield strength: 1300 MPa,elongation: 10.5%,HRC: 43.5,impact energy: 10 J.Metallographic analysis and TEM analysis results showed that: the matrix of 15-5 PH under different aging treatment are lath martensite with high density dislocation,the width is about 0.2 ?m;the reverted austenite which can improve the toughness emerged along the boundary of lath martensite formed after aging treatment;The major type of precipitate is copper rich phase.The size error of ?–Cu phase obtained by the dynamic calculation is 15% under the corresponding conditions,it stated the reliability of calculation.In order to improve the strength and toughness of martensitic precipitated hardening stainless steel simultaneously,the alloy is redesigned based on 15-5 PH stainless steel,reducing the C content to ultra-low level,adding cobalt element with different content(3%,6%,9%),obtaining the newly martensitic hardening stainless steel and studying the effect of cobalt on phase transformation and the regulation of second-phase precipitation,the calculation result showed that cobalt was mainly dissolved in matrix which plays the role of solid solution strengthening,and the cobalt can also decrease the diameter of cooper rich phase.