Effect Of Heat Treatment Process On The Microstructure And Properties Of 7Cr14 Martensitic Stainless Steel

The properties of martensitic stainless steel can be change through heat treatment,and martensitic stainless steels have huge application requirements in high-end applications such as aerospace industry,heavy transportation,nuclear power,and knife and scissors that are closely related to people's lives.The microstructural change of martensitic stainless steel during heat treatment,especially the influence of the shape,size and distribution of carbides on the properties of the material is particularly important.This article takes 7Cr14 martensitic stainless steel as the research object to study the effects of austenitizing temperature,austenitizing holding time and tempering temperature on the structure and properties of 7Cr14 steel.Through differential scanning calorimetry(DSC)analysis and transmission electron microscopy(TEM),the structure changes and laws of carbide precipitation of 7Cr14 steel after solid solution during heating process were studied.The main research results are as follows:The austenitizing temperature and holding time during the quenching process have a greater impact on the structure and properties of 7Cr14 steel.The structure of 7Cr14 martensitic stainless steel after quenching is martensite,carbide and retained austenite.As the quenching temperature increases,the number of carbides decreases and the content of retained austenite increases.When the quenching temperature increases from 950?to 1100?,the hardness of the steel increases,and when the quenching temperature increases to 1150?,the hardness of the steel decreases significantly.Compared with the quenching temperature,the quenching holding time has little effect on the structure and properties of 7Cr14 steel.The carbides after quenching are mainly M₂₃C₆type carbides.The tempering structure and properties of 7Cr14 steel are also various at different tempering temperatures.The tempering process of 7Cr14 steel should be low temperature tempering.The low temperature tempered structure of 7Cr14 martensitic stainless steel is tempered martensite,carbide and a small amount of retained austenite,and the high temperature tempered structure is tempered sorbite.As the tempering temperature increases,martensite gradually begins to decompose and carbides precipitate.The carbides in the steel after tempering are mainly undissolved M₂₃C₆type carbides and a small amount of secondary carbides precipitated during the quenching process.As the tempering temperature increases,the hardness of 7Cr14 steel decreases and the tensile strength decreases.When tempered at low temperature,the tensile strength of the material is generally higher and the elongation after fracture is lower.When tempered at high temperature,the tensile strength of the steel is lower and the elongation after fracture is higher.The best heat treatment process for 7Cr14martensitic stainless steel is that:quenching temperature is between 1050?and 1100?,holding time is between 25min-30min,and then tempering temperature is between 200?and300?.The overall performance of the steel is the best.After tempering,the hardness value of the steel is greater than 56HRC,the tensile strength is greater than 1930MPa,and the elongation after fracture is greater than 3.8%.The precipitation of carbides in the martensite matrix during the heating process of 7Cr14 martensitic stainless steel has a certain law.Through differential scanning calorimetry(DSC)analysis and transmission electron microscopy(TEM)to study the 7Cr14 steel after solid solution,it is found that the precipitation order of carbides in the martensite matrix of7Cr14 steel during the heating process is:martensite?M₂C and M₃C?M₂₃C₆,and reverse austenite was found in the material at 310?.