Effect Of Heat Treatment On Microstructure And Properties Of Martensite Heat-resistant Steel

In recent years,martensite heat-resistant steel is often used as thermal power units and other high temperature key components for its good physical properties and relatively low price.Because of the high temperature and high pressure of high temperature parts,it is the key to increase its working efficiency and service life that to improve the properties of martensite heat-resistant steel.The research of martensite heat-resistant steel has been one of the hot spots in recent years,in order to meet the requirements of higher temperature and higher strength of industry.In order to improve the comprehensive properties of martensitic heat-resistant steel,the thermodynamic simulation of the sample was carried out,followed by quenching,tempering,solid solution heat treatment.The microstructure were analyzed by OM,SEM,EDS and XRD qualitatively and quantitatively,and the mechanical properties were studied too.The main research contents and results are as follows:?1?The temperature-phase composition crave and the main precipitation phase were simulated by the thermodynamic software:the theoretical A₁ and A₃ temperature of the sample were 821?and 923?respectively,and the single-phase austenite phase region was wide;the main precipitated phase is M₂₃C₆,laves phase and MX phase,and the melting point of MX phase is as high as 1350?and the composition is stable,which can strengthen the matrix.?2?The microstructure and properties of specimen that quenching at 950¹070?and tempering at 740?was studied:With the increase of quenching temperature,the ferrite and diffuse distribution of carbide,turned into the tempered sorbite that kept the position of martensite slowly,and coarsening when the quenching temperature higher than 1040?;M₂₃C₆in the matrix dissolved completely when quenching at 1040?,then new M₂₃C₆ and cementite precipited after tempering;?ferrite precipited when quenching at 1010?,MX precipited in its internal,and M₂₃C₆ that vary in size precipited in its internal and grain boundary and micropores formed in its surrounding after tempering;The hardness and strength were increased and the plasticity was dropt with the increase of quenching temperature,the optimum heat treatment technology was quenching at 1040?+tempering at 740?within the scope of the experiment,when the R.?R and A were 782.1 MPa,570.7 MPa and 20%respectively.?3?The microstructure and properties of specimen that quenching at 1040?and tempering at 650⁷70?was studied:With the increase of tempering temperature,the tempered sorbite that kept the position of martensite transformed into equiaxed grain gradually,and coarsening when 770?;The small carbide particles dissolved and larger particles grew up in matrix after tempering,and the coarsened carbide distributed along the original austenite grain boundary when tempering at 770?;The?ferrite grain boundary precipited M₂₃C₆ first,and then MX and small M₂₃C₆ precipited in its internal successively,which made the its size smaller,color darker,and formed more micropores in its surrounding;The hardness and strength were decreased and the plasticity was increased with the increase of tempering temperature,the optimum heat treatment technology was quenching at 1040?+tempering at680?within the scope of the experiment,when the R.?R and A were 874.0 MPa,706.2 MPa and 16%respectively.?4?The microstructure and properties of specimen that quenching at 1040?and tempering at 650?and then solid solution for 1⁹h at 1040?was studied:There was more?ferrite transformed when the solution time increased,the strip shape of the?ferrite disappeared,the pearlite distribution evenly,and the phase components became close gradually after solution for 9 h;Matrix been strengthened after solid solution for 3 h,so that the hardness and room temperature tensile strength was highly stable at 38 HRC and 1350 MPa respectively;The tensile strength of specimens of 400?was 1410 MPa,and was similar to the tensile strength under the room temperature that with the same solid solution process,the high temperature mechanical property was well under the experiment temperature.