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Microstructure consisting of ferrite,bainite and retained austenite can be obtained through intercritical anneal- ing and isothermal treatment in bainite transformation region for low silicon TRIP(transformation induced plasticity)steel containing niobium.Effects of strain rate,Nb content and soaking temperature in bainite region on microstructure and mechanical properties of test steels were investigated.It is shown that as strain rate ranges from 10~(-2)to 10~(-4)s~(-1),the volume fraction of transformed martensite from retained austenite, as well as tensile strength,elongation rate and strength-ductility product,increases.When Nb is added,the volume fraction of retained austenite decreases,but tensile strength and yield strength increase.While Nb content reaches 0.014%,the steel exhibits high elongation and combination of strength and ductility.Higher retained austenite volume fraction and good mechanical properties are obtained in the test steels when the soaking temperature in bainite region is 400℃.The maximum values of tensile strength,total elongation rate and strength-ductility product can reach 739 MPa,38% and 28082 MPa%,respectively.
Microstructure consisting of ferrite, bainite and retained austenite can obtained through intercritical anneal- ing and isothermal treatment in bainite transformation region for low silicon TRIP (transformation induced plasticity) steel containing niobium. Effects of strain rate, Nb content and soaking temperature in bainite region on microstructure and mechanical properties of test steels were investigated. It is shown that the strain rate ranges from 10 -2 to 10 -4 s -1, the volume fraction of transformed martensite from retained austenite, as well as tensile strength, elongation rate and strength-ductility product, increases. Nb Nb was added, the volume fraction of retained austenite decreases, but tensile strength and yield strength increase. Whilst Nb content reaches 0.014%, the steel exhibits high elongation and combination of strength and ductility .Higher retained austenite volume fraction and good mechanical properties are obtained in the test steels when the soaking temperature in bai The maximum values of tensile strength, total elongation rate and strength-ductility product can reach 739 MPa, 38% and 28082 MPa%, respectively.