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通过临界退火、临界回火以及回火的多步热处理方式,研究了低碳低合金钢的组织演变与力学性能.结果表明,临界退火后的组织为板条状的临界铁素体及贝氏体/马氏体的双相组织.经临界回火后,为临界铁素体、回火贝氏体/马氏体以及残余奥氏体的多相组织.残余奥氏体呈粒状和条状,分布在铁素体/贝氏体(马氏体)相界面及贝氏体/马氏体板条之间,含量高达29%,并在回火后保持稳定,主要通过C,Mn,Ni和Cu在逆转奥氏体中的富集来稳定.临界退火及回火过程中,Nb C在铁素体及贝氏体/马氏体中析出,呈球状、椭圆形或不规则形状,平均尺寸为10 nm;富Cu的析出相在临界回火及回火过程中形成,呈球状分布于铁素体及残余奥氏体中,尺寸在10~30 nm之间.通过残余奥氏体的应变诱导塑性(TRIP)效应及纳米析出相的析出强化作用,实验钢具有优异的力学性能:屈服强度高于700 MPa,抗拉强度高于900 MPa,均匀延伸率高于20%,总延伸率高于30%.
The microstructure evolution and mechanical properties of low carbon and low alloy steel were studied by means of critical annealing, critical tempering and tempering multi-step heat treatment.The results show that the critical-annealing ferrite and lamellar Body / martensite dual phase microstructure after critical tempering, critical ferrite, tempered bainite / martensite and residual austenite multiphase tissue residual austenite was granular and strip , Distributed in the ferrite / bainite (martensitic) phase interface and bainite / martensite lath between up to 29%, and remained stable after tempering, mainly through the C, Mn, Ni And Cu in the reverse austenite enrichment to stabilize the critical annealing and tempering process, Nb C in ferrite and bainite / martensite precipitation, spherical, oval or irregular shape, the average The size of 10 nm; Cu-rich precipitates formed in the critical tempering and tempering process, was spherical distribution in ferrite and retained austenite, the size of 10 ~ 30 nm by the residual austenite Strain-induced plasticity (TRIP) effect and the precipitation strengthening effect of the nano-precipitated phase, the experimental steel has excellent mechanical properties: yield strength higher than 700 MPa, tensile strength To 900 MPa, the uniform elongation higher than 20%, a total elongation higher than 30%.