含铌TRIP钢连续退火后的组织性能及强化机理

Microstructure,mechanical properties and strengthening mechanism of Nb-bearing TRIP steel after continuous annealing process

在实验室模拟了含铌与无铌TRIP钢的连续退火工艺过程,通过金相显微技术(OM)、扫描电镜(SEM)、透射电镜(TEM)、背散射电子衍射技术(EBSD)、X射线衍射(XRD)和拉伸实验等检测手段研究了TRIP钢的组织性能,分析了TRIP钢中残余奥氏体稳定性的影响因素及强化机理.结果表明:在连续退火工艺条件下,Nb的存在细化了TRIP钢的微观组织,与未添加Nb的钢相比,添加Nb可以提高TRIP钢中残余奥氏体含量和残余奥氏体碳含量.含铌TRIP钢中残余奥氏体主要以团块状或薄膜状分布于铁素体与贝氏体晶界,极少部分以细小球状分布于铁素体晶内.含铌TRIP钢热轧后的主要析出物为Fe3C和(Nb,Ti)(C,N),退火后的主要析出物为(Nb,Ti)(C,N).细小含铌析出物的析出强化导致了随着退火温度的升高,屈服强度和抗拉强度升高.

The continuous annealing processing of transformation-induced plasticity （TRIP） steel was simulated in lab.The microstructure and mechanical properties were analyzed by optical microscopy （OM）,scanning electron microscopy （SEM）,transmission electron microscopy （TEM）,electron-backscatter diffraction （EBSD）,X-ray diffraction （XRD） techniques and tensile test.The factors influencing the stabilization of retained austenite and the strengthening mechanism of TRIP steel were analyzed.The experimental results showed that fine grains in the microstructure of Nb-bearing TRIP steel formed during continuous annealing processing because of the existence of Nb.The Nb-bearing TRIP steel has more retained austenite and more carbon in retained austenite than the TRIP steel without niobium.It is found that retained austenite in the Nb-bearing TRIP steel is bulky or thin filmy at ferrite and bainite grain boundaries and few fine globular ones exist in the ferrite matrix.Fe 3C and （Nb,Ti）（C,N） are the main precipitates in the Nb-bearing TRIP steel after hot rolling.After continuous annealing,（Nb,Ti）（C,N） is the only main precipitates.Obviously the yield strength and tensile strength increase with increasing annealing temperature,which results from the precipitation strengthening of fine Nb-bearing precipitates.