节约型双相不锈钢TRIP效应致塑性增量及其固溶温度依赖性

Intrinsic Increment of Plasticity Induced by TRIP and Its Dependence on the Annealing Temperature in a Lean Duplex Stainless Steel

在Gleeble-3800试验机上进行了经1000~1200℃固溶处理后的节约型双相不锈钢(LDX)的拉伸变形实验,利用TEM分析了其加工硬化特性的微观机制,利用XRD测定计算了不同条件下形变诱导马氏体的饱和转变量。基于加工硬化规律对变形温度(室温~100℃)的敏感性,分别提出了室温变形时TRIP效应诱发塑性增量(或均匀延伸率增量)的量化指标:表观塑性增量(Δe)、单位体积马氏体诱发的平均塑性增量(Δe^→)及只与奥氏体稳定性有关的本征塑性增量(Δe^*),探讨了固溶温度对它们的影响规律。结果表明:LDX中形变诱导马氏体相变(SIMT)存有γ→ε→α′与γ→α′2种机制,引发TRIP效应并使LDX表现出"三阶段"加工硬化特征。不同固溶温度分别对应不同的临界变形温度(Md),使LDX在M_d温度变形时不存在TRIP,固溶温度越高,Md越低、Δe越小。随着固溶温度增加,Δe^→逐渐增加,而Δe^*则逐渐减小,即奥氏体越稳定,TRIP本征增量越小。此外,Δe^→与Δe^*均与奥氏体稳定性系数(k)间存在一定的线性关系。

Recently,advanced lean duplex stainless steels(LDXs)with exceptionally good tensile properties by transformation-induced plasticity(TRIP)have been developed to respond to the skyrocketing raw material cost.In these new alloys,TRIP in the metastable austenite phase is expected to dominate overall deformation of the steels.Solution annealing,as a critical step of production processing,affects the austenite characteristics in LDXs,such as volume fraction and mechanical stability of austenite,which in turn influences its TRIP behavior.In order to further develop advanced LDXs,an assessment in the plastic increment of TRIP and its dependence on solution treatment are necessary.In this work,the tensile deformation test of a LDX which was annealed in the range of 1000~1200℃ was carried out on a Gleeble-3800 machine.The microstructural mechanism of work hardening characteristics was characterized by TEM,and the saturation of strain-induced martensite(SIM)under different conditions was calculated by XRD.Some quantitative indicators which can characterize the plastic increment of TRIP were proposed,including apparent plastic increment(Δe),average plastic increment(Δe^→)induced by unit volume SIM and intrinsic plastic increment(Δe^*)related only to mechanical stability of austenite.Meanwhile,their dependences on annealing temperature were discussed.The results show that SIM can develop in two ways of γ→ε→α′andγ→α′whereby the work hardening of the LDX exhibit a"three-stage"characteristic.There is a critical deformation temperature(Md)where the TRIP is absent at every annealing temperatures.The higher the annealing temperature is,the smaller the Mdand the Δe are.As annealing tempera Δe^→ture increases,e increases,whileΔe*decreases,indicating a fact that the more stable the austenite is,the smaller the intrinsic plastic increment of TRIP is.In addition,both Δe^→ and Δe^*show a linear relationship with the austenite stability coefficient(k).