γ/ε双相Fe-19Mn合金在拉伸变形过程中的组织演变和加工硬化行为

Microstructural Evolution and Work Hardening Behavior of Fe-19Mn Alloy Containing Duplex Austenite and ε-Martensite

采用OM、EBSD、TEM、XRD和拉伸实验等方法,研究了γ-奥氏体/ε-马氏体双相Fe-19Mn-0.0017C(质量分数,%)合金在拉伸变形过程中的组织演变和加工硬化行为。结果表明,Fe-19Mn发生了变形诱导马氏体相变,并且随着变形量的增加,相变过程由以γ→ε相变为主转变为以ε→α’相变为主。对比分析加工硬化率的变化与相含量的变化,表明ε→α’相变比γ→ε相变具有更高的加工硬化能力。同时,在变形过程中,ε-马氏体不仅发生了位错滑移,还形成了■孪晶,以满足ε-马氏体的变形协调。在γ→ε和ε→α’双重相变引起的相变诱导塑性(TRIP)效应、γ-奥氏体/ε-马氏体/α’-马氏体中的位错滑移,以及ε-马氏体的孪生变形等机制的共同作用下,Fe-19Mn的抗拉强度和总延伸率分别达到722 MPa和31%,显示出良好的强塑性匹配。

As the excellent combination of strength and ductility,the high manganese steel has been used in the manufacturing field of automobile,liquefied natural gas(LNG)ship and oil and gas exploitation.On the other hand,due to the good damping capacity within a certain Mn content range,it has also been used to make components on the machines to reduce vibration and noise.So high manganese steel is considered to be a structural and functional integrated material with great application prospects.Many factors can affect the mechanical properties and damping capacity,such as chemical composition,grain size and heat treatments.Among these,carbon concentration has a complicated influence on them.For example,a high carbon concentration will improve mechanical properties,but in return deteriorate damping capacity.In order to acquire a material with good damping capacity and suitable strength and ductility,ultralow carbon Fe-19Mn-0.0017C(mass fraction,%)alloy was designed.The microstructura evolution and mechanical properties of the alloy during tensile process were investigated by means of OM,EBSD,TEM,XRD and tension test.The results show that Fe-19Mn shows deformation-induced martensite transformation,which changes fromγ-austenite→ε-martensite transformation toε-martensite→α’-martensite transformation as the amount of deformation increases.Analysis of the strain hardening rate(ln(dσtrue/dεtrue))combined with the fraction of constituent phases reveals that the transformation ofε-martensite→α’-martensite is more effective in improving work hardening rate than that ofγ-austenite→ε-martensite.This is,on one hand,because of the lower strength ofε-martensite which is caused by the lack of carbon solution strengthening;and on the other hand,α’-martensite has higher hardness thanε-martensite,which can impede dislocation movement more effectively.In addition,{101ˉ2}<1ˉ011>εdeformation twins are formed to accommodate deformation ofε-martensite except for dislocation slip during tensile process.The combined action of transformation induced plasticity(TRIP)effects ofγ-austenite→ε-martensite→α’-martensite transformation,dislocation slip ofγ-austenite/ε-martensite/α’-martensite and■deformation twinning makes Fe-19Mn with ultralow carbon concentration have an excellent combination of strength and ductility,whose tensile strength and total elongation can reach 722 MPa and31%,respectively.