回火温度对Mn-Ni钢亚稳奥氏体形貌及其力学性能的影响

 利用了X射线衍射仪（XRD）、电子背散射衍射（EBSD）和透射电子显微镜（TEM）研究了回火温度对一种Mn-Ni钢亚稳奥氏体形貌及其力学性能的影响。结果表明，随着回火温度的升高，室温亚稳奥氏体的体积分数逐渐升高。当回火温度为600和625 ℃时，亚稳奥氏体主要以片层状在回火马氏体板条间析出，且排列方向与周围的马氏体板条平行，这种片层状亚稳奥氏体分布较为均匀，尺寸较小，约为60～100 nm，且稳定性较高；当回火温度为650 ℃时，试验钢中出现尺寸较大的块状奥氏体在回火马氏体界面的交叉处不均匀析出。分析表明，块状奥氏体有利于提高钢的塑性，不利于改善钢的低温韧性；而片层状奥氏体能大幅度的改善钢的低温韧性。

Effects of Tempering Temperature on Morphology of Metastable Austenite and Mechanical Properties of Mn-Ni Steel

Effects of tempering temperature on morphology of metastable austenite and mechanical properties of Mn-Ni steel were investigated by X-ray Diffraction (XRD), Electron Back Scattering Diffraction (EBSD) and Transmission Electron Microscope（TEM）. The results show that the volume fraction of metastable austenite at room temperature increased with the increase of tempering temperature. When tempering temperature was 600 and 625 ℃, metastable austenite mainly precipitated in the shape of thin film along the lath boundaries of tempered martensite, paralleling to the surrounding martensitic laths. This thin film metastable austenite had a dense distribution, with the thickness ranging from 60 to 100 nm, and had a good stability; when the tempering temperature was 650 ℃, thin film metastable austenite decreased dramatically and large block metastable austenite precipitated unevenly on the intersections of grain boundaries of tempered martensite. Analysis indicates that block metastable austenite is beneficial to the ductility of test steel, but it goes against to improving low temperature toughness; while thin film metastable austenite can improve low temperature toughness significantly.