亚临界区淬火温度对一种新型“锰代镍”低温钢组织演变及力学性能的影响

Effects of Intercritical Quenching Temperature on Microstructural Evolution and Mechanical Properties of a New Type of Cryogenic Steel With Ni Replaced by Mn

利用X射线衍射仪(XRD)、电子背散射衍射(EBSD)和透射电子显微镜(TEM)研究了亚临界区淬火温度对一种新型"锰代镍"低温钢组织演变及力学性能的影响。结果表明,随着亚临界区淬火温度的升高,室温亚稳奥氏体的体积分数逐渐降低。当亚临界区淬火温度为700和740℃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,厚度约为100nm,且稳定性较高;当亚临界区淬火温度为780℃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,不同热处理制度下基体"有效晶粒"尺寸、所生成的亚稳奥氏体体积分数及其稳定性的不同是导致不同亚临界区淬火温度下试验钢低温韧性差异的主要原因。

Effects of intercritical quenching temperature on microstructural evolution and mechanical properties of a new type of cryogenic steel with Ni replaced by Mn were investigated by XRD, EBSD and TEM. The results show that the volume fraction of metastable austenite at room temperature decreases with the increase of intercritical quenching temperature. When interctritical quenching temperature is at 700 or 740℃, metastable austenite mainly precipitates in the shape of thin film along the lath boundaries of tempered martensite, paralleling to the surrounding martensitic laths. This ＂film-type＂ metastable austenite is uniformly distributed and stable, with a thickness of about 100 nm. When intercritical quenching temperature is 780 ℃, the volume faction of ＂film type＂ metastable austenite decreases, and large ＂blocky-type＂ metastable austenite appears at the junction of interface of tempered martensite. Analysis indicates that the differences on ＂effective grain size＂ of matrix, volume fraction of metastable austenite and its stability caused by different heat treatment process lead to the difference on low temperature toughness of the tested steel at different intercritical quenching temperature.