EBSD技术在厚规格管线钢DWTT研究中的应用

Application of EBSD technology on DWTT research of thickness specification pipeline steel

利用电子背散射衍射（EBSD）技术和金相分析软件,结合DWTT性能测试,对3种厚规格X70管线钢板的微观组织、取向成像特点、有效晶粒尺寸和DWTT性能进行了分析。结果表明,3种管线钢的取向差分布均在2°~15°和47°~60°两区间,呈现＂双峰＂分布特点。铁素体基体与母相奥氏体间存在一定的取向关系是管线钢中晶界取向差＂双峰＂分布的主要原因。在针状铁素体或贝氏体为基体的显微组织中,引入适量细化的多边形铁素体可以降低其平均有效晶粒尺寸,但多边形铁素体体积分数过多、晶粒尺寸过大时,反而会使有效晶粒尺寸增大。有效晶粒细化是提高试验钢DWTT断裂韧性的主要原因。

The orientation image characteristic of microstructure of three thickness specification pipeline steels was analyzed by means of electron back scatter diffraction（ EBSD） technology combining with DWTT test. The results show that the misorientation of the three pipeline steels are all distributed at the range of 2°-15° and 47°-60°,which presents ＂doublet peak＂feature. The main reason of this is the existing of the certain orientation relationship between ferrite and parent austenite. Adding appropriate refined polygonal ferrite to the steel whose matrix is acicular ferrite or bainite could decrease the mean effect grain size. However,the excessive volume fraction and too large grain size of polygonal ferrite would increase the effect grain size. The refined effect grain size is the main reason to improve the DWTT fracture toughness of test steels.