77MnA线材脆性断裂与心部马氏体分析

Analysis on Brittle Fracture of 77MnA Wire Rod and Core Martensite

在77MnA线材拉拔终端、拉拔中段和拉拔之前发生脆性断裂的试样中都存在心部马氏体,并且,在拉拔中段的试样中马氏体断成竹节状,在拉拔终端的试样中马氏体与屈氏体基体之间存在孔洞。可以认为脆性的马氏体不能在拉拔过程中与屈氏体协调形变是导致试样开裂的原因。心部马氏体中铬、锰等稳定奥氏体的元素明显偏高,因此,77MnA线材脆性断裂与成分偏析也有一定关系。

Core martensite can be found existing in the brittle fracture samples of 77MnA wire rod in the intermediate and final drawing stages as well as prior to the drawing process, and in the intermediate drawing stage the martensites in the sample are broken into bamboo knot shape and in the end stage holes are existing between martensites and troostites in the test sample. It＇ s considered that in the process of drawing the martensites can＇ t be coordinately transformed together with the troostites, and it will inevitably lead to the fracture of the sample. In the core martensites the austensite stabilizers such as Cr and Mn are prominently higher. It＇ s concluded that the brittle fracture of 77MnA wire rod is related with the segregation of compositions to some extent.