慢速加热中针状奥氏体形成过程的观察

OBSERVATION ON THE FORMATION PROCESS OF ACICULAR AUSTENITE DURINC SLOW-HEATING-UP

30CrMnSiA钢经1250℃预先淬火后在慢速(0.5℃/min)加热过程中,奥氏体最先呈短针状在原马氏体板条界上渗碳体处形核,而后沿原板条界长大连接成针状,进一步长大连接呈网状且布满整个原板条界,最后,沿垂直于原板条界方向长大连接,使原奥氏体晶粒复原,保留了原粗大的条状特征.在奥氏体刚形成时,未溶渗碳体呈短棒状分布于原马氏体板条界上.且部分渗碳体具有相同的空间取向.在转变结束前,余下少量的铁素体呈菱形.奥氏体可能是以台阶机制形成的.

During heating-up process at the rate of 0. 5癈/min of 30CrMnSiA steel, which is pre-quenched at 1250癈, austenite nucleates, in the form of short needle at the site of comentites on the boundary of prior martensite laths. Next, the austenites grow up and connect with each other to form acicular austenites along the boundary of o-riginal laths, and then the acicular austenites form a net array around boundary of prior ones. Finally, the austenites grow up in the vertical direction of the boundary of laths so that the original austenite grain reappeares and the fea-ture of thick lath remains. When austenites begin to nucleate, undissolved cementites in the shape of short rod pre-cipitate at orientation along the boundary of prior martensite laths and some cementites hold the same orientation. When the formation of austenite is near completion, the remaining ferrites are in the shape of rhombus. The austen-ites may form by the superledge-mechanism.