两段式冷却对C-Mn钢奥氏体中温转变的影响

Influence of two-stage cooling on intermediate transformation of undercooled austenite in C-Mn steel

采用Formastor全自动相变仪进行了两段式冷却条件下C-Mn钢的热膨胀试验,并结合组织观察和显微硬度测量,研究了冷却速度以及发生部分先共析铁素体转变对奥氏体中温转变的影响。结果表明:随着冷却速度的增大和先共析铁素体含量的增加,贝氏体相变开始温度和结束温度均降低,贝氏体转变量减少;奥氏体随冷却速度的增大,转变产物由铁素体+珠光体逐渐变为魏氏组织铁素体+珠光体、网状铁素体+魏氏组织+贝氏体、马氏体的趋势;而对已发生部分先共析铁素体转变的过冷奥氏体,随先共析铁素体含量的减少,组织由魏氏组织+贝氏体向魏氏组织+马氏体转变。

Characteristics of intermediate transformation of undercooled austenite in C-Mn steel were investigated by means of two-stage cooling dilatometric experiments on a full-automatic transformation test instrument Formastor, and microstructure observation and micro- hardness tests of the experimental samples. Both the effect of cooling rate on the intermediate transformation of the single-phase austenite and the effect of proeutectoid ferrite content in the undercooled austenite matrix, in which different degree of partial transformation of proeutectoid ferrite had occurred, on the intermediate transformation of the remaining austenite were analyzed. The results show that with the increasing of cooling rate and proeutectoid ferrite content, both the bainite transformation start temperature and finish temperature decrease, and the amount of transformed bainite decreases. For the single-phase undercooled austenite, when the cooling rate increases, the transformation products may change from the ferrite plus pearlite to widmanstatten ferrite, ferrite net plus widmanstatten structure plus bainite, and lath-shape martensite gradually. While for the undercooled austenite in which partial transformation of proeutectoid ferrite has occurred, with the decreasing of the proeutectoid ferrite content the bainitic transformation products may change from widmanstatten structure plus bainite to widmanstatten structure plus martensite.