淬火回火低碳合金钢亚温退火过程中奥氏体的形成

本文研究了原始组织分别为“回火马氏体”和“回火冷轧马氏体”的10Mn CrNi Mo V钢亚温退火过程中奥氏体的形成。研究结果表明:奥氏体形成是形核和长大的过程。奥氏体优先在位于铁素体晶界和铁素体板条界上的碳化物处形核。奥氏体长大,在较低的亚温退火温度下,由晶界扩散控制,而在较高的亚温退火温度下,则由体积扩散所控制。亚温退火过程中发生锰的再分配,在奥氏体/铁素体界面上锰浓度有极大值,而在邻近的铁素体中的锰浓度有极小值,它减慢奥氏体的长大速度并控制显微组织的均匀化。奥氏体形态对原始组织很敏感,当原始组织为“回火马氏体”时,奥氏体为纤维状和半网状的混合形态;当原始组织为“回火冷轧马氏体”时,奥氏体为等轴状。

AUSTENITE FORMATION IN QUENCHED AND TEMPERED LOW-CARBON-ALLOY STEEL DURING INTERCRITICAL ANNEALING

The austenite formation process during intercritical annealing 10MnCrNiMoVsteel with original microstructures of both tempered martensite and temperedcold rolled martensite is studied. The experimental results show that the auste-nite formation consists of nucleation and growth stages. Austenite preferen-tially nucleates on the carbides located on grain boundaries and lath bounda-ries of ferrite. The growth of austenite is controlled by boundary diffusion atlower intercritical annealing temperature and by bulk diffusion at higher inter-critical annealing temperature. The manganese is redistributed during intercri-tical annealing. There exist maxima of manganese concentration at the auste-nite/ ferrite interface and minima of manganese concentration in the adjacentferrite. It slows down the growth of austenite and dominates the final homo-geneity of microstructure. The austenite morphology is structurelly sensitive,such as the mixture of fibrous and quasi-net austenite is obtained from tem-pered martensite structure, and the equiaxed austenite is obtained from temperedcold rolled martensite.