初始组织对20CrMnTi钢伪渗碳过程中奥氏体化相变与晶粒长大行为的影响

研究了20CrMnTi钢球化退火过程中的渗碳体析出行为及其与铁素体回复和再结晶的相互作用,着重分析了热轧态、淬火态和球化态3种初始组织在伪渗碳过程中的奥氏体化相变与晶粒长大行为。结果表明,热轧态和淬火态试样分别具有均匀粗大的“铁素体+珠光体”组织和均匀细化的马氏体板条组织;在球化态试样中,由于球化时碳化物析出与马氏体基体回复、再结晶的相互作用,基体组织与碳化物均存在微观非均匀现象。经伪渗碳后,奥氏体平均晶粒尺寸按热轧态、淬火态和球化态次序依次减小,但不均匀性因子按该次序依次增大;与初始组织相关的奥氏体形核密度与形核均匀性是控制渗碳过程中奥氏体晶粒长大行为的关键因素之一。

Effect of initial microstructure on austenite transformation and grain growth behavior of 20CrMnTi steel during pseudo-carburizing process

The cementite precipitation behavior of 20CrMnTi steel during spheroidizing annealing and its interaction with ferrite recovery and recrystallization were studied, and the effects of initial microstructure as-in hot-rolled state, quenched state and spheroidizing annealed state on austenite transformation and grain growth behavior during pseudo-carburizing were emphatically analyzed. The results show that coarse ferrite + pearlite microstructure and uniform fine lath martensite microstructure can be found in the hot-rolled and quenched specimens, respectively. However, the matrix and the carbide microstructures in the spheroidized specimens are nonuniform in micro-scale due to the interaction of carbide precipitating with recovery, recrystallization of martensite matrix. During pseudo-carburizing, the average grain size of austenite decreases in the order of hot rolled state, quenched state and spheroidizing annealed state, but the non-uniformity factor increases in the same order. The nucleation density and homogeneity of austenite related to the initial microstructure are one of the key factors controlling the austenite grain growth behavior during carburizing.