利用EBSD, HRTEM与热膨胀仪等实验手段对低碳中锰钢在淬火+回火 (QT) 与淬火+片状淬火+回火 (QLT) 工艺下的奥氏体形貌与相变过程进行了对比分析. 结果表明, QT与QLT工艺下所生成的回转奥氏体形貌、尺寸、位置以及由此导致的奥氏体稳定性差异是造成实验钢力学性能特别是低温冲击韧性巨大差异的最主要原因. 热力学与动力学分析表明, 由于QLT工艺在淬火+片状淬火 (QL) 阶段完成了C和Mn元素的第一次配分, 因而相比于QT热处理工艺, QLT工艺下回转奥氏体在生成速率显著提高的同时其生长模型也由一维双向增厚模式演变成一维单向增厚模式.
With the development of marine resources and its emerging markets, the marine equipments such as offshore drilling platform, subsea oil and gas transportation pipeline, and storage equipment of oil and gas are developing actively. It is urgent to develop a new type of steel with low cost and excellent toughness to satisfy the demand of marine equipment. In this work, the morphology of austenite and phase transition process in medium manganese steel during quenching and tempering (QT) and quenching, lamellarizing and tempering (QLT) heat treatments were investigated by using EBSD, HRTEM and thermal dilatometer. The results show that the discrepancy of stability in austenite caused by its shape, size and location leads to the more excellent toughness during QLT heat treatment compared to QT. It has been found from thermodynamical and dynamical viewpoint that the formation rates of reverted austenite during QLT heat treatment are significantly larger relative to QT due to the partition process of C and Mn elements in the lamellarizing stage. Moreover, two growth models of film-type reverted austenite are distinct during two heat treatments: the unidimensional two-sided growth mode during QT and unidimensional one-sided growth mode during QLT.
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