低合金TRIP钢中奥氏体逆相变行为对残余奥氏体影响的研究

Low alloy TRIP steel with martensitic matrix is an ideal material for automotive steel due to its excellent high strength and ductility balance and stretch-flangeability. The content and stability of retained austenite (RA) is a key factor determines the ductility of the TRIP steel. The RA in the low alloy TRIP steel with martensitic matrix is obtained though austenite reversion by intercrtical annealing and austempering. However, the previous studies are mainly concerns the effects of austempering temperature and time on the content and stability of RA. There is no systematic study on the effects of austenite reversion on the RA up to now. In order to make a better synergistic effect to control the RA, it is important to clarify the effects of austenite reversion on the formation of RA and the mechanisms for it. The Fe-Mn-Si-C low alloy TRIP steel is used in study. Quantitative study of the effects of intercritical annealing temperature and time on the austenite microstructure evolution and alloying elements partitioning will be performed at first. After this, the effects of austenite reversion on the content and stability of RA will be studied systematically. On the other hand, the intrinsic correlation between the microstructure of reverted austenite and retained austenite will be quantitatively studied. Through this study, the effects of reversion on the formation of RA can be clarified theoretically. In addition, this work can also provide theoretical and experimental evidences for the further adjust and control the high strength and toughness of the low alloy TRIP steel.

低合金马氏体基相变诱导塑性(TRIP)钢因具有优异的强塑性匹配和拉伸凸缘性能而成为汽车钢的理想材料。TRIP钢中残余奥氏体的含量与稳定性是决定其塑性的关键因素。马氏体基TRIP钢通过临界间退火奥氏体逆相变和贝氏体等温淬火工艺获得残余奥氏体。然而，以往的研究大多局限于等温淬火温度、时间对残余奥氏体含量及稳定性的影响，而奥氏体逆相变对残余奥氏体的影响，目前尚未有系统性研究。为更好发挥逆相变与贝氏体相变的协同作用调控残余奥氏体，需阐明逆相变对残余奥氏体形成的影响及其作用机理。本课题以低合金TRIP钢为研究对象，在定量研究退火温度和时间对奥氏体组织演变与合金元素配分影响的基础上，系统阐述逆相变对残余奥氏体含量及稳定性的影响；并量化分析逆转变奥氏体与残余奥氏体微观组织的内在关联性。通过本课题，不仅可从理论上揭示逆相变对残余奥氏体形成的影响，还可为进一步调控高强韧性低合金TRIP钢提供理论和实验依据。

马氏体基相变诱导塑性(TRIP)钢中残余奥氏体的含量与稳定性是决定其塑性的关键因素，马氏体基TRIP钢通过部分奥氏体逆相变和贝氏体等温淬火工艺制备。针对以往奥氏体逆相变对残余奥氏体影响研究的不足，本项目旨在揭示逆相变对残余奥氏体形成的影响及其作用机理，为更好发挥逆相变与贝氏体相变的协同作用调控残余奥氏体提供理论指导。项目以TRIP钢为研究对象，在定量研究退火温度和时间对奥氏体组织演变与合金元素配分规律的基础上，系统阐述逆相变对残余奥氏体含量及稳定性的影响，逆变奥氏体与残余奥氏体微观组织的内在关联性。.研究发现，加热速率和温度对逆变奥氏体组织形貌有重要影响。快加热速率或高逆相变温度促进了块状奥氏体的形成，反之则有利于针状奥氏体的形成。块状奥氏体不伴随置换性元素Mn、Si的配分，而针状奥氏体则伴随有元素Mn、Si的配分。随着退火时间的延长，针状奥氏体的Mn元素富集逐渐达到平衡含量。逆变奥氏体含量对残余奥氏体含量影响不明显，但逆变奥氏体组织形貌对残余奥氏体有显著影响。块状奥氏体转变为了块状残余奥氏体，而针状奥氏体则转变为了薄膜状残余奥氏体。这一重要发现表明，可以通过控制逆变奥氏体组织形貌来调控残余奥氏体。其次，残余奥氏体中的碳富集量超过了T0预测值，具有较好的化学稳定性。.其次，块状逆变奥氏体体积分数提高，TRIP钢屈服强度和抗拉强度提高，但延伸率降低，而针状奥氏体情况则具有接近40%的延伸率，抗拉强度接近1GPa的优越性能，TRIP效应得以充分的发挥。因此，奥氏体逆相变行为，特别是逆变奥氏体的组织形貌对残余奥氏体具有决定性作用。基于此，本项目还深入研究了逆变奥氏体的精细化调控。研究发现，渗碳体是块状奥氏体的形核位点，粗大尺寸的渗碳体颗粒促进了块状奥氏体的形成；先存残余奥氏体在逆相变过程中可直接长大形成针状奥氏体，避免了块状奥氏体的形成。本课题揭示了逆变奥氏体的形成机制，逆相变对残余奥氏体形成的影响，为调控高强韧性TRIP钢提供了理论和实验依据。.