汽车用低密度TRIP钢中残余奥氏体机械稳定性研究

Taking into account that the surface quality and galvanizing property of traditional high Si-TRIP steel are poor, partial or total substitution of Si by Al will be employed in this project. The density of TRIP steel can also be reduced by adding high content Al. As a result, the weight of vehicle is reduced, energy saving and emission reduction are also realized. Because the mechanical properties of TRIP steel is related to the mechanical stability of retained austenite (RA), it is essential to research the mechanical stability of RA in low-density high Al-TRIP steel. .By conducting hot/cold rolling, heat treatment and stepwise uniaxial tensile tests, combining XRD, EBSD, SEM and TEM, the influences of Al content and heat treatment conditions on volume fraction and mechanical stability of RA will be investigated. Furthermore, the influences of carbon content, morphology, size, distribution of RA on the mechanical stability of RA will be in investigated. At last, the influences of deformation temperature, strain rate and stress state on the mechanical stability of RA will be also investigated. The results will provide theory foundation for developing low-density TRIP steel with good galvanizing property, to realize the reduction of weight of vehicle. This project has better application prospect due to further energy saving and emission reduction.

本项目针对传统高硅TRIP钢表面质量和涂镀性能较差的现状，提出采用以铝替代或部分替代硅来生产TRIP钢。在TRIP钢中加入较高含量的铝还可以降低TRIP钢的密度，达到降低车身重量、节能减排的目的。由于TRIP钢的力学性能与残余奥氏体的机械稳定性密切相关，就有必要研究低密度高铝TRIP钢中残余奥氏体机械稳定性。.本项目利用热/冷轧实验、热处理实验、分阶段拉伸实验，结合XRD、EBSD、SEM、TEM等分析设备研究铝含量和热处理条件对低密度TRIP钢中残余奥氏体含量及其机械稳定性的影响。此外，还要研究残余奥氏体的碳含量、形貌、尺寸、分布位置等内在因素以及变形温度、应变速率、应力状态等外部因素对残余奥氏体机械稳定性的影响。该项目的研究结果可以为开发具有良好涂镀性能的低密度TRIP钢奠定理论基础，实现车身重量的降低，达到进一步的节能减排，因此本项目具有良好的发展前景。

本项目以含铝TRIP钢为研究对象，首先研究了铝含量和热处理工艺对TRIP钢显微组织和力学性能的影响。指出当铝含量从2%增加到6%，TRIP钢中的铁素体平均晶粒尺寸增加、残余奥氏体体积分数降低，其强塑积也随之降低。低的两相区退火温度和高的贝氏体等温温度有利于提高TRIP钢的抗拉强度。接着研究了残余奥氏体形貌和尺寸对其机械稳定性和力学性能的影响。实验结果表明，大块状残余奥氏体其机械稳定性最差，薄膜状残余奥氏体的机械稳定性最高，小块状残余奥氏体稳定性位于两者之间。块状残余奥氏体对抗拉强度和瞬时应变硬化指数的贡献较高，而薄膜状残余奥氏体有利于获得较高的延伸率和强塑积。最后研究了应变速率、变形温度和应力状态对残余奥氏体机械稳定性和力学性能的影响。发现在0.0001~0.01/s应变速率范围内，实验钢的强度对应变速率不敏感，应变速率对残余奥氏体几乎没有影响。随变形温度从-50 ℃升高至100 ℃，实验钢的屈服和抗拉强度降低，但延伸率和强塑积增加，残余奥氏体的机械稳定性也随之增加。在双向拉伸应力状态、单向拉伸应力状态和单向剪切应力状态下，残余奥氏体的机械稳定性依次增加。通过本项目的研究，可丰富含铝TRIP钢中残余奥氏体机械稳定性控制的相关理论，为推动含铝低密度TRIP钢在汽车车身上的应用、促进汽车轻量化的发展做出贡献。