研究了不同的前躯体组织对于经临界区再加热—淬火—中温配分(IQ&P)处理所得的0.22C—1.9Mn—1.32Si多相钢的组织形貌和力学行为的影响. 相同的热处理工艺参数下,采用前躯体为马氏体(M)的组织设计倾向于在多相钢中获得板条状的铁素体和薄膜状(或短针状)的残余奥氏体;而采用前躯体为贝氏体—铁素体(B—F)的组织设计则倾向于在多相钢中获得块状的铁素体和近颗粒状的残余奥氏体.在本工作所用IQ&P工艺下, B—F前躯体多相钢尽管抗拉强度高达976 MPa, 但其延伸率只有26.7 %,使得其强塑积仅仅只有26 GPa•%; 而采用M前躯体设计可以使钢获得强度和塑性的优良结合,其强塑积超过31 GPa•%. 就均匀变形阶段的加工硬化行为而言,B—F前躯体多相钢尽管具有较高的加工硬化指数, 但其组织中的残余奥氏体稳定性较差, 因而瞬时加工硬化指数—真应变曲线的波动性很大, 随真应变的增大在外观上呈锯齿状;而M前躯体多相钢尽管加工硬化指数略低, 但其组织中的残余奥氏体具有较高的稳定性,因而瞬时加工硬化指数—真应变曲线较为平滑, 随真应变的增大呈逐次升高的趋势.产生上述不同力学行为的原因与钢中残余奥氏体和基体组织的形貌、比例和分布状态均有关,而上述因素从根本上又取决于不同前驱体自身的组织形貌与微观结构特征.

The effects of different precursor microstructure on the morphology and mechanical properties of the 0.22C—1.9Mn—1.32Si multiphase steel which was obtained by the treatment of intercritical reheating—quenching and partitioning (IQ&P) heat treatment were examined. Under the same IQ&P heat treatment parameters, multiphase microstructure which contains lath—like ferrite matrix and film or short needle—like retained austenite can be obtained by the martensite (M) precursor steel; while multiphase steel which has a bainite—ferrite (B—F) precursor can obtain a microstructure of equiaxed—like ferrite matrix and particale like retained austenite. After the IQ&P process, tensile strength of the multiphase steel which has a B—F precursor is up to 976 MPa, but elongation of this kind of steel is only 26.7%, and thus the product of strength and elongation of this kind of steel is only 26 GPa•%; while multiphase steel which has a M precursor has realized the combined properties of high strength and excellent ductility, product of strength and elongation of this kind of steel reaches 31 GPa•%. As for the work hardening behavior of the uniform elongation stage, although B—F precursor multiphase steel has a higher work hardening index n than the M precursor multiphase steel, stability of the retained austenite in this kind of steel is relatively poor, variation behavior curve of the instantaneous n value with true strain for this kind of steel shows a notched—like shape; as for the multiphase steel which has a M precursor, retained austenite in this kind of steel is relatively stable, variation behavior curve of the instantaneous n value with true strain for this kind of steel is much more steady, which shows a trend of gradual increasing. The reason for the different tensile testing and work hardening results above is related to the morphology, proportion and distribution state of the retained austenite and matrix microstructures, which is due to the effect of different morphology and microstructure characteristics of the precursor phases by the roots.