Fe-Mn-Al轻质高强钢组织和力学性能研究

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Fe-Mn-Al LIGHT-WEIGHT HIGH STRENGTH STEEL

对热轧态与固溶处理后Fe-Mn-A1轻质高强钢进行力学性能检测及组织形貌观察，分析950～100℃固溶处理工艺对其组织和力学性能的影响规律．根据真实应力一应变曲线和加工硬化曲线分析拉伸变形特征，对比拉伸变形前后微观组织形貌和XRD谱，研究其微观变形机理．研究结果表明，所设计的成分体系实验用钢，热轧后为奥氏体基体与少量带状铁素体的双相组织，密度为6．55g／cm3，达到了轻质高强的设计目标．固溶处理有利于奥氏体晶粒长大与带状铁素体的破碎分解，使钢板强度降低而塑性提高，但是过高的固溶温度会促进铁素体长大，使铁素体体积分数增大，钢的断后伸长率降低．1050℃固溶处理后Fe-Mn-A1钢抗拉强度为925．9mPa，断后伸长率为50．20％，强塑积为46．48GPa％．连续的应变强化行为使得Fe-Mn-A1钢获得高强度与塑性的良好匹配，稳定硬化阶段应变范围越宽，断后伸长率越大；较高的层错能使其变形机理区别于TRIP和TWlP效应，变形后仍为奥氏体＋铁素体双相组织，变形后奥氏体中可以观察到Taylor晶格、高密度位错墙以及微带结构，为明显的平面滑移特征．

The automobile industry pays lots of attention on a new kind of steel with excellent combination of strength and ductility as well as the lower density, aiming at developing more affordable and safe vehicles with less fuel composition and air pollution. Fe-Mn-A1 steel, adding more A1 and C elements into twinning induced plas- ticity （TWIP） steel, shows amazing mechanical properties, corrosion resistant and weight reduction than traditional steel. The mechanical properties and microstructure of Fe-27Mn-11.5AI-0.95C-0.59Si steel after hot rolling and sol- id solution treatment were investigated to analysis the evolution within the range of 950～1100 ℃. Based on the true stress-strain curves and corresponding strain hardening rate, the characteristic of Fe-Mn-AI steel could be ob- tained. The deformation mechanism was learned by comparing the microstructure and XRD after tensile deforma- tion. The results show that, with the designed composition system, hot rolled steel has the duplex structure of aus- tenite matrix and small amount of banded ferrite with tensile strength of 1315.6 MPa and density of 6.55 g/cm3, which achieves the research targets of high strength and light-weight. Solid solution treatment contributes to austen- ire growth and banded ferrite crushing. But exorbitant temperature results in coarse and higher volume fraction of ferrite, and the ductility drops as well as the strength. The tensile strength and elongation of the steel solution treat- ed at 1050℃ are 925.9 MPa and 50.20%, respectively. Product of tensile strength and elongation is 46.48 GPa %. Continuous strain hardening behavior provides Fe-Mn-A1 steel with perfect combination of strength and ductility.The wider the constant hardening stage, the larger of measured elongation. With the estimated stack fault energy of 86 mJ/m^2, the dual phase structure of austenite and ferrite is retained after tensile deformation other than transfor- mation induced plasticity （TRIP） or TWIP effects, and the microstructure of deformed sample, including Taylor lat- tice, high density dislocation wall and microband, shows the obvious characteristic of planer gliding with obvious slip bands on the surface of deformed austenite. The dislocation gliding observed by TEM is consistent with MBIP theory and should be confirmed by a mount of experiments and contrast in further.