不同应变速率下Fe-29Mn-3Al-3Si钢的冲击性能及微观组织研究

Microstructure and impact property of Fe29Mn3Al3Si steel at different strain rates

采用分离式Hopkinson压杆对冷轧退火态Fe-29Mn-3Al-3Si TWIP钢进行650 s^-1~3800 s^-1范围内高应变速率的动态冲击压缩实验。采用扫描电镜(SEM)、电子背散射衍射技术(EBSD)、X射线衍射(XRD)和透射电镜(TEM)等研究手段对冲击前后试样的微观组织结构进行表征。结果表明,在高速冲击条件下该TWIP钢具有正应变速率强化特性,且主要变形机制是孪生诱导塑性(TWIP)。随着应变速率及应变量增大,材料强度增加,形变孪晶数量增加,孪晶与位错交割加剧。在压缩变形过程中,〈001〉取向的晶粒易产生滑移和孪生,为软的晶体取向;而〈110〉取向晶粒中孪生和滑移的概率减少,为硬的晶体取向。随形变量的增加,逐渐形成〈110〉丝织构。高速冲击变形中的绝热效应使位错发生动态回复而对形变孪晶影响较少。TWIP效应、加工硬化、动态回复以及形变孪晶界的动态Hall-Petch效应大幅提高材料的高强度并保持高的塑性。

The dynamic compression test of the cold-rolled and annealed Fe29Mn3Al3Si TWIP steel was conducted by Split-Hopkinson Pressure Bar(SHPB)at high strain rates ranging from 650 s-1 to 3800 s-1.The microstructure of samples before and after impacting was characterized by scanning electron microscope(SEM),electron back scattering diffraction technology(EBSD),X-ray diffraction(XRD)and transmission electron microscopy(TEM).The results show that the materials exhibit positive strain rate sensitivity under high-speed impact.The main deformation mechanism is the twinning induced plasticity(TWIP).With the increase of strain rate,the strength of the material increases,and the number of deformation twins(DTs)increase,and the interaction between DTs and dislocations also increases.During the compression deformation process,the〈001〉oriented grains is soft owing to be easy for slipping and twinning,while the〈110〉oriented grains is hard owing to be difficult for slipping and twinning.With the increase of strain,the fiber texture gradually formed.The adiabatic heating induced by high strain-rate can make dislocation to dynamic recovery but has not obvious influence on DTs.The TWIP effect,work hardening,dynamic recovery and dynamic Hall-Petch induced by DTs improve greatly the strength of materials and keep the high ductility.