The dynamic impact response of AISI 321 steel at strain rate of 4000, 5500, 6500 and 7500 s⁻¹ was investigated using the split Hopkinson pressure bar system. The alloy samples processed to have grain size of 0.24, 3, 13 and 34 µm were studied. While the yield strength and hardness increases with decrease in grain size, strain hardening rate is comparable for all grain sizes. Microstructural evaluation of the impacted specimens using high-resolution electron backscattered diffraction (HR-EBSD) technique showed grain boundary strengthening, deformation twinning, deformation-induced martensitic transformation, dislocation multiplication during slip and precipitation of carbides that act as barriers to dislocation motion as additional source of strengthening. Slip and twinning were the dominant deformation mechanisms observed in the steel. Twinning, dislocation multiplication during slip and carbide precipitation contributed more strongly to strain-hardening in coarse-grained (CG) specimen while stain-induced martensite and grain boundary strengthening are the most beneficial to strengthening in the ultra-fine-grained (UFG) specimens. The temperature rise in the specimens during impact increases with strain rate. This slowed the kinetics of twinning, phase transformation and dislocation interaction especially in CG structure. Both XRD and HR-EBSD texture results confirmed the development of {110}||CD (CD: compression direction) texture in the austenite phase at the expense of {100}||CD and {111}||CD fibres. Thermomechanical instability leading to the formation of adiabatic shear band (ASB) occurred in the test specimens as they deformed at high strain rates. While the amount of deformation twinning and αʹ-martensite decreases towards the ASB, only the carbides and small fraction of αʹ-martensite are observed inside the ASB. Grain refinement via rotational dynamic recrystallization occurred within the ASB. The extent of grain refinement increased with increase in initial grain size of the test specimen.

AISI 321钢在4000、5500、6500和7500 s ^-1应变速率下的动态冲击响应使用分开的Hopkinson压力杆系统进行了研究。研究了加工成具有0.24、3、13和34 µm晶粒尺寸的合金样品。尽管屈服强度和硬度随着晶粒尺寸的减小而增加，但应变硬化速率对于所有晶粒尺寸都是可比的。使用高分辨率电子背散射衍射（HR-EBSD）技术对受冲击试样的显微组织评估表明，晶界强化，形变孪生，形变引起的马氏体相变，滑移过程中的位错倍增以及碳化物的沉淀是位错运动的障碍。加强的来源。滑移和孪生是在钢中观察到的主要变形机制。结对 滑移和碳化物析出过程中的位错倍增对粗晶粒（CG）试样的应变硬化贡献更大，而污点诱导的马氏体和晶界强化对超细晶粒（UFG）试样的强化最有利。试样在冲击过程中的温升随应变速率的增加而增加。这减慢了孪晶，相变和位错相互作用的动力学，特别是在CG结构中。XRD和HR-EBSD织构结果均证实了{110} || CD（CD：压缩方向）织构在奥氏体相中的发展，但消耗了{100} || CD和{111} || CD纤维。当试样以高应变速率变形时，会导致绝热剪切带（ASB）形成的热机械不稳定性。虽然形变孪晶和αʹ-马氏体的数量向ASB减小，但在ASB内部仅观察到碳化物和少量的αʹ-马氏体。在ASB内通过旋转动态重结晶进行晶粒细化。晶粒细化程度随试样初始晶粒尺寸的增加而增加。