Strain Rate Dependent Ductility and Strain Hardening in Q&P Steels
Strain Rate Dependent Ductility and Strain Hardening in Q&P Steels
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DOI：
10.1007/s11661-020-06127-y
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发表时间：
2021-01-19
影响因子：
2.8
通讯作者：
Clarke, Kester D.
中科院分区：
文献类型：
--
作者：
Finfrock, Christopher B.;Thrun, Melissa M.;Clarke, Kester D.
由于其高强度，可成形性和可承受的成本，淬火和分区（Q&P）钢已显示出降低车辆质量的潜力，从而降低服务期间的燃料消耗。此外，由于每辆车使用的钢材质量较低，因此与炼钢过程相关的能源消耗也减少了。Q&P钢利用亚稳残留奥氏体的形变诱发马氏体相变（DIMT）来增强延展性和应变硬化。因此，机械性能的改善取决于精确控制奥氏体的化学和机械稳定性的能力。考虑到影响奥氏体稳定性的众多因素，优化微观结构以延迟颈缩或断裂是具有挑战性的，特别是随着温度和应变速率的增加。在10（-4）~ 10（-1）s（-1）的应变速率范围内对临界区退火的C-Mn-Si Q&P钢进行拉伸试验，以评估对DIMT和板材拉伸性能的影响。当应变速率从10（-4）s（-1）增加到10（-1）s（-1）时，均匀延伸率从大约19%减小到14%。这种均匀延伸率的降低与应变局部化开始附近的应变硬化指数的降低有关。基于本研究的实验数据和对以往研究的回顾，可以推测DIMT的强化贡献是由以下竞争效应控制的：（i）在较高应变速率下由变形引起的热积聚引起的DIMT的化学驱动力降低和（ii）马氏体形核位点数量增加。这表明针对特定变形条件定制奥氏体稳定性可以进一步优化可成形性和车辆碰撞行为。
Due to their high strength, formability and affordable cost, quenched and partitioned (Q&P) steels have shown the potential to reduce the mass of vehicles, thereby decreasing fuel consumption during service. Furthermore, because a lower mass of steel is used in each vehicle, energy consumption associated with the steelmaking process is also reduced. Q&P steels utilize the deformation-induced martensitic transformation (DIMT) of metastable retained austenite to enhance ductility and strain hardening. Accordingly, improvement of mechanical performance is contingent on the ability to precisely control the chemical and mechanical stability of austenite. Considering the multitude of factors that influence austenite stability, optimizing microstructures to delay necking or fracture is challenging, particularly as temperature and strain rate increase. Tensile tests of an intercritically annealed C-Mn-Si Q&P steel were performed over a range of strain rates (10(-4) to 10(-1) s(-1)) to evaluate effects on the DIMT and sheet tensile properties. As strain rates increased from 10(-4) to 10(-1) s(-1), the uniform elongation decreased from approximately 19 to 14 pct. This reduction in uniform elongation is associated with a decrease in the strain hardening exponent near the onset of strain localization. Based on experimental data from this study and review of previous research, it is postulated that the strengthening contribution of DIMT is controlled by competing effects of: (i) a decreasing chemical driving force for DIMT caused by deformation-induced heat accumulation at higher strain rates and (ii) an increasing number of martensite nucleation sites. This suggests that tailoring austenite stability for specific deformation conditions could enable further optimization of formability and vehicle crash behavior.