Assessing neighbourhood effects on martensitic transformations in complex-phase steels

Transformation-Induced Plasticity and complex-phase steels exploit deformation-induced austenite-to-martensite transformations to achieve both exceptional strength and ductility. Prior grain-averaged measurements during beamtime MA4750 have demonstrated the sensitivity of austenite stability, a key predictor of mechanical properties, to austenite grain orientation, size and neighbourhood configuration. However, deviations from these Type-II relationships were observed, - for example, the orientation of martensite grains was correctly predicted from the parent austenite grain orientation and the Type-I stress state of the material, but these predictions failed 25% of the time, which was attributed to the presence of Type-III sub-grain strain fields that modify the local martensite orientation selection criteria. Scanning 3D X-Ray Diffraction and DCT will therefore be used in-situ to measure these features over a range of complex-phase steel alloy compositions and deformation levels.

相变诱导塑性（Transformation-Induced Plasticity）与复相钢依托形变诱导的奥氏体-马氏体相变，可同时实现优异的强度与塑性表现。此前在束流时间MA4750（beamtime MA4750）期间开展的晶粒平均测量已证实，作为力学性能关键预测指标的奥氏体稳定性，对奥氏体晶粒取向、尺寸及邻域构型具有敏感性。然而，研究观测到与第二类（Type-II）相变关系存在偏离的现象：例如，尽管可通过母相奥氏体晶粒取向与材料的第一类（Type-I）应力状态，准确预测马氏体晶粒的取向，但此类预测仍存在25%的失败率，该现象被归因于第三类（Type-III）亚晶粒应变场的存在——此类应变场会改变局部马氏体取向选择准则。因此，本研究将采用扫描三维X射线衍射（Scanning 3D X-Ray Diffraction）与DCT开展原位测量，以在多种复相钢合金成分与变形量条件下，表征上述关键特征。