Influence of pre-strain on microstructural characteristics and tensile deformation behaviour of a cold-rolled Al-containing medium Mn steel

• Published in: Journal of materials science Vol. 55; no. 12; pp. 5296 - 5310
• Main Authors: Wang, Jiao-Jiao, Hui, Wei-jun, Xie, Zhi-qi, Zhang, Yong-jian, Zhao, Xiao-li
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.04.2020; Springer; Springer Nature B.V
• Subjects: Aluminum; Annealing; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Cold; Cold rolling; Cold stamping; Cold-rolled steel; Control engineering; Crystallography and Scattering Methods; Deformation mechanisms; Diffraction; Dislocation density; Electron backscatter diffraction; Electron microscopy; Elongation; Luders lines; Manganese steels; Martensite; Martensitic transformations; Materials Science; Mechanical properties; Metal sheets; Metals & Corrosion; Microscopy; Microstructure; Plastic deformation; Plastic properties; Polymer Sciences; Retained austenite; Service life; Sheet-steel; Solid Mechanics; Steel; Strain; Tensile deformation; Twinning; Twins; Ultimate tensile strength; X-rays
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-019-04337-3

Automobile steel sheet parts often experience unavoidable plastic deformation during cold stamping forming and service life. In this study, we explored the microstructure variation and tensile deformation behaviour of a cold-rolled Al-containing medium Mn steel (0.25C–8.67Mn–0.54Si–2.69Al, wt%) subjected to different degrees of pre-straining by tensile testing, scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction and X-ray diffraction. The cold-rolled steel sheet processed by intercritical annealing at 725 °C for 60 min exhibited a superior combination of strength and ductility [the product of ultimate tensile strength (UTS) and total elongation (TEL), UTS × TEL] as high as 69 GPa% due to the TWIP (twinning-induced plasticity) and TRIP (transformation-induced plasticity) plasticity-enhancing mechanism during tensile deformation. The tensile behaviour, which originally exhibited notable Lüders plus Portevin–Le Châtelier (PLC) banding phenomenon, was significantly changed by pre-straining. The strength increased, while the TEL and UTS × TEL decreased linearly with an increase in the pre-strain. A pre-strain equalling to the Lüders strain, i.e. 3%, could cause an elimination of the Lüders bands, while it had almost no influence on the PLC bands. The increase in the dislocation density, the enhanced stability of retained austenite and the strain-induced martensite and mechanical twins caused the reduction and elimination of the Lüders bands with increasing amounts of pre-strain.