Microstructure Development and Mechanical Properties of Low-Silicon-Content TRIP-Assisted Steels after Coiling Process

• Published in: Steel research international Vol. 87; no. 2; pp. 146 - 156
• Main Authors: Hosseini, Seyed Mohammad Kazem, Zarei-Hanzaki, Abbass, Yue, Steve
• Format: Journal Article
• Language: English
• Published: Weinheim Blackwell Publishing Ltd 01.02.2016; Wiley Subscription Services, Inc
• Subjects: bainite transformation; Mechanical properties; Microstructure; retained austenite; Simulation; Steel; Temperature; thermomechanical process; TRIP-assisted steels
• ISSN: 1611-3683; 1869-344X
• DOI: 10.1002/srin.201400525

In the present study, laboratory simulation of hot‐strip rolling followed by coiling process was carried out in order to investigate the effect of bainite transformation on microstructure development and mechanical properties of low‐silicon‐content TRIP‐assisted steels. Following a typical multistage isothermal deformation and cooling path, compression samples were quenched into a salt bath at various temperatures within bainite transformation range and held for different periods of time. The results indicated a decrease in either bainite holding time or temperature resulted in an increase in TS, whereas both T‐El% and formability index have shown maximum values at some intermediate bainite holding temperature and time. Variation of TS with holding time was correlated to the fraction of martensite and microstructural coarsening whilst the changes in T‐El% and formability index were appeared to follow the same trend as VRA. Additionally, the presence of thermal martensite provides a shielding effect on RA particles during straining, thereby postponing strain‐induced transformation of austenite to martensite during subsequent deformation. Variations of T‐El% and formability index with bainite holding temperature were also rationalized by considering the effect of bainite holding temperature on the characteristics of retained austenite and its surrounding matrix. Thermomechanical control processing (TMCP) of TRIP‐assisted steels is introduced as a potential energy saving alternative to the common processing route of cold‐roll and two‐stage heat treatment process. The present research indicates that an outstanding balance of strength–ductility can be achieved through development of a multiphase microstructure when it is subject to a typical multi‐stages cooling/deformation program followed by short bainitic holding.