The Effect of Thermo-Mechanical Processing Parameters on Microstructure and Mechanical Properties of a Low Carbon, High Strength Steel

• Published in: Steel research international 2014-03, Vol.85 (3), p.307-313
• Main Authors: Li, Da-Zhao, Liu, Yong-Chang, Cui, Tian-Xie, Li, Jian-Min, Wang, Yu-Tian, Fu, Pei-Mao
• Format: Article
• Language: English
• Subjects: Carbon; Coiling; Ferrites; Finishing; High strength steel; High strength steels; lath-like ferrite; Mechanical properties; Microstructure; Parameter identification; polygonal ferrite; retained austenite film; Steels; Strength; thermal mechanical control processing technology; Yield strength
• ISSN: 1611-3683; 1869-344X
• DOI: 10.1002/srin.201300097

High‐strength steel investigation is focused on the production of low carbon microalloying steel, particularly in the enhancement of steel strength through microstructure control, which is an urgent problem nowadays. This paper investigates the effect of various thermal mechanical control processing parameter on the properties and microstructures of Mn–Ti low carbon steels. The steel exhibited yield strength of 920 to 1069 MPa, elongation of approximately 10%, and impact absorbed energy between 16.7 and 45.3 J. At constant coiling temperature, more lath‐shaped carbonless ferrites, retained austenitic films with finer width, and island‐like twin martensites were generated. Strength and yield ratio increased with increase in finishing rolling temperature, but impact absorbed energy and total elongation decreased. When the finishing rolling temperature and coiling temperature were 860 and 220°C, respectively, the steel exhibited the highest strength and yield ratio but the lowest plasticity and toughness. At increased coiling temperature and unchanged finishing rolling temperature, more lath‐shaped ferrites with greater width were generated and gradually changed from carbonless to low‐bainite because of precipitations inside them. The width of the retained austenite increased with increase in coiling temperature. Thus, the strength and yield ratio decreased, but plasticity and impact toughness increased. The morphology of carbon‐free bainite ferrites (BFs) and remained austenite films which are located between them and acicular ferrite containing dislocation are presented in figure (a). The morphology of martensite (M) and dislocations (D) in acicular ferrite are indicated in figure (b).