Abstract
Abstract The effects of deformation on transformation kinetics during continuous cooling and microstructure evolution of a medium carbon high strength steel were investigated by metallographic method, dilatometry and X-ray diffraction etc. The results show that ausforming accelerated the ferrite and martensite transformation, but significantly retarded the bainite transformation. In addition, the amount of retained austenite decreased first and then increased, while the carbon content in retained austenite increased with the accumulation of strain. The change trend of the average dislocation density in martensite with strain showed the opposite trend as that of the amount of retained austenite. Moreover, the martensite laths were refined by ausforming. The work provides the theoretical reference for the design of parameters of thermalmechanical controlled process (TMCP) in the production of medium-carbon high strength steels.
Highlights
Controlled rolling and controlled cooling technology, normally termed as thermalmechanical controlled process (TMCP), has been successfully adopted in the production of high strength steels for many years[1,2]
According to the classification method to identify the microstructure proposed in Wang et al.[19], it is observed that the microstructure of non-deformed specimen consists of ferrite (F), bainite (B), martensite (M) or martensite/austenite (M/A) islands and Retained austenite (RA)
This may be attributed to the fact that more nucleation sites are induced by deformation, which is beneficial to the ferrite transformation at high temperature, resulting in more ferrite in deformed specimen
Summary
Controlled rolling and controlled cooling technology, normally termed as thermalmechanical controlled process (TMCP), has been successfully adopted in the production of high strength steels for many years[1,2]. Different continuous cooling schedules lead to different microstructures and mechanical properties. The study on continuous cooling process of steels is important. Some investigations focused on effects of cooling rate and strain on microstructure evolution during continuous cooling[6,7]. Summarizing existing literatures, the stability of RA, which is affected by chemical composition, morphology and phase transition temperatures, is widely investigated. Hu et al.[13] studied the effect of ausforming at bainite transformation temperature on RA in a C-Mn-Si bainitic steel. They claimed that the carbon content in RA increased first and decreased with strain. Few studies on the effect of high-temperature ausforming on RA with
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