Bainite transformation affected by predeformation and stress in G55SiMoV steel

Abstract

The influence of predeformation and stress on the isothermal bainite transformation has been investigated in G55SiMoV steel via microstructure observation and kinetic analysis. It was found that the bainite transformation became faster and at the end of isothermal holding the bainite fraction increased under the applied stress condition. When the stress increased to 150 MPa, the bainite distribution became to be nonrandom in G55SiMoV steel. Different deformation conditions, in which both promotion and inhibition occurred in the same steel, were created. The promoting and inhibiting factors affected bainite transformation comprehensively. 20% deformation could promote the bainite transformation when it deformed at 900°C, but prevent bainite transformation when it deformed at 750°C. Increase of ferrite nucleation rate caused by distortion and dislocation, would suppress the growth of bainite carbides and make most carbides without full growth be finer and shorter.

Effects of Plastic Stress on Transformation Plasticity and Microstructure of a Carbide-Free Bainite Steel

“…It was claimed that axial stress increases bainite transformation amount and accelerates bainite transformation kinetics [1][2][3][4][5][6]. Carbide-free bainite steel, which has excellent strength and toughness combination, is a new generation of advanced high strength steels [6][7][8][9][10][11].…”

The Effect of Large Stress on Bainitic Transformation at Different Transformation Temperatures

“…Shipway and Bhadeshia found an interesting phenomenon, that the acceleration of an elastic stress on bainitic transformation is more significant at a higher transformation temperature because the mechanical driving force accounts for larger proportion in the total driving force. Hase et al and Tian et al later reported similar results. However, these studies only considered the stress below the yield strength of austenite.…”

“…Some studies reported that the effect of an elastic stress on bainitic transformation is more obvious at a higher transformation temperature . At a higher transformation temperature, the chemical driving force is lower, so that mechanical driving force accounts for more proportion.…”

“…One is below the yield strength of parent austenite and the other is above the yield strength of austenite. Most researchers reported that both types of stress accelerate bainitic transformation, because the stress provides additional mechanical driving force despite a few contradictory reports …”

The Effect of Stress on Bainite Transformation, Microstructure, and Properties of a Low‐Carbon Bainitic Steel

“…However, Umemoto et al reported that no significant difference of bainite morphology is observed for applied stress lower than the yield stress. In addition, it was reported that the rate of bainite reaction becomes faster and the final volume fraction of bainite increases under the stress . The study by Zhou et al indicated that the promotion degree of stress on the bainitic reaction increases with stress, but the rate of increment gradually slows down when the applied stress is larger than the yield strength of austenite.…”