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

Abstract

The effects of applying external stress on bainite transformation, microstructure, and mechanical properties are investigated by metallography, dilatometry, etc. Results show that compressive stress during bainite transformation accelerates the bainite transformation and increases the final bainite amount due to the additional mechanical driving force. The lath‐like bainite becomes shorter, and smaller blocky martensite/austenite islands form under stress during the bainite reaction. Different from the results with stress during bainite transformation, applying stress after bainite transformation during isothermal holding cannot increase the volume fraction of bainite, and no obvious change in bainite morphology is observed. In addition, the subsequent martensite transformation is promoted during the cooling process. Moreover, the less amount of retained austenite (RA) but more carbon content in RA is obtained with applying stress after the bainite reaction. Finally, the tensile strength increases, while the elongation decreases when the external stress is imposed after bainite transformation.

Microstructure and Properties of a Medium‐Carbon High‐Strength Bainitic Steel Treated by Boro‐Austempering Treatment

“…Carbide-free bainitic steels with the combination of high strength and good ductility have been considered as potential candidates for the third generation of advanced high-strength steels (AHSS). [1][2][3][4][5][6][7] Normally, bainitic steels are isothermally held at temperatures between the bainitic start temperature (B s ) and martensitic start temperature (M s ) after complete austenitization followed by being cooled to room temperature, [8][9][10][11] which is termed as austempering. Thus, the final microstructure consists of carbide-free bainite, retained austenite (RA), and a small amount of martensite.…”

Effect of deformation temperature on bainitic transformation and microstructure of a medium carbon high strength bainite steel

“…ND-300 refers to the specimen nondeformed and isothermally held at 300 • C. DS-360, DS-600, and DS-860 represent deformed specimens at 360, 600, and 860 • C, respectively. Equation (1) was used to calculate the amount of RA based on the integrated intensities of the various diffraction peaks [24,26]:…”

Comparison of the Impact Wear Performances of Quenching and Partitioning and Quenching and Tempering Steels

“…The G value was taken from the literature. [ 20 ] The RA volume fraction ( V RA ) in the QT200 sample was calculated as 0.1%. The V RA in the QP samples matched with the trend calculated by the CCE model, and the measured V RA values of QP190, QP220, and QP250 were 19.25%, 14.5%, and 10.1%, respectively.…”