Numerical simulations of gradient cooling technique for controlled production of differential microstructure in steel strip or plate

Abstract

Numerical studies were conducted to investigate the applicability of cooling strategies for controlledly producing a microstructure in the steel strip or plate, which changes as function of the plate length. In the numerical simulations, the water spray cooling was varied as function of the plate length and as a result, the different parts of the plate were cooled at different rates. We applied the previously developed numerical code where the transformation latent heat is coupled with the heat conduction and transfer model, which has also been calibrated to correspond to experimental laboratory cooling line. The applicability of the method was investigated for controlledly creating alternating bainite and polygonal ferrite regions in plates of two different thicknesses (0.8 cm and 1.2 cm thick plates) by cooling different parts of the plate to different temperatures before switching off the water cooling so that polygonal ferrite forms in the part which has been cooled to higher temperature and bainite forms in the low temperature part. The simulation results indicate that the controlled production of such alternating regions is possible, but the resulting regions in the studied scenario cannot be very thin. The transition regions between the ferrite and bainite regions in the simulated cases are in the range of 5–15 cm. Controlled production of zones consiting of softer phase in the otherwise bainitic steel could offer a possibility for creating designed tracks in a steel bainitic strip or plate, where the mechanical working or cutting of the material is easier.

Keywords

• modelling
• numerical simulations
• differential treatment
• temperature control
• phase transformations
• steel