Speaker
Description
In-line control of plate microstructure to achieve near-net mechanical properties requires a combination of the correct time temperature strain path during rolling and accelerated cooling strategy to control the grain size and final material phases. This paper firstly reviews the process routes available to produce thermo-mechanically control rolled steel products using the combination of rolling and accelerated cooling. Next a description is given of a recent installation of MULPIC plate cooling technology at JSW’s plate mill at Anjar, India. This technology has been integrated into the existing rolling process and is capable of being used in two ways. Firstly, MULPIC can be used for intermediate cooling, which is applied during the hold phase of controlled rolling and is more traditionally performed using air cooling. This hold time is required to allow the plate to finish rolling below the recrystallisation stop temperature. Secondly, final plate cooling can be applied after the last rolling pass to achieve the desired temperature-time cooling path which determines the room temperature phase fractions and transformed grain size distribution.
The paper also describes the off-line system which allows simulations to be performed of both the rolling and cooling processes. The objective of the rolling model is to describe the incoming high temperature microstructure to MULPIC. Predictions of grain size, residual strain and phase fraction are included. The model uses a prediction of the through thickness temperature evolution during rolling to calculate the effects of recrystallisation, grain growth and precipitation. The cooling model uses these inputs to simulate the phase transformations of austenite into a combination of ferrite, pearlite, bainite and martensite. The resultant transformed grain size distribution together with other material properties are then used to predict the final mechanical properties. Results are presented to demonstrate the accuracy of the model against measurements from production.