Assessment thermo-mechanically control rolled-plate capability

Our lab facilities, combined with tools that offer good numerical predictions, allow our industrial customers to save money and time on trial and error experiments.

Ulrike Lorenz & Alexandre Van Sintejan

In 2021, OCAS was requested to re-assess the thermo-mechanically rolled feasibility range under current air-cooling conditions of a heavy-plate mill in terms of maximum dimensions and as a function of strength and Charpy impact toughness requirement. The assessment considered mill-constraints such as the increased slab dimensional feasibility, maximum plate width, and minimum transfer bar length to avoid flatness defects.

BEYOND CURRENT PRACTICE

To estimate the toughness performance of a product rolled to a thickness beyond current practice, the assumption was made that toughness depends only on the final austenite microstructure, and the required fine-grained microstructure is obtained by the thermo-mechanical rolling process. The strength evolution as a function of thickness was estimated based on mill experience. Rolling schedules and microstructure evolution during thermo-mechanical rolling were numerically simulated. Using realised industrial process and product data, a reference austenite microstructure after thermo-mechanical rolling could be defined, enabling the required toughness in the final product. In close contact with the steel plant, the boundary conditions for the simulations were fixed and calculations for rolling simulations were performed for different thicknesses, leading to the target austenite microstructure. A first estimate of a thermo-mechanically plus air-cooling feasibility range could be given.

EXTENDING THE ASSESSMENT

The effect of changes in process target parameters on microstructure were simulated as well. The output allowed us to formulate recommendations to further improve the feasibility range under current mill constraints. Furthermore, the simulations allowed the assessment to be extended, assuming the mill was equipped with advanced cooling capabilities. In the recent past, OCAS had performed on lab scale a number of lab rolling simulations, comparing the influence of air cooling and such advanced cooling during plate processing. The results of these simulations have led to a good understanding of the influence of microstructures on properties and an estimate on the thermo-mechanically plus advanced cooling feasibility range could be given as well.