Papers by Author: A.A. Howe

Abstract: Thermomechanical simulation serves to simulate industrial conditions under closer control and much more cheaply than through works trials, and also under ideal conditions (e.g. constant temperature and strain rate) more suitable for input to metallurgical models which can then be applied to real cases. It is remarkable how much effort in Industry and Academia, and how many conferences, are devoted to this issue. Moreover, many of the questions being addressed do not appear to change very much over the years [1]. The continuing stream of new rolled grades requires new experimental quantification and adjustment to models, because we do not as yet have a physically-based model powerful enough to extrapolate safely to substantially different compositions and process conditions. But that is only part of the story. Quantitatively sufficient simulation of the existing grade portfolio is a surprisingly complex, multi-facetted problem. An example is presented in Fig.1 [2] of the model in routine use for Tata Steel’s plate mill at Scunthorpe, UK. Many variables are involved in the prediction of the optimum rolling schedule in terms of productivity, plate geometry, and final properties, each of which will be associated with its own errors. Its configuration around the microstructural development during rolling brings in a range of variables which are very difficult to measure on plant, and are usually implied from laboratory studies. Extensive plant data exist but are seldom transferable to other mills owing to the individual set-up of each mill and its associated data measurement facilities. Similarly, great care has to be taken to avoid systematic differences between laboratory simulation, pilot rolling, and results on plant, owing to subtleties of the set conditions and accuracy of measurement. An overview of such experience in Tata Steel’s European plate and strip mills is given here.

Abstract: Thermomechanical Controlled Processing (TMCP) including accelerated cooling after the final hot rolling pass is a well-established technology, widely applied in HSLA steel plate production. However, there are still certain limitations, especially for thicker plate. The rolling schedule includes a long holding period (HP) after the roughing stage to allow the temperature to fall sufficiently for optimised TMCP during finishing. Intermediate Forced Cooling (IFC) applied during the HP can increase productivity by decreasing the required hold time, can restrict austenite grain growth, and can also improve the subsequent strain penetration in thick plate with further metallurgical benefits. Multi-pass plane strain compression (PSC) tests have been performed on the thermomechanical compression (TMC) machine at Sheffield University including different severities of IFC. Clearly it is impossible to simulate all aspects of the temperature and strain gradients present in thick plates in laboratory specimens, and most of the tests were conducted at temperatures and strains calculated by Finite Element modelling as relevant to specific positions through the plate thickness. However, some aspects of the gradients were addressed with tests using cold platens. The results have indeed shown that IFC can shorten the HP and reduce austenite grain growth and its variation across thick plate.