Papers by Author: S.V. Parker

Abstract: The combined effect of Al and Nb additions on the static softening behavior of C-Mn steels was investigated. The compositions of the steels studied in this work are representative of the recently developed TRIP-assisted steels: a base composition of 0.2wt.%C, 2wt.%Mn, 50ppmN, three different Al levels, 0.03 (base steel), 1 and 2wt.%, and two Nb contents of 0.03 and 0.07wt.%. Double-hit torsion tests were performed at different deformation temperatures (925-1065oC) and pass-strains (=0.2 and 0.35). It was found that solute Al produced a significant retardation on the static softening kinetics, this effect being enhanced by the addition of Nb. Additionally, below 1000oC the addition of 2 wt.%Al promotes the γα phase transformation to occur concurrently with softening. For the Nb microalloyed steels strain induced precipitation also occurred, resulting in a complex interaction between softening, phase transformation and strain induced precipitation.

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: The effect of Al addition on the static softening behavior of C-Mn steels was investigated. The compositions of the steels studied are representative of the recently developed TRIP-assisted steels: a base composition of 0.2%C, 2%Mn, 50ppm N and three different Al levels, 0.03 (base steel), 1 and 2%. Double-hit torsion tests were performed at different deformation temperatures, in the range 950°C to 1100°C, and pass-strains, =0.2 and 0.35. It was found that solute Al produced a significant retardation on static recrystallization kinetics, equivalent to that exerted by 0.026%Nb for the 1%Al steel and to 0.05%Nb for the 2%Al steel. Additionally, at the lowest temperatures (950-1000°C) and 2%Al level, austenite to ferrite phase transformation was found to be concurrent with softening, enhancing retardation in the mechanical softening.