Effect of cold and hot rolling and normalising on the structure and properties of welded joints

Tubes are of two kinds; welded and seamless. Welded tubes are invariably inferior to seamless tubes due to the presence of a heat-affected zone and a weldment, both of which show different microstructures to that of the base metal. However, welded tubes are much cheaper, and if by some economical post-weld treatment the microstructure and properties of weld and base metal could be homogenised, this would then provide an added advantage for welded tubes. With this in view, different rolling and normalisation treatments were carried out on welds of low-carbon steel and low-alloy steel. For simplicity, welded sheets were used instead of tubes for carrying out these experiments, since the metallurgical and experimental conditions would be the same, as far as this problem is concerned, in both cases. Rolling was carried out at temperatures of up to 1100°C, and at reductions of up to 40%, for both types of steel examined. Normalisation was also carried out at temperatures of up to 1200°C, to study its effect. A study of the structure and mechanical properties indicates that homogenisation occurs after 30% hot-rolling reduction at 1000°C in the case of low-alloy steel, and after 30% reduction at 1100°C in the case of low-C steel. This homogenisation could not be achieved by normalisation at any of the normalisation temperatures employed. After tubes are welded, they can therefore be rolled to a 30% reduction in thickness at the specified temperature, to secure homogenisation of the structure and properties of the weldment and base metal, thereby producing a tube equivalent to seamless, but of a much lower cost. © 1978.