Study on the Directionality of Mechanical Properties of Heavy Steel Plate (150 mm Thick.) for Boiler

Abstract

The directionality of tensile properties and impact values of heavy plate (150 mm thick.) for boiler was experimentally studied. We obtained the following results. (1) Tensile test a) No directionality was found in tensile strength and yield point. b) Elongation and reduction of area decreased as the angle between the axis of the test specimen and the rolling surface or direction increased, especially in the thickness direction the reduction of area markedly decreased. c) Nominal stress-strain curve for each direction was nearly same and the directionailty were observed after the yield point on the nominal streess-strain curve. Especially in the thickness direction, fracture occurred slightly above the yield points. d) Each specimen generally followed the same true stress-strain curve, but the true stress and strain at the fracture point larger was in the rolling direction than in the trasverse direction, and larger in transverse direction than in thickness direction. e) The fracture appearance of the specimens in the thickness direction and near the direction was brittle resulted in lamella tearing. The non-metalic inclusion were found in the planes parallel with the rolling surface. The directionality seemed to be caused by notch effect of these nonmetalic inclusion. (2) Impact test a) Impact values decreased as the angle between the axis of the test specimen and the rolling surface or direction increased. In the thickness direction, the impact value for the transverse direction was larger than that of the specimen which had a notch in the rolling direction. b) It was found that non-metalic inclusion existed parallel to the rolling surface and further extended toward the rolling direction than toward the transverse direction. As a result, the impact value in the transverse direction decreased in comparison with in the rolling direction; and in the thickness direction, the impact value of the specimen which had a notch in transverse direction was larger than the specimen which had a notch in rolling direction. c) The influence of directionality was not so severe as in the case of other reports. It is owing to the configuration of the non-metalic inclusions, which is not as long in the rolling direction as in the case of those reports because this steel plate is thicker and its rolling ratio is smaller. d) The 3.5 kg-m/cm^2 transition temperature was lower in the rollig direction than in the transverse direction, and also were lower in the transverse direction than in the thickness direction. e) No directionality was found in the energy transition temperature. f) The fracture section of the thickness direction was slightly different from the brittle fracture as usually observed. It had many lamella tearings.