In a hot-rolled H-beam, covering the upper surface of web by insulator (web-insulating) and cooling the outside surface of flange by water (flange-cooling by water) after rolling are considered effective measures for reducing the residual stress. To confirm this, the relation between the residual stress and the time of their treatment under various finishing temperature conditions was investigated using the analytical method for thermal stress. This method is characterized by taking phase transformation into consideration.
The outline of results obtained is as follows;
(1) The longer the time to insulate web or to cool flange after rolling is and the smaller the difference in finishing temperature between flange and web is, the lower the tensile residual stress in flange and the compressive residual stress in web are. Namely the residual stress is reduced in the whole cross section in this case.
(2) In the case of large size H-beam (H : 900×300×16×28 mm), the time to cool flange (heat transfer coefficient : 250 kcal/m2·h·°C) after rolling for reducing the residual stress in web is about a quarter of the time to insulate web.
(3) It is possible to reduce the residual stress below the required value by combining the control of the difference in finishing temperature with the control of the difference in cooling rate between flange and web after rolling.
(4) The choice of either web-insulating or flange-cooling by water after rolling should be made by considering the influence on the metallurgical quality and the ease of control as well as the effect of reducing residual stress.
