Mechanical Properties of Hot-Stamped Spherical Shell Q235 Steel after Exposure to Elevated Temperature

Abstract

The welded hollow sphere is formed by hot stamping of the steel plate, and the mechanical properties of the steel after hot stamping are the key to accurately evaluate the stress performance of the welded hollow sphere. In this paper, the Q235 steel used to manufacture the welded hollow sphere and the formed welded hollow spheres were made into tensile coupons. The mechanical properties of hot-stamped spherical shell Q235 steel without flattening treatment after water cooling from elevated temperature were studied by experiments. The stress–strain curves, elastic modulus, percentage elongation of fracture, yield strength, and ultimate strength of steel were analyzed. The results showed that hot stamping can improve the mechanical properties of Q235 steel to some extent. The exposure temperature and the method of water cooling have little effect on the elastic modulus of the hot-stamped spherical shell Q235 steel, but they have significant effects on the percentage elongation of fracture, yield strength, and ultimate strength. With the increase of exposure temperature, the percentage elongation of fracture presented a decreasing trend, and the higher the exposure temperature, the more obvious the decreasing trend. Before 500°C, the yield strength and ultimate strength of steel showed a decreasing trend, and it increases with the increase of exposure temperature after 500°C. Based on the experimental results, the stress–strain model and the mechanical properties calculation formula of the hot-stamped spherical shell Q235 steel after water cooling were proposed, and the mechanical properties relationship between the hot-stamped spherical shell Q235 steel and the original Q235 steel was obtained.