The tensile strength of ordinary HT250 at room temperature is slightly lower than the strength calibrated by its brand, which is 239mpa. The tensile strength of low alloy HT250 added with trace alloy elements exceeds its brand, which is 280.4mpa, which is 17.3% higher than that of ordinary HT250. The tensile strength of HT300 added with alloy elements is 308.7mpa, which is higher than that of low alloy HT250.
The elongation of the three grades of gray cast iron samples is about 0.5%, indicating that the plasticity of the three grades of gray cast iron samples is very poor at room temperature and belongs to brittle materials.
The tensile curves of ordinary HT250 and low alloy HT250 are shown in the figure.
It can be seen from the figure that the tensile curves of ordinary HT250 and low alloy HT250 have no obvious straight line section and yield point, indicating that the samples of two grades of gray cast iron are brittle materials, and the tensile strength value of low alloy HT250 added with trace alloying elements is higher than that of ordinary HT250 at any stage before reaching its tensile strength.