Effects of strain rate on tensile strength of steel specimens of HAZs with stress concentrations

It is well known that the strain rate affects tensile behavior; for example, it affects the tensile strength and fracture elongation of metals. When examining the tensile behavior of steel, it is important to pay attention to the heat-affected zone (HAZ) as well as the base metal. The effects of the strain rate on the tensile strength were investigated by using specimens with stress concentrations; in particular, the tensile strength of SM400, SM490, and HT780 were obtained from HAZs by performing tensile tests at strain rates of 0.085%/s, 85%/s, and 1.000%/s. The HAZs were simulated by using a thermal/mechanical simulator. The main results are summarized as follows: 1) Regardless of the grade of steel, the tensile strength of specimens that underwent ductile fracture increase at high strain rates, whereas the tensile strength of specimens that underwent brittle fracture did not increase. 2) Regardless of the grade of steel and regardless of whether welding heat was supplied or not, the rate of increase in the tensile strength as a result of the high strain rate can be predicted from the tensile strength, which can be determined by static testing.