Abstract
In this paper, the effect of hardness on the tensile strength of hot die steel JIS SKD61 in a high temperature environment was investigated by a tensile test using an extensometer. The tensile test was performed under four conditions from room temperature to 500℃. The hardness of the experimental material is in the range of 41.4HRC to 51.4HRC under five conditions. As a result of the experiment, the following was found. Regardless of the test temperature, the tensile strength and 0.2% proof stress increase as the hardness of the test specimen increases. In addition, the relationship between the strength (tensile strength and 0.2% proof stress) and hardness at each temperature can be approximated by a linear regression, whose slope is nearly independent of the temperature. Under the environment at 100℃ and 300℃, the strength ratio of tensile strength and 0.2% proof stress is almost equal, and the strength ratio shows almost constant value regardless of hardness. In an environment at 500℃, the strength ratio of 0.2% proof stress and tensile strength is different, and the strength ratio of 0.2% proof stress is smaller than that of tensile strength.
