Ductile-to-Brittle Transition Characteristics by Charpy Impact Test of Shot-Peened Low Alloy Steel

The materials and parts used in severe environments require high toughness and strength. This study examined the transition characteristics using Charpy impact tests after modification by a surface treatment of 4340M steel. Seven different test specimens were manufactured according to the surface treatment, and Charpy impact tests were conducted over temperatures of −100 °C, 50 °C, 0 °C, 50 °C, and 100 °C. Despite changing the conditions in the test specimens, the ductile-to-brittle transition temperature (DBTT) according to the change in absorbed energy was unclear because of the high strength and high hardness caused by the surface treatment, but it generally formed over the low-temperature range of −50 to−75 °C. The percent of brittle fracture did not decrease below 50%, even at 100 °C. High strength and hardness were maintained when surface modification of 4340M steel by shot peening was performed, even in the low-temperature range, and the deterioration of toughness was not significant. Hence, the uses and application temperature range of the material can be expanded. Thus, increasing the impact resistance against material destruction will allow the this material by shot peening to be applied to parts and equipment used in severe environments.