Softening Behavior of a Cold Work Tool Steel and High-Boron Tool Steel Fabricated by Directed Energy Deposition

Journal article, 2024

Prolonging the life of hot stamping dies in the automotive industry is challenging. Surface modification is an effective way to improve the durability of the dies. In this study, two tool steel grades, one cold work tool steel (V4E) and one high-boron tool steel (HBS), are deposited on a tool steel substrate using directed energy deposition, followed by tempering. Softening behavior at high temperatures of 550 and 600 °C is investigated. In the key findings, it is revealed that both steels exhibit remarkable hardness, surpassing the substrate even after extended exposure to high temperatures. HBS shows excellent softening resistance in terms of hardness at 550 °C but experiences a significant drop at 600 °C. V4E demonstrates an overall superior softening resistance due to its thermal stable MC (M represents metal) carbides and the relatively stable dislocation density. Microstructural analysis highlights some unique features, such as borides in HBS and dendritic structures in V4E. In this study, the correlation between microstructure characteristics and hardness evolution is revealed, providing some insights into how these materials resist softening to enhance the longevity and performance of hot stamping dies.