Analysis of solidification microstructure and cracking mechanism of a matrix high-speed steel deposited using directed-energy deposition

Abstract

This study investigated the microstructure and cracking mechanism of a matrix high-speed steel fabricated by direct energy deposition. The combined effect of rapid solidification and chemical composition on microstructure and cracking mechanism during deposition were investigated. Excessive solute segregation into inter-dendritic regions due to rapid solidification caused formation of retained austenite in the interdendritic region and formation of alpha'-martensite in the dendritic region. The excess solute segregation decreased equilibrium solidification temperature and caused formation of low-melting eutectic carbides in the inter-dendritic region. These carbides increased hot-cracking susceptibility, and caused solidification cracking and liquation cracking in the inter-dendritic region. In contrast, tensile residual stress in deposited layers may have caused cold cracking in alpha'-martensite near the hot crack tips. Cold cracks contributed to growth of macroscopic longitudinal cracks throughout the specimen by bridging the hot cracks formed during solidification or reheating.(c) 2022 Elsevier B.V. All rights reserved.