Effect of P21 buffer layer on interfacial bonding characteristics of high‑carbon tool steel hardfaced through directed energy deposition

Abstract

The elevated hardness of high‑carbon tool steel (M2) powder makes it an effective material for hardfacing components requiring strong wear resistance. However, if the brittle M2 powder is deposited on a ductile substrate, significant stress occurs during cooling, leading to defects, such as cracks at the interface between the substrate and deposited regions. Therefore, in this study, ductile P21 powder was deposited as a buffer layer between the substrate and the deposited M2 layer to prevent interface defects. To confirm whether this P21 buffer layer effectively prevents interfacial defects, bending, impact, and tensile tests were performed. No interfacial defects were observed in the cross-section of the deposition specimen when a P21 buffer layer was applied. The average hardness of the surface deposited M2 region was 733 HV, similar to that of the carburized substrate. As-built (M2) specimen showed 94% lower in weight reduction than the carburized material after the wear test. The specimen without a buffer layer revealed cracks propagating along the interface between the deposited region and substrate, with the lowest impact energy absorption of 25 J. However, the energy absorption of the specimen with a P21 buffer layer was 60% higher than that without a buffer layer. The tensile test results show 7% increase in tensile strength with the buffer layer and 244% increase in elongation. This study demonstrated that high hardness and wear resistance could be achieved through M2 deposition and confirmed the improved strength and toughness with a P21 buffer layer.