Carbide engineering in high-carbon tool steels to enhance processability by powder bed fusion – laser beam

Additive manufacturing (AM) is ideal for producing molds and tools with enhanced functionalities, since it can build up intricate, near-net-shaped components layer by layer, providing a leaner process chain. Therefore, metal AM techniques, such as the widely used powder bed fusion-laser beam (PBF-LB), have found their way into industrial applications. Yet, its wider adoption still has to come, also because of limited material options. In PBF-LB of steels, low-carbon, highly alloyed types like stainless and maraging steels are successfully processed but are limited to niche applications and not ideal for applications requiring high-carbon steel with inherent high hardness. While desirable for such applications, high-carbon tool steels are difficult to process by PBF-LB mainly due to their high susceptibility to crack formation. The focus of the present work is to investigate how the formation of carbides affects the PBF-LB processability. Therefore, various powder blends of Fe-1.1C-0.5Cr-X (X = Ta, W) alloys with varying content of the carbide-forming elements Ta and W are prepared and subsequently processed by PBF-LB to produce bulk samples. The following characterization reveals that the microstructures consist of varying fractions of carbides embedded in a matrix composed of martensite and retained austenite. We correlate the carbide formation and the resulting austenite to martensite ratio to crack formation and determine the hardness and compressive properties of the additively manufactured steels.