Karakterisering av additivt tillverkat martensitiskt rostfritt stål

Abstract

Metal Binder Jetting (MBJ) is an additive manufacturing process that enables the production of complex metal components. However, the relationship between the manufacturing process, heat treatment, microstructure and mechanical properties still requires further understanding. In this report, MBJ-manufactured martensitic stainless steel was investigated with the aim of characterizing the microstructure after different heat treatment cycles and relating these changes to the mechanical properties. Four samples that had undergone different heat treatment processes were analyzed. The microstructure was examined using light optical microscopy (LOM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive Xray spectroscopy (EDS). Hardness measurements were performed to evaluate how the different treatments affected the mechanical properties. Grain size, carbide distribution, crystal structure, and chemical composition were studied and compared between the samples. The results show that heat treatment has a clear influence on both microstructure and hardness. Samples that had only been sintered exhibited lower hardness and a more heterogeneous microstructure, whereas normalization contributed to more distinct grain boundaries and a more stable microstructure. The sample that had undergone normalization followed by austenitizing and tempering (process 411) showed the highest hardness, just below 700 HV 1. This could be related to a combination of favorable carbide distribution, relatively controlled grain size and the presence of martensite. The XRD analysis revealed differences in crystal structure between the samples, where the normalized samples showed an increased fraction of BCC-related phases. In contrast, the EDS results showed only minor differences in chemical composition, indicating that the differences in hardness are primarily due to the effect of heat treatment on the microstructure rather than variations in alloy composition. In summary, this report shows that MBJ-manufactured martensitic stainless steel requires a well-adapted heat treatment cycle in order to achieve high hardness and a favorable microstructure. Among the investigated treatments, normalization followed by process 411 appears to be the most promising route for achieving the desired properties. This report is written in Swedish.