Substrate-Assisted Binder Jetting of M2 High-Speed Steel: Mechanisms of Printing Defects and Sintering Densification Behavior

Binder jetting (BJ) can avoid crack defects caused by residual thermal stress in the additive manufacturing of high-speed steel (HSS). However, the research on BJ-fabricated HSS remains limited and the printing and sintering processes for M2 HSS are still not well understood. The mechanisms of printing defects and microstructure evolution behavior have not been fully elucidated. In this research, orthogonal experiments are designed and conducted to investigate the effects of layer thickness, inkjet concentration, and powder spreading speed on the forming quality (relative density) of green parts. The types and causes of printing defects are identified and the formation mechanism of layer-shifting defects is analyzed. A method involving an additional printing base is proposed to eliminate layer shifting. An optimized debinding-sintering curve is established and the influence of sintering temperatures (1280–1320 °C) on the relative density, dimensional shrinkage, pore morphology, microstructure, and mechanical properties of BJ M2 HSS is investigated. The transformation mechanisms of carbides are elucidated. The study shows that the BJ M2 HSS achieves a relative density of 99.06% and an average friction coefficient of 0.37 at 1320 °C, with ultimate tensile strength and hardness reaching 858.7 MPa and 628.4 HV. Furthermore, the effects of substrates with different thermal conductivities (graphite and zirconia) on the relative density and warpage of sintered M2 HSS parts are analyzed. The substrates with high thermal conductivity can enhance sintering efficiency but exacerbate deformation. To address this, a graphite-zirconia composite substrate is developed. The results of this study can provide a theoretical foundation for the binder jetting fabrication of high-performance, defect-free M2 HSS.