Additive manufacturing and heat treatment of Dievar tool steel

Abstract

Dievar tool steel was newly produced by laser powder bed fusion (PBF) method and systematically evaluated after different heat treatments. Additive manufacturing parameters were optimised to achieve low porosity, and various post-processing heat treatment routes were applied. In the as-built state, the steel exhibited an ultimate tensile strength of 1876 MPa, 12 % total elongation, and a notch toughness of 29 J. Its microstructure consisted of a martensitic matrix with 23 % retained austenite (RA) and nanoscale aluminium oxides or Mo-rich precipitates. The majority of RA transformed into martensite during tensile loading at room temperature, revealing a transformation-induced plasticity (TRIP) effect not previously documented for Dievar. Among post-processing conditions, oil quenching from 1025 °C with double tempering at 610 °C provided the best impact toughness of 28 J, while direct tempering at 610 °C/2 h achieved the highest tensile strength of 2114 MPa with 12 % elongation, though toughness decreased to 13 J. While 7 % RA persisted after direct tempering, the combined quenching and tempering route led to its complete transformation to martensite. Larger V-rich particles appeared in the matrix after quenching from 1025 °C.