Effect of heat treatment on microstructure and mechanical property of selective laser melted high speed steel

Abstract

Based on selective laser melting (SLM), the high speed steel samples with nearly full density and low defects were prepared by using the printing strategy consisted of preheated printing substrate, low laser power and slow scanning speed. The effect of solid-solution oil-quenching as well as 1-4 times high temperature tempering on the microstructure and mechanical properties of selective laser melted high speed steel was contrasted and analyzed. The results demonstrate that fine austenite grains can be obtained due to the high melting/cooling rate in SLM process, solving the problems of coarse ledeburite organization and carbide network in high speed steel. The structure of steel is martensite and retained austenite after solid-solution oil-quenching. High speed steel sample transformed into tempered martensite during multiple tempering, accompanied with a large number of micro-sized and nano-sized carbides precipitated. The quenched and triple tempered Tempered-Ⅲ sample has a hardness of 60HRC, a flexural strength of 3621 MPa and a bending fracture strain of 10.1%, exhibiting an outstanding combination of hardness, strength and toughness. The bending fracture strain of high speed steel decreases owing to the coarsening of carbides in four times tempering. The integration of SLM, solid-solution oil-quenching and high-temperature tempering, which forms the combined effects of fine-grain strengthening, martensitic hardening and precipitation strengthening, provides a new approach for complex shaped high speed steel parts with high strength and toughness.

Keywords

• high speed steel
• heat treatment
• selective laser melting
• precipitation strengthening
• mechanical property