A new way to net-shaped synthesis tungsten steel by selective laser melting and hot isostatic pressing

摘要

In this work, a novel tungsten steel was in-situ prepared using selective laser melting (SLM) and hot isotropic pressing (HIPing). The sample is firstly prepared by SLM from powder mixture of maraging steel and WC for the net-shaped manufacturing requirement. Then, the effects of HIPing on microstructure evolution and mechanical properties of SLMed WC/maraging steel composite were investigated with focus on in-situ reaction. The as-SLMed sample presents a composite structure of gamma (Fe, Ni) (austenite) and WC, which transits into alpha-Fe (ferrite and martensite) matrix with a large amount of Fe(Ni)-W-C eta phase precipitates after HIPing. The eta phase, which shows two morphologies (sub-micro and nano scales), locates mainly in grain boundary and inner-grain of alpha-Fe, respectively. The interfaces between eta, WC and alpha-Fe were determined using transition electron microscopy from barely existing partial melted WC. A stable graded multi-scaled structure appears between partial melted WC and matrix. After the HIPing process, the ultimate tensile strength and yield strength increase from 980 MPa to 561 MPa-1470 MPa and 1025 MPa, respectively, with a slight decrement in elongation from 7% to 6%.