Effect of hot isostatic pressing-uniform rapid quenching on microstructure, defect characteristics, and mechanical properties of high-carbon tool steel fabricated by material extrusion additive manufacturing

초록

This study explores the effect of hot isostatic pressing assisted by uniform rapid quenching (HIP-URQ) on the densification, microstructural homogenization and mechanical properties of AISI D2 tool steel fabricated by material extrusion additive manufacturing (MEX). The MEX-built D2 material exhibited residual porosity and interlayer defects, which were effectively eliminated through the HIP-URQ process conducted at 150 MPa and 1050 degrees C, followed by gas quenching. Microstructural analyses (OM, SEM, XRD, EBSD, TEM) were conducted to identify the phase composition of the HIP-URQ and tempered specimen (HU-HT). The results revealed the formation of a fully martensitic matrix characterized by a uniform distribution of Cr7C3 carbides, resulting in a highly dense and microstructurally homogeneous material. Notably, the HU process simultaneously promoted densification and microstructural uniformity by suppressing interlayer defects and refining carbide dispersion throughout the matrix. Despite the presence of slightly coarser martensite and a lower carbon content in the HUHT specimen in comparison to the furnace-quenched specimen (AQ-HT), the higher carbide density and densification contributed to superior properties. The HU-HT demonstrated a hardness of 705.8 HV, YS: 1929 MPa, UTS: 2342 MPa, and EL: 2.25%, thus exhibiting superior performance. The results demonstrate that HIP-URQ enables simultaneous densification and microstructural optimization, providing a promising post-treatment route to enhance the strength-ductility balance of sintered MEX-fabricated high-carbon tool steels.

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