High-Strength D2 tool steel via material extrusion additive manufacturing and post-heat treatment

초록

AISI D2 tool steel was fabricated using metal-materials extrusion additive manufacturing (M-MEX), followed by heat treatment to optimize its microstructure and mechanical properties. These were compared with conventional wrought D2 materials. The as-sintered M-MEX D2 showed a pearlite matrix with a higher fraction of low-angle boundaries and developed substructures, in contrast to the fully ferrite matrix of the as-fabricated wrought D2. MEX D2 also retained near-spherical carbides (2-5 mu m), evenly distributed as in the starting powder, whereas wrought D2 contained coarse carbides exceeding 5 mu m, often reaching tens of mu m. After heat treatment, both materials transformed into fully lath martensite with sub-micron carbide precipitation. Heat-treated MEX D2 achieved a tensile strength of similar to 2.09 GPa and elongation of 1.27 %, representing a 15.5 % increase in strength and 170 % increase in elongation compared to heat-treated wrought D2 (1.81 GPa and 0.47 %). Fractography revealed extensive carbide fracture in wrought D2, whereas MEX D2 exhibited limited carbide cracking, with matrix substructure dominating the fracture surface. These results demonstrate that the M-MEX process, combined with heat treatment, yields finer carbides, reduced carbide cracking, and significantly improved mechanical performance, highlighting its potential as a superior manufacturing route for high-strength D2 tool steel.

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