Microstructure and mechanical properties of H13 tool steel fabricated by high power laser powder bed fusion

A high power (>2 kW) laser powder bed fusion (HP-LPBF) additive manufacturing technology was used to fabricate H13 tool steel in this study. The influences of laser energy density ( E v ) on the microstructure and mechanical properties of the as-built H13 were studied. The results show that the relative density (RD) increases with the increasing E v , and nearly full dense samples (RD > 99.5%) can be obtained with E v above 40 J/mm 3 . The microstructure of the as-built H13 consists of prior austenite grains (PAGs), lath martensite and residual austenite. With the increase of Ev , microstructural features including the average width of PAGs, the average grain size of lath martensite, the content of residual austenite and the fraction of the high-angle grain boundaries (HAGBS) remain basically unchanged, whereas the dislocation density increases. Several V-rich and Cr-rich precipitates with diameters of 10–40 nm formed in the matrix as the result of the in-situ tempering effect during the HP-LPBF process. The in-situ tempering effect is stronger at higher Ev . As the Ev increases from 47.6 J/mm 3 to 100 J/mm 3 , the build rate and elongation (El) of the as-built H13 decrease, whereas the ultimate tensile strength (UTS) and yield strength tensile (YS) improve continuously. The sample built at 100 J/mm 3 achieves excellent YS (1540 ± 25 MPa) and good UTS (1920 ± 30 MPa) and El (3.1 ± 0.6%) in comparison with the H13 fabricated by the conventional LPBF using low-power laser (500 W). Meanwhile, the build rate (40 mm 3 /s) is about 8–40 times higher than that of the conventional LPBF. The excellent mechanical property of the HP-LPBF H13 is mainly attributed to dislocation strengthening and precipitation strengthening, followed by grain boundary strengthening. The present study provides a potential way to realize the additive manufacturing of high strength H13 tool steel products with a high build rate.