Microstructural evolution and mechanical properties of an additively manufactured high-strength steel

In this study, the microstructural evolution and mechanical properties of a new type of steel fabricated by selective laser melting (SLM) with subsequent tempering treatment were discussed. The as-built sample consisted of cellular structures, lath martensite accompanied by carbides and little residual austenite. After tempering at 560 degrees C for 2 h, the matrix transformed from the supersaturated martensite to the tempered lath martensite, followed by residual austenite complete dissolution and more carbides precipitation. The as-built sample showed a high strength (yield strength:1335 +/- 10 MPa, ultimate tensile strength:1555 +/- 2 MPa) and a considerable ductility (elongation to failture:7.7 +/- 1.4 %). The outstanding strength was attributed to fine grains and high number density of dislocations. A superior mechanical properties, including the yield strength of 1762 +/- 25 MPa, ultimate tensile strength of 1850 +/- 39 MPa and elongation of 5.6 +/- 0.8 % have been achieved in the SLMed steel after tempering. The as-built sample exhibits a higher uniform elongation (-7.0 %) compared with tempered 560 degrees C sample(-2.6 %), which may be attributed to its excellent work hardening behavior.