Microstructure, Hardness, and Tensile Properties of Additively Manufactured Low‐Alloy Steel: A Review

As additive manufacturing (AM) shows great promise in generating functional parts, the list of printable ferrous alloys is growing steadily. Low‐alloy steels are such alloys that hold the prospect of being low cost and possessing high strength for structural applications. The AM community is increasingly focusing on examining the properties of such low‐alloy steels fabricated using different additive techniques. However, the impact of various printing conditions and heat treatments used after printing on the properties of AM low‐alloy steel has not yet been well reviewed. In this review, the microstructure, hardness, and tensile properties of nine different low‐alloy steels (4130, 4140, 4340, 5115, 5120, 8620, 8740, 24CrNiMo, Bainidur) have been discussed under different printing parameters and postprinting treatment conditions. In general, the microstructure of additively manufactured low‐alloy steels contains martensite, tempered martensite, and bainite with a small percentage of retained austenite. The hardness and tensile strength of AM low‐alloy steels are higher than the wrought counterparts. However, the microstructure, hardness, and tensile properties significantly change based on the processing parameters and postprinting heat treatments.