Effects of Y content on laser melting-deposited 24CrNiMo steel: Formability, microstructural evolution, and mechanical properties

24CrNiMo alloy steel is often used to fabricate high-speed railway brake discs. To improve the properties of the alloy prepared via laser melting deposition (LMD) and investigate the role of the rare-earth (RE) element in the LMD of 24CrNiMo steel, three types of powders with different contents of the RE element Y (0, 0.02, and 0.2 wt%) were used. The morphology, composition, and distribution of phases and defects in the alloys were examined using optical microscopy, scanning electron microscopy, electron backscatter diffraction, X-ray diffraction, and transmission electron microscopy. The mechanical properties of the alloys were determined via Vickers hardness and tensile tests. The temperature field and stress field distributions in the forming process were simulated via the finite-element method. The results indicated that adding an appropriate amount of Y (0.02 wt%) can help to reduce defects, refine grains, form a uniform microstructure and fine second phases, and improve the mechanical properties of the alloy. However, adding too much Y (0.2 wt%) causes element segregation, cracks, and large inclusions, which degrade the mechanical properties of the alloy.