Microstructure, hardness, and tribological performance of D2 tool steel fabricated by laser cladding using pulsed wave and substrate heating

Abstract

D2 steel is a tool grade steel that presents hot cracking problems during the solidification process due to its alloying elements. On the other hand, additive manufacturing processes have great potential to manufacture, repair, and functionalize metal parts due to their low heat input, minimal distortion, and excellent metallurgical bonding. In this work, D2 metallic powder was deposited by the laser cladding process using pulsed wave, without and with preheating of the substrate. Through ANOVA statistical analysis using a complete factorial design 24, the optimal regions were determined to obtain D2 deposits with minimum dilution and depth, and maximum widths, heights and high hardness. Once the optimal parameters of the process were established, the coatings were deposited without and with preheating the substrate where, regardless of the condition, coatings without defects and good metallurgical adhesion were obtained. Coatings with preheating obtained higher cooling rates, where lower laser powers promoted higher rates; while in the coatings without preheating, lower duty functions promoted higher rates. The austenite, martensite and M7C3 eutectic carbides phases were obtained, with austenite being the main phase due to the C content in solid solution due to the cooling rates achieved. The coatings in as-built condition, reached hardness values between 606 and 711 HV (55–60 HRC), where the preheated coatings obtained the highest values. On the contrary, the coatings without preheating showed a better wear resistance (7.672 x10-6 mm3/Nm) due to the formation of tribo-layers due to the formation of oxides due to the higher amount of austenite.