SLM-manufactured 30CrMnSiA alloy: Mechanical properties and microstructural effects of designed heat treatment

Microstructures and mechanical properties of 30CrMnSiA alloy parts fabricated by forged annealing and selective laser melting (SLM) processes were compared in this study. SLM fabricated (SLMed) 30CrMnSiA alloy parts possess higher hardness and tensile strength than forged annealed (FAed) parts, however, a characteristic of low plasticity and impact toughness was observed in SLMed parts. Therefore, this research designed a reasonable heat treatment mode, which was divided into three periods to modify the microstructure in SLMed 30CrMnSiA alloy parts. The first period was repeated full annealing at 900 °C for 1 h to eliminate microstructure inhomogeneity, especially carbides segregation and ununiformed grain morphologies. The second period was air blast quenching from 900 °C to ambient temperature to achieve super saturation solid solution or martensite in parts. The last period was tempering at 650 °C for 1 h to fulfill martensite decarburization and carbides spheroidization. As a result, tempered sorbite as an equilibrium microstructure in ambient environment was obtained in SLMed 30CrMnSiA alloy parts. The optimum comprehensive mechanical properties of SLMed parts with an average hardness of 24.8 HRC, a tensile strength of 860 MPa, a plasticity of 16.9% and an impact toughness of 29.1 J were achieved by performing the designed heat treatment mode. It considerably enhanced the plasticity and impact toughness of SLMed 30CrMnSiA alloy parts, which were 1.41 and 2.55 times of parts without heat treatment. Accordingly, industrial applications of SLMed 30CrMnSiA alloy parts were supposed to be widened by this study.