Investigation into the microstructure and properties of wire arc additive manufactured 09MnNiDR steel

Cryogenic 09MnNiDR steel was prepared using arc additive manufacturing technology. Following manufacture, its phase composition, microstructure, and crystal structure were analyzed by spectrometer, X-ray diffraction, optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). In addition, the mechanical properties of arc additive manufactured 09MnNiDR were determined by microhardness measurements, tensile testing, and Charpy impact testing. Results showed that the material displayed good quality form without defects, such as holes, cracks, solid inclusions, incomplete fusion and penetration, or unfavorable shape and size. Furthermore, it displayed good internal metallurgical bonding and has a metallographic structure composed mainly of ferrite and granular bainite. High-resolution TEM suggested sharp grain edges, as well as a large number of crystal defects, such as dislocations and martensite–austenite islands in the 09MnNiDR crystal structure. The material showed relatively uniform microhardness distribution on the longitudinal and transverse sections with average values of 188.2 and 167.5 HV0.2, respectively. Also, the material exhibited superior mechanical properties. Prior to heat treatment, the material presented a yield strength of 436 MPa, a tensile strength of 552 MPa, an elongation of 30%, and a Charpy impact value of 96 J at −70°C.