Co-strengthening and deformation behaviors of hybrid additive manufactured U75V/15-5PH bimetal via optimized heat treatment

Bimetals composed of U75V pearlitic steel and 15-5 precipitation hardening (PH) steel were successfully processed by a hybrid additive manufacturing method. However, the U75V/15-5PH bimetal in the as-deposited condition showed inferior mechanical properties owing to the inhomogeneous microstructures. Herein, optimized heat treatment for the co-strengthening of U75V/15-5PH bimetal was designed by investigating the microstructural evolution and mechanical properties thoroughly. Results showed that the mechanical properties of the U75V steel region were recovered after solution treatment, reflected in the formation of lamellar pearlite. For the additive 15-5PH steel region, the formation of martensitic phase and NbC carbides contributed to the strengthening in the solution condition. Furthermore, this region was further hardened by the massive precipitation of Cu-riched precipitates induced by aging treatment. Due to the difference in yield strength of U75V/155PH bimetals with various locations, the deformation transfer phenomenon from U75V steel to 15-5PH stainless steel was detected during the uniaxial tensile tests. After heat-treated through the solution and aging treatment, the optimized yield strength, ultimate tensile strength, and elongation of the U75V/15-5PH bimetal achieved 878 MPa, 1201 MPa, and 11.2%, respectively. This study demonstrated experimentally that the mechanical performance of the U75V/15-5PH bimetal with various microstructures could be improved by designing a suitable solution and aging heat treatment.