Direct aging effect on the mechanical properties of directed energy deposited CuNiAl-containing low-alloy steel

Abstract

Although CuNiAl-containing steels can be applied to additive manufacturing owing to their acceptable weld-ability, only a limited number of studies have investigated. In this study, the mechanical properties of directed energy deposited CuNiAl-containing low-alloy steel, including its direct aging effect, were investigated. The optimized processing parameters were estimated by the response surface methodology, and achieved 100% dimensional accuracy with a high relative density. Direct aging induces B2-NiAl and Cu-rich phase coprecipitation in the matrix, and the precipitation size increases with increasing aging time. The evolved nano-precipitates enhance the hardness of the CuNiAl-containing low-alloy steel from 155 to 256 Hv owing to precipitation hardening. Long-term aging induces both grain growth and Cu-rich phase transition from a body-centered cubic to a 9R structure that result into slight hardness decrement after 12 h of aging. The uniaxial tensile test results indicated that both the yield ratio and strain-hardening exponent changed as the aging time increased, which affected discontinuous yielding in the as-built and short-term aged specimens. This result indicates that CuNiAl-containing steel has sufficient additive manufacturing processability, which can be an alternative strategy for developing maraging steels with low Ni content.