Effects of laser scanning speed on the microstructure and mechanical properties of 2205 duplex stainless steel fabricated by selective laser melting

Abstract

Specimens of duplex stainless steel (DSS) fabricated by selective laser melting (SLM) exhibit excellent strength but poor plasticity, which has limited their applications. To improve the plasticity and to achieve a strength-plasticity matching, the effect of the laser scanning speed on the density, phase, microstructure, and mechanical properties of 2205 DSS specimens fabricated via SLM is investigated. The results reveal that the molten metal is solidified according to the kinetic sequence L → δ + L → δ → δ + γ for the SLM forming process, and the sample is completely composed of the ferrite phase. The content of austenite cannot be effectively enhanced by a change in the laser scanning speed. The mechanical properties of the samples are primarily affected by the presence of pores. A scanning speed of S700 (700 mm/s) results in the formation of fewer pores, which gives rise to a high yield strength of 896.80 MPa but a poor plasticity of 15.34 %. Decreasing the scanning speed to below 700 mm/s reduces the yield strength, but it also significantly increases the elongation. The elongation of the specimens fabricated using a laser scanning speed of 500 mm/s increases to 23.09 %, and they exhibit excellent strength-plasticity matching. This increased elongation at lower scanning speeds is attributed to higher density, lower dislocation density, decreased number of grain boundaries and the higher proportion of high-angle grain boundaries (HAGBs) of the specimens. Therefore, a significant decrease in the scanning speed can improve the plasticity of the specimens fabricated by the SLM method. By changing the laser scanning speed, the density, microstructure and mechanical properties can be optimized to further improve the plasticity of the specimens.