Laser-treatment-induced surface integrity modifications of stainless steel
Na Gong, Yuefan Wei, Tzee Luai Meng, Rahul Karyappa, Jing Cao, Chee Kiang Ivan Tan, Ady Suwardi, Qiang Zhu, Hongfei Liu
Abstract
Abstract Scanning of a high-power laser beam on the surface of martensitic stainless steel (SS420) has been studied, addressing the effect of scanning rate V on integrity modifications in the near-surface regions. Structural, compositional, and crystallographic characterizations revealed the presence of ablations, surface melting/resolidification, surface oxidations, and austenite ( γ -phase) precipitations when V ≤ 20 mm s −1 . Melt pool (MP), heat affected zone (HAZ), and base material have been clearly distinguished at the cross-section of the slow-scanned samples. Adjacent MPs partially overlapped when V = 5 mm s −1 . The γ -phase precipitations solely occurred in the MPs, i.e., of ∼ 400 μ m deep for V = 5 mm s −1 , while oxidations dominantly occurred in the surface regions of shallower than ∼30 μ m within the MPs. Compositional analysis revealed increased Cr-, Mn-, and Si-to-Fe ratios at the laser-scanned surface but without variations along the surface normal direction. The enhanced surface hardness has been achieved up to 805 HV, and the hardness monotonically decreased when moving deeper (i.e., ∼1000 μ m) into the base material. These observations shed new light on surface engineering of metallic alloys via laser-based direct energy treatments.