Laser-treatment-induced surface integrity modifications of stainless steel

Scanning of a high-power laser beam on the surface of martensitic stainless steel (SS420) has been studied, addressing the effect of scanning rate Von integrity modifications in the near-surface regions. Structural, compositional, and crystallographic characterizations revealed the presence of ablations, surface melting/resolidification, surface oxidations, and austenite (7-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 gamma-phase precipitations solely occurred in the MPs, i.e., of 400 mu m deep for V = 5 mm s(-1), while oxidations dominantly occurred in the surface regions of shallower than similar to 30 mu 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.,similar to 1000 mu m) into the base material. These observations shed new light on surface engineering of metallic alloys via laser-based direct energy treatments.