Influence of Time Interval on the Removal Mechanism and Surface Quality During Continuous-Pulsed Hybrid Laser Removal of Oxide Scale from Q235B Steel

Q235B low-carbon steel is widely used in engineering fields due to its excellent comprehensive properties and cost advantages. However, its high-temperature oxide scale significantly compromises the quality of subsequent welding and coating processes. This study proposes a continuous‑pulsed hybrid laser method for oxide scale removal, with a focus on investigating the influence of the time interval Δt between the continuous‑wave and pulsed lasers on removal quality and the underlying mechanisms. Combining numerical simulation and experimental validation, the study systematically analyzes the oxide removal mechanisms, surface morphology evolution, microstructure, and nanohardness changes under different Δt. The results suggest a threshold effect: when Δt ≤ 10 ms, plasma shielding induced by the continuous laser weakens removal efficiency; when Δt ≥ 15 ms, the shielding is substantially reduced and the continuous laser's preheating effect enhances the material's absorptivity to pulsed laser energy, promoting spattering and increasing removal amount. The optimal Δt = 15 ms achieves the lowest surface oxygen content and highest removal amount. Under this condition, surface grains are significantly refined with a 58.8% reduction in average grain size and increased GND density, leading to a 51.5% enhancement in nanohardness from 3.30 GPa to 5.00 GPa. This work elucidates the critical role of the time interval in hybrid laser removal, providing theoretical and experimental foundations for efficient, high-quality oxide scale removal and surface property enhancement on low‑carbon steel.