Effect of preheating conditions on UV laser direct coloring of stainless steel surfaces

Metal surface laser coloring technology has attracted much attention because of its wide range of applications and significant advantages. The principle is based on the interaction between the laser and the metal surface, through the modulation of laser parameters (such as wavelength, power, and pulse width) to induce oxidation, microstructural reconstruction, or the equipartitional excitation resonance effect of the metal surface layer, so as to achieve accurate and controllable color generation. Current research focuses on multi-material compatibility, color stability, and dynamic regulation mechanisms, with the combination of nanostructured design and ultrafast laser technology further expanding the color gamut and resolution. In particular, UV laser metal coloring has significant advantages in terms of processing accuracy and color expression due to its short wavelength (<400<i>n</i><i>m</i>). In this paper, we investigated the effect of preheating temperature on the UV laser coloring of a 304 stainless steel surface, compared to the laser power, focus distance, scanning speed on the effect of color formation and microstructure, the use of a spectrometer to analyze the reflectance spectra of samples, the use of spectroscopy to analyze the surface of the constituent elements, the comparative analysis of the color gamut range of color changes, and the study of the preheating effect of the coloring mechanism. The results show that the preheating of the stainless steel surface produces better color uniformity and saturation, a wider color gamut, and a higher percentage of the surface oxide composition, mainly related to the preheating temperature on the laser initial absorption rate and the reduction of thermal conductivity.