Influence of laser cleaning pretreatment on microstructure and mechanical properties of 3Cr13-9Cr18MoV welded joints

A systematic investigation was conducted on the comprehensive influence mechanism of laser cleaning process parameters on the surface morphology characteristics and subsequent quality of laser-welded joints of 3Cr13-9Cr18MoV martensitic stainless steel. The optimization of laser cleaning parameters is essential in the pretreatment stage of laser welding. This helps prevent thermal damage or incomplete cleaning of the substrate, thereby significantly improving the metallurgical integrity and comprehensive mechanical properties of the weld seam.A statistical method involving a multi-factor orthogonal experimental design combined with analysis of variance was employed. A quantitative relationship between process parameters and welding quality was established, with weld microhardness and tensile strength as key response variables. The influence of laser cleaning parameters on the quality of welded joints was comprehensively evaluated through multi-scale analysis methods, including hardness distribution testing, tensile strength measurement, and microstructure characterization. The experimental design focused on four key process parameters: laser power P (100 W–350 W), scanning frequency f1 (60 Hz–100 Hz), pulse frequency f2 (2 kHz–5 kHz), and travel speed v2 (10 mm/s–14 mm/s). Three levels were assigned to each parameter in the optimization study. The research results indicated that there were significant process window limitations in laser cleaning parameter settings. Excessive laser power, slow travel speed, high scanning frequency, or high pulse frequency could cause thermal damage to the substrate material, resulting in surface ablation, microcracks, and other defects. Conversely, inadequate laser power, excessive travel speed, insufficient scanning frequency, and low pulse frequency may result in ineffective removal of surface oxide films, rust, and organic pollutants. As indicated by the analysis of variance (Table 3), among many influencing factors, scanning speed was identified as the most influential parameter affecting weld seam microhardness distribution, while laser power exhibited the most dominant effect on the tensile strength of the welded joint. Through variance analysis, the optimal combination of laser cleaning parameters was identified as laser power 150 W, pulse frequency 5 kHz, scanning frequency 80 Hz, and scanning speed 10 mm/s.Microstructure analysis revealed that laser cleaning with optimized parameters led to a 38.1% reduction in the width of the heat-affected zone on the 3Cr13 martensitic stainless steel side, decreasing from 98.7 μm in the original state to 61.1 μm (Fig. 9). The columnar crystal structure in the weld zone was significantly refined, with a higher proportion of equiaxed crystal zones. In contrast, the microstructure of the heat-affected zone on the 9Cr18MoV side remained relatively unchanged, which was attributed to its higher alloying element content (Fig. 10). The mechanical performance test results showed that laser pretreatment resulted in a uniform hardness increase across the welded samples. The weld zone exhibited an average hardness of 399.5 HV, representing a 4.8% enhancement compared to untreated samples (381.2 HV) (Fig. 11). More importantly, fractographic analysis further confirmed that laser pretreatment effectively suppressed defect formation, such as welding pores and hot cracks. Consequently, the joint tensile strength was remarkably improved from 478.35 MPa before laser pretreatment to 703.12 MPa, an increase of 47% (Fig. 12), while maintaining a reasonable elongation rate of 4.67%.The optimal laser cleaning parameters for 3Cr13-9Cr18MoV dissimilar martensitic stainless steel welded joints were successfully established through systematic process optimization. This research confirms that the optimized laser pretreatment process significantly improves the quality of welded joints through multiple mechanisms, including microstructural refinement in the weld zone, improved hardness distribution, and enhanced tensile strength. The findings not only elucidate the quantitative relationship between laser cleaning parameters and welding quality but also provide theoretical foundations and practical guidelines for implementing laser cleaning-assisted welding technology in tool manufacturing applications.