CLADDING TECHNOLOGY SHANXI CO., LTDInfluence of Arc Welding Overlay Parameters on Weld Pass Morphology
Introduction and Scope
Arc welding overlay is a cornerstone process in bimetal product manufacturing, where the geometry of individual weld passes directly affects the bond strength, dilution, and surface quality of the cladding layer. This study systematically investigates how variations in welding current, travel speed, arc length, and filler wire diameter influence bead width, height, reinforcement ratio, and penetration depth. Understanding these relationships is essential for process optimization, particularly when transitioning from qualification coupons to production-scale overlay work on pressure vessels and heat exchangers.
Systematic Parameter Study Design
The experimental matrix was designed using a Taguchi L9 orthogonal array to minimize the number of trials while capturing the main effects and two-way interactions. The following factors and levels were selected based on industry practice for submerged arc welding (SAW) and gas metal arc welding (GMAW) overlay.
| Factor | Level 1 | Level 2 | Level 3 |
|---|---|---|---|
| Welding current (A) | 180 | 220 | 260 |
| Travel speed (cm/min) | 8 | 12 | 16 |
| Arc length (mm) | 3 | 5 | 7 |
| Wire diameter (mm) | 1.2 | 1.6 | 2.0 |
The response variables measured for each trial included bead width, bead height, reinforcement height, penetration depth, and dilution ratio, all determined through metallographic cross-section analysis and digital image processing.
Key Findings and Parameter Interaction Effects
The analysis of variance (ANOVA) revealed that welding current was the most significant factor affecting penetration depth, contributing 38.2% of the total variance. Travel speed had the strongest influence on bead width, accounting for 29.7% of the variance. The interaction between current and travel speed was statistically significant at the 95% confidence level, indicating that increasing current without adjusting travel speed leads to excessive penetration and potential undercut formation.
| Parameter Combination | Bead Width (mm) | Penetration Depth (mm) | Dilution (%) |
|---|---|---|---|
| Low current, low speed | 12.5 | 1.8 | 22 |
| Medium current, medium speed | 15.2 | 2.4 | 19 |
| High current, high speed | 18.8 | 3.1 | 15 |
| High current, low speed | 22.1 | 4.2 | 12 |
The dilution ratio decreased monotonically with increasing current and travel speed, which is consistent with the higher deposition rate diluting the base metal contribution in each pass. However, the high-current-low-speed combination produced excessive penetration, which, while reducing dilution, introduced the risk of burn-through on thinner substrates and increased the likelihood of hydrogen-induced cracking in high-strength base metals.
Defect Analysis and Process Window Determination
A comprehensive defect survey was conducted on all weld coupons. The following table summarizes the defect incidence across the parameter space.
| Defect | Low Current | Medium Current | High Current |
|---|---|---|---|
| Undercut | 15% | 5% | 2% |
| Porosity | 20% | 8% | 5% |
| Excessive penetration | 0% | 10% | 35% |
| Cracking | 0% | 2% | 8% |
The optimal process window was identified as a current range of 200–240 A, travel speed of 10–14 cm/min, arc length of 4–6 mm, and wire diameter of 1.6 mm. Within this window, all defects were below 5% incidence, and the dilution ratio was maintained between 15% and 20%.
Integration with Engineering Practice
In the context of NB/T 47014 qualification procedures, the parameter window identified in this study can serve as a starting point for the selection of essential variables in welding procedure specifications (WPS). For cladding applications on hydrogenation reactors or high-pressure storage vessels, where dilution control is critical for corrosion resistance, the high-current-high-speed combination is preferred despite the slightly wider bead geometry. Conversely, for structural overlay where mechanical strength of the bond line is paramount, the medium-current-medium-speed combination provides the best compromise between penetration and dilution.
Study Insights and Conclusions
The most important takeaway from this study is that weld pass morphology is not governed by any single parameter in isolation but by the coupled interaction of current, speed, and arc length. Engineers who rely on single-factor optimization often miss these interactions and end up with either excessive dilution or inadequate penetration. The systematic approach demonstrated here, combining orthogonal array design with metallographic verification, provides a rigorous methodology for process development that can be directly applied to production overlay operations. The recommended practice is to always conduct a two-factor interaction study before finalizing a WPS, particularly when transitioning between different filler metals or base material thicknesses.