Effects of Process Parameters on Argon Arc Surfacing Weld Dimensions and Microstructure

Literature Overview

This study focuses on Gas Metal Arc Welding (GMAW) and Gas Tungsten Arc Welding (GTAW) surfacing/cladding processes, investigating how electrical parameters (current, voltage, pulse frequency), gas parameters (flow rate, nozzle diameter), and mechanical parameters (travel speed, torch angle, wire feed speed) affect both the dimensional geometry and the metallurgical microstructure of argon arc cladding welds. The research bridges the gap between macroscopic weld shape control and microscopic structural integrity, offering a holistic perspective on surfacing process optimization.

Key Technical Parameters and Their Effects

Current and Voltage Effects on Weld Geometry

The welding current directly controls the heat input and thus the dilution rate and weld pool dimensions. For GMAW surfacing with a 1.2 mm wire diameter, currents between 120–180 A produce weld widths of 10–16 mm with reinforcement heights of 2–4 mm. The arc voltage, which determines the arc length, influences the weld width independently: at constant current, increasing voltage from 22 V to 28 V widens the weld by approximately 2 mm due to increased arc force and wider heat distribution.

Microstructural Response

The cooling rate at the solidification front is governed primarily by the travel speed and heat input. At high travel speeds (>300 mm/min), the cooling rate exceeds 50 °C/s, producing fine dendritic structures with minimal grain boundary precipitation. Conversely, at low speeds (<150 mm/min), cooling rates drop below 15 °C/s, allowing sufficient time for carbide precipitation (Cr23C6 in austenitic overlays) and grain boundary segregation of sulfur and phosphorus.

The study reveals that pulse welding parameters—specifically the pulse current (Ip), background current (Ib), and pulse frequency (f)—provide additional levers for microstructural control. A pulse current of 250–300 A with a background current of 80–100 A at a frequency of 50–100 Hz produces a weld pool that cycles between deep penetration and shallow remelting, resulting in a refined grain structure with reduced dilution compared to DC continuous welding at equivalent average current.

Shielding Gas and Surface Quality

The shielding gas composition and flow rate significantly affect both weld surface quality and the nitrogen/oxygen content of the deposit. Pure argon at 12–18 L/min provides excellent shielding for austenitic and nickel-based alloy overlays, with nitrogen pickup typically below 0.03% and oxygen below 0.05%. For nickel-based alloys (Inconel 625, Hastelloy C276), the addition of 5% CO2 to the argon shield can improve wetting and reduce surface porosity, though it slightly increases carbon pickup in the overlay.

The nozzle diameter must be selected to ensure adequate gas coverage: a minimum of 15 mm standoff distance requires a nozzle diameter of at least 20 mm to prevent wind-induced shielding disruption. In outdoor or drafty environments, a gas lens or secondary gas curtain may be necessary to maintain weld integrity.

Engineering Considerations for Multi-Layer Cladding

For thick cladding layers (>6 mm), the study recommends a multi-layer strategy:

1. Bond layer: Low current (100–120 A), high speed (300 mm/min), low dilution (<20%) to ensure metallurgical bond without excessive base metal contamination.
2. Fill layers: Moderate current (140–160 A), moderate speed (220–260 mm/min) for efficient deposition with controlled dilution (20–30%).
3. Cap layer: Optimized for surface finish and composition, using pulse parameters to achieve fine grain structure and smooth surface profile.

The interpass temperature between layers should be monitored and controlled. For austenitic stainless steel overlays, exceeding 250 °C risks sensitization; for nickel-based overlays, temperatures above 150 °C can promote unwanted intermetallic formation at the fusion boundary.

The comprehensive parameter-microstructure-property relationships established in this study provide a robust framework for process qualification under NB/T 47014 and ASME IX, ensuring that cladding procedures are not merely empirically developed but are grounded in metallurgical understanding.