Dual-Pulse MIG Process Parameters Effect on Dissimilar Stainless Steel Weld Quality

Literature Overview

Published in the Transactions of the Welding Journal (Vol. 39, Issue 7, 2018) by Hu Yu and colleagues from South China University of Technology, this paper addresses the challenging problem of welding dissimilar stainless steel joints between 2205 duplex stainless steel and 316L austenitic stainless steel using dual-pulse MIG (DPMIG) welding. The study investigates the effects of strong pulse count, weak pulse count, and welding speed on weld bead quality, utilizing wavelet analysis of electrical parameters, tensile testing, and metallographic examination. This work is significant because dissimilar stainless steel welding is common in industrial piping systems where different corrosion resistance requirements exist across joint interfaces.

Core Technical Findings

The authors establish a clear hierarchy of parameter influence on weld quality: welding speed has the greatest effect, followed by weak pulse count, then strong pulse count. The fracture location analysis reveals that failure predominantly occurs at the weld metal or the 316L base metal side adjacent to the weld, indicating that the 316L side represents the weaker link in the joint. Increasing welding speed reduces heat input, accelerates cooling rates, and shortens the time available for ferrite transformation, resulting in finer microstructures.

Parameter Influence and Quality Metrics

Dual-Pulse MIG Process Mechanism

The dual-pulse MIG process combines strong pulses for deep penetration with weak pulses for surface refinement and cooling control. In dissimilar stainless steel welding, this dual-pulse strategy offers unique advantages for managing the microstructural evolution in both the weld metal and the heat-affected zones of the two dissimilar base metals. The strong pulses provide the energy necessary for adequate penetration through the thicker 2205 section, while the weak pulses between strong pulses allow partial solidification of the weld cap, reducing the weld bead width and promoting a more compact microstructure.

The wavelet analysis of electrical parameters provides insight into the droplet transfer behavior during welding. The characteristic electrical signatures of strong and weak pulses can be used to monitor and control the welding process in real-time, enabling adaptive control strategies that maintain consistent weld quality despite variations in joint fit-up or travel speed. This electrical monitoring approach is particularly valuable for production environments where consistent quality is essential for pressure-containing applications.

Microstructural Evolution and Mechanical Behavior

The microstructural analysis reveals that increasing welding speed leads to finer ferrite distributions in the weld metal due to accelerated cooling rates that shorten the time available for ferrite-to-austenite transformation. This is particularly relevant for the 2205 duplex stainless steel side, where maintaining a balanced ferrite-austenite ratio (typically 40-60% ferrite) is critical for achieving adequate mechanical properties and corrosion resistance. Excessive cooling rates can lead to excessive ferrite content, which may promote intergranular corrosion and reduce toughness.

The fracture location at the 316L side indicates that the austenitic base metal heat-affected zone represents the weakest region of the joint. This is attributed to the grain coarsening and sensitization effects in the 316L HAZ, where the thermal cycles cause carbide precipitation at grain boundaries, reducing local strength and corrosion resistance. The weld metal itself, being a compositionally mixed material between 2205 and 316L filler, may develop a modified austenitic or austenitic-ferritic microstructure that provides adequate but not superior mechanical properties.

Engineering Practice for Dissimilar Steel Welding

In industrial piping systems, dissimilar stainless steel joints are commonly encountered in heat exchangers, chemical processing equipment, and marine applications where different sections of the piping require different corrosion resistance characteristics. The 2205/316L combination is particularly common in oil and gas production systems, where 2205 provides superior chloride stress corrosion cracking resistance while 316L offers excellent general corrosion resistance at lower cost. The DPMIG process parameters identified in this study provide a practical basis for developing welding procedures for such joints.

The finding that welding speed is the dominant parameter has direct implications for welding procedure specification. Tight control of travel speed is essential, and automated welding systems with precise speed control are strongly recommended for production applications. The weak pulse count optimization provides an additional degree of freedom for fine-tuning weld quality without significantly affecting productivity. The strong pulse count, having the least influence, can be set to provide adequate penetration with minimal process variation.

Study Insights and Outlook

This paper makes a valuable contribution to the understanding of dissimilar stainless steel welding using advanced pulsed MIG processes. The systematic parameter influence analysis, combined with electrical parameter monitoring and microstructural characterization, provides a comprehensive technical basis for procedure development. The identification of the 316L side as the fracture-prone region highlights the need for careful consideration of joint design and post-weld treatment to mitigate the weakness of the austenitic HAZ. Future research should investigate the long-term corrosion performance of these dissimilar joints, particularly under chloride-containing environments where the 316L side may be susceptible to pitting and crevice corrosion. The dual-pulse MIG approach demonstrated here offers a promising pathway for achieving high-quality dissimilar steel welds with improved process control and mechanical reliability.