TIG Welding of Pure Nickel and Nickel Steel Dissimilar Metal Joints

Literature Overview

This study by Yu Lirong, published in 1993 in the Chinese journal "Welding" (焊接), addresses the fundamental challenge of TIG welding pure nickel (Ni) and nickel-steel dissimilar metal joints. The research was conducted at the Jiangsu Province Chemical Equipment Manufacturing and Installation Company, reflecting the practical needs of the chemical industry where nickel-based materials are extensively used for their outstanding corrosion resistance in aggressive environments. The work is particularly significant because nickel-steel dissimilar joints are common in heat exchangers, reactors, and piping systems where nickel-lined or nickel-clad components are joined to carbon or low-alloy steel structural parts. The paper provides practical welding procedure development guidance that remains relevant today.

Core Technical Points

Pure nickel (Ni 99.6%) has a unique combination of properties that make it challenging to weld. It has a low thermal conductivity (approximately 90 W/m·K, lower than carbon steel), a low coefficient of thermal expansion, and a tendency to form hot cracks due to its narrow solidification range and sensitivity to sulfur and phosphor impurities. The TIG welding of pure nickel requires careful control of the welding parameters to avoid excessive heat input, which can lead to grain growth, loss of mechanical properties, and hot cracking.

Parameter	Pure Nickel (Ni)	Nickel-Steel Joint
Welding current	80–160 A	100–200 A
Arc voltage	10–14 V	12–16 V
Travel speed	150–400 mm/min	200–500 mm/min
Filler wire	ERNi-1 or ERNi-2	ERNi-1 or ERNi-2
Shielding gas	100% Ar or Ar + 2% He	100% Ar or Ar + 5% He
Preheat	0–100 °C	100–200 °C
Interpass temperature	<150 °C	<200 °C

The authors emphasize the importance of filler metal selection for dissimilar nickel-steel joints. ERNi-1 (Ni-Fe) filler wire is recommended for joints between pure nickel and carbon or low-alloy steel, as it provides good ductility and resistance to solidification cracking. The nickel content in the weld metal should be maintained above 60 percent to ensure adequate corrosion resistance, while the iron content provides sufficient strength and compatibility with the steel side.

Process Analysis and Engineering Implications

From a metallurgical perspective, the TIG welding of pure nickel requires strict control of sulfur and phosphor content in both the base metal and the filler metal. Sulfur in excess of 0.015 percent can promote hot cracking by forming low-melting-point Ni-S compounds at the grain boundaries during solidification. The authors recommend using filler wire with sulfur content below 0.005 percent and phosphor content below 0.010 percent. The welding procedure should also include a thorough cleaning of the base metal surfaces to remove oxide scales, oils, and contaminants that could introduce additional impurities into the weld pool.

For nickel-steel dissimilar joints, the authors highlight the importance of managing the dilution ratio between the nickel filler metal and the steel base metal. Excessive dilution by the steel can reduce the nickel content in the weld metal below the threshold for adequate corrosion resistance, while insufficient dilution can lead to a brittle weld metal with poor mechanical properties. The recommended approach is to use a multi-pass welding technique with the first pass applied to the nickel side to establish a nickel-rich layer, followed by subsequent passes that gradually transition to the steel side. The dilution ratio should be monitored by spectroscopic analysis of the weld metal, with a target nickel content of 55–70 percent for most applications.

Key Questions and Reflections

A critical question that arises from this work is the long-term performance of nickel-steel dissimilar welds in corrosive environments. The weld metal, with its intermediate composition between pure nickel and steel, may be susceptible to intergranular corrosion or pitting corrosion in chloride-containing environments. The authors suggest that post-weld heat treatment (PWHT) at 550–600 °C for 1–2 hours can improve the microstructure and reduce residual stresses, but the PWHT must be carefully controlled to avoid sensitization of any austenitic components in the weld metal.

Another reflection is the evolution of welding technology since 1993. While the fundamental principles described in this paper remain valid, modern welding equipment with precise current and voltage control, advanced shielding gas delivery systems, and real-time monitoring capabilities can improve the consistency and quality of nickel welding. The paper also does not address the use of laser welding or electron beam welding for nickel-steel joints, which offer deeper penetration and lower heat input, potentially reducing the dilution ratio and improving weld quality.

Summary

This study provides valuable practical guidance for the TIG welding of pure nickel and nickel-steel dissimilar metal joints, which are essential components in chemical equipment manufacturing. The key technical points include strict control of sulfur and phosphor content, appropriate filler metal selection, multi-pass welding technique to manage dilution, and careful control of welding parameters to minimize heat input and prevent hot cracking. For engineering practice, the work serves as a foundational reference for welding procedure development, and its principles continue to be relevant in modern fabrication environments where nickel-based materials are used for their superior corrosion resistance.