Effect of backing gas mixtures on corrosion properties of stainless steel grade 304 weld metal by autogenous GTAW

Pitting corrosion would pose difficulty for the cleaning of equipment used in food processing, even when using the Cleaning in Place (CIP) process. It tends to occur at a location requiring welding. In general, Gas Tungsten Arc Welding (GTAW) is the most applicable process for food and drug equipment. To improve the properties of the weldment, filler metals are commonly used. However, the use of thin-sheet stainless steel in the application of filler metals would be difficult in food processing. In this research, the weld metal properties would be improved only by using N-2 mixing to the backing gas during welding. Experiments were conducted using various mixtures of N-2 on 1.5, 2.0, and 3.0 mm thicknesses of 304 stainless steel. The roots of weld metal taken from the samples were evaluated for corrosion properties in 3.5%NaCl from the polarization curves. The results showed the improvement of pitting corrosion from 379 mV to 757 mV, while the general corrosion rate decreased from 0.00477 mm/y to 0.00099 mm/y with 100%Ar and 100%N-2, respectively. Both Nitrogen content and solidification rate together affected the solidification modes and ferrite contents that would affect the corrosion properties. At least 15% N-2 mixing would be sufficient for weld metal property improvement. Due to the decrease of ferrite content from N-2 addition, solidification cracking susceptibility test by fishbone test was acceptable with no cracking observed, showing the potential to recommend N-2 mixtures for actual production. (C) 2021 The Author(s). Published by Elsevier B.V.

Automated summary

The research demonstrates that using different mixtures of N-2 can improve the properties of weld metal in cleaning food processing equipment. By adding N-2, the pitting corrosion potential can be increased and the general corrosion rate can be decreased. At least 15% N-2 mixture is sufficient to improve the properties of weld metal and reduce the occurrence of solidification cracking.