This allowed a standard to be set by studying a sample of uncontaminated or low contamination welds. The second set was left in its "as is" condition; basically none of the surface contaminants were removed in order to prevent contamination. This weld is much like what would occur in the workplace if no cleaning was applied to the steel previously. Contaminants such as oil, rust particles, and common dirt were present in this case. The third set of samples was made "dirtier" by adding contaminants such as oil and carbon. This was the worst case scenario. In other words everything that could or would go wrong, did go wrong. All the samples were welded using GTAW at 90 amps and 5% thorated tungsten. The first and second set of samples were welded with a full flow of shielding gas at 40cfh. The third set of samples, the shielding gas was turned down to 10cfh to strictly limit the amount of shielding, and allowing the weld to be exposed to air born contaminants. All samples were left to cool in the ambient atmosphere of 85-90C.
Once the welds were completed and had cooled to room temperature, the samples were cut and prepared for optical inspection. This included cutting, mounting, sanding, polishing, and etching the samples. The etch was accomplished with a hydrochloric acid etch. The samples were then examined under a microscope at X50 (see figures 1-12).
Results and Discussion.
The normal weld had all the characteristics of a proper weld: a clear fusion/HAZ boundary and full penetration. The weld cap, or top of the weld, was rounded and did not cause undercut. Upon inspection of the weld under a microscope, there was very little martensite or ferrite. .
The simple contamination weld had some interesting developments. The HAZ/ fusion boundary became fuzzy, or darker due to the formation of more martensite and ferrite in the fusion zone (Fig. 3-5). The weld cap flattened out and cause a slight undercut in the base metal (Fig.
