The parent metal (Figure 2) shows a mill annealed structure ASTM 6-8 grain. The pressure welded sample (Figure 3) shows complete fusion in the grain with size remaining in the ASTM 5-6 range. (Figure 4) shows the fillet weld. There is a void in the center (not uncommon) that can cause premature failure by collecting carbon.
The heat affected zone shows considerable grain growth which weakens the material and makes it susceptible to carbon penetration. Pressure welding gives a complete fusion of parent metals with no voids and no grain growth, thus making it as strong as the parent metal. Conventional fillet welds cause considerable grain growth, possible voids and a definite weakening of the parent metal in the area of the weld.
330 alloy, HC1-nitric acid etch. Carbon particles in austenite grain. Grain size ASTM 6-8. 50X
330 alloys, HC1-nitric acid etch. Weld shows complete fusion, constant grain size in weld and heat affected zone. Grain size ASTM 5-6. 50X
Top area shows fillet material. Middle area shows large grain with heat affected zone ASTM 2-4. Bottom is parent material with grain of ASTM 2-4. Bottom is parent material with grain of ASTM 6-8, showing incomplete penetration gap of 1/8î. 50X
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