Abstract
The report is composed of a study of the influence of four factors, oxygen, hydrogen, ferrite content and welding conditions, on the blowholes in the weld metal, using covered arc-welding electrodes for the pitting corrosion resistant austenitic stainless steel with high nitrogen concentration (25Cr-13Ni-1Mo-0.35 N). Compositions of gas in the blowholes of weld metal were also checked.
The experimental results were as follows;
1) As the amount of hydrogen in weld metal increases, so does the number of blowholes in a circumstances where oxygen content are high (0.06%). The number of blowholes decreases when oxygen content are lower and the influence of hydrogen for blowholes also decreases. The number of blowholes is very few at 0.04% oxygen and 5 ppm hydrogen.
2) The number of blowholes much fluctuates by welding conditions when both oxygen content (0.06%) and hydrogen content (8 ppm) are high. When oxygen content (0.04%) and hydrogen content (5 ppm) are both lower, the number of blowholes in weld metal decreases and blowhole is almost exempted from the influence of welding conditions.
3) The number of blowholes does not change until ferrite content exceeds 5% but it begins to increase when ferrite content exceeds 50%.
4) Hydrogen and nitrogen gas were found in the blowholes of weld metal with oxygen content 0.06% and hydrogen content at 8 ppm.
5) It can be concluded that prevention of blowhole in stainless steel weld metal with high nitrogen concentration (0.29-0.34%) could be achieved by lowering oxygen content less than 0.04% and hydrogen content at 5 ppm.
