WYL tells you how to deal with 304 stainless steel tube surface blackened?
If the inner and outer surfaces of 304 stainless steel tubes are black, there are three ways to avoid this:
1. Improve the purity of argon used for welding 304 stainless steel tube into pure argon.
2. Argon gas should be used to protect the back.
3. Use a backside protector on the back, which is a protector that can save argon gas.