welding SS 304L

After melting and during cooling, first appear some delta ferrite and then just austenite. No more phase transformations. This should be the final microstucture, regardless welded either by GTAW or GMAW process.

Kind regards

Stainless steel is unstabile material, therefore, be careful with the energy input. GTAW results in higher energy input than the other systems. You have SS 304 L (low carbon), this is better than normal SS 304. Since the Crom atoms are capturing the carbon atoms, the unstabile structure can be easily disturbed by heat input. The result is phenomen called Crom - carbure development that shall completly damage the heat affected zone. You can notice small holes through the whole thicness of the material.

To avoid this phenomen, the use of 304 L type is better, however, high welding speed and cooling the heat affected zone during welding, continue with further passes after cooling are essential measures.

tugrul

Austenite is a metastable phase at room temperature. There are some other types of Stainless steels (ferritic, for example).

One thing can occur when welding stainless steels is the precipitation of chromium carbides on the grain boundaries. This carbides can have a formula Cr₂₃ C₆ and therefore if enough carbon is present, at grain boundaries the chromium content can be lower than 12% and the steel loose its "stainless" condition which is given by the formation of a continuous layer of chromium oxide.

If the steel is a "low carbon" one means that carbon content must be lower than 0,03%, so it's very difficult to deplete the chromium content as carbides if you don't have carbon enough.

This phenomenon of Cr depletion as grain boundaries carbides is called "sensitization".

Kind regards

thankyou for all these comments. They ll be a great help in my project. Is there any website where i can get a few micrographs of SS 304L weld zone.. Thnx once again