304 Stainless Steel
SAE 304 stainless steel is the most common stainless steel. The steel contains both chromium (between 15% and 20%) and nickel (between 2% and 10.5%) metals as the main non-iron constituents. It is an austenitic stainless steel. It is less electrically and thermally conductive than carbon steel and is essentially non-magnetic. It has a higher corrosion resistance than regular steel and is widely used because of the ease in which it is formed into various shapes. It can be magnetic at weld seams, this is due to some delta ferrite. This may form also in autogenous weld metal and the high temperature heat affected zone of a weld, where partial transformation to delta ferrite can occur on heating and where cooling is too rapid for full re-transformation.
Hence, overall, welds in many of the 300 series austenitic stainless steels, made with no filler or approximately matching filler will typically show mildly magnetic properties.