Can one assume that stainless steel that can be hardened is magnetic?
All steels are hardenable if you use the right process. Most stainless steels are magnetic but usually more weakly than mild steel.
actually stain less steel is mainlly three first one is austenitic, 2nd one is ferritic, and 3rd is martensitic. These three types of steels are identified by their microstructure or predominant crystal phase. Austenitic. Austenitic steels have austenite as their primary phase (face centered cubic crystal). These are alloys containing chromium and nickel (sometimes manganese and nitrogen), structured around the Type 302 composition of iron, 18% chromium, and 8% nickel. Austenitic steels are not magnetic and not hardenable by heat treatment. The most familiar stainless steel is 304 containing 18-20% chromium and 8-10% nickel. Ferritic. Ferritic steels have ferrite (body centered cubic crystal) as their main phase. These steels contain iron and chromium. Ferritic steel is somewhat magnetic, less ductile than austenitic steel, and is not hardenable by heat treatment. Martensitic. Martensitic steels have orthorhombic martensite as their main phase. Martensitic steels are low carbon steels. They are magnetic, and may be tempered and hardened. Martensite gives steel great hardness, but it also reduces its toughness and makes it brittle. If you ran around the house with a magnet, checking on the items you know are stainless steel, you would probably find that cookware and flatware are not magnetic, but cutlery might be slightly magnetic.
Most of the 300 series stainless metals are not magnetic, but if it is cast, it is magnetic. Welds are considered casting, so the welds are magnetic even though the items that are welded together are not. The 400 series stainless may have a few types that are magnetic. I suppose generally the hardenable factor has a bearing if you consider that 400 series can be hardened more readily than the 300 series. Source: Working in metal fabrication shops.
