Acient Korea Casting Technology

Why is the stainless cast steel magnetic?

• Casting product buyers often raise an issue why the CF8 (cast 304) or CF8M (cast 316) stainless steel is a little bit magnetic. Since most products produced in steel mills such as the round bar, billet and sheet are non-magnetic, casting users often expect the processing conditions equivalent to non-magnetic products STS 304 and 316.
• While the AISI class 316 and the ASTM class CF8M are called as the austenite stainless steel, the 430 and CB-30 are called as the ferrite stainless steel. Such classification is defined by various steel crystal structures. The austenite stainless steel is ductile and non-magnetic. The ferrite stainless steel is harder, less ductile, and magnetic. The ratio of such structures present in a particular steel is mainly determined by the chemical analysis, although other factors may need to be considered. Of course, it can be also changed by heat treatment depending on the steel type.
• CB-30 and 430 are ferromagnetic because their main phase distribution is ferrite. AISI 316 is intrinsically austenite and it hardly attracts the magnet.
• CF8 and CF8M in the casting specification are generally austenite, but these contain 5 to 20% ferrite in general and thus are a little bit magnetic.
• The composition of 304 and 316 and that of CF8 and CF8M are almost identical. Then, why do they have different codes?
  It is because that it is possible to produce plate material in the uniform quality since the plastic processing such as extrusion, drawing and rolling gets easier if the ferrite phase of 304 or 316 is reduced or removed. Consequently, the chemical composition of the plastic processed material is a little bit adjusted when the product is produced.