The change in coercive force when cooled is comparable to the theoretical prediction for iron, based on a model of domain wall motion inhibited by inclusions. Averaged over the ten steels tested the maximum permeability decreased by 8%, the coercive force increased by 14%, and the residual and saturation flux densities increased by 4% and 3%, respectively. Cooling to 77K resulted in harder magnetic properties. The decrease in coercive force with reduced carbon content is attributed to fewer carbide inclusions which inhibit domain wall motion. The carbon content of the steels was found to affect the permeability and coercive force, with lower-carbon steels displaying significantly higher permeability and lower coercive force. Despite having harder magnetic properties than fully annealed steels some of the as-received steels still display soft magnetic properties adequate for magnetic applications. Our room temperature measurements indicate significantly harder magnetic properties than those quoted in the ASM International Handbook, which studied fully annealed stainless steel samples. The steel samples studied were in the annealed state as received from the manufacturer. Cast material manufacturers do not have the same requirements and therefore, can use a slightly harder alloy that contains ferrite.The magnetic properties of ten types of ferritic and martensitic stainless steels have been measured at room temperature and at 77K. By reducing or eliminating the quantity of ferrite in the chemical composition, wrought material manufacturers are able to make an alloy that is easier to roll into sheets or bars. Cast 316 or CF8M is slightly magnetic, however, because it is not entirely austenite and contains from 5 – 20 percent ferrite. Ferritic stainless steels, such as 430 and CB-30 grades, are harder, less ductile, and magnetic due to their predominately ferrite makeup.Īlthough ASTM grade CF8M and AISI 316 are both austenitic stainless steels, AISI 316 is nonmagnetic because it is essentially austenite. Austenitic (300 series) stainless steels, which are the most common, have an austenitic crystalline structure and are softer, ductile, and also nonmagnetic. The terms “austenitic” and “ferritic” refer to the crystalline structures. To answer this question, we must first look at the different classifications of stainless steels.
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