Influence of Mn/S on the Outgas Property and the Machinability of Type 430F and Development of a New Free-machining Ferritic Stainless Steel for HDD Components

The influence of Mn/S on the outgas property and the machinability of type 430F has been investigated and the following results were obtained. 1) The degree of outgas decreased with Mn/S because of enhancement of the chemical stability of sulfide by substitution of Cr for Mn in sulfide. 2) The machinability in turning and drilling decreased with Mn/S. The reasons have been suggested that the aspect ratio of sulfide got larger and also the hardness of sulfide increased with Cr contents in sulfide. On the basis of the above results, a new free-machining ferritic stainless steel, DHS1 has been developed for hard disk drives, which has 19Cr-0.35Mn-0.26S+Pb, Te ;mass%. This advanced steel is superior in machinability and corrosion resistance to type 430F and also has low outgas emissivity.