Recently, there have been reports on the biological influences of refined material, e.g., the antibacterial action, promotion of mammalian cell growth for medical equipment usage. We investigated the effect of the controlling grain size of austenitic stainless steel on microorganism adhesion, using familiar organisms, i.e., lactic acid bacteria in yogurt as gram positive bacteria and dry yeast used in bread making as a fungus. The results suggest that the adhesion of lactic acid bacteria is reduced and the adhesion of yeast is promoted when the grain size is of nanometer order. In contrast, the opposite outcome is obtained when the grain size is of micrometer order, particularly larger than 3 µm. Note that the optimal condition of the contact material grain size is different for each organism, then this phenomenon enables us select grain size in accordance with the desired purpose, e.g., fermentation.
Difficulties in press forming, such as the occurrence of fractures, wrinkles, and springback, are more severe when using ultrahigh-strength steel (UHSS) than when using mild steel owing to the poor formability of UHSS. To make matters worse, the shape of a frame part, for which UHSS is often used, is, in many cases, complex and curved in the top and/or side view. Countermeasures against defects in a UHSS part are, therefore, so specialized that it would be highly advantageous in the press forming of a UHSS sheet if a new forming technology with wider applicability to curved shapes could be developed. In this study, a new forming technology that is effective in the press forming of curved-in-top-view parts was developed. The new forming technology consists of two processes. The 1st process is preforming and the 2nd process is cam bending. The key in this technology is the optimum design of the preformed shape to obtain an accurate final shape after the 2nd process. The new technology was applied to forming a curved-in-top-view hat shape of steel of 590 to 1470 MPa grade, and its suppression effects on the above-mentioned problems was confirmed by both CAE and trial pressing.