制御圧延・加速冷却によるオーステナイト系ステンレス鋼の材質と炭化物の析出形態

抄録

This paper surveys the application of controlled rolling and accelerated cooling process-(thermomechanical control process=TMCP)-to austenitic stainless steels (AISI304, 304L, 316, 316L). The TMCP makes it possible to produce high-strength stainless steels while retarding carbide precipitation at grain-boundaries. The high strength is achieved by refining microstructures, and the ausforming effect which increases dislocation density. The 10% oxalic acid test reveals that, a sensitized TMCP type 304L does not easily form a ditch structure. The ferric sulfate-sulfuric acid test shows that the corrosion rate relating to chromium depleted zones of the TMCP type 304L is equal to that of the solutionized one. In a sensitized TMCP type 304L, sheet-like M₂₃C₆ carbide precipitates dispersively at grain-boundaries and subgrain-boundaries of the un-recrystallized grain. This is very different from the continuous precipitation at grain-boundaries in solutionized stainless steel. It is presumed that the dispersed precipitation leads to a discontinuous chromium-depleted zone and as a result, the sensitized TMCP type 304L does not form a ditch structure.