高窒素オーステナイトステンレス鋼の組織と機械的性質に及ぼす時効の影響(相変態・材料組織)

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The effect of aging on microstructures and mechanical properties of 1%N-23%Cr-4%Ni-2%Mo austenitic stainless steel aged at 600〜800℃ for up to 1000h were investigated with electron microscope, analysis of extracted residues, ferrite scope, and mechanical tests such as hardness, tensile, and Charpy impact. Chromium nitrides precipitated on grain boundary at the aging temperature below 650℃, while lamellar precipitates, which were composed of plate like Cr_2N and martensite, were formed above 700℃. σphase precipitated at 700℃ for 1000h and above 750℃ for longer than 100h. Martensite was also observed around σ pohase, and the total amount of martensite was 40-50% after aging at 700-800℃ for 1000h. Age hardening was observed above 700℃ and hardness, which increased with aging time and temperature, reached about Hv 500 after aging at 800℃ for 1000h. Increase in tensile strength by aging was higher than that in proof strength, because of pronounced increase in work hardening rate by aging. Strengthening by aging depended mainly on the amount of lamellar precipitates and additionally on σphase and its surrounding martensite at higher temperature. Tensile ductility and impact toughness were decreased by aging due to lamellar precipitates and σphase.
社団法人日本鉄鋼協会の論文
2007-03-01