高温強度に及ぼす熱処理の影響

種々の炭素量を持つ18Cr-12Ni鋼の性質

抄録

Effects of solution treatment (1000∼1250°C×1hr) and aging treatment (650∼800°C×2hrs) on smooth and notch creep rupture strengths (600°C, 22.5kg/mm2) of 18Cr-12Ni stainless steels with carbon contents varying from 0.018 up to 0.386 weight percent were studied. All steels except the one with the lowest carbon content showed a maximum strength at the solution temperature of 1080°C. The appearance of the maxima was explained in connection with the increase of age hardening and the grain growth, both of which were brought about by raising the solution temperature. The former had the effect of decreasing creep rate (increasing rupture life), and the latter caused premature intergranular rupture (decreasing rupture life), thus they balanced each other, yielding a maximum in rupture life at some solution temperature.
With increasing rupture ductility (of smooth specimens), the ratios of notch rupture lives to smooth rupture lives increased, though the relation showed a considerable scattering. Notch weakening was observed in the highest carbon steel specimens which were solution treated at higher temperatures, i.e., in the case of the lowest rupture ductility.
The effect of aging temperature was negligible as compared with that of solution temperature. Aging at 750°C gave the best results, 800°C giving an over aging.
By increasing carbon content the rupture lives inereased. Beyond 0.15% of carbon, however, there was not much tangible improvement but rather an adverse effect appeared on notch rupture lives.
The grain growth of the highest carbon steel was retarded because of the existence of retaining undissolved carbide thus the rate of decrease of rupture life due to the rise of solution temperature was slower in the highest carbon steel than in the lower carbon steels.