高温用 2 1/4 Cr-1 Mo 鋼の研究

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2 1/4Cr-1 Mo steel are generally used for the huge reactor vessels that operate at high pressure and elevated temperature, because of its good short and long time elevated tensile properties and its good resistance to hydrogen attack. Requirements for higher operating volume and pressure have accelerated a demand for reactor vessels of extra heavy gauge wall thickness and upgraded mechanical properties throughout the thickness. To obtain informations needed for effetive uses of 2 1/4Cr-1 Mo steels, a fundamental and systematic study was carried out on the heavy gauge steels of 100-400mm in thickness. In this study, the effect of cooling rates from austenitizing temperature on microstructures, the effect of cooling rates and tempering cycles on mechanical properties and elevated temperature tensile properties were investigated. The results obtained are as follows : (1) Uniform bainitic structure is obtained when the cooling rate is faster than 6℃/min, and the blockish ferrite increases with decrease rate, which deteriorates mechanical properties. (2) The effect of various heat treatment cycles on room temperature tensile properties is shown as a function of LARSON-MILLER'S tempering parameter, and 2 1/4Cr-1 Mo steels in the ultimate tensile strength range from 56kg/mm^2 to 90kg/mm^2 can be manufactured by the suitable tempering cycles. (3) To maintain excellent notch toughness, the cooling rate faster than 6℃/min is desirable and in the special case of manufacturing high tensile steels which are tempered at low temperature (UTS is over than 70kg/mm^2), 10-15℃/min or faster cooling rate is recommendable. (4) By applying the results mentioned above, 365mm thickness forged shell was cooled in agitating water and the excellent mechanical properties and satisfactory bainitic structure was obtained throughout the thickness.
社団法人日本鉄鋼協会の論文
1970-11-01

高温用 2 1/4 Cr-1 Mo 鋼の研究

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