25Cr-20Ni 耐熱鋳鋼の機械的性質におよぼす析出相の影響

概要

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Effects of precipitation phases on the mechanical properties at room temperature and on the creep rupture strength at 800℃ of 25Cr-20Ni heat-resistant cast steel containing carbon ranging from 0.06 to 0.4% were investigated. The results obtained were summarized as follows : (1) With increasing the aging time at 800℃, massive σ-phase of angular type which existed in the as-cast specimen with 0.06% of carbon changed to the shape of globular type, and the widmanstatten type appeared in the grain. Changes of the amount and the shape of the σ-phase had an important influence upon the creep rupture strength and the ductility. (2) Both eutectic carbides of M_7C_3 and M_<23>C_6 which existed on the grain boundaries of the as-cast specimen with 0.2% of carbon began the in situ transformation to σ-phase after the aging for 300 hr and substituted completely the σ-phase for the carbides after the aging for 5000 hr. The structural unstability due to the in situ transformation of carbides to σ-phase deteriorated remarkably the creep rupture strength and the elongation. (3) The eutectic carbides in as-cast specimen with 0.4% of carbon were identified mainly to M_<23>C_6, the shape and the amount of which were not changeable even after long period of aging. After the aging for 1000 hr, secondary carbides were observed in the grain and the coalescence of these carbides decreased the creep rupture strength.
社団法人日本鉄鋼協会の論文
1970-05-01