高速度工具に關する研究 (XVI)

概要

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Following the 15th report (Tetsu-to-Hagane, 39, June 1953, No.6, 614∿619), the tempering behaviour of a C 0.65%, W 15.92%, Cr 4.30%, V 0.76% and Co 2.64% high speed steel variously austempered was studied by means of dilatometric and micrographic examination and hardness test. The results obtained were summarized as follows : (1) Austempering at 600℃ did not cause the isothermal transformation of austenite, but appeared to condition the austenite so that lower-bainite would form on the cooling process at the expense of martensite and austenite, and consequently decreased the amount of martensite and retained austenite at room temperature. As a result, after this austempering the inital softening on tempering at 300°∿400℃ little occured. (2) After austempering at the temperature range of 250∿300℃ with the resultant isothermal transformation of austenite to accicular lower-bainite, the final structure contained a little martensite and appreciable quantities of retained austenite, which decreased the hardness at room temperature and caused a large amount of secondary hardening on tempering. (3) The formation of lower-bainite in austempering, regardless of either on isothermal process or on cooling process, appeared to increase the stability of retained austenite so that the subsequent secondary Ar" trausformation was more difficult to occur than that after oil quenching.
社団法人日本鉄鋼協会の論文
1953-10-25