クロム鋼(鍛造ロール鋼)の熱處理の研究

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In order to determine the good conditions of heat-treatment of a roll steel containing 0.80% carbon, 1.62% chromium, studies on austempering and martemrering were made. Isothermal transformation curves i.e. S-curves and the hardenability by gradient quenching were determined. Relations between Ar" transformation velocity and quantity of the retained austenite, residual stress as well as quenching crack were studied by various isothermal treatments. Effects of pre-heating on the residual stress were also determined, The results obtained were as follows. 1) S-curves of the steel were complicated having three noses of Ar and Ar' transformations at about 650°, 450° and Ar" at 150°, respectively. When the maximum heating temperature increased the S-curve shifted to the right, showing that hardenability increased though the temperatures of these nose were not altered. 2) It was notable that the condition of isothermal treatment had close relations to the Ar" transformation velocity, the residual stress, the quantity of the retained austenite and the quenching crack ; i.e. when the holding time in incubation period increased, the Ar" transformation velocity, the residnal stress and the quenching crack increased though these were decreased quickly, when the holding exceeded the incubation period. 3) When the steel was quenched in a temperatures below 200℃, and isothermally treated the transformation proceeded slowly, increasing the quantity of retained austenite and free from quenching crack. 4) When the steel was surface-hardened, the residual stress was a compression at surface and a tension at center ; the amount of these stresses increased as the diameter and the heating time increased, further in the case, in distribution state of the tangential residual stress, an unusual point was observed.
社団法人日本鉄鋼協会の論文
1952-08-25

クロム鋼(鍛造ロール鋼)の熱處理の研究

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