熱間ねじり試験による鉄鋼の熱間加工性の評価に関する研究
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概要
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Occurrence of cracks in tube-making, particularly in piercing tube blanks, constitutes one of the important problems, and has been studied on its various aspects since many years ; research efforts have also been made to find an effective method for determining the optimum working temperature, however, without any satisfactory result. It was seemed that the hot twisting test was a valid method for advancing these studies, but because the deformining mechanism in the course of twisting was not as yet clarified, the extent and scope of this validity were not considered to be sufficiently established. For this reason, the author developed a device capable of easily measuring not only the torque and the number of revolutions at fracture, but also the secondary stress in gauge direction caused by twists, and examined the twisting deformation patterns and importance of the secondary stress in determining the hot workability. In this way, the following conclusions were obtained. (1) The secondary stress occurring in the course of twisting is the phenomenon accompanying shearing, and acts as tension at a temperature higher than the recrystallization temperature. (2) There exists a certain relationship between the shearing strain (ε′) and the absolute temperature (T_K) at which the secondary tensile stress appears within the range of austenite temperature examined. ε′=ε_O・(T_K)^<-R> It seem to us that there is a close relationship between this fact and the recrystallization of material. (3) The intensity of secondary tensile stress (σ_t) is determined by strain (ε), strain rate (ε^^.) and absolute temperature (T_K) ; and these correlation can be expressed in the equation. σ_t=log K・(ε^m・ε^^.^n・T^A_K) where m, n and A are the constants incidental to a particular material ; n indicates the sensitivity to speed, A represents that to temperature. (4) The patterns of deformation in hot working of steel can be generally classified into three types, in relation to the stress, the strain and the fracturing shape. (5) The relation of the coefficient of hot torsional working (⊿R) and the critical deformation (δ) in piercing can be expressed in following common equation. log δ=δ_o+k・⊿R where k and δ_o are the constants incidental to a particular material.
- 社団法人日本鉄鋼協会の論文
- 1966-12-01
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