高炭素鋼鋼塊の加熱過程における内部亀裂の発生について : 鋼塊の熱応力亀裂に関する研究 IV

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概要

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• Through a series of experiments and theoretidal calculations we disovered that 1.4t circular ingots (400mm ⨖×1, 500mm) and 1.7t square ingots (400mm ⨖×1, 500mm) of high-carbon-chromium steel suffer cracking due to to thermal stress when heated to the rolling temperature in a reheating furnace. The results obtained are as follows : (1) To find out the period and the surface-center temperature difference at which the internal cracking may take place, we heated the ingots at varios heating speeds in a Batch type furnace. Cracks developed only in the ingots in which transformation had been completed, and whose surface-center temperature difference at the completion of transformation was over 230℃∿240℃ in calculated value. And this critical temperature difference was identical with both of the circular and the spuare ingots. (2) From the inspection of many of the ingots of the above two types which had under gone cracking after heating in a continuous reheating furnace, we could find again that cracking took place only in the ingots whose core had completed transformation with surface-center temperature difference of more than about 240℃. Thus we can say that the continuous furnace of this type must have the heating capacity smaller than 30t/h to prevent cracking. (3) With several typical examples of heating curves of ingots in the continuous furnace, we made calculations of the thermal stress which occurs inside the ingots and found that elastic-plastic stress and plastic strain increase violently at the core of the ingot when the core completes the transformation. But in all the calculations of rapid heating the maximum thermal stress value remains in this case constant at 9.1 kg/mm^2 with the exception of the increase of plastic strain. On the other hand, if the increase of plastic flow delays in proportion to the increase of plastic strain and strain rate because the plastic flow is retarded by the triaxial tension stresses of the core part, the increase of the stress in the flow state becomes greater than the fracture stress of 13 kg/mm^2 and consequently it causes thermal stress crackings. Thus we can explain the occurrence of thermal stress crackings in rapid heating. (4) From the results of the above experiments and calculations, we could devise the way of heating effectively and without cracking the ingots which are very liable to crack like those of high-carbon-chromium steel. By the use of this method we are now able to obtain a heating capacity of more than 40t/h without any crackings.

• 1964-01-01

著者

• 原 隆啓

  山陽特殊製鋼株式会社

関連論文

• 高炭素鋼鋼塊の加熱過程における内部亀裂の発生について : 鋼塊の熱応力亀裂に関する研究 IV
• 鋼種による熱応力亀裂の発生度合を比較するための高温弾性率および熱膨脹率の測定 : 鋼塊の熱応力亀裂に関する研究 III
• 鋼塊の加熱過程における熱応力について : 鋼塊の熱応力亀裂に関する研究 II
• 加熱過程における鋼塊内部の温度分布について : 鋼塊の熱応力亀裂に関する研究 I
• 110 加熱過程における内部亀裂の生因について : 鋼塊の熱応力亀裂に関する研究 II(加工, 日本鉄鋼協会第 64 回(秋季)講演大会講演大要)
• 109 鋼塊における熱応力の理論的解法について : 鋼塊の熱応力亀裂に関する研究 I(加工, 日本鉄鋼協会第 64 回(秋季)講演大会講演大要)

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