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

Abstract

According to the kinds of steels there are some differences in the frequency of thermal stress crackings which occur in the heating process of ingots. In this report, we measured Young's modulus and the coefficient of thermal expansion of typical steels, within the temperature range of room tempereature to 1000°C, because they influence the thermal stress. And using the results we compared the rate of frequency of thermal stress crackings according to the kinds of steels.The results obtained are as follows:(1) It was found that the Young's modulus decreases rectilinearly up to 400°C and curvilinearly over about 500°C to 600°C in all the steels tested. And the modulus is not influenced greatly by a small change of the components, the inclusions heat treatment, etc. of steels, but there is some difference among the kinds of steels classified roughly.(2) As for the coefficient of thermal expansion there is little difference with a small change in heat treatment for the same kind of steels but a considerably large difference according to the components of steels. This influence of the components is not very great under the transformation point but it becomes very great above the point (i. e. Austenite range). Especially when carbon content increases, the coefficient of thermal expansion increases heavily.(3) To estimate the magnitude of thermal stress which occurs when steels complete the transformation we utilized Young's modulus and coefficient of thermal expansion, and found that thermal stress increases chiefly in accordance with the increase of carbon content.It follows from this that thermal stress is greatest in hyper-eutectoid steel of JIS SK2, SUJ 2, 3. Consequently we can conclude that thermal stress crackings are most liable to occur in these kinds of high-carbon steel.