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

抄録

When high-carbon steel or high-carbon-chromium steel ingots of comparatively large size are heated in a reheating furnace, cracks are often observed in their inside.
Author has studied experimentally and theoretically the conditions under which these ingots develop cracks under thermal stress during the heating process. This report describes the method of calculating the interior temperature distribution in the ingots to calculate their internal thermal stress.
With steels, generally thermal properties (thermal conductivity, specific heat and total heat) will change with temperature, so it is not easy to calculate heat transmission briefly.
Thus considering these thermal properties he devised a finite-difference equation by which we can calculate the heat transmission with comparative ease. And he recognized that the calculated value thus obtained accords perfectly with the observed value in a reheating furnace.
The following facts have been discovered through this theoretical calculation;
(1) During the heating process of an ingot the temperature difference between surface and core (i. e. surface-center temperature difference) reaches a maximum when the ingot undergoes a transformation, because of the heat absorption for the transformation.
With low-carbon steels the surface-center temperature difference becomes greatest, long before the core of the ingot completes the transformation. But with high-carbon steels (especially with hypereutectoid steels) the surface-center temperature difference becomes greatest just before the time of completion of transformation.
(2) The maximum surface-center temperature difference at which the core of a highcarbon chromiun steel ingot completes the transformation is determined only by the mean surface temperature elevating rate within the transformation range. To control this temperature difference t he surface temperature elevating rate has only to be controlled in this transformation range.