鋼に対する合金元素としての窒素（第6報）鋼の青熱脆性に及ぼす酸素及び珪素の影響

Abstract

The present investigation has been carried out to explain the mechanism of blue-brittleness in steels. In the 3rd∼6th reports under this title, it has been shown that the blue-brittleness would not occur in steels free from the nitrogen and that the more the nitrogen content in steels is the more clearly the blue brittleness appears.In present investigation the follwoing experiments were carried out.(A) The effect of the annealing in nitrogen or in hydrogen atmosphere was determined by the tensile test at 0∼350° on the specimens shown in Table 1 and the results of these were plotted in Fig. 1∼5.(B) The effect of cold work on the blue-brittleness was examined on the specimens shown in Table 2, that is tempered for 1 hour at 180° after cold work at room temperature ; the tensile values of these are plotted in Fig. 6∼8.(C) The effect of different testing speed was determined on the specimens shown in Table 3 and the tensile values of these are plotted in Fig. 9,10.(D) The change of specific gravity on the specimens tempered for 1 hour at 0∼350° after cold work at room temperature was measured as shown in Table 4.(E) The figure of stress by Fry’s method were examined on the specimens that had used for the tensile test at each testing temperature. From those experiments the following results were obtained.(F) In accordance with either the increase or decrease of nitrogen content in steels by heating it in nitrogen or in hydrogen atmosphere, the degree of blue brittleness varied.(G) The blue-brittleness decreased on the specimens in which some parts of nitrogen had been precipitated by cold working and tempering.(H) The temperature range of blue brittleness moved to a higher temperature range with the increase of testing speed.(I) There is a clear correlation between the blue brittleness and Fry’s figure of stress.From the present and former investigations authors concluded the mechanism of blue brittleness as follow :The blue brittleness in steel is due to the precipitation of nitride or carbide from α-iron by the existence of working stress : and the brittleness by nitrogen appears much more exactly in lower temperature range than that by carbon.