日本金属学会誌

J. Japan Inst. Metals, Vol. 14, No. 5 (1950),
pp. 37-42

Nitrogen as the Alloying Element in Steel (3rd Report) The Effect of Nitrogen on the Blue Brittleness in Steels (1st Part)

Yunoshin Imai and Teturo Ishizaki


Abstract:

The present investigation has been carried out to ascertain the effect of nitrogen on blue brittleness in steels. In the 1st and 2nd report of ``Nitrogen as the alloying element in steel, it has been shown that the phenomenon of the temper brittleness is due the presence of the nitrides separated along the solubility line below the AN point. Another type of bittleness, usually observed in C-steels is ``blue brittleness,'' which manifests itself during working or stressing at the temperature from 100° to 300°C, or by cold-worked steel becoming brittle if heated to this temperature. To as certain the effect of nitrogen on the blue brittleness, the short time tensile properties at the temperature from 0° to 320°C for the steels showed in Table 1~Table 4 were determined. All specimens employed for this investigation were air cooled from 950°C, and then slowly cooled after tempered for 3 hours at 550°C. The tensile values of each steels are plotted in Fig. 2~Fig. 29, and the increased percent of tensile strengh and decreased percent of elongation or reduction of are at blue brittleness range are plotted in Fig. 8, 14, 23, and 28.
From the present investigation anthers concluded the effect of the nitrogen on the blue brittleness in steels is as follows :
(1) There is a clear correlation between the blue-brittleness and nitrogen as shown in Fig. 8, 14, 23, and 28.
(2) The blue-brittleness did not occur in steels free from the nitrogen and the more nitrogen content is in steels, the more blue-brittleness clearly appears.
(3) In pure iron the blue drittleness increased severely at the nitrogen content rang from 0° to 0.007%, and with more nitrogen content, the blue brittleness increased slowly.
(4) By the existence of carbon, the severely increased range of blue brittleness is reduced.
(5) The blue brittleness appeared at about 70°C and the maximum point of tensile strength moved to high temperature with the increase of nitrogen.
(6) The blue-brittleness is decreased by the existence of manganese, but according to increasing of nitrogen content, the blue-brittleness clearly appears and the beginning point of blue-brittleness moved to low temperature.
(7) In the steels containing less nitrogen, the blue brittleness is recovered slowly by heating, and in the steels containing more nitrogen the recovey is rapid.


(Received 1949/9/18)

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