窒素を含む20% Cr-Fe合金の純粋窒素中における高温度の窒素吸収について
耐熱材料における合金元素としての窒素の作用について-VI
1960 年 46 巻 2 号 p. 157-162
詳細
1960 年 46 巻 2 号 p. 157-162
This paper deals with the influence of nitrogen content of 20% Cr-Fe alloys containing 0·04%N, 0·11%N, 0·23%N, 0·33%N, or 0·24%N plus 0·13%C on the austenite formation due to the nitrogen absorption of these alloys in one-atmospheric pure nitrogen. The austenite formation due to the nitrogen absorption and the thermal behavior of the formed austenite were clarified. The results obtained were as follows:
(1) The depth of the single austenite zone formed at the surface of 20% Cr-Fe alloys by the nitrogen absorption during the heating for 4 hours in the pure nitrogen at 1250°C was 0·4-0·6mm, and the nitrogen content at the surface zone was 0·5-0·6%. The weight increase due to the nitrogen absorption was decreased gradually as the nitrogen content of the alloys was increased from 0·04% to 0·33%. When 0·13%C was added to 20% Cr-Fe alloy containing 0·24%N, the nitrogen absorption was promoted.
(2) The single austenite zone at the surface was richer in carbon than the cabon conent in the inner zone consisting of a mixture of both austenite and ferrite, which was presumed to be caused by the diffusion of cabon from the inner zone into the outer surface consisting of single austenite phase during the nitrogen absorption. As regards to the carbon content in the single austenite zone, it was found in the alloy containing 0·24%N plus 0·13%C that the surface zone was likely to have fairly lower carbon level than that in the inner zone.
(3) The austenite which was formed in the nitrogen bearing alloys by the nitrogen absorption at 1250°C was found to decompose in to ferrite and Cr2N during the furnace cooling. The change from ferrite to austenite on heating was found to occur at about 900°C-1050°C.
(4) It was found that the austenite retained by quenching the single austenite zone formed by the nitrogen absorption was sensible to the subzero treatment considerably, and the stabilization of the retained austenite during the holding at room temperature after the quenching was not pronounced.
(5) On the tempering at 600°C, such retained austenite became unstable, and decomposed rather rapidly by the tempering at 700°C or thereabouts.
