日本金属学会誌

J. Japan Inst. Metals, Vol. 40, No. 11 (1976),
pp. 1184-1192

The Effect of Heat Treatment and Metallurgical Structure on Decarburization Behavior of 2\frac14Cr-1Mo Steel in High Temperature Sodium

Taishi Moroishi1 and Yoshiaki Shida1

1Central Research Laboratories, Sumitomo Metal Industries Ltd., Amagasaki

Abstract:

2\frac14Cr-1Mo steel is a candidate for the construction materials of the LMFBR secondary system. The effect of heat treatment and metallurgical structure on the decarburization behavior of the steel in sodium was studied.
Fourteen kinds of heat treatment were performed on 2\frac14Cr-1Mo steel sheets in order to obtain almost all the possible metallurgical structures. Test specimens cut from those sheets were immersed in a static sodium pot, in which titanium sponges were contained as carbon and oxygen absorbers. The tests were conducted at temperatures from 550 to 700°C, for up to 4000 hr. Carbon analysis, metallographic and X-ray diffraction examinations were done to interpret the decarburization behavior of the specimens in terms of heat treatments and metallurgical structures.
The conclusions are as follows.
(1) Heat treatment condition affects the decarburization rate or 2\frac14Cr-1Mo steel in sodium. This is more remarkable in the lower test temperatures.
(2) Metallurgical structures can be ranked in the order of decarburization resistance as follows; tempered martensite, tempered bainite, pearlite, martensite, and bainite. Bainite of higher carbon content is less favorable.
(3) The decarburization rate seems to be controlled by the dissolution process of carbides and accordingly is related to the stability of carbides. Dissolution of M3C is rapid and is considered to be controlled by carbon diffusion is the dissolution process.
Heat treatment is considered one of the most important factors, when 2\frac14Cr-1Mo steel is used in the high temperature sodium environment.


(Received 1976/05/13)

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