日本金属学会誌

J. Japan Inst. Metals, Vol. 63, No. 9 (1999),
pp. 1137-1140

Effect of Morphology of Grain Boundary Nitride on the Ductility ofFe-30 mass%Cr Alloys

Tadashi Fukuda

Institute for Materials Research, Tohoku University, Sendai 980-8577

Abstract:

Effects of morphology of grain boundary nitride on the ductility of Fe-30 mass%Cr alloys containing N from 0.004 to 0.13 mass% were investigated. Two kinds of heat treatments were adopted to obtain the morphologies of continuous grain boundary nitride and of discontinuous grain boundary nitride. Tensile tests were carried out at temperatures ranging from 4.2 K to room temperature. Ductility was evaluated by transition temperatures in reduction of area.
The results obtained are summarized as follows:

(1) Upper shelf in reduction of area of the specimen containing discontinuous grain boundary nitride is higher than that of the specimen containing continuous grain boundary nitride.

(2) Transition temperature of the specimen containing discontinuous grain boundary nitride is lower than that of the specimen containing continuous grain boundary nitride.

(3) The area rate of intergranular fracture surface which appears in cleavage fracture surface observed in the specimen containing discontinuous grain boundary nitride is smaller than that which appears in cleavage fracture surface observed in the specimen containing continuous grain boundary nitride. The area rate of intergranular fracture surface which appears in dimple fracture surface also shows similar observation result.

(4) Initiation of microcracks for brittle fracture may be caused by decohesion at the interfaces between the matrix and grain boundary nitride.


(Received April 20, 1999; In Final Form July 1, 1999)

Keywords:

high chromium ferritic steel, ductility, grain boundary nitride, morphology of precipitate, transition temperature


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