The role of magnesium-containing spheroidizer and counteraction of misch metal in the intermediate temperature intergran
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The Role of Magnesium-Containing Spheroidizer and Counteraction of Misch Metal in the Intermediate Temperature Intergranular Embrittlement of Ferritic Nodule Iron S.F. CHEN, T.S. LUI, and L.H. CHEN Because of its high potential for structural application at temperatures from 300 ~ to 500 ~ the mechanical properties of ferritic nodule iron in this intermediate temperature range have attracted much attention, t~-n Low ductility with intergranular fracture often exists when ferritic nodule iron deforms in tension in this temperature range, t2-6] a phenomenon which has been called intermediate temperature intergranular embrittlement. The embrittlement also plays an important role in cyclic loading, as revealed by the data of low cycle fatigue and rotatory bending fatigue, tTl The intermediate temperature intergranular embrittlement can be enhanced by the triaxial stress field, because the material contains graphite nodules that are low in load carrying capacity. An intentional change of the nodule shape by, e . g . , rolling or swagging prior to the mechanical test can vary the stress state and the severity of embrittlement.tsJ Refinement of the ferfltic grain size and graphite nodule size is also effective to avoid the brittle fracture and ductility loss. However, the metallurgical factors of the embflttlement are still not well known, although some speculations have been reported.t6] Our recent article ts] has illustrated that magnesium oxide (MgO) particles serve as the crack initiation sites of the intermediate temperature intergranular fracture. S.F. CHEN, Graduate Student, and T.S. LUI and L.H. CHEN, Professors, are with the Department of Materials Science and Engineering, National Cheng-Kung University, Tainan, Taiwan 70101, Republic of China. Manuscript submitted November 12, 1993. VOLUME 25A, OCTOBER 1994--2305
Table I.
Chemical Composition of the Misch Metal Used in this Study (in Weight Percent)
Ce 48.05
La 31.94
Table II.
C 3.34 3.42 3.41 3.40
Nd 13.75
Pr 4.55
Sm 0.34
Fe 1.37
Chemical Composition of the Materials Used in this Investigation (in Weight Percent)*
Si 3.90 3.88 3.87 3.91
Mn 0.025 0.020 0.030 0.028
P 0.041 0.044 0.038 0.040
S 0.009 0.011 0.014 0.010
Mg 0.043 0.020 0.0
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