Fe-18CrおよびFe-18Cr-C合金の高温酸化挙動に及ぼす素地粒度および粒成長の影響

抄録

In the present study, scaling behaviours of Fe-18Cr and Fe-18Cr-C alloys, especially effects of the alloy grain size and its growth at 900 and 1000°C in 760 Torr oxygen were examined by thermogravimetric methods, X-ray diffraction and electron probe microanalysis. At 1000°C, breakaway oxidation due to a matrix grain growth was observed for fine grained Fe-18Cr and this was suppressed for coarse grained specimens which had been prepared by annealing at 1200°C for 5 hr. However, the oxidation behaviour of the coarse grained Fe-18Cr containing 0.057%C as well as the fine grained specimens containing 0.10%C showed the development of nonprotective oxide scales. The grain growth of Fe-18Cr and Fe-18Cr-C was not remarkable at 900°C, and the fine grained Fe-18Cr produced only Cr₂O₃-rich scales. Moreover, the oxidation behaviour of the coarse grained specimens followed an approximate parabolic rate law. Both the fine and coarse grained Fe-18Cr-C alloys showed the breakaway oxidation behaviour even at 900°C, and produced rapid growing stratified scales composed of the outer Fe oxide layer and the inner Fe, Cr spinel layer. The formation of the nonprotective oxide scales on the Fe-18Cr-C specimens may be mainly attributed to the decarburization from the alloys at high temperatures.