Anomalous Contraction near 500℃ in Austenitic Heat-Resisting Alloys Containing Chromium and Nickel

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The effect of major alloying elements on the anomalous contraction in the vicinity of 500℃ during tempering in typical austenitic heat-resisting alloys containing chromium and nickel was studied by dilatometric, magnetic, and metallographic methods. The anomalous contraction seemed to be attributable not to precipitation of carbides or nitrides, but to an internal arrangement of some substitutional elements such as chromium, nickel, iron and cobalt, and it was observed in a wide composition range of the austenitic phase of the quaternary iron-chromium-cobalt-nickel system ; it was most prominent in the neighbourhood of about 20 per cent chromium in the ternary chromium-nickel-cobalt system, especially near the compositions of 20 per cent chromium-80 per cent nickel and 20 per cent chromium-20 per cent nickel-60 per cent cobalt, and was observed not only in alloys of homogeneous austenitic phase, but also in some austenitic alloys containing ferrite or other phases such as sigma in the iron rich corner of the quaternary system of iron-chromium-cobalt-nickel. It was considered that this anomaly is related probably to the anomaly near the composition of 75 atomic per cent nickel-25 atomic per cent chromium in the binary system of chromium-nickel, which, although lately much under discussion, might be due to an order-disorder transformation.
東北大学の論文