CrおよびNiを含む各種オーステナイト系耐熱合金中の500°C附近の異常性について

抄録

The relations between the contraction at about 500°C on tempering and the alloying elements in typical austenitic heat-resisting alloys containing chromium and nickel were investigated by dilatometric, magnetic, and metallographic methods. From the results, it was made clear that the contraction at about 500°C which was observed in those austenitic heat-resisting alloys was not caused by a precipitation of carbide or nitride, but by an anomaly, which was observed widely in the range of the austenite phase in the Fe-Cr-Co-Ni quaternary system ; it was most remarkable in the neighbourhood of about 20 per cent chromium in the Cr-Ni-Co ternary system, particularly at 20 per cent chromium-80 per cent nickel and 20 per cent chromium-20 per cent nickel-60 per cent cobalt, and was observed in the alloys not only of homogeneous austenite phase but also of the mixed structure containing other phases such as ferrite in the iron side of the Fe-Cr-Co-Ni quaternary system. It was considered that this anomaly may have a relation with the anomaly in the alloy in the vicinity of 75 atomic per cent nickel-25 atomic per cent chromium which, although lately much under discussion, has been considered to be due to an order-disorder transformation.