低Ni-Cr鋳鉄におけるNiの影響について

Abstract

On the low Ni-Cr cast iron containing approximately 1.0 to 3.0%Ni and 0.5 to 1.5%Cr, the effect of the Ni contents on the thermal expansion, growth, resistance to oxidation and microstructure, which are the basic properties of low alloy heat-resisting cast iron, were studied. The results obtained are as follows:(1) Mechanical properties of cast iron containing approximately 2.0%Ni and 1.5%Cr are good. When the Ni content is increased to about 3.0%, almost same values are obtained in relation to the tensile strength irrespective of the Cr content.(2) Cast iron containing approximately 2.0%Ni and 1.5%Cr indicates the lowest thermal expansion value. When Ni content is increased to about 3.0%, a tendency of expansion is recognized.(3) Cast iron containing approximately 2.0%Ni and 1.5%Cr also indicates the lowest value in growth rate. The growth rate becomes clearly larger with increasing Ni content.(4) A similar tendency is observed between the resistance to oxidation and at the growth rate, but the effect of the Ni content on the weight gain is somewhat stronger than that of the Cr content.(5) Plain cast iron is poor in thermal expansion, growth rate, and resistance to oxidation. At some testing temperatures, however, the above cast iron is superior to cast iron containing a small amount of Ni and Cr.(6) On the microstructure of cast iron containing approximately 1.0 to 2.0%Ni, graphite becomes smaller and cementite increases with increasing Cr content. When the Ni content is increased to about 3.0%, graphite becomes larger and cementite decreases to some extent.It is concluded that the Ni content ranging from 1.0 to 2.0% acts effectively on the basic properties of low alloy heat-resisting cast iron in the range of Cr contents from 0.5 to 1.5%, but an undesirable effect appears when the Ni content is increased to about 3.0%.