Abstract
In order to obtain Cr base alloys with excellent creep strength and hot workablity, about twenty kinds of alloys containing 15∼30%Fe and 5∼25%Mo were prepared by vacuum melting. The composition range in which hot working is possible by swaging was determined, and effects of Fe and Mo on the high temperature properties, deformation resistance, age hardening and bending creep properties, etc. were examined. The effect of cleanliness of the alloys on the age hardening properties, and harmful elements to the hot working were investigated.
The results obtained are as follows:
(1) The age hardening properties chiefly depend on the precipitation of the σ phase which is determined by the alloy composition and its property is retarded by raising the alloy’s cleanliness.
(2) Nitrogen affects most seriously the high temperature ductility in three elements of C, N and O.
(3) The oxidation reisting properties becomes considerably deteriorated in the composition containing more than 20%Mo in the test condition of 100 hr heating at 1000°C in air.
(4) The deformation resistance at 1100°C and 1200°C increases with increasing Mo content when the Cr content is constant, or with increasing Cr content when the Mo content is nearly constant.
(5) The composition range in which hot working is possible by swaging depends on the phase behaviour, the deformation resistance and the brittleness which are determined by the alloy’s composition.
(6) The creep property tends to be improved by raising the alloy’s cleanliness and also by increasing the Mo content when the Cr content is constant and by increasing the Cr content when the Mo content is constant. The creep property of the worked alloy is superior to that of cast alloy having the same composition and the reason is considered to be due partly to the spheroidization of Cr oxide.
