Study on Cr Base Heat Resistant Alloys (Report 1)

Abstract

As the demand toward heat resistant alloys is rising these days, there has been a tendency of looking for heat resistant materials in cast or sintered materials from the point of getting high temperature strength. Particularly, chromium base alloys are promising as heat resistant casting alloys, though not yet commercial as alloys. In this report in the first step the author took up Cr-Mo-Fe system alloys as basic composition in Cr 60%:Mo 15%:Fe 25%, and made experimental studies on the influence of preparing of these alloys in the atmosphere and small quantities of C and Si content in them upon the properties of these alloys. It is difficult to prepare these alloys, the melting points of them being so high. As the Fe content decreases, it becomes even more difficult to make homogeneous alloys. In order to prepare these alloys, crucibles to be used must be of the quality showing no great corrosion by Cr₂O₃ and with adequately high softening temperature. Furthermore, it is necessary to use a melting furnace which can smoothly reach the high temperature of 1700°. The hardness of these alloys at room temperature and at rather high temperatures are great while the decline of hardness due to the rise of temperature is less. Creep strength at high temperatures is also very high. The coefficients of thermal expansion are less than イ-301. In the range up to 1050°, we cannot find distinguished phase transformation. But these alloys are considerably brittle at room temperature compared with other heat resistant alloys. In the range up to 0.4% C content, as the carbon content increases, the preparing of alloys becomes easy, and at room temperature and high temperatures hardness and creep strength become higher, but ductility decreases. Such a decrease of ductility is largery due to the crystal growth and the precipitation of brittle metallic compounds around the boundaly of the grains. There is still room left for further investigation as to whether the improvement of ductility should depend only on the vacuum melting and casting method with raw materials well chosen or not.