20th International Forgemasters Meeting - IFM 2017

Low thermal expansion superalloys are thought to be candidates to reduce the clearance between some parts in turbo machines in order to improve the efficiency. Alloy903, Alloy909, HRA9291), etc. which were previously developed are well known as commercial low thermal expansion superalloys. The low thermal expansion properties of these alloys are obtained by the mechanism to control the thermal expansion by magnetro-striction in Fe-Ni-Co austenite matrix. On the other hand, the high temperature strengths of these alloys are obtained by the precipitation strengthening mechanism by adding Al, Ti, and Nb. These alloys, however, have not been applied for large turbo machine parts because it is difficult to produce large ingots without freckle segregations of these alloys. In this study, the effect of chemical compositions in HRA929 on the tendency to cause freckle segregations was investigated by thermodynamic calculation, and then small samples of some alloys selected by the calculation were made in a laboratory and cold and hot deformability, thermal expansion property, mechanical properties, oxidation resistance, etc. were investigated in order to produce large products of a low thermal expansion superalloy. As a result, the chemical compositions were optimized and a modified alloy, HRA929M, was developed. Finally, a trial production of HRA929M was demonstrated and a three-ton class forging was successfully produced. *HRA is a trade mark of Hitachi Metals, Ltd. registered in Japan. 1) K. Sato, T. Ohno ; Superalloys1992(conference proceedings), TMS-AIME (1992), p.247.