No abstract

The creep strength by a fine distribution of titanium carbides in 9Cr heat resistant steel has been investigated. In order to distribute titanium carbides finely, the concentration of nitrogen was decreased to avoid large titanium nitrides remaining after normalising, and the normalising temperature was raised to 1573 K to dissolve titanium carbides into the matrix. The rise of the normalising temperature to 1573 K causes an increase of the amount of d phase, which has a bad influence on toughness, and hence the composition of the steel was adjusted and the holding time at normalising was shortened to repress the growth of d phase. In the developed steel, very fine titanium carbides precipitated densely, and the creep strength of the steel increased remarkably. It is presumed that the movement of dislocations was obstructed by fine titanium carbides in the form of laths in the matrix.MST/5987

No abstract

Fundam~ental study of the high temperature deformation of titanium aluminide. TiAl, has been conducted in order to develop the manufacturing process using isothermal forging. Theflow stress was exactly expressed using Zenner-Hollomon parameter as well as common metals. The recrystallization occurred during high temperature deformation, and structure was transformed from the lamellar structure to the fine recrystallized grain structure. And there were some deformation conditions where TiAl could be deformed without any defects up to 800/0 degree of reduction from as cast state.On the basis of above information. manufacturing of pancakes was carried out by isothermal forging. It was confirmed that it was possible to work plastically even from cast ingots samples and that mechanical properties could be improved by isothermal forging.These results suggest that the isothermal forging is a extremely effective process for manufacturing processes of TiAi.