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 δ 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 δ 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.
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