Effect of Titanium on the Microstructure of 15Cr-14Ni Heat Resisting Steels

Abstract

The microstructures and hardness of 15Cr-14Ni-Ti type heat resisting steels aftersolution and aging treatments were investigated in order to obtain some information for the development of a high strength heat resisting steel.
It was found that the hardness of the steels increased with increasing titanium content and with decreasing the solution temperature. This is due to the dispersion hardening caused by undissolved. titanium carbide particles, as explained by Orowan's by-pass process.
The solubilities of carbon and titanium carbide at solution treatment temperature were determined for some steels and the result indicated that these solubilities decreased with increasing titanium content.
The diameter of undissolved carbide particle increased with increasing titanium content and with increasing solution temperature. The dispersion density of these particles, which showed the maximum value at 0.36%Ti, decreased with increasing the solution temperature.
The chronological change of chromium and titanium carbides precipitated during heating was observed morphologically. Coarsening of cubic M₂₃C₆ carbide during aging was interpreted by Lifshitz-Wagner theory, and was controlled by the diffusion of chromium. The precipitation hardening in the investigated steels was attributed to the dispersion effect of chromium and titanium carbides.