Abstract
The effect of titanium additions on the ductility of a 26%Cr steel containing about 0·005%C and 0·025%N was investigated. The microstructural changes which occurred during slow cooling werefollowed by means of chemical analysis, optical microscopy, X-ray diffraction and microprobe analyses performed on specimens water quenched from various temperatures within the range 2400°–600° F (1316°–316°C). The results were correlated with changes in room-temperature tensile properties and it was found that the low ductility of coarse-grained 26%Cr territic stainless steel was caused by the formation of a grain-boundary carbide or carbonitride phase at a temperature of about 1650°F(900°C). A titanium addition of 5(C+N) improved the ductility by preventing grain-boundary precipitation. TiN formed in the molten steel and, upon solidification, the random distribution of TiN particles served as nuclei for precipitation of chromium carbides within the grains. Increasing the titanium addition to 9·4(C+N) resulted in a significant decrease in ductility compared to the steel with a titanium addition of 5(C+N). This was attributed to dispersion strengthening by TiC precipitates for specimens quenched from above 1400°F (760°C) and acceleration of the 885°F(475°C) reaction for specimens furnace cooled to below 1400°F(760°C).
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