The influence of precipitates on the texture and formability of high purity iron-based alloy sheet.

Abstract

A study has been made of the influence of titanium carbide and boron nitride precipitates on the texture and formability of high purity iron-based alloy sheet. Four Fe-Ti-C alloys with the following compositions were investigated: Fe - 0. 011% Ti - 0.004% C, Fe - 0.09% Ti - 0.018%C, Fe - 0.47% Ti - 0.09% C and Fe - 0.48% Ti - 0.011%C. The ratio of titanium to carbon in the first three alloys was approximately 4:1, the stoichiometric ratio for the formation of titanium carbide. The latter alloy was used to study the effect of excess titanium in solution. An Fe - 0.01%B - 0.015%N alloy was also studied to investigate the effect of boron nitride on texture and formability. The alloys were hot rolled and given various heat treatments to produce a range of precipitate dispersions. The materials were then cold rolled 85% and annealed, using a heating rate of 50°C/hour. Plastic strain ratio (R) and mechanical property measurements were made on the annealed sheet at 0°, 45° and 90° to the rolling direction, using a uniaxial tensile test. The Erichsen test was used to assess stretch-formability, and inverse pole figure data were determined on selected specimens. The presence of titanium carbide precipitates usually led to a small improvement in the average plastic strain rate (R) of each of the Fe-Ti-C alloys after recrystallisation. The presence of titanium in solution resulted in a further small increase in R in the recrystallised condition. Grain growth after primary recrystallisation led to increases in R in both high purity iron and the Fe-Ti-C alloys. The greatest rates of increase in R with grain growth were exhibited by those materials with the highest values of R in the just recrystallised condition, and an R value of 2. 4 was obtained on the Fe - 0.48% Ti - 0.011% C alloy after annealing at 830°C. The coarse boron nitride precipitates in the Fe-B-N alloy had little effect on R. High R values were favoured by the presence of {222}, {332} and {211} orientations and by the absence of {200}, {310} and {420} orientations. The results indicated that the recrystallisation textures developed by a combined oriented nucleation and growth mechanism. The Erichsen values exhibited by the Fe-Ti-C alloys were generally higher than those for high purity iron, while those for the Fe-B-N alloy were very low. The correlation between Erichsen value and mechanical properties was quite poor