The Effect of the Trace Elements Additions on the Character of the Grain Boundary Population in High Purity α-iron

Abstract
The grain boundary misorientations and CSL frequencies in ultra high purity a-iron and iron doped with carbon (up to 200ppm) and sulphur (about 70ppm) have been determined by Electron Backscattered Diffraction to examine the effect of these elements on the character of the grain boundary population (CGBP). It was found that the binary Fe-S alloy exhibits a much higher fraction of low angle boundaries (LANGB) than iron and the other alloys, including the ternary Fe-C-S alloy. The effect of the recrystallization annealing temperature on the CGBP has been also examined ; the LANGB frequency decreases with increasing temperature. In the Fe-S alloy this effect is shifted towards a higher temperature range (725-870 °C). Also the initially high frequency of LANGB decreases with annealing time and resulting grain growth. The increased fraction of LANGB in the Fe-S alloy is interpreted as result of S reducing the rate of LANGB elimination, by a sulphur segregation dragging effect. The effect of C in the Fe-C-S alloy is attributed to the observed decrease of sulphur segregation to the grain boundaries.