THE EFFECT OF THE TRACE-ELEMENTS ADDITIONS ON THE CHARACTER OF THE GRAIN-BOUNDARY POPULATION IN HIGH-PURITY ALPHA-IRON

The grain boundary misorientations and CSL frequencies in ultra high p urity a-iron and iron doped with carbon (up to 200ppm) and sulphur (ab out 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 ex hibits a much higher fraction of low angle boundaries (LANGB) than iro n and the other alloys, including the ternary Fe-C-S alloy. The effect of the recrystallization annealing temperature on the CGBP has been a lso examined; the LANGB frequency decreases with increasing temperatur e. In the Fe-S alloy this effect is shifted towards a higher temperatu re range (725-870 degrees C). Also the initially high frequency of LAN GB decreases with annealing time and resulting grain growth. The incre ased fraction of LANGB in the Fe-S alloy is interpreted as result of S reducing the rate of LANGB elimination, by a sulphur segregation drag ging effect. The effect of C in the Fe-C-S alloy is attributed to the observed decrease of sulphur segregation to the grain boundaries.