The influence of sulphur content on the static recrystallisation of cold worked low carbon aluminium-killed strip steels

The static recrystallisation (SRX) after cold work was studied in four low carbon Al-killed steels with varying sulphur content ranging from 2 to 140 ppm. The sulphur had an indirect but significant effect on the SRX behaviour by the presence of coarse MnS particles on which the AlN precipitated heterogeneously during coiling after hot rolling. The mean size of the AlN/MnS compound particles was generally too coarse to be effective for Zener-pinning of moving boundaries during recrystallisation thereby rendering the AlN ineffective in influencing the SRX process. In the low sulphur content steels, however, with virtually no MnS present, very fine AlN nucleated homogeneously in the matrix or heterogeneously on grain boundaries or dislocations during coiling, with size often less than 30 nm in diameter. These AlN particles were more effective in Zener-pinning of dislocations and moving recrystallisation fronts, thereby retarding the start of SRX by up to 100 times at low coiling temperatures of about 600 °C.