| The stress corrosion behaviour of mild steel (0.03-0.04 wt.% C) in a boiling aqueous solution of 860g Ca(NO₃)₂·4H₂O and 30g NH₄NO₃/ℓ was studied with specimens under constant load, related to Al content and grain size of specimen. Grain size of Al steel was controlled by annealing temperature and time of the specimens. Grain size remained nearly constant for the specimen with Al content up to 0.37 wt.%, however, grain became coarser for Al content from 0.37 to 1.01 wt.%, and a further increase in Al content did not affect grain size. The decreased grain size of specimen annealed in the γrange was explained in terms of delay of grain growth due to γto αphase change. And grain size of ferrite phase increased with increasing annealing temperature and time. Failure time, under constant load, as a whole increased with increasing grain size. Variation of failure time was discussed in terms of segregation of carbon at the grain boundary, and precipitation of Al₂O₃and cementite in the grain. |
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