Segregation-induced intergranular brittleness of ultrahigh-purity Fe–S alloys

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Abstract
The hot ductility of ultrahigh–purity Fe–S alloys doped with 20 to 100 ppm sulphur has been studied by tensile tests at a strain rate of ε = 2 × 10−3 S−1. A well defined ductility trough between 850 and 1100°C was found in alloys containing ~50 ppm sulphur. This minimum sulphur content necessary to produce an intergranular embrittling effect is much higher than in steels containing aluminium and nitrogen doped with 10 ppm sulphur. The role of sulphur in reducing hot ductility is explained in terms of the intergranular brittleness caused by the presence of sulphur on grain boundaries, which decrease their cohesion. The intergranular hot brittleness of Fe–S alloys can be attenuated by dynamic recrystallization at low sulphur contents. In this case the dynamic recrystallization rate must be higher than the void nucleation and propagation rate. The hot ductility minimum temperature shifts with increasing sulphur content and seems to change in the same manner as the sulphur solubility limit temperature in austenite. MST/238