STRENGTH OF GRAIN BOUNDARIES IN IRON-BASE ALLOYS.

A review is given of the current state of understanding of the strength of grain boundaries in iron-base alloys at low and high temperatures and in aggressive media as influenced by the presence of elements from Groups IV to VI. It is shown that, at bulk concentrations of less than 100 ppm, carbon segregates at equilibrium and increases intergranular cohesion, whereas similar amounts of sulfur, selenium, and tellurium, which also segregate at equilibrium, have a potent weakening effect. A number of Groups IV to VI elements can become concentrated in grain boundaries due to solute rearrangements during carbide precipitation and due to equilibrium segregation under the influence of alloying elements, such as nickel and chromium. These effects, which are important in alloy steels, are reviewed.