The grain boundary segregation of solutes and the effects of alloying on the phosphorus induced intergranular fracture were investigated in high purity iron-phosphorus alloys with carbon, molybdenum, chromium, nickel or silicon. The solutes were dissolved and the specimens were heat-treated in the ∝phase region, unless dislocations were intentionally introduced through the γ-∝ transformation. Thus the effects of each alloying elements were studied under simplified conditions.
Carbon is the most important element in affecting the intergranular fracture. The carbon at grain boundaries increases the boundary cohesion as its inherent effect. It also drives off phosphorus atoms from the grain boundary. With these two effects, carbon reduces the intergranular fracture very effectively. Molybdenum and chromium reduces the intergranular fracture, perhaps through the attractive interaction with phosphorus to neutralize its detrimental effect. They may increase the grain boundary cohesion as their inherent effect. Nickel reduces the intergranular fracture through the solution softening. Silicon has the same effect, of which mechanism is now being studied.