The influence of manganese on the fracture toughness of nickel steels

The effect of manganese content on the fracture toughness of a high-purity martensitic 0.6% C, 5% Ni steel has been determined after tempering below 350°C. The intergranular mode, characteristic of the brittle fracture of material with only trace manganese content, was eliminated by the addition of between 0.1% and 0.6% of that element. However, the purposeful addition of manganese introduced slow crack growth along an intergranular path prior to fast fracture which could in turn, be eliminated by testing in a dry environment. Although this environmental sensitivity prevented the full potential toughness of the material being realised in normal atmospheres the manganese addition effectively improved the toughness, and it is suggested that this is consequential to a change in the fracture criterion.