Origin of intergranular fracture in martensitic 8Mn steel at cryogenic temperatures

The fracture behavior of 8Mn steel at −196 °C has been investigated by a comparison with that of 9Ni steel. 8Mn steel fails by a mixture of cleavage and intergranular fracture, in contrast to 9Ni steel, which shows cleavage fracture when impact tested at −196 °C. This shows that intergranular fracture in 8Mn steel is not due to the segregation of solutes, including Mn, reducing the grain boundary strength, but to the higher strength of the matrix compared to that of the grain boundary.