On the 410°C embrittlement of Ni9 steel

The brittling regularity of Ni9 steel tempering at 410°C has been studied. Its toughness at −196°C depends on the heat treatment regime and on the steel quality. The brittling process at 410°C occurs simultaneously with the precipitating and accumulating process of the carbide in the steel at the grain boundaries mainly. The heat treatment regime brought about refinement of grains (IHT) and can reduce the degree of the brittling at 410°C largely, because it causes very dispersed carbide distribution in grain. It is shown by Auger spectra that the toughness at −196°C of Ni9 steel tempering at 410°C is harmed by the oxygen and sulphur existing in the steel.