Research on Fracture Behavior of High Nitrogen Austenitic Stainless Steels at Cryogenic Temperature

This paper investigates the ductile to brittle transition (DBT) behavior of 19.55Cr-19.5Mn-2.26Mo-0.96N, 19.56Cr-19.4Mn-2.29Mo-0.82N and 19.84Cr-18.9Mn-2.26Mo-0.88N steels from 77K to 290K by Charpy V-Notch (CVN) impact tests, and then reveals the possible fracture mechanism by SEM and TEM. With the concentration of nitrogen increasing, the ductility at low temperature decreases rapidly and the DBTT increases. The fracture modes are transgranular and intergranular fractures. Fracture facets along {1 1 1} γ and annealing twin boundary appear in the impact fractures at low temperature. River patterns which are the typical features of cleave fracture facets and tear ridges which are the typical feature of quasi-cleave fracture facets exist at cryogenic temperature. The change of fracture patterns of high nitrogen austenitic stainless steels is dimple→shallow dimple→mixture of quasi-cleavage facet and dimple→cleavage facet.