Microstructural and Mechanical Aspects of High Nitrogen Steels at Cryogenic Temperature
Charpy V-Notch impact tests of N1, N2 and N3 steels from 77K to 293K are possessed in this paper. With increasing the nitrogen concentration, the ductile to brittle transition temperature (DBTT) increases. The toughness of the tested steels decreases rapidly with decreasing the 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. Fracture facets with river patterns, with tear ridges, along annealing twin boundary and cross the annealing twin plane are observed in this investigation. Critical dislocation density of crack tips ρc=[6π(τp)2/(KIc)2]2 can affect ductile to brittle transition (DBT) behavior at cryogenic temperature. Deformation twinning is also frequently observed at cryogenic temperature. Crack forms along the coherent twin boundary between one twin and the matrix.
Zhengyi Jiang and Chunliang Zhang
Z. R. Zhang et al., "Microstructural and Mechanical Aspects of High Nitrogen Steels at Cryogenic Temperature", Advanced Materials Research, Vols. 97-101, pp. 733-736, 2010