Journal
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
Volume 881, Issue -, Pages -Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.msea.2023.145372
Keywords
N50 austenitic stainless steel; B addition; Grain boundary segregation; First-principles calculations; Cryogenic mechanical properties
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The effect of boron on the microstructure and cryogenic mechanical properties in N50 austenitic stainless steel after aging treatment was investigated. It was found that the nucleation and growth of Cr2N were significantly suppressed in 25B steel due to the retarded diffusion of Cr, Mo, and V atoms caused by B. The segregation of B at grain boundaries weakened the precipitation of nitride and enhanced the cohesion of grain boundaries, synergistically suppressing the initiation and extension of intergranular cracks. The impact toughness of 25B-N50 steel at both 77 K and 4.2 K was about 2.5 times higher than that of 0B-N50 steel, reaching 200 J.
The effect of boron on the microstructure and cryogenic mechanical properties in N50 austenitic stainless steel after aging treatment was revealed by a comparative investigation of 0B and 25B (25 ppm) N50 steels. The results showed there is a large amount of irregular block and rod-like Cr2N precipitated along grain boundaries with intra-granular precipitation of lamellar Cr2N in 0B steel; nevertheless, the nucleation and growth of Cr2N were significantly suppressed in 25B steel. It is related to the retarded diffusion of Cr, Mo, and V atoms caused by the pre-occupied B atoms during the precipitation of nitride. Theoretical calculations verify that the high B segregation at grain boundaries is caused by both equilibrium and non-equilibrium segregation. The weakened precipitation of nitride and the enhanced cohesion of grain boundaries by segregated B synergistically suppress the initiation and extension of intergranular cracks. The impact toughness of 25B-N50 steel at both 77 K and 4.2 K can reach 200 J, which is about 2.5 times higher than that of 0B-N50 steel.
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