Redistribution of C and N Atoms in High Nitrogen Martensitic Stainless Steel During Cryogenic Treatment

The redistribution of C and N atoms during cryogenic treatment is crucial for the microstructure evolution and properties of high nitrogen martensitic steel. Here, the distinct redistribution behavior of C and N atoms in a martensitic stainless steel with 0.3 wt% C and 0.5 wt% N after cryogenic treatment were investigated by the atom probe tomography. Carbon clusters begin to form after cryogenic treatment at - 60 degrees C and gradually increase with the decrease of cryogenic treatment temperature. While Mo-N and Cr-N pairs are homogeneously distributed in the matrix even after cryogenic treatment at -120 degrees C, and then form enrichment phenomenon when the cryogenic temperature is deeply lowered to - 190 degrees C. It is found that the distinct redistributions of C and N atoms are associated with the different interaction energy between substitutional atoms and them. The stronger interaction between Cr, Mo atoms and N delays the segregation of N during the cryogenic treatment. Finally, the mechanical properties results confirmed that the deep lower cryogenic treatment is a promising method to improve the hardness and strength in the high nitrogen martensitic stainless steel.