Papers by Keyword: Nitrogen Alloying

Abstract: Austenitic stainless steels are strong candidates for cryogenic applications such as liquid hydrogen storage (20 K) and nuclear fusion technology (4 K) but suffer from low yield strength. In this study, austenitic stainless steels with varying nitrogen contents were evaluated. TMCP-processed and solution-annealed plates were manufactured using a pilot-scale rolling mill, and their microstructures were characterised. Tensile tests were performed from room temperature down to-180°C to assess the cryogenic yield strength of the plates. At all temperatures TMCP significantly increased the yield strength e.g. by a factor of 2 at room temperature, with the effect being mainly due to substantial dislocation hardening. The thermally activated component of yield strength depended mainly on nitrogen content via dislocation-nitrogen interactions, which was found to be much weaker in TMCP plates. Solution annealed plates therefore presented remarkable yield strength at cryogenic temperatures for the highest nitrogen level investigated.

Abstract: A computer program in Python was developed based on the mathematical model, which allows obtaining preliminary calculations of the diffusion coefficient and nitriding time of a punch part. As a result of a numerical experiment, the process of nitrogen diffusion into the depth of the part was studied. The redistribution of nitrogen occurs as a result of diffusion due to the nitrogen concentration gradient in the volume of the part and the high quenching temperature. The numerical experiment confirms the full-scale experiment. Nitrogen penetration into the depth of the metal occurs precisely at the quenching temperature. The nitrogen content in the internal nitriding zone due to the nitrogen released from the surface layer increases and decreases on the surface with the exposure time of the part. Computer modeling and research of the diffusion coefficient in the process of heat treatment after ion nitriding made it possible to establish that for tool steels, diffusion along grain boundaries occurs. Thus, the use of complex ion nitriding (CIN), i.e. ion nitriding and subsequent heat treatment of nitrided parts allows you to change the phase composition and increase the depth of the nitrided layer due to nitrogen doping, control the nitrogen concentration and hardness along the depth of the nitrided layer due to selected modes.

Abstract: The cyclic hardening–softening response, the cyclic stress–strain curve and the substructure evolution of a high nitrogen duplex stainless steel S32750 have been evaluated and the results compared with reference to low and medium nitrogen duplex stainless steels, S32205 and S32900 grades, respectively. The beneficial effects of nitrogen on the cyclic properties of most modern alloys have been analyzed in terms of the flow stress components, i.e. the internal and the effective stress.