Nitrogen-Substituting Carbon Significantly Improves Softening Resistance of H13 Hot-Work Die Steel

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2024-06, Vol.55 (6), p.1916-1931
• Main Authors: Wang, Hai-Jian, Feng, Hao, Li, Hua-Bing, Zhou, Gang, Zhu, Hong-Chun, Zhang, Shu-Cai, Jiang, Zhou-Hua
• Format: Article
• Language: English
• Subjects: Alloying elements; Carbides; Carbon; Carbon nitride; Characterization and Evaluation of Materials; Chemistry and Materials Science; First principles; Free energy; Hardness; Heat of formation; Hot work tool steels; Hot working; Lattice parameters; Materials Science; Metallic Materials; Nanotechnology; Nitrogen; Original Research Article; Precipitates; Softening; Steel; Structural Materials; Surfaces and Interfaces; Thermal stability; Thin Films
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-024-07367-y

In this study, the thermal stability of H13 hot-work tool steel was significantly improved through the use of nitrogen as a substitute for carbon. The results indicated that the 0.3C-0.2N and 0.2C-0.3N steels exhibited better hardness stability than H13 steel (0.4C-0N). In particular, the 0.2C-0.3N steel exhibited substantially improved hardness stability. The softening resistance mechanism was revealed from the perspectives of precipitates, dislocations, laths, and variants through first-principles calculations, thermodynamic and kinetic models, and variant reconstruction. First, for precipitate stability, the results of first-principles calculations and kinetic analysis showed that substituting N with C reduced the formation energy of carbides and facilitated the formation of carbonitrides. For 0.2C-0.3N steel, which had the highest activation energy, both the diffusion of alloying elements and the coarsening of carbonitrides were significantly inhibited. Second, in terms of dislocation evolution, the most stable lattice constant, highest interstitial atom content and lowest carbide precipitation content were the keys to inhibiting dislocation recovery. Finally, the dislocation and heat-induced boundary migration stimulated the selection of variants, resulting in the coarsening and coalescence of laths. The change from V17 to V1 variant pairs was dominant for the lath coalescence of 0.2C-0.3N steel.