Effect of nitrogen on microstructure and secondary hardening of H21 die steel

  • Jin-bo Gu
  • Hua-qing Liu
  • Jing-yuan LiEmail author
  • Yan-bin JiangEmail author
  • Rui-jin Chang
Original Paper


The effect of nitrogen on the microstructure and secondary hardening of H21 die steel was studied by using scanning electron microscope, X-ray diffraction, transmission electron microscope and dilatometer. The results demonstrate that nitrogen can enhance the secondary hardening behavior of H21 hot-working die steel without toughness lose. Nitrogen addition increases the austenitic phase zone, decreasing austenite transformation temperature and martensite transformation temperature, thereby increasing the retained austenite stability. Retained austenite in quenched steel can dissolve a large quantity of alloy, thereby decreasing the coarsening rate of the precipitates. Trace nitrogen could intensify the refinement of pearlite by decreasing the diffusion rate of alloying element into carbides. Nitrogen increases the amounts and precipitation temperature of the undissolved V(C, N) and suppresses the growth of prior austenite before quenching. During tempering process, parts of nitrogen in V(C, N) dissolved back into the matrix, resulting in the distorting lattice of ferrite, thereby reinforcing the matrix. Meanwhile, the solid-dissolved nitrogen inhibits the growth of carbides by decreasing the diffusion rate of alloying elements.


Nitrogen Secondary hardening H21 die steel Precipitate 



The authors acknowledge financial support from National Key Research and Development Program of China (2016YFB0300200) and National Natural Science Foundation of China (Grant No. U1660114).


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Copyright information

© China Iron and Steel Research Institute Group 2018

Authors and Affiliations

  1. 1.School of Materials Science and EngineeringUniversity of Science and Technology BeijingBeijingChina
  2. 2.Key Laboratory for Advanced Materials Processing of Ministry of EducationUniversity of Science and Technology BeijingBeijingChina

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