The thermal process for hardening the nitrocarburized layers of a low-carbon steel

作者：Chen, Wanglin; Huang, Yonghao; Xiao, Hui; Meng, Xianna^*; Li, Zhe; Chen, Zhaoxiang; Hong, Yue; Wu, Cuilan^*

来源：Scripta Materialia, 2022, 210: 114467.

DOI：10.1016/j.scriptamat.2021.114467

• Nitrocarburizing
• Undesirable microstructure
• Austenitizing
• Isothermal transformation
• Bainitic structure

Undesirable microstructures, with thin or uneven compound layers, pores, pearlitic structures, vein-like nitrides, etc., are detrimental to mechanical and tribological properties of nitrocarburized components. Here, we report a novel heat process in which a thicker nanobainitic layer, consisting of gamma' lamellas and alpha-Fe laths with high-density alpha ''-phase GP-zones, is obtained by heating the undesirable nitrocarburized layer at 700 degrees C (austenitizing) followed by isothermal aging at 225 degrees C for 14 h. The total phase- transformation sequences of this process are described as: epsilon + gamma' -> gamma-N/C -> gamma' + alpha-Fe + GP-zones. The thicker nanobainitic layer exhibits much higher hardness, load-bearing capacity, fracture toughness and wear resistance as compared to the nitrocarburized layer, and corresponding mechanisms for strengthening and toughening are shown.

• 单位
  广东工业大学; 佛山科学技术学院