Novel Martensitic High Carbon–Nitrogen Steel Produced by Casting at Low Pressure

• Published in: Steel research international 2023-03, Vol.94 (3), p.n/a
• Main Authors: Coha-Vesga, Pablo Miguel, Mendoza-Oliveros, Martín Emilio, Pérez-Villamil, Fabio Raúl, Coury, Francisco Gil, Mujica-Roncery, Lais
• Format: Article
• Language: English
• Subjects: Air cooling; Alloying elements; Carbon; carbon–nitrogen steels; Chromium; cold work tool steels; computational thermodynamic; Electric induction furnaces; Emission analysis; Hardness; Heat treatment; Iron and steel making; Low pressure; Martensitic stainless steels; Mechanical properties; microstructures; Molybdenum; Nitrogen; Optical emission spectroscopy; Optical microscopy; Precipitates; Production methods; Scanning electron microscopy; Spectrum analysis; Thermomechanical treatment
• ISSN: 1611-3683; 1869-344X
• DOI: 10.1002/srin.202200686

Nitrogen‐containing steels have become an attractive material in industrial fields due to their excellent mechanical properties. Nevertheless, the current manufacturing methods to produce nitrogen steels are linked to technologies with high working pressures. Alloying elements such as Cr, Mn, and Mo enhance the solubility of nitrogen in the melt, which allows the production at atmospheric pressure. Herein, carbon–nitrogen martensitic steels are produced at low pressure (7 × 105 Pa). The composition is designed through the CALPHAD method using two carbon contents (0.7 and 1.3 wt%). The alloy is produced in an induction furnace under N2 atmosphere to mitigate desorption. Thermomechanical and heat treatments are performed. The alloys are analyzed using optical emission spectroscopy, X‐ray diffraction, optical microscopy, and scanning electron microscopy (SEM) with energy‐dispersive spectroscopy (EDS). The mechanical evaluation is conducted using hardness analysis. The steel presents a nitrogen content of 0.15 wt%, in agreement with the thermodynamic calculations. SEM and EDS results show the presence of Cr and Nb precipitates in a martensitic structure. The highest hardness values are obtained in specimens heat treated by tempering at 400 °C for 2 h and air cooling, achieving 57.4 and 59.7 Hardness Rockwell C for samples with 0.7 and 1.3 wt% C, respectively. New carbon–nitrogen martensitic steels are produced at low pressure. The composition is designed through the Thermo‐Calc software. Thermomechanical treatments are performed. The alloys are analyzed chemically and structurally. The mechanical evaluation is conducted. Results show the presence of primary and secondary precipitates in a refined martensitic structure. The highest hardness value achieved is 59.7 hardness Rockwell C.