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

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 x 10(5) 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 N-2 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 degrees 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.