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

Abstract

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.

Corrosion resistance of nitrogenated high-carbon martensitic stainless steel designed and produced at nitrogen low pressures

“…The database used for this design was TCFE9. The alloys were produced in an induction furnace with a controlled nitrogen atmosphere, to get equilibrium and avoid possible desorption of nitrogen to the environment upon melting and solidification, and thus avoid heterogeneous zones or the production of bubbles in the steel [1]. Si3N4 powder (Alfa Aesar, 85-95% purity) was used as a nitrogen source, and the pressure used in the process was the Tunja atmospheric pressure, one of the highest cities in Colombia, 2,822 m (~7x10 4 Pa, 0.69 atm).…”

“…These carbides rich in niobium are seen in Figure 4(d) and should have a stoichiometry of (Nb,Mo)C or (Nb,Mo)(C,N)0,5 [23]. According to the thermodynamic calculations in Figure 2, these carbides are formed at temperatures around 1300 °C and are expected to be M(C,N) [1]. The presence of precipitates found in the steel can improve mechanical properties such as wear resistance or hardness, however, this can lead to an impoverishment of other properties, such as corrosion resistance [15].…”

“…The use of nitrogen combined in martensitic steel has demonstrated that it can improve properties like corrosion and mechanical resistance [1], making this kind of steel attractive for use in tools, bearings, ball screws, and antifriction bearing materials, among others [2]. Its applications can be seen reflected in the industrial field in sectors such as machinery manufacturing, medical equipment, and aerospace.…”

“…The relevance of this work consisted of being able to carry out the production of martensitic steel under lowpressure conditions, specifically in atmospheric conditions such as that of the city of Tunja, Colombia at 0.69 atm, taking into account that nitrogenated steels are normally produced at pressures greater than 4 atmospheres [1], [8], [17], [18], [19], [20], [21], [22], and being able to analyze some of its behavior and measurement of properties such as hardness and resistance to corrosion. Although there are studies about this kind of materials, there is still a large field of research about the behavior of this type of new materials produced under these conditions.…”