Nitrided Ferro Chrome Manufacturing Process

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Nitrided ferro chrome is mainly used in the production of Nitrogen-containing stainless steel. At present, the nitrided ferro chrome can replace part of the nickel, and adding a certain amount of nitrided ferro chrome to the nickel-containing stainless steel can improve the strength and corrosion resistance of the steel.

nitrided-ferro-chromium
nitrided ferro chrome

The traditional preparation of nitrided ferro chrome is liquid nitriding and solid nitriding. The liquid nitriding can produce nitride ferrochrome with 2-3% of nitrogen, which is too low for the production of stainless steel. The solid nitriding uses the NH3 or N2 as the raw materials, smelting with the ferrochrome in the vacuum furnace. The content of chromium in ferrochromium nitride produced by the solid-state nitriding method is 7-9%. Ferrochrome nitride produced by solid-state nitriding can be remelted to densify the alloy, but the nitrogen content is reduced to 2.0-2.5% during the remelting process.

Self-propagating high-temperature synthesis (SHS) is a method for producing both inorganic and organic compounds by exothermic combustion reactions in solids of different natures. (Wikipedia). After the self-propagating reaction starts, the heat generated by the reaction maintains the progress of the reaction.

The self-propagating process equipment is simple, the energy consumption is low, the impact on the environment is small, and the obtained product has high purity.

Nitrided Ferro Chrome (SHS) Production

Produce nitrided ferro chrome by SHS, no external heat is required in the reaction process. The heat released by the reaction of the raw materials is sufficient to maintain the progress of the reaction。

SHS reaction principle

A reduction reaction occurs between Cr2O3,  Fe2O3, and aluminum, and the heat of the reaction itself maintains the continuation of the reaction.

Cr2O3+2Al→2Cr+Al2O3

Fe2O3+2Al→2Fe+Al2O3

6NaNO3+10Al→5Al2O3+3Na2O+3N2

Thermodynamic conditions

Self-propagating thermodynamics is the basis for judging whether a self-propagating reaction can proceed and continue. Through thermodynamic calculations, the maximum temperature reached in the reaction can be calculated, so that it can be judged whether the heat released by the reaction can melt the raw materials or plan.

The application of NaNO3

The experiment shows that the reaction heat of the charge should be controlled at about 3138.00kJ/kg.

Nitrided Ferro Chrome Products Analysis

Ferrochromium nitride prepared by the self-propagating method

The self-propagating reaction is sufficiently carried out, and the melt and the slag are always in a molten state during the reaction, which ensures that the melt and the slag can be separated as much as possible. Although the decomposition of urea will generate a large amount of gas, it has little effect on the state of the metal block and slag, and will not produce a large number of holes, but form bubbles with a certain pressure. The gas can break through the metal layer and the slag layer and be released into the air. Holes are formed on the surface. Adding urea will not affect the separation of metal and furnace slag.

ferrochrome nitride
ferrochrome nitride

Nitriding Medium

Urea decomposes when heated to produce NH3. NH3 is used as a nitriding medium for nitriding, and the reaction rate is much higher than that of N2, and metal nitrides with higher N content can be obtained. Therefore, urea is selected as the nitriding agent.

Conclusion:

  1. According to the thermodynamic calculation and experimental study, produce nitride ferro chrome by SHS is available.
  2. There is mainly FeCr in the nitride ferro chrome, and with a small amounts of impurities. Cr62.7%, Fe33.25%, N3.42%, and the impurities are less than 1%. Comply with the production standard of nitride ferro chrome.
  3. After adding NaNO3 as an exothermic agent, the combustion of ferrochromium nitride can be fully carried out, and the obtained ferrochromium nitride is denser. This process has little pollution and requires simple equipment.

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