CrN and Cr2N difference and the production

 Metal chromium and nitrogen will form metal chromium nitriding substances with different nitrogen contents under different conditions. Common metal chromium nitrides are CrN and Cr2N, which are called chromium nitrides. Both chromium nitride and Cr2N are important metallurgical second phases of heat-resistant alloys. Especially for special steels, they can be used as reinforcement additives. However, CrN and C12N have different physical, chemical and mechanical properties. It is generally believed that the comprehensive service performance of CrN is higher than that of Cr2N, for example, the acid and alkali corrosion resistance of CrN is significantly higher than that of Cr2N. Therefore, the market demand for chromium nitride conforms to the proportional relationship between nitrogen content and price.

In this paper, nitrogen containing chromium powder and chromium high nitrogen nitride (with nitrogen content more than 15%) were prepared by two-step method. The technological process is as follows: through the self propagating reduction reaction between aluminum powder and chromium trioxide, sodium nitrate is added as the heating agent and urea as the nitrogen increasing agent to prepare nitrogen containing chromium powder as the precursor for further nitridation; The metal chromium powder containing nitrogen is pressed and formed in a high-temperature nitriding furnace, and high-purity nitrogen is introduced. The temperature, nitrogen pressure and nitriding time are controlled to prepare chromium nitride powder containing 15%~20% nitrogen.

The first step is to prepare metal chromium powder by self propagating reduction reaction, and add urea as an additive in the reaction for nitridation to prepare metal chromium powder raw materials with a certain nitrogen content. The results show that according to the original production ratio, 5%~15% urea is added to provide nitrogen, and sodium nitrate and aluminum powder are added as heating materials according to practical experience. After the completion of self propagating reduction nitriding reaction, the smelted metal block contains metal chromium and Cr2N, in which the nitrogen content accounts for 2%~6% of the total metal block mass.

The second step is to prepare high nitrogen metal chromium nitride with the above nitrogen-containing metal chromium powder as raw material. The results show that the metal chromium powder containing nitrogen is pressed and placed in a high temperature nitriding furnace, and high purity nitrogen is introduced to start the nitriding reaction. It is characterized by two stages: the first stage, the nitriding temperature is 900~950 ℃, the nitrogen pressure is 10~120kPa, and the nitriding time is 12~15h; In the second stage, the nitriding temperature is 800~900 ℃, the nitrogen pressure is 10~120kPa, and the nitriding time is 8~10h. The obtained metal chromium nitride is mainly CrN and a small amount of Cr2N, with nitrogen content of 15%~20%.

Compared with the existing preparation methods, the technology adopted in this paper has significant beneficial effects as follows: the mature self propagating reduction technology is used to prepare metal chromium, and the nitriding agent is added to reduce the metal chromium to obtain nitrogen-containing metal chromium powder with nitrogen content of 2%~6% as the precursor. High nitrogen chromium powder with nitrogen content higher than 15% can be prepared by nitriding with high-purity nitrogen in high-temperature nitriding furnace. This method has the characteristics of simple process and short flow, and can meet the requirements of industrial production with high output and low cost. The nitrogen content of the product is more than 5% higher than that of the existing product of direct nitriding of metal chromium powder to produce high nitrogen chromium powder.

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