This paper investigates the process of nitrogen alloying in gear steel by bottom blowing nitrogen during refining process （LF and VD） as a substitute for nitrogen-containing alloy cored wires， focusing on solving the core challenge of stably controlling the nitrogen content in molten steel. Through thermodynamic and kinetic analysis， the influence mechanisms of key factors such as molten steel composition （especially S and O content）， nitrogen partial pressure， nitrogen blowing flow rate and time were elucidated. To achieve stable control of nitrogen content through the following measures：Strictly control the sulfur

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［S］ content of the molten steel entering the LF station to ≤ 0.025%， reducing interfacial resistance and enhancing nitrogen pickup efficiency； During the LF refining stage， employ optimized nitrogen partial pressure （0.4 MPa-0.7 MPa） and flow rate 0.9 m³/（min·t）， combined with controlled nitrogen blowing time to manage the initial nitrogen increase.In the VD vacuum treatment stage， the bottom blowing nitrogen process （partial pre

ssure 0.7 MPa， flow 0.6 m³/（min·t）） is flexibly adopted to achieve the fine adjustment and stability of nitrogen content by using the dynamic balance between nitrogen increase and nitrogen removal.Production practice results demonstrate that through the above comprehensive control means， utilizing nitrogen as the stirring gas in both LF refining and VD vacuum treatment enables effective alloying operation， and the final nitrogen content of gear steel grade 20MnCrS5 can be stably controlled within the target range of （100-140）×10

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. The study also find that the S content in molten steel is the key factor affecting the effect of nitrogen increase by blowing nitrogen in LF， and the lower the S content （

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［S］≤0.025%）， the higher the nitrogen increase rate （approximately 6.9×10

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min

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）.In VD vacuum refining process， nitrogen is used instead of argon， and the coexistence phenomenon of nitrogen increase and nitrogen removal in molten steel exists， which shows the phenomenon of nitrogen increase with an approximate rate of 2.19×10

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min

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.