The Methods To Improve Electromagnetic Pure Iron Wear Resistance

Electromagnetic pure iron is a widely used soft magnetic material. It has high magnetic induction and is suitable for making magnetic parts that work in a strong magnetic field. Electromagnetic pure iron materials are cheap, and the heat treatment process is simple. At present, they are widely used in civil aircraft products. However, the alloying element content of electromagnetic pure iron material is almost zero, there is no alloy strengthening phase, and its hardness is the lowest among iron metals. Electromagnetic pure iron is often used as parts such as the shell, armature, valve core, and movable iron core of solenoid valves.

The structure and execution of the solenoid valve are roughly similar to a small actuator. At the same time, electromagnetic pure iron parts play the role of general structural parts, even transmission parts, and must have certain mechanical strength and good wear resistance. Many electromagnetic pure iron parts of the solenoid valve move relative to each other when they are working, and surface friction occurs. If the material hardness is not enough, it will seriously affect the working life of the device. Therefore, the surface of the pure iron material must be strengthened. Nitriding process can improve the surface hardness of pure iron. However, the nitriding treatment of electromagnetic pure iron has the risk of reducing its magnetic properties. Therefore, finding a suitable nitriding process can improve the surface hardness of the pure iron material while keeping its magnetic properties within the required range of actual use. , It is necessary.

The Beijing Institute of Aeronautical Materials has optimized the nitriding process according to the characteristics of flight control servo actuators in civil aircrafts working in a strong magnetic field. While ensuring the magnetic performance requirements of B5000, B10000, coercivity and maximum permeability, the surface hardness It was increased to more than 900 HV, and good results were obtained. Their research uses DT4A electromagnetic pure iron material, the surface roughness is controlled at 1.6 μm, the sample is annealed at 900 ℃ before nitriding, and the surface hardness after annealing is 120 HV0.01. The nitriding medium is pure ammonia gas. Before entering the nitriding medium, the sample is kept at 350°C for 40 min. During the holding time, compressed air is filled. After the nitriding is completed, it is filled with 110 kPa pressure nitrogen and cooled to below 150°C.

The uniformity and thickness of the surface dense layer after nitriding are the most critical factors that determine the hardness of pure iron after nitriding. The nitriding process must ensure that a continuous surface dense layer is formed, and the thickness should be above 5 μm. Through comparative experiments, it was found that under the following process conditions: temperature 450℃, holding time 240min, ammonia decomposition rate 6-7/%, this surface dense layer can be obtained. X-ray diffraction shows that the surface phase is composed of γ'phase, Fe3N (ε phase) and α phase, and a dense continuous mixed layer of γ'phase and ε phase is formed on the surface. The presence of the mixed layer improves the surface hardness of the sample. The test proved that the surface hardness reached HV0.01 = 986. The increase in nitriding time can increase the thickness of the mixed layer, but it hardly thickens after reaching about 5 μm.

The magnetic performance test of the sample showed that the low magnetic properties of the sample B500 and B1000 decreased by 16% and 10%, respectively, the medium magnetic properties of B2500 decreased by 4%, but the strong magnetic properties of B5000 and B10000 only decreased by 1.5% and 1%. Compared with the technical requirements in GB/T 6983-1986 "Technical Conditions for Electromagnetic Pure Iron Bars", the low magnetic properties and medium magnetic properties are relatively low, but the strong magnetic properties can meet the requirements of the national standard; the coercivity of the sample and the maximum The magnetic permeability also meets the requirements of the national standard.

The above research proves that, in response to the requirement of electromagnetic pure iron material in the flight control servo actuator for strong magnetic field work, by adjusting the nitriding process parameters, the sample can achieve the strength of strong magnetic performance, coercivity and maximum permeability after nitriding. The technical indicators can meet the comprehensive requirements of its magnetic performance and hardness, so that the surface wear resistance of electromagnetic pure iron parts can be solved, and the long life of civil aircraft flight control servo actuator products can be realized.

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