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Compound Gas Nitriding Treatment Process For Swing Arm Bogies

The bogie is an important structure to ensure the safe operation of rail transit vehicles, and it is also the core structure for light rail or subway trains to run smoothly at high speed. The crank arm is a key part of the bogie structure. Its functions are as follows: First, when the vehicle starts to run in a curve at a certain speed, the front wheel corresponding to the outer wheel rim contacts the inner side of the outer rail, and the two squeeze each other to produce guidance. force, and the guiding moment is caused by the guiding force, so that the bogie rotates relative to the line; the second is to brake and adjust the speed of the vehicle.

The following figure shows the structure of the bogie, where the arrow points are where the arm parts are located.

It can be seen from the above analysis that the crank arm is subjected to complex interactive forces during the driving process of the rail transit vehicle, which requires the crank arm not only to have good comprehensive mechanical properties, but also to have excellent wear resistance and size. stability. In this paper, according to the technical requirements of the crank arm, on the basis of the nitriding process, a small amount of NO gas is added to the nitriding atmosphere, and the crank arm is subjected to compound gas nitriding treatment. Deformation of the arm after compound gas nitriding.

Technical requirements and heat treatment process analysis of crank arm

The conventional nitriding arm has defects such as excessive dimensional accuracy, small thickness of the white light layer, and insufficient continuity of the white light layer. In order to improve the above-mentioned shortcomings of conventional nitriding treatment of the arm, this paper adds a small amount of NO gas to the nitriding atmosphere on the basis of ordinary nitriding, and performs compound gas nitriding treatment on the arm, and counts the compound gas nitriding. The deformation of the arm parts after treatment was analyzed, and the microstructure of the arm parts after compound gas nitriding was analyzed. Under the condition of compound gas nitriding, the nitriding production cycle of the arm can be shortened to less than 28h.

The formulation of the compound gas nitriding treatment process of the arm

The conventional nitriding process uses NH3 as the nitriding material. The composite gas nitriding process in this paper adds CO2 and trace NO on the basis of the original NH3.

The composite gas nitriding process mainly includes pre-oxidation, nitriding, pre-cooling and furnace release. During pre-oxidation, the interior of the furnace is communicated with the atmosphere through ventilation holes. The flow rate of NH3 in the nitriding process is 6000mm3/h, and the flow rate of NH3 in the precooling stage is 2000mm3/h. During the nitriding process, 1% to 6% of CO2 and trace NO (the proportion of less than 1%) are mixed into NH3 to achieve the purpose of composite gas nitriding. CO2 and NO can improve the adsorption and activity of N atoms in the nitriding process, thereby increasing the thickness and continuity of the nitriding layer and reducing the nitriding cycle.

Analysis of White Bright Layer Treated by Compound Gas Nitriding

Due to the complex stress process of the arm, quenching and tempering is performed before nitriding to improve the microstructure of the arm and ensure comprehensive mechanical properties. The morphology of the white bright layer of the arm after conventional nitriding treatment and composite gas nitriding treatment was compared under the same nitriding time (28h).

Under the conventional nitriding process, the white bright layer of the arm is obviously thinner, and a continuous white bright layer cannot be formed at the position of the spheroidal graphite. The measurement results of the thickness of the white bright layer show that after the composite gas nitriding treatment, the thickness of the white bright layer is 10-12 μm except for the vicinity of individual graphite positions, and the thickness of the white bright layer obtained by the conventional nitriding treatment is 3-5 μm.

Compared with conventional nitriding, the composite gas nitriding treatment used in this study can significantly improve the uniformity of the white bright layer and shorten the nitriding production cycle. The reason is that the addition of CO2 and trace NO can reduce the tendency of active N atoms to combine to generate N2, and increase the adsorption efficiency of active N atoms on the surface of the workpiece. In addition, the activated carbon atoms generated by the decomposition of CO2 gas can be deposited on the surface of the graphite ball to promote The formation of the white bright layer, thereby improving the continuity of the white bright layer. Therefore, the thickness and continuity of the white bright layer after the composite gas nitriding process of the arm parts are significantly improved compared with the conventional nitriding process.

The crank arm is a key part of the bogie and plays an important role in ensuring the safe operation of subway trains and light rails. This paper adopts the composite gas nitriding process to carry out nitriding treatment on the arm, and analyzes the influence of the composite gas nitriding process on the white bright layer and dimensional accuracy of the arm. The specific conclusions are as follows.

1) After the composite gas nitriding treatment, the thickness of the white bright layer of the arm is stable at 10-12 μm, and the continuity of the white bright layer is improved, which fully meets the technical requirements for use.

2) After compound gas nitriding treatment, the outer diameter and inner hole diameter at the end of the arm have small deformation and good dimensional accuracy.