C-N-O-S multi-element co-infiltration and evolution of microstructure and properties of Q235 steel for leveling gaskets of extra-large railway steel beam bridges
In order to effectively extend the service life of Q235 steel beam bridge leveling gaskets,the surface modification of C-N-O-S multi-element infiltration technology was carried out.The effect of different parameters coupling on the microstructure,hardness,wear resistance and weather resistance of the modified layer was studied.The results show that the multi-layer structure of the modified layer is related to co-infiltration temperature,and there is a critical value between 640℃and 650 ℃,below the critical temperature,it is composed of the compound layer,diffusion layer and oxidation layer.When the critical temperature is exceeded,the modified layer comprises compound and oxidation layers.The thickness of the modified layer is affected by co-infiltration temperature,ammonia and infiltration promoting agent flow rates,and the temperature and ammonia flow rate affect the structure of each layer.The infiltration promoting agent flow rate has an obvious effect on the diffusion layer.The hardness of the modified layer is 2-3 times of that of the substrate,the hardness of the three-layer structural layer decreases continuously from the surface to substrate.The hardness of the two-layer structural compound layer is uniform,with sharp decrease in hardness in the interface area.The lowest friction coefficient of the modified layer is 0.2468,which is about 1/3 of the base material.The highest free-corrosion potential of the modified layer is-0.4845 V,and the lowest free corrosion current density is 1.187 × 10-6 mA/cm2,which is reduced by 2 orders of magnitude compared to the substrate.
leveling steel gaskets for railway steel beam bridgeservice lifemulti-element co-infiltrationmicrostructure and properties
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