特大铁路钢梁桥调平垫片用Q235钢的C-N-O-S多元共渗及组织性能演变

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

为有效延长钢梁桥Q235钢调平垫片的服役寿命,采用C-N-O-S多元共渗技术进行改性处理,研究了不同参数耦合对改性层组织、硬度、耐磨性及耐候性的影响。结果表明,改性层多层结构与共渗温度有关,在640℃与650℃之间存在临界值,临界温度以下由化合物层、扩散层及氧化层组成,当超过临界温度时,由化合物层和氧化层组成。改性层厚度受共渗温度、氨气及催渗剂影响机制不同,共渗温度及氨气流量对渗层各层结构均有影响,扩散层受催渗剂流量作用明显;改性层硬度是基材的2~3倍,三层结构渗层硬度由表层向基材不断降低;两层结构化合物层的硬度均匀,在界面区硬度陡降。改性层摩擦因数最低为0.2468,约为基材的1/3。改性层自腐蚀电位最高达-0.4845 V,自腐蚀电流密度最低为1.187×10-6 mA/cm2,较基体降低2个数量级。

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.