气体氮碳共渗中NH3和CO流量对低碳钢渗层组织及其性能的影响

摘要

The microstructure and properties of the nitrocarburized layer are greatly affected by the nitriding potential and carbon potential in the atmosphere which can be directly controlled by the flow rate of NH3 and CO during nitrocarburizing. The effects of NH3 and CO flow on the microstructure and properties of the compound layer were investigated by scanning electron microscopy, X-ray diffractometer, microhardness tester and electrochemical analyzer. The results show that the thickness and porosity of the compound layer increases with the increasing NH3 flow during gas nitrocarburizing. With the rising of CO flow, the compound layer becomes more compact, but the thickness of the compound layer increases first and then decreases. The addition of C in the nitrocarburized layer can restrain the formation of γ' phase forming and promote the formation of ε phase. While the excess C would result in the emerging of θ phase. Fortunately, the permeated C show limited impact on the corrosion behavior of the compound layer. The combined effects of NH3 and CO on nitrocarburized layers can be realized through raising the flow rate of NH3 and the corresponding flow rate of CO appropriately, thus a thicker and compact compound layer with good corrosion-resistance can be formed successfully.%通过调控气体氮碳共渗过程中的NH3和CO流量来调控气氛中的氮化势和碳势, 从而调控共渗层的微观组织和性能.采用扫描电镜、X射线衍射仪、显微硬度计和电化学分析仪研究了气体氮碳共渗过程中的NH3和CO流量对低碳钢氮碳共渗层的微观组织结构及其性能的影响.研究结果表明:气体氮碳共渗气氛中, 随着NH3流量的增加, 化合物层厚度增大但致密性降低;随着CO流量的增加, 化合物层致密性逐渐增大, 但渗层厚度先增大后减小.氮碳共渗过程中C的加入可抑制γ'相的形成而促进ε相的产生, 过量的C会形成θ相, 但是C的渗入对渗层腐蚀性能影响较小.NH3和CO对氮碳共渗过程中的协同作用表现为, 当NH3流量增加时, 可相应增加CO流量来获得较厚、致密、耐腐蚀的化合物层.