45#钢Cr-N包埋共渗涂层的组织特征及形成机理

目的研究在45~#钢表面包埋共渗沉积Cr_2N涂层提高其耐蚀性的可行性。方法采用包渗法,对在1100℃下保温不同时间,得到不同时期的氮铬共渗涂层。利用扫描电镜及能谱仪、X射线衍射仪研究氮铬共渗层的微观组织及其生长机制,利用极化曲线评估涂层耐蚀性能。结果 45~#钢氮铬包埋共渗在保温4 h时可获得最佳涂层,涂层组织为Cr_2N层(约15μm)、Cr的沉积层(约10μm)、Cr的扩散层(约15μm)。Cr_2N层呈现强烈的(002)晶面择优取向;Cr沉积层为Fe-Cr合金及铬的碳化物相(Cr_7C_3,Cr_3C_2)。在模拟燃料电池腐蚀液中,45~#钢、45涂层样品、304不锈钢自腐蚀电位和自腐蚀电流分别为-0.521 V和230.63μA·cm~(-2),-0.448 V和10.89μA·cm~(-2),-0.299 V和5.26μA·cm~(-2)。当腐蚀电位高于0.3 V时,涂层样品会二次钝化,腐蚀电流低至1.43μA·cm~(-2)。结论沉积Cr_2N的45~#钢样品相对原样其耐蚀性有很大提高,并且当腐蚀电位达到0.3 V以上时,其耐蚀性能优于304不锈钢。

Microstructure Characteristics and Formation Mechanism of Co-Deposition Coating on Plain 45# Carbon Steel via Simultaneous Chro-mising and Nitriding by Pack Cementation Process

The work aims to study the feasibility of increasing the corrosion resistance of 45# plain carbon steel by forming a Cr2N coating layer. Cr2N co-deposition coatings at different stages were obtained by holding the temperature for different dura-tions at 1100℃. The microstructure and formation mechanism of the coatings were studied by using SEM, EDS and XRD. Corrosion resistance of the coatings was assessed by virtue of electrochemical anodic polarisation curves. Optimal coating was obtained for 45# steel Cr2N pack infiltration when holding time was 4 h. The coating consisted of a top Cr2N layer (≈15μm), a deposited layer of Cr (≈10μm) and diffusion layer of Cr (≈15μm). The top Cr2N layer had strong (002) predominant crys-tal orientation. Carbide phases of Fe-Cr alloy and Chromium (Cr7C3, Cr3C2) were found in the deposited layer of Cr. In the si-mulated corrosive liquid of fuel cell, the self-corrosion potentials of 45# steel, 45# coating sample and 304L stainless steel were?0.521 V,?0.448 V and?0.299 V respectively, and self-corrosion current 230.63μA·cm-2, 10.89μA·cm-2 and 5.26μA·cm-2 respectively. Coating samples showed secondary passivation and the corrosion current was 1.43μA·cm-2 when corrosion po-tential exceeded 0.3 V. Compared with the uncoated steel, corrosion resistance of the Cr2N coated 45# steel increases signifi-cantly, and is superior to that of 304SS when the corrosion potential is more than 0.3 V.