原子力显微镜评价奥氏体不锈钢晶间腐蚀敏感性的研究

Identification of Sensitization of Austenitic Stainless Steel to Intergranular Stress Corrosion Cracking by Atomic Force Microscopy

由13Cr可焊马氏体不锈钢(WMSGSS)制造的油气管线由于价格便宜,相对于昂贵的耐腐蚀合金来说是一个很有竞争力的选择。但是实验室试验和现场经历表明,13Cr马氏体不锈钢焊接接头热影响区发生了沿晶应力腐蚀开裂(IGSCC)。对于低等级的马氏体不锈钢来说,沿晶应力腐蚀开裂机理被认为是在晶界的碳化物附近存在贫铬区。对于中等级和高等级马氏体不锈钢来说,只在实验室试验发现有应力腐蚀开裂。它们的应力腐蚀开裂机理还没有明确,虽然最可能的应力腐蚀开裂机理也被认为和低等级马氏体不锈钢的应力腐蚀开裂机理类似。原子力显微镜(AFM)已开始广泛用于材料显微组织和环境敏感断裂的研究中。高等级马氏体不锈钢焊接接头对晶间腐蚀/应力腐蚀开裂敏感性很有希望由原子力显微镜检测到。在原子力显微镜技术应用于这项研究之前,用由304不锈钢准备的不同敏化度的试样来确定它的适用性是十分有益的。本文用原子力显微镜研究了不同敏化程度的304不锈钢的晶间腐蚀敏感性并和SEM和EDS结果进行了对比。

Oil and gas flow lines of 13 Cr weldable martensitic grade stainless steel （WMSGSS） offers a very cost effective alternative to more expensive corrosion resistant alloys. However, laboratory tests and field experience indicates the 13 Cr steel undergoes inter-granular stress corrosion cracking （IGSCC） in the heat affected zone of the welds. The IGSCC mechanism of lean grades is considered to be chromium depletion near carbides at grain boundaries. For medium and rich grades, the cracking has only been found in laboratory tests. For these grades the mechanism has not been clarified, although the most likely mechanism is considered to be similar to that of the lean grades. Atomic force microscopy （AFM） has been extensively used in the study of microstructures of materials and environmentally induced fracture. The sensitisation of rich grade martensitic stainless steel weld to intergranular corrosion/SCC maybe identified by AFM. Before this technique is used in the study, it would be beneficial to start the technique by using sensitised specimens made of standard 304 stainless steel to verify the suitability. In this paper the sensitisation of a series of 304 stainless steel samples with different degree of sensitisation was studied by means of AFM together with scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS） techniques and the results agree with each other.