煉焦爐平煤門鎳基超合金膜片之腐蝕及斷裂現象探討

The Phenomena of Corrosion and Cracking of Ni-base Superalloy Plate in Coke Oven

本研究主要是探討煉焦爐平煤啂口之鎳基超合金膜片的腐蝕及斷裂現象。為了解其腐蝕及斷裂發生的途徑、起因和機構，本研究分別進行現場調查及目視檢測，並利用分光分析儀（Spark）分析膜片的化學成分，OM和SEM觀察試片表面結構、以及EDS和X RD分析腐蝕生成物的化學成分及組成。綜合分析之結果顯示：（1）Inconel 600膜片的腐蝕為高溫硫化及氧化腐蝕破壞，其腐蝕形態為沿晶腐蝕。（2）由於膜片表面形成的Cr2O3及(Cr, Fe)2O3氧化膜之保護性不夠佳，無法有效的阻礙鎳向外擴散，導致於硫化腐蝕發生。（3）膜片斷裂的形態為腐蝕疲勞破裂，其成長機構為沿晶腐蝕發生在應力集中之處，在反覆熱循環殘留熱應力的作用下，使得裂縫得以成長，並以穿晶破裂的形態蔓延。

This case study was performed to shed light on the phenomena of corrosion and cracking of Ni-base superalloy plate in coke oven. To understand the corrosion mechanism and cause of cracking, many supporting tests were carried out. Fieldwork and visual investigation were conducted to collect the background of the applied system and its environment of failed plate. Spark was used to verify whether the material was properly selected. The surface morphology of the failed plates was observed by using optical microscopy (OM) and scanning electron microscopy (SEM), respectively. The chemical compositions of scale were measured by energy dispersive spectrometer (EDS) and X-ray diffraction (XRD), respectively. Based on the observations and test results, it can be concluded that the Inconel 600 alloy was under both sulfide and oxide attack at high service temperature, resulting in a form of intergranular corrosion. The Cr2O3 and (Cr, Fe)2O3 scales were not adequately protective, and were less resistant to Ni migration from the substrate toward the scales. Therefore, sulfide reaction occurred. The fracture surfaces resulted from a corrosion fatigue cracking (CFC). CFC was caused by the combination of intergranular corrosion and cyclic thermal stress. The cracks propagate across the grains in the transgranular failure mode. .