合金元素及熱處理製程對高強度低合金鋼腐蝕行為之研究

Abstract

高強度低合金鋼(High Strength Low Alloy Steels)由於具有優良的降伏強度、低溫韌性、可焊接性及抗蝕性，因此被廣泛使用在海洋工程領域及國防工業中，材料機械性質及抗蝕性為工程應用上必受重視之課題，特別在海洋工程中具有嚴苛的海洋腐蝕環境，通過添加微量合金提升鋼的機械性質及耐蝕性，通常會添加微量鉬、鉻、銅、鎳、鋁、矽等合金元素以提升抗蝕性，合金元素對於提升鋼的抗蝕性方法為：抑制其電化學反應，及促進表面保護層的生成以減緩鋼基材腐蝕速率。在本研究中，第一部份探討添加微量鎳及銅合金元素對於高強度低合金鋼抗蝕性影響，並且與商用S690Q海洋用鋼進行比較；第二部分為研究添加微量鎳及銅合金的高強度低合金鋼在不同熱處理後對於抗蝕性的影響。利用動電位極化曲線評估高強度低合金鋼在不同腐蝕環境下之抗蝕性，並利用表面分析技術：掃描式電子顯微鏡觀察腐蝕後表面形貌及腐蝕產物橫截面形貌，最後以X射線繞射分析、電子微探儀及X射線光電子能譜學鑑定腐蝕產物組成及合金元素分佈。電化學實驗結果顯示添加微量鎳及銅合金元素有助於提升抗蝕性，並且抑制陽極溶解速率，表面分析結果顯示合金元素富集於腐蝕產物層之中，有助於腐蝕產物生成致密及貼合性以提升抗蝕性；而第二部份實驗結果顯示，鎳銅高強度低合金鋼在回火溫度660oC時抗蝕性最好，回火溫度提高至780oC則抗蝕性降低。

High strength low alloy steels have been widely used in the marine engineering and defense industry due to their superior yield strength, toughness and weldability. Although these materials have superior mechanical properties, the corrosion resistance is the other important issue especially when they are used in the marine environment. In this study, we investigated the effect of nickel and copper addition on the corrosion resistance of high strength low alloy steels in the marine environment, and the effect of heat treatments on the corrosion resistance of the new designed NiCu steel. The potentiodynamic polarization curve was conducted using a Gamry Reference 600 potentiostat to evaluate the corrosion performance of two high strength low alloy steels. The surface morphology and composition of corrosion products formed on the material surface after corrosion treatment were analyzed using scanning electron microscopy (SEM), electron probe micro-analyzer (EPMA), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The preliminary electrochemical measurement and surface analysis results showed that higher amount of Ni and Cu addition can improve the corrosion resistance of high strength low alloy steels. In the EPMA analysis, it was found the corrosion layer of higher Cu and Ni containing alloy was enriched with copper. The new designed NiCu steel have the best corrosion resistance at tempering temperature of 660 oC.