熱軋鋼捲銹皮組織對酸洗性之影響研究

The Influence of Scale Structure of Hot-Rolled Steels on the Pickling Performance

熱軋鋼材在進行冷軋之前，須將表面銹皮以酸洗的方式去除。酸洗的難易與銹皮之特性有很大關連，本研究即在探討熱軋鋼捲之酸洗性與銹皮結構之關係。試驗材料為同材質之三捲熱軋鋼捲，採用三種濃度之鹽酸酸洗液，在85℃進行酸洗。研究發現酸濃度愈高，各試片之洗淨時間愈短；不同鋼材及不同位置都有不同的酸洗性質。一般而言，尾端料比頭端料難酸洗，中央位置與邊緣位置之酸洗性則無明顯差異。銹皮的組成以Fe3O4為主，Fe2O3則隨鋼捲之位置而異，鋼捲邊緣位置都確定有Fe2O3，但中間部位則不一定有。鋼捲之銹皮特性相當複雜，同一鋼捲之頭尾端、邊緣或中心、上下表面之銹皮厚度、緻密或鬆散、裂紋之多寡和方向、銹皮組成（尤其是Fe2O3）都不一致，導致酸洗性的不同。經歸納後發現影響銹皮酸洗難易度之內在因素主要有三：（1）銹皮厚度、（2）銹皮緻密性、（3）銹皮組成，尤其是Fe2O3層的量及連續性。

Before the cold-roll process, pickling is applied to the hot-rolled coils to remove the oxide scale on the surface. The pickling efficiency is affected by the scale properties. Understanding of the relationship between these two is the main purpose of this study. Three hot-rolled coils with same compositions were pickled at 85℃, under hydrochloric acids with three concentrations. The higher acid concentration, the shorter the pickling time for all these three steels. The pickling rate of oxide scale at various locations and coils are different. Basically, the oxide at the end coil is easier to be removed than the beginning coil. Magnetite (Fe3O4) is the major oxide structure for all these three coils. Hematite (Fe2O3) exists on most of the side area but not on the center of the coils. The oxide structures are complicated, either compact or loose, thick or thin, with or without hematite. They are all different at various positions, including outer or inner part, edge or center of steel coil. The major factors affecting the pickling rate are scale thickness, compactness, and the oxide structure, especially the amount and continuousness of hematite.