sphc碳鋼熱軋厚鋼捲銹皮鬆脫缺陷解決.doc

SPHC碳鋼熱軋厚鋼捲銹皮鬆脫缺陷解決* A Solution to Scale Loosening of Thick Hot-Rolled SPHC Steel Coils* 廖啟民 ■ 林筵進2 ■ 黃朝琪1 C.M. Liao1 Y.C. Lin2 C.C. Huang1 熱軋鋼捲理想的表面銹皮層是不易脫落的，若銹皮容易鬆脫，會在重捲線上造成銹皮飛揚；此外，雷射切割時飛揚的銹粉會遮蔽雷射感測器，影響切割品質。中鋼公司6mm以上之高厚度SPHC熱軋產品發生銹皮鬆脫已是長時間之問題，時而嚴重時而趨緩，其發生機構及成因也未真正釐清。為了解決此一陳年問題，本研究由銹皮組織結構分析、現場製程因素釐清、銹皮轉化驗證三大區塊切入。 綜合三區塊之結果，確認銹皮之鬆脫與製程中的出爐溫度、完軋溫度、盤捲溫度，以及軋機之軋延力及張力都沒有關係，問題發生在生產之後鋼捲的冷卻過程。銹皮會鬆脫之鋼捲，盤捲後是經過緩冷，內層之FeO有足夠時間轉化成Fe3O4；而正常鋼捲之冷速較快，故沒有完全轉化。緩冷之下，所有延性佳之FeO都轉化為延性較差之Fe3O4；此外，最終銹皮厚度越厚，故在鋼捲解捲時，上表面受到壓應力之擠壓，緩冷之銹皮就比快冷者容易破裂，因此較易發生銹皮鬆脫。 關鍵詞：熱軋鋼材、銹皮鬆脫、銹皮組織、銹皮轉化 The ideal oxide scale on the surface of hot-rolled steel coils should remain intact when decoiling. Loosening and peeling-off of oxide scales decrease the laser-cutting efficency by desensitizing the lasers?detecting sensors. China Steel Corporations hot-rolled coils with thickness greater than 6 mm have oxide scale loosening problem for sometime. The mechanism and cause of oxide scale loosening were unknown and should be investigated. This study focused on production process clarification, scale structure analysis, and scale transformation simulation to determine the mechanism and cause of the oxide scale problem. Results showed that the cooling off time is critical for having the scale lossening problem instead of the slab temperature, finishing temperature, coiling temperature, and rolling force and tension. When the coil was slowly cooled to room temperature, the FeO is completely transformed to Fe3O4. The Fe3O4 forms brittle scales that break off easily when de-coiling. Quick cooling decreases the transformation ratio of Fe3O4 scales and thereby lessens the scale loosening problem. Key Words: hot-rolled steel, scale loosening, scale structure, scale transformation 壹、前　言 熱軋鋼捲理想的表面銹皮層是不易脫落的，若銹皮容易鬆脫，會在重捲線上造成銹皮飛揚，影響健康；另外，雷射切割時飛揚的銹粉會遮蔽雷射感測器，影響切割品質；此外，鋼捲儲放時更容易發生銹蝕，影響表面品質。中鋼公司熱軋厚板（6mm以上）銹皮鬆脫是困擾多年之問題，其發生機構及成因也未真正釐清。近年之剔退比例又逐漸上升，發生時大多整捲都有，且只在解捲時發生於上表面，且都發生在某一條熱軋產線，而另一條產線則無此現象。 本研究解析此缺陷發生之原因，並提出解決方案。 貳、實　驗 實驗之進行架構