某熱軋鋼帶工廠調質重捲線上背輥驅動側輥頸於生產時斷裂，由力學計算、巨觀破損特徵分析與液滲檢測結果研判，輥頸圓角處蝕孔為斷輥主因，該處在軋延時的反覆彎曲應力下，於蝕孔處產生周向裂痕，進而於常態變動負荷下斷裂。圓角上的蝕孔推斷為背輥與套環發生間隙腐蝕，導致腐蝕因子侵入，而圓角處的加工痕更加速腐蝕的作用。針對上述要因，建議：(1)下線時，徹底清理套環與背輥間隙間的殘留物質；(2)拆卸套環時，配合處若有腐蝕即作更換，另對背輥圓角處液滲檢測，一旦發現點蝕應即時磨除並避免研磨損傷；(3)新輥製作時，檢測圓角表面粗糙度，並確認圓角與套環緊配處液滲檢驗合格；同時，建議背輥圓角處增加耐蝕塗覆，有助於提升該處的抗蝕能力。

The 4-Hi rolling mill of a Temper and Recoil line (TNRL) is quite common to handle hot-rolled band coil. The top back-up roll was broken around drive-side roll neck during normal operation. After evaluating the stress of roll, doing detailed visual inspection of fracture parts and liquid penetration test (PT), we speculated that the root cause was the pitting at the fillet of the roll neck. These tiny pits could induce high-stress concentration at the fillet and form several circumferential cracks by rotating bending stress during rolling process and then fracture eventually. The crevice corrosion between back-up roll and the thrust ring was inferred that induced the corrosive element to intrude the fillet. The obvious turning marks at the fillet also promoted corrosion reaction. It is recommended to exclude such failure mechanism by: (1) Remove all substances which stuck at the clearance between back-up roll and the thrust ring during off-line maintenance. (2) Replace the thrust ring if there is obvious corrosion at the fitting area. Grind the tiny pits found by dye penetration testing (PT) immediately, but don’t damage the fillet. (3) Check the surface roughness of the fillet and do PT test prior to assembling the thrust ring. Besides, it’s recommended to apply proven corrosion-resistant coating on the fillet of back-up roll.