带钢边部裂纹产生机理与全流程预防方案
During the production of hot-rolled and cold-rolled steel strips, edge cracks are a typical and frequently occurring quality defect. Even if the cracks are minor, they can lead to increased cutting edge loss and unqualified appearance of the products. In severe cases, they can cause the steel strip to break, leading to machine downtime and production halt, and subsequently, they may cause failure in stamping and bending processes, directly resulting in batch grade reduction, customer complaints and economic losses.
Many production teams discovered cracks and merely adopted temporary remedies by increasing the cutting edge length, but failed to address the root cause, resulting in the recurrence of defects. This article, based on the metal deformation mechanism and practical on-site experience, thoroughly analyzes the causes and evolution patterns of the edge cracks in the steel strip, and provides corresponding full-process prevention and control measures to help the front-line personnel completely solve this problem.
I. Common Types and Appearance Characteristics of Edge Cracks on Steel Sheets
Based on the on-site production conditions and according to their morphology and distribution, edge cracks can be mainly classified into four categories, which can be quickly distinguished by comparison:
The longitudinal edge cracks extend along the rolling direction, varying in length. They are mostly concentrated on the edges of the strip steel and appear in a continuous or intermittent pattern. These cracks are the most common type, mainly caused by edge stress concentration and the extension of original defects in the billet.
The transverse edge cracks are perpendicular to the rolling direction. They are mostly in the form of short strips or fine lines, often appearing in patches at the head and tail areas of the strip steel, and are closely related to the fluctuations in rolling tension and sudden temperature changes.
The jagged edge has an irregular saw-tooth shape. It is accompanied by local peeling and chipping. This is usually caused by improper pressing of the stand roll or disorderly metal flow at the edge.
The deep-through cracks extend from the surface into the matrix of the base material, with a large depth, and are highly likely to cause interruption bands during rolling. They are mostly caused by deterioration of the original defects such as inclusions and shrinkage cavities within the billet.
II. Core Mechanism of Edge Cracks in Strip Steel
From the perspective of metal plastic deformation and mechanics, the edges of the strip steel are inherently stress concentration areas, which is the fundamental condition for the generation of cracks.
During the rolling process of the strip steel, the base metal is subjected to plastic elongation under the pressure of the rolls, and the metal in the middle of the plate surface flows smoothly; while the edges of the strip steel have no lateral constraints, and the metal has a large degree of freedom for lateral flow, with alternating compressive and tensile stresses within the material, resulting in stress values much higher than those in the central area of the plate surface.
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