1. Underfilled Corners
1.1 Defect Characteristics: Underfilled corners are caused by missing metal at the corners of a steel section due to incomplete hole filling. This defect presents a rough surface, often occurring along the entire length, but sometimes only locally or intermittently.
1.2 Causes: Inherent characteristics of the pass prevent the corners from being processed; improper mill adjustment and improper reduction distribution. Insufficient reduction at corners, or uneven extension across the workpiece, resulting in excessive shrinkage; severe wear of the pass or guide plates, excessive width, or improper installation; low workpiece temperature, poor metal plasticity, and difficulty filling corners at the pass; severe localized bending in the workpiece, which can easily lead to underfilled corners after re-rolling.
1.3 Control Methods: Improve pass design, strengthen mill adjustment, and properly distribute reduction; properly install guides and promptly replace severely worn pass and guide plates; and adjust reduction according to workpiece temperature to ensure adequate corner filling.
2. Steel Section Dimension Excess
2.1 Defect Characteristics: A general term for steel section dimensions that do not meet standard requirements. When the deviation from the standard dimensions is significant, the steel section presents a deformity. This defect has numerous names, most often based on the location and degree of deviation. Examples include out-of-roundness and length.
2.2 Causes: Irrational pass design; uneven pass wear, improper fit between new and old holes; poor installation of mill components (including guides), resulting in broken safety mortars; improper mill adjustment; uneven billet temperatures, resulting in localized non-conformity within a single billet, and overall length non-conformity and oversizing of low-temperature steel billets.
2.3 Control Methods: Properly install all mill components; improve pass design and strengthen mill adjustment operations; pay attention to pass wear. When replacing a new finish pass, consider replacing the pre-finish pass and other related passes at the same time, depending on the specific situation; improve billet heating quality to achieve uniform billet temperature. For some profiles, changes in cross-sectional shape after straightening may cause a certain dimension to not meet specifications. In this case, re-straightening can be performed to eliminate the defect.
3. Steel Section Scab
3.1 Defect Characteristics: Metal lumps adhered to the surface of the steel section during rolling. Their appearance is similar to scabs, but they differ primarily in that their shape and distribution on the steel section surface exhibit a certain regularity. Non-metallic oxide inclusions are often absent beneath the scab. 3.2 Causes: Severe wear of the roughing mill pass produces intermittent active scars on the fixed surface of the section steel; foreign metal objects (or metal scraped off the workpiece by the guide device) press into the workpiece surface, forming scars; periodic bumps or pits form on the workpiece surface before the finished hole, resulting in periodic scars after rolling. Specific causes include: poor groove notching; sand holes or loss of groove; groove damage caused by “blackhead” workpiece or adhesion of protrusions such as scars; workpiece slipping in the pass, causing metal to accumulate on the deformation zone surface, resulting in scars after rolling; and partial scratches (scratches) or bending of the workpiece by mechanical equipment such as the chute, roller table, or steel turning machine, which can also cause scars after rolling. 3.3 Control Methods: Promptly replace the groove if it is severely worn or has foreign matter on it. Carefully inspect the groove surface before changing rolls and avoid using grooves with pinholes or poorly scored marks. Strictly prohibit rolling black steel to prevent groove loss or damage. When handling steel jams, be careful not to damage the groove. Keep all mechanical equipment before and after the rolling mill smooth and flat, and properly install and operate it to avoid damage to the workpiece. During rolling, be careful not to allow foreign matter to press into the workpiece surface. The billet heating temperature should not be too high to prevent the workpiece from slipping within the die.
4. Section Steel Missing Metal
4.1 Defect Characteristics: Metal is missing along the length of one side of the section steel. The defect lacks the hot rolling mark of the finished groove, is darker in color, and is rougher than normal. This defect usually occurs along the entire length, but can also occur locally. 4.2 Causes: Misaligned grooves or improper guide installation can cause metal to be missing from a certain section of the workpiece, resulting in incomplete hole filling during re-rolling. Poor hole design, incorrect turning, or improper mill adjustment can result in insufficient metal entering the finished hole, resulting in incomplete hole filling. Differential wear of the front and rear holes can also cause missing metal. Twisting or significant local bending of the workpiece can lead to localized missing metal after re-rolling.
4.3 Control Methods: Improve hole design and strengthen mill adjustments to ensure proper hole filling. Tighten mill components to prevent axial roll movement, properly install guides, and promptly replace severely worn holes.
5. Scratches on Steel Sections
5.1 Defect Characteristics: Grooves caused by the sharp edges of equipment and tools during hot rolling and transportation. These grooves vary in depth, with visible bottoms. They generally have sharp corners and are often straight, but can also be curved. They may be single or multiple, running the entire length or partially across the steel section surface. 5.2 Causes: Sharp edges on the hot rolling area floor, rollers, steel transfer equipment, and steel turning equipment cause scratches when the workpiece passes through. Poorly machined guide plates with uneven edges or severely worn guide plates with foreign matter, such as scale adhering to them, cause scratches on the workpiece surface. Improper installation and adjustment of guide plates result in excessive pressure on the workpiece, causing scratches. Unrounded edges on the rims cause scratches when the workpiece jumps through the rims.
5.3 Control Methods: Guides, rims, floor, and rollers must be smooth and flat, free of sharp edges. Ensure proper installation and adjustment of guide plates, avoiding misalignment or excessive tightening to prevent excessive pressure on the workpiece.
6. Steel Section Waves
6.1 Defect Characteristics: Waves are undulations along the length of a steel section caused by uneven rolling deformation. These can be localized or continuous. The longitudinal undulations at the waist of I-beams and channels are called waist waves; the longitudinal undulations at the leg edges of I-beams, channels, and angles are called leg waves. I-beams and channels with waist waves have uneven longitudinal waist thickness. In severe cases, this can lead to overlapping metal and tongue-shaped voids.
6.2 Causes: Waves are primarily caused by inconsistent elongation coefficients across the workpiece, resulting in severe tension and shrinkage. This typically occurs in areas with greater elongation. The main factors causing elongation variations across the workpiece are as follows: improper reduction distribution, roll skew and groove misalignment, severe wear of the grooves at the front or rear holes of the finished product, and uneven workpiece temperature.
6.3 Control Methods: When replacing the finished hole mid-roll, both the front and rear holes should be replaced simultaneously, taking into account product characteristics and specific circumstances. Strengthen rolling adjustment operations, rationally distribute reduction, and tighten all rolling mill components to prevent groove misalignment. This ensures uniform elongation across the workpiece.
7. Steel Twist
7.1 Defect Characteristics: Twist occurs when different cross-sections along the length of the steel are angled differently around the longitudinal axis. When twisted steel is placed on a horizontal inspection stand, one side of one end may be raised, and sometimes the other side of the other end may also be raised, forming a certain angle with the stand. When the twist is severe, the entire steel bar may even become twisted.
7.2 Causes: Improper installation and adjustment of the rolling mill; roll centerlines not aligned in the same vertical or horizontal plane, axial movement of the rolls, and misalignment of the grooves; improperly installed or severely worn guide plates; uneven temperature or reduction of the rolled piece, resulting in uneven elongation; improper adjustment of the straightening machine; turning the steel, especially large pieces, on one end while hot on a cooling bed, which can easily cause end twisting.
7.3 Control Methods: Strengthen the installation and adjustment of the rolling mill and guide plates. Avoid using severely worn guide plates to eliminate torsional torque on the rolled product; strengthen straightening machine adjustments to eliminate torsional torque applied to the steel during straightening; avoid turning the steel over on one end of the cooling bed while hot to prevent twisting of the ends.
8. Steel Bend
8.1 Defect Characteristics: Longitudinal irregularities are generally referred to as bends. The names of the steel’s bends are: sickle-shaped uniform bends are called sickle bends; wavy, repetitive bends are called wave bends; and bends are defined as bends where one side of an end angle warps inward or outward (or, in severe cases, curls up). 8.2 Causes: Before straightening, Improper rolling mill operation adjustments or uneven temperature of the rolled piece can cause uneven extension of different parts of the rolled piece, resulting in camber or elbow. A large difference in upper and lower roller diameters or improper design and installation of the finished product exit guide plate can also cause elbow, camber, or wave bend. An uneven cooling bed, inconsistent roller speeds, or post-rolling cooling can all cause wave bend. Uneven metal distribution across the product cross-section and inconsistent natural cooling rates can cause camber in a fixed direction even if the steel is straight after rolling. During hot sawing, severe saw blade wear, excessive sawing speed, high-speed collision of the hot steel on the roller conveyor, and collision of the steel end with protrusions during transverse movement can cause elbows or corners. Improper handling of the steel during lifting and intermediate storage, especially when handling while red hot, can cause various types of bends. After straightening, in addition to corners and elbows, normal wave bends and cambers in the steel should be straightened after the straightening process. 8.3 Control Methods: Strengthen rolling mill adjustments, properly install guides, and prevent excessive bending of rolled products during rolling. Strengthen the operation of hot saws and cooling beds to ensure crop length and prevent bending of steel. Strengthen straightening machine adjustments and promptly replace severely worn straightening rollers or shafts. To prevent bending during transportation, install spring baffles in front of the cooling bed rollers. Strictly control the temperature of the straightened steel according to regulations, and stop straightening if the temperature is too high. Strengthen the storage of steel in intermediate warehouses and finished product warehouses to prevent bending of steel by compression or being caught by crane cables.
9. Improper Shape of Steel Sections
9.1 Defect Characteristics: There is no metal loss on the steel section surface, but the cross-sectional shape does not meet the specified requirements. This defect has various names, varying with the type. Examples include oval shapes in round steel; diamond shapes in square steel; skewed legs, wavy waists, or missing legs in channel steel; large or small top angles or uneven legs in angle steel; skewed legs and uneven waists in I-beams; and collapsed shoulders, convex waists, concave waists, widened legs, or overlapping legs in channel steel.
9.2 Causes: Improper design, installation, or adjustment of straightening rollers, or severe wear; unreasonable straightening roller pass design; severe wear of straightening rollers; improper design, wear, or improper installation of the pass and guide devices for the rolled steel;
9.3 Control Methods: Improve the straightening roller pass design and select straightening rollers appropriately based on the actual dimensions of the rolled product. When bending channels and automotive wheel meshes, the second (or third) lower straightening roller in the straightening machine’s forward direction can be made convex (with a crown height of 0.5-1.0mm) to help eliminate concave waist defects. For sections requiring a guaranteed working surface with unevenness, control should begin during rolling, and strengthen straightening machine adjustment operations.
10. Steel Cutting Defects
10.1 Defect Characteristics: Various defects caused by poor cutting are collectively referred to as cutting defects. Cutting defects are irregular scratches on the steel surface caused by hot shears. Saw damage to the surface caused by the saw blade while it is hot is called sawing. Slashing or sawing defects where the cut surface is not perpendicular to the longitudinal axis after cutting. Shortcuts where the hot-rolled, shrunken portion of the rolled piece is not completely removed. Tearing is a small, localized crack on the sheared surface after cold shearing. Burrs are metal fringes left on the end of the steel after sawing (shearing).
10.2 Causes: The sawed steel is not perpendicular to the saw blade (cutting edge), or the workpiece is excessively curved. Equipment: excessive saw blade curvature, worn or improperly installed saw blades, and excessive gap between the upper and lower cutting edges. Malfunctioning of the flying shear. Operational: cutting (sawing) too many pieces of steel simultaneously, cutting too little of the end, incompletely cutting the hot-rolled, shrunken portion, and various other operational errors. 10.3 Control Methods: Improve incoming material conditions and implement measures to prevent excessive bending of the rolled material head, maintaining the incoming material direction perpendicular to the shearing (sawing) plane. Improve equipment conditions by using saw blades with minimal or no curvature, selecting appropriate saw blade thickness, promptly replacing worn saw blades (cutting edges), and properly installing and adjusting the shearing (sawing) equipment. Enhance operation and minimize shearing (sawing) cuts to prevent excessive lifting and bending of the steel. Ensure the necessary end removal, completely removing the hot-rolled shrinkage, and avoid various operational errors.
11. Steel Straightening Marks
11.1 Defect Characteristics: Surface scratches caused during the cold straightening process. These defects lack any traces of hot working and often exhibit a certain pattern. There are three main types: pitting (or straightening pits), fish scales, and damage. 11.2 Causes: Shallow straightening roller pass, severe steel bending before straightening, incorrect steel feeding during straightening, or improper straightening machine adjustment can cause damage-type straightening marks. Localized damage to the straightening roller, metal lumps adhering to the roller surface, localized protrusions on the roller surface, severe wear of the straightening roller, or high roller surface temperatures can cause metal adhesion, which can result in fish-scale-shaped straightening marks on the steel surface.
11.3 Control Methods: Do not use straightening rollers that are severely worn or have significant straightening marks. If the straightening roller is locally damaged or has metal lumps adhering to it, polish it immediately. When straightening angle steel and other sections, the contact surface between the straightening roller and the steel moves significantly (caused by a difference in linear speed), which can easily cause the straightening roller to heat up and cause scraping, resulting in straightening marks on the steel surface. Therefore, cool the straightening roller surface with cooling water. Improve the straightening roller material or quench the straightening surface to increase surface hardness and wear resistance.
Post time: Sep-17-2025