Causes of strip steel surface defects and preventive measures

　　Loose sand sheet iron

　　Shapes that appear:

　　The iron sheet is dark brown, round and fine, distributed in loose sand

　　Cause of occurrence:

　　1) The high-temperature rolled piece is rolled on the roll with rough surface, and the secondary scale formed by the finishing mill is pressed into the loose sand scale;

　　2) High carbon content and high finishing temperature are easy to occur.

　　Preventive measures:

　　1) Strengthen roll cooling water to prevent rough surface of work roll of finishing mill;

　　2) Management of roll change;

　　3) Control the rolling temperature.
 

　　Meteoroid iron sheet

　　Shapes that appear:

　　The iron sheet is irregularly distributed on the plate surface, and its shape is meteoric along the rolling direction

　　Cause of occurrence:

　　The cold hard layer film of the work roll at the front stage of finish rolling peels off in a meteor shape. This defect is easy to occur when the elongation of the rolled piece is too large

　　Preventive measures:

　　1) Strengthen roll cooling water;

　　2) Management of roller cooling water nozzle;

　　3) Limit rolling rhythm;

　　4) Consider reduction distribution;

　　5) Management of roll change.
 

　　Spindle iron sheet

　　Shapes that appear:

　　The spindle shape is a deep pressed iron sheet, 1) wider, longer and deeper than the meteor shape iron sheet, 2) most of them are in an uncertain position and scattered

　　Cause of occurrence:

　　Remove the poor iron oxide scale, and the residual part of the primary iron oxide scale is formed by pressing.

　　Preventive measures:

　　1) Completely remove the primary iron oxide scale;

　　2) Charge the reheating billet after removing the surface iron sheet;

　　3) All slabs shall be repaired.
 

　　Linear iron sheet

　　Shapes that appear:

　　Linear elongated sheet iron

　　1) Independent of position and width

　　2) Most of them are due to too long time in the furnace.

　　Cause of occurrence:

　　1) The exposure of tubular bubbles on the billet surface is formed by oxidation,

　　2) S and Cu precipitated from grain boundary of slab structure in reheating furnace, resulting in hot brittleness and defects.

　　Preventive measures:

　　1) Check slab quality;

　　2) Adjust heating temperature and heating time
 

　　Trace iron sheet

　　Shapes that appear:

　　The red spindle shaped iron sheet is combined with the pressed irregular black iron sheet.

　　Cause of occurrence:

　　1) Sundries on guard plate or poor rotation of roller table

　　2) The secondary sheet iron on the strip steel is accumulated into large pieces for many times, adhered to the strip steel, and then rolled into the strip steel surface.

　　Preventive measures:

　　1) Strengthen the management of rolling line and all operation lines;

　　2) Ensure that the surface of roll, looper roll and sliding plate is smooth and smooth.
 

　　Banded iron sheet

　　Shapes that appear:

　　The oxide scale is pressed into a certain position in the width direction, and the iron scale is in strip shape, continuous or discontinuous

　　Cause of occurrence:

　　One or more nozzles blocked

　　Preventive measures:

　　Prevent nozzle blockage
 

　　Woody iron sheet

　　Shapes that appear:

　　The iron sheet is fine and uniform in the form of wood grain.

　　Cause of occurrence:

　　The rough rolled secondary iron sheet is not removed completely, which generally occurs in materials with low Mn and S

　　Preventive measures:

　　1) Check the wear of rough roll;

　　2) Check the water pressure and quantity of descaling water.
 

　　Scaly iron sheet

　　Shapes that appear:

　　The pressed iron sheet has a fish scale pattern.

　　Cause of occurrence:

　　The finishing rolling temperature is high, and the generated secondary iron oxide scale is pressed in. Strip steel with high carbon content is easy to occur.

　　Preventive measures:

　　Reduce the rolling temperature of finish rolling
 

　　Red iron sheet

　　Shapes that appear:

　　There is a thin layer of red iron sheet on the surface, which is banded or linear in shape, or covers the whole board surface

　　1) Mainly in silicon killed steel;

　　2) Sometimes black and red

　　Cause of occurrence:

　　1) Poor peeling of primary iron oxide scale

　　2) The secondary iron oxide scale is difficult to remove and remains.

　　Preventive measures:

　　1) Check heating temperature and furnace atmosphere

　　2) Ensure proper rolling temperature
 

　　Transverse fold

　　Shapes that appear:

　　1) Irregular bending and crease in the width direction of the steel plate;

　　2) Easy to generate in low carbon steel and strip steel coil

　　3) Slightly wrinkled.

　　Cause of occurrence:

　　1) Improper air pressure of tension roll and pressure roll during uncoiling;

　　2) Change of yield point of raw materials;

　　3) Poor strip shape;

　　4) Coiling temperature is too high;

　　Preventive measures:

　　1) The pressure roller shall be properly used during uncoiling;

　　2) Improve strip shape;

　　3) Reduce coiling temperature;

　　4) Uncoil after complete cooling.
 

　　Coiling indentation

　　Shapes that appear:

　　In the first few circles of the strip steel coil area, the strip steel head and the fan-shaped plate of the drum are stuck with large concave indentations

　　Cause of occurrence:

　　1) During coiling, the strip steel is stamped after the second coil at the head;

　　2) Defects caused by stamping of drum sector plate

　　Preventive measures:

　　1) Adjust the roll gap and air pressure properly

　　2) Open the wrapper roll in advance;

　　3) Improve the accuracy of the drum roundness.
 

　　Roller print

　　Shapes that appear:

　　Concave and convex marks with certain pitch appear on the front or back of the steel plate

　　Cause of occurrence:

　　1) Various rollers on rolling and finishing lines with sundries (concave branding)

　　2) All kinds of rollers on the rolling and finishing lines are stamped on the steel plate due to concave defects (convex branding)

　　Preventive measures:

　　1) Thoroughly inspect various rollers;

　　2) Prevent foreign matters on the roll;

　　3) Select the roll without defect when changing the roll;

　　4) Clean the guide plate to prevent sundries from biting in
 

　　Crease

　　Shapes that appear:

　　There are many cross distributed strip marks on the front and back sides of the thin strip steel, and the pitch is equal to the circumference of the finishing roll at the rear section and the working roll of the whole machine

　　Cause of occurrence:

　　The strip steel is folded into the rear section of the finishing mill and the roller of the finishing mill, leaving a folding mark on the roller surface.

　　Preventive measures:

　　1) Replace the roll;

　　2) Properly adjust the roll profile curve;

　　3) Properly adjust the front and rear tension of the rolling mill.
 

　　Scratch

　　Shapes that appear:

　　1) Irregular and irregular sharp instrument scratch;

　　2) Simultaneous occurrence of both sides;

　　3) Inside of most output coils

　　Cause of occurrence:

　　1) Caused by loose strip steel during uncoiling;

　　2) The lifted strip steel coil slides in the width direction;

　　Preventive measures:

　　1) Good strip shape;

　　2) Give a certain tension when uncoiling;

　　3) Pay attention to hoisting;
 

　　Scratch

　　Shapes that appear:

　　1) Shallow and fine scratches occur continuously or intermittently for one or several days in the rolling direction;

　　2) It is mainly produced on the reverse side, glossy, present and absent.

　　Cause of occurrence:

　　1) Scratches caused by poor rotation of the roller of the conveying roller table;

　　2) Abrasion of fixed protrusions on rolling and finishing lines.

　　Preventive measures:

　　1) Thorough inspection of roller deck rollers;

　　2) Ensure good rolling line channel;

　　3) Remove the fixed protrusions.
 

　　speckle

　　Shapes that appear:

　　1) The surface of the steel plate is irregular and irregular with concave spots;

　　2) There are many such defects in the coil with cracked edges.

　　Cause of occurrence:

　　Iron filings and other sundries with cracked edges are attached to the steel plate during rolling and pressed to form such defects:

　　1) Clean the slab side to prevent edge cracking;

　　2) Do not close the side guide plate too early;

　　3) Clean the rack roller table, etc.

　　Preventive measures:

　　1) Clean the slab side to prevent cracking;

　　2) Do not close the side guide plate too early;

　　3) Clean the rack roller table, etc.