The surface is spotted, smeared, or watery.
Poor alkali washing.
Bonding mark
The annealed steel coils are bonded together to each other, which is called bonding. After the flattening, the point-like circular arc creases are point-stick; the arc-shaped creases appearing in the rolling direction are strip-shaped bonds; serious surface bonding, The flat unwinding is torn or voids become a waste roll.
1 Rolling steel take-up tension is too large or the tension is fluctuating, the shape of the plate is not good, causing bulging, and bonding occurs at a large pressure between layers;
2 strip steel surface roughness is too small;
3 steel is too soft, less carbon and silicon content;
4 The heat treatment furnace temperature is too high or the annealing cooling rate is too fast; the steel coil is collided and injured before loading the furnace.
Oxidized color
The surface is oxidized and its color gradually transitions from dark blue in the sides to light blue, brown, and pale yellow, collectively referred to as oxidized color.
1 When the annealing cover is not tightly sealed or leaks, the steel coil is oxidized;
2 cover furnace annealing process, high temperature furnace (roller temperature is greater than 110 ° C), resulting in steel coil oxidation;
3 The protective gas dew point is too high or the hydrogen content is too low. The pre-washing time is insufficient before heating, residual oxygen exists in the furnace, and the steel coil is annealed in an oxidizing atmosphere.
Thermal burn
The band is not bright.
The surface of the steel strip is caused by the oil film rupturing and the steel strip is in direct contact with the work roll.
Emulsion spot
The annealed steel sheet surface exhibits an irregular or island-like black, brown pattern.
1 The emulsion is not exhausted at the exit of the rolling mill, and carbonized upon heating to form spots;
2 The end of the rack outlet hair dryer pressure is small, blowing is not clean;
3 When the belt is worn, the fan is not open, and the fan is closed when the tail is closed;
4 After the furnace is installed, the pre-purging time is insufficient, and the emulsion is carbonized to form spots when heated.
Scratch
The surface presents a straight, thin, shallow groove. Parallel to the rolling direction, continuous or intermittent, different density, no regularity, smoother before smoothing, the color of the groove is grayish black, scratched after leveling, burr, metallic bright color.
1 pickling, rolling, leveling, finishing parts of the unit in contact with the strip have sharp edges or hard objects, resulting in relative motion;
2The various rollers (pinch roller, pinch roller, guide plate) of the finishing line are not operated to cause scratches;
3 When the coil is unwound or coiled, the strip speed changes or the relative movement between the layers.
Wrinkle
The surface presents uneven wrinkles, which occur mostly in a sheet of less than 0.8 mm. The edges of the wrinkles are at an angle and are severely creased into pleats.
| Proof strength Rp0.2 (MPa) | Tensile strength Rm (MPa) | Impact energy KV (J) | Elongation at fracture A(%) | Reduction in cross section on fracture Z(%) | As-Heat-Treated Condition | Brinell hardness (HBW) |
|---|---|---|---|---|---|---|
| 882 (≥) | 192 (≥) | 13 | 12 | 21 | Solution and Aging, Annealing, Ausaging, Q+T,etc | 121 |
carbon and silicon cold steel plate is the interlayer inside the substrate. This defect does not necessarily appear on the surface, and it often appears as single-sided or double-sided bubbling.
The bubbles are not welded or poorly welded during hot rolling.
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