Summary of 12 common defects of cold-rolled stainless steel plate
Surface inclusions Defect characteristics: The surface of stainless steel cold-rolled plate presents point-like, block-like or line-like non-metallic inclusions, which are intermittently or continuously distributed along the rolling direction, and its color is reddish-brown, dark gray or white. In severe cases, stainless steel cold-rolled plates will have holes, cracks, and broken belts. Causes: 1) Poor slag making during steelmaking, high viscosity of molten steel, poor fluidity, slag can not float, and there are many non-metallic inclusions in steel. 2) The casting temperature is low, the boiling is poor, and the inclusions are not floating. 3) During continuous casting, the protective slag belt is mixed into the steel. 4) The non-metallic materials in the molten steel tank, ingot mold or injection pipe are not cleaned.
Scarring
Defect characteristics:
Irregular tongue-like, fish-scale black spots appear on the surface of the stainless steel cold-rolled plate, the distribution area is unequal, and the depth of the pressure is uneven. This kind of iron sheet is difficult to wash off in the pickling process, and when the iron sheet falls off, a pit is formed.
Causes:
1) In terms of steelmaking, the inner wall of the ingot mold is not cleaned, and the mold wall falls off the meat. When injecting, the steel rot splashes, sticks to the mold wall, oxidation, the casting temperature is low, sometimes interrupts the injection flow, and when the steel injection continues, the ingot is formed, and the protective slag is added to the inappropriate, resulting in the splashing of molten steel.
2) In terms of steel rolling, the residual scars on the surface of the slab are not cleared, and they are left on the stainless steel cold-rolled plate after rolling.
Press into the iron oxide scale
Defect characteristics:
Defects are punctate, strip-like, or fish-scale black spots, distributed in different sizes, and oppressed by uneven depths. This kind of iron sheet is difficult to wash off in the pickling process, and when the iron sheet falls off, a pit is formed.
Causes:
1) The heating temperature of the slab is too high, the time is too long, and there is a strong oxidizing atmosphere in the furnace, and the furnace is pressed in when the iron oxide scale is rolled.
2) The high-pressure water pressure is insufficient, and the iron oxide scale is not cleaned before continuous rolling.
3) The high-pressure water nozzle is blocked, and the local iron oxide scale is not removed.
4) The number of open groups of the scale collection pipeline is insufficient, and the scale removal is not clean.
Under-pickling
Defect characteristics:
When the upper and lower surfaces of the stainless steel cold-rolled plate are serious, the entire plate surface is strip-like, black-gray streaks, and dull.
Causes:
1) The temperature and cooling rate of each part of the stainless steel cold-rolled plate are different, that is, the temperature and cooling rate of the head, middle and tail along the length of the stainless steel cold-rolled plate and the edge and middle along the width are different, so that the iron sheet structure and thickness of each part of the stainless steel cold-rolled plate are different, generally speaking, the head and middle of the stainless steel cold-rolled plate are 30-50 °C higher than the tail temperature, therefore, the head iron sheet is thicker, and the tail iron sheet is thinner, therefore, in the case of the same pickling speed, it is easy to produce local unwashed.
2) The pickling process is inappropriate, such as the concentration and temperature of pickling are low, the pickling speed is too fast, the pickling time is insufficient, or the ferrous concentration is high and the acid is not replenished in time.
3) The tensile coefficient of the stretch descaler is not enough, so that the iron sheet is not fully broken and peeled, which affects the pickling effect.
4) Poor shape of stainless steel cold-rolled sheet, such as sickle moon bend, wave shape, etc., makes the mechanical descaling effect poor, and it is easy to cause local under-pickling.
Bond marks
Defect characteristics:
The annealed steel coil layers are bonded together with each other, which is called bonding, and the point-like arc crease is produced after flattening, and the point bonding is presented in rows of arc-like creases along the rolling direction, and the surface bonding is severe, and the flat uncoiling is torn or holes appear to become waste coils.
Causes:
1) The tension of the rolling coil is too large or the tension fluctuates, and the plate shape is not good, resulting in bulge and bonding at the part where the pressure between the layers becomes large.
2) The surface roughness is too small.
3) The steel is too soft, and the amount of carbon and silicon is small.
4) The temperature of the heat treatment furnace is too high or the annealing and cooling rate is too fast.
5) The steel coil is injured by collision before loading the furnace.
Oxidized color
Defect characteristics:
The surface of the stainless steel cold-rolled plate is oxidized, and its color gradually transitions from dark blue on the edge to light blue, brown and light yellow, which is collectively referred to as oxidized color.
Causes:
1) When annealing, the protective cover is not tightly sealed or leaks, resulting in oxidation of stainless steel cold-rolled coils.
2) The annealing process of bell furnace is discharged at high temperature (the temperature of the steel coil is 110 °C), which leads to the oxidation of the stainless steel cold-rolled coil.
3) The dew point of the shielding gas is too high or the hydrogen content is too low, the blowing time before heating is insufficient, there is residual oxygen in the furnace, and the stainless steel cold-rolled coil is annealed in an oxidizing atmosphere.
Emulsion spots
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Defect characteristics:
The surface of the annealed stainless steel cold-rolled sheet presents an irregular or island-like black, brown pattern.
Causes:
1) The emulsion at the outlet of the rolling mill is not exhausted, and it is carbonized when heated, forming spots.
2) The pressure of the hair dryer at the outlet of the end frame is small, and the blowing is not clean.
3) The fan is not turned on when the belt is worn, and the fan is turned off when the tail is flicked.
4) After the furnace is installed, the blowing time is insufficient, and the emulsion carbonizes to form spots when heated.
Scratches
Defect characteristics:
The surface of the stainless steel cold-rolled plate presents straight and thin grooves of different depths. Parallel to the rolling direction, continuous or intermittent, sparse and inconsistent, no certain regularity, the scratch before leveling is smoother, the color of the groove is gray-black, scratched after smoothing, there are burrs, and it is metallic bright color.
Causes:
1) The parts of pickling, rolling, leveling and finishing units in contact with the stainless steel cold-rolled plate have sharp edges and corners or hard objects, resulting in relative motion.
2) The various rollers of the finishing line (pinch rollers, compression rollers, guide plates, etc.) do not run and cause scratches. 3) When uncoiling or coiling, the speed of stainless steel cold-rolled plate changes or the relative movement between layers.
Wrinkle
Defect characteristics:
The surface of the stainless steel cold-rolled plate presents uneven wrinkles, which mostly occur in stainless steel cold-rolled plates less than 0.8mm, and the wrinkle edges are at a certain angle, and the serious wrinkles are folded into pressed folds.
Causes:
1) The stainless steel cold-rolled plate deviates, stretches on one side, and wrinkles on the other side.
2) The plate shape is poor, there are large side waves or middle waves, and when the stainless steel cold-rolled plate passes through the leveling machine, straightening machine or pinch roller, there are wrinkles at the wave shape.
3) Improper adjustment of the straightening machine and uneven deformation.
Roll printing
Defect characteristics:
Periodic pits or convex huddles appear on the surface of the stainless steel cold-rolled plate, and severe roll marks lead to the rolling through of the stainless steel plate.
Causes:
1) The weld of the stainless steel cold-rolled plate is too high or unevenly cleaned, which causes sticking rolls during continuous rolling.
2) There are hard metal objects (welding beads, metal shavings, etc.) or dirt stuck on the roller, and when rolling or flattening, the hard objects or dirt are pressed on the surface of the stainless steel cold-rolled plate, leaving indentations.
3) Peel off the meat from the work roll.
Embossing
Defect characteristics:
The pits of a certain depth on the surface of the stainless steel cold-rolled plate are imprinted, periodic, somewhat different, and the color of the defects is brighter.
Causes:
1) In the production process, a variety of auxiliary rollers (tension rollers, compression rollers, clamping rollers, straightening rollers, etc.) are glued to iron filings and dirt.
2) Iron filings and foreign objects fall into the stainless steel cold-rolled sheet stack.
Tower-shaped
Defect characteristics:
The shape defects of the steel coil are higher (or lower) than the other circle on the end face of the stainless steel cold-rolled coil, continuous, shaped like a pagoda, and mostly appear in the inner (outer) ring part of the stainless steel cold-rolled coil.
Causes:
1) The centering device of the coiler is out of order, and the strip is misaligned.
2) Stainless steel cold-rolled coil is not straight, such as Kamakul bending, narrowing, etc.
3) The plate shape is poor, and there are large side waves, which makes the stainless steel cold-rolled coil exceed the control limit of the photocell.
4) The operation is not properly adjusted, the shrinkage of the reel is small, and the pusher pushes out the stainless steel coil. The inner ring is pulled out.