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The effect of defects in hot strip rolling on pickling

Description: This paper main writes what factors affect pickling in steel hot rolling.

Title: The effect of defects in hot strip rolling on pickling

Keyword:hot strip rolling, hot rolling, pickling, Hot Rolled Coil

Related Productrolling mill rolls

  1. The influence of hot rolling width deviation

The width deviation of hot rolled strip refers to the deviation from the nominal width within the full length of the strip. In actual production, the strip width is often narrow in the middle and wide at both ends. The effects are as follows:

  • The cutting edge is too wide, it is not easy to be cut after cutting into the broken edge
  • When the strip width is too narrow, the cutting edge is too narrow, and when the center of the strip is deviated, there may be an empty cut through the disc, resulting in an empty cut narrow rule.

 

  1. The influence of hot rolling thickness deviation

Due to the uneven temperature and tension fluctuation of the rolled piece during the rolling process, the head is usually 0.15 to 0.20 mm thicker than the tail. Either one side is thick and the other is thin, or one section is thick and the other section is thin. The main influence on cold rolling and pickling is: it causes difficulties in the welding of parallel coils.

 

  1. Surface inclusions and iron oxide scale pressing

The iron oxide scale is pressed in. It is easy to find from the outside. Most of the inclusions and iron scale pressing are difficult to remove by pickling; slight inclusions and iron scale pressing, even if they can be acid washed away, will cause other parts If the surface of the board is pickled, individual cases will leave pit marks on the board surface. After cold rolling, the pit marks will expand and cause waste.

 

  1. Too long tongue plate

Long tongues mostly appear at the tail of hot-rolled steel strips. It is caused by the fact that the tails of the strips lose control during the rolling process and allow them to extend freely. Steel coils with long tongues are not conducive to uncoiling, and often require multiple repetitions to disassemble. At the same time, due to the increase in the amount of cutting head, the metal yield rate is reduced.

 

  1. Sickle and S bend

The sickle bend and the S bend refer to the sickle and S-shaped changes of the strip centerline along the length of the strip. The main impacts are:

Raw materials with sickle bends and S bends will inevitably cause the strip to deviate when rolling in the continuous mill and in the cold rolling mill, and in severe cases, it will cause the strip to break. At the same time, when they are cut on the disc cutter, they often cannot guarantee the uniformity and value of the band edge.

 

  1. The effect of iron oxide scale on pickling

Generally, the iron oxide scale of common carbon steel will form three layers at 575 ℃: the outermost layer is Fe2O3 about 2%, the middle layer is about 18% Fe3O4, and the inner layer is Feo+Fe3O4 (enriched body) 80% of which mainly FeO , The most suitable pickling condition is when the oxide scale contains the largest amount of richenite, and there is no Fe2O3. For hot-rolled plates, when the final rolling temperature is relatively low (about 850°C), this condition can ensure that the thinnest iron oxide layer is obtained, and the risk of Fe2O3 is the least. (The iron oxide scale has a great relationship with the winding temperature. Generally, medium and low temperature winding are required)

 

  1. The influence of chemical composition

In addition to iron atoms, steel also contains atoms of other elements. Some of these elements will make the iron oxide scale very loose (such as magnesium, calcium, etc.), and the acid solution can easily penetrate into the iron oxide scale and contact the richite iron oxide or matrix iron. Therefore, pickling becomes easier, and some elements will make the iron oxide scale more dense, making pickling more difficult, and may even be completely unsuitable for ordinary pickling.

For example, the oxide scale of silicon steel contains SiO2, which is an oxide that is difficult to dissolve in sulfuric acid solution, and often a thin oxide film remains on the surface of the strip after pickling. In particular, it should be pointed out that aluminum-containing steel, although the generated iron oxide scale is relatively dense, but because the generated aluminum oxide can be dissolved in acid, aluminum-containing steel is still relatively easy to pickle.

  1. Factors Affecting Iron Scale on the Surface of Hot Rolled Coil

Larger rolling temperature

Smooth roll

Low finishing temperature

Low coiling temperature

Higher cooling rate

 

Are all conducive to the pickling of hot rolled coils

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