Steel rolling refers to the pressure processing process of changing the shape of ingot and billet between rotating rollers, which can be divided into hot rolling and cold rolling. Hot rolling needs to heat the raw material billet to 1100~1250 ℃, and implement high temperature rolling processing production. Hot rolling strip is a typical production process of hot rolling.

At present, the hot rolled strip control technology is mature, the instrument configuration is advanced, the product quality is relatively stable, and the production line operation rate is high. However, because the rolling process is complex, the operation of each process and the state of the equipment will affect the quality of the product, resulting in the defect of the product.

Production process of hot rolled strip steel

Hot-rolled strip production process

Common defects of strip steel

I. Press-in scale

Press-in scale

1. Characteristics of defects

A kind of surface defect formed by scale pressed into the surface of steel strip during hot rolling is called press-in scale. According to the different causes, it can be divided into furnace (primary) scale, (secondary) scale generated in the rolling process or (secondary) scale formed by roll oxide film falling off and pressed into the surface of strip steel.


①There are serious longitudinal cracks on the surface of billet;

②Improper heating process or heating operation of billet makes it difficult to remove the iron sheet in furnace;

③The low pressure of the high pressure descaling water and the blockage of the nozzle cause the scale pressed into the surface of the strip during the rolling process;

④The fast rolling rhythm and poor cooling of the roll cause the oxide film on the roll surface to fall off and press into the surface of the strip.


Affect the surface quality and coating effect of steel strip.

4.Prevention and elimination methods

①Strengthen billet quality acceptance, slabs with serious longitudinal cracks on the surface should be used after clearing qualified;

②Formulate the billet heating process reasonably and heat the slab according to the requirements of the regulations;

③Check the high pressure descaling water system equipment regularly to ensure the descaling water pressure and avoid nozzle blockage;

④Reasonable control of rolling rhythm, ensure roller cooling effect, prevent roller surface oxide film off.

II. Rolling skin

Rolling skin

1.Defect characteristics

Attached to the surface of the steel strip, the irregularly warped metal sheet is called scar, showing leaf, feather, strip, fish scale, tongue end and so on. Scar is divided into two kinds, one is connected with the body of steel, and converted to the plate is not easy to fall off; The other is not connected with the body of the steel, but glued to the plate, easy to fall off, after falling off to form a smoother pit.


①The original defects such as scar and heavy skin on the slab surface are not cleaned up and remain on the surface of the steel strip after rolling;

②The residue after flame cleaning is left on the slab surface, which is rolled and pressed into the surface of the steel strip.


Resulting in metal stripping or holes in the process of post-processing.

4.Prevention and elimination methods

Strengthen slab quality acceptance, it is found that there are scars on the slab surface and the residue should be cleaned up after flame cleaning.

III. Bubble


1. Characteristics of defects

The irregularly distributed circular or elliptic convex hull defects on the surface of steel strip are called bubbles. Its outer edge is smooth, and after the bubble is rolled, the surface of the steel strip is cracked or peeled. Some bubbles are not raised, after leveling, the surface is bright, and the shear section is stratified.


①Due to poor deoxidation and improper nitrogen blowing, too much gas is gathered inside the slab;

②Slab in the furnace for a long time, subcutaneous bubble exposure, aggregation.


It may lead to stratification or poor welding in the process of post-processing and use.

4.Prevention and elimination methods

①Strengthen slab quality acceptance and do not use slabs with exposed bubble defects;

②Heat the slab strictly according to the regulations to avoid the slab in the furnace for too long.

IV. Broken


1. Characteristics of defects

The surface of the strip is overlapped or rolled through, torn and so on.


①Improper adjustment of roll gap or poor fit between roll profile and incoming plate profile, uneven strip extension;

②Uneven slab local heating temperature or rolling temperature;

③The opening of the finished rolling side guide plate is not reasonable;

④Second flow mismatch during finishing rolling.


The rolling process is interrupted, and the steel plate with rolling defects cannot be used.

4.Prevention and elimination methods

①Reasonable configuration of roll shape, pay attention to roll gap adjustment;

②Strengthen slab heating temperature control to ensure uniform rolling temperature;

③Set the opening degree of the finished rolling side guide plate reasonably;

④Maintain consistent flow per second during continuous rolling.

V. Roll marks

Roll marks

1. Characteristics of defects

The surface of the steel strip is periodic distribution, the appearance of irregular convex and concave defects called roll printing.


The roll cracking, partial broken, or foreign body on the surface, so that the local roll surface is concave, convex, rolling or finishing processing, pressure into the surface of the steel belt to form convex and concave defects.


Convex roll printing may lead to folding defects in the post-sequence rolling process. Concave roll printing may lead to holes in the subsequent rolling process.

4.Prevention and elimination methods

①Check the surface quality of the roll regularly, and deal with it in time when the roll is broken or sticks foreign bodies;

②Check the roller surface quality in time to prevent roller surface damage or foreign body adhesion when abnormal conditions such as stuck steel, tail swing and rolling rot occur in the rolling process;

③When the roller mesh is found, stop the machine immediately to check the surface quality of the roller.

VI. Flat coil

Flat coil

1. Characteristics of defects

The phenomenon that the steel coil is oval is called flat coil.


①Steel coil in the process of handling, bear too much impact;

②Steel coil tension is low, horizontal coil stacking or multilayer stacking steel coil.


Affect the packaging and handling of steel coils, serious flat coils can not be used unwinding.

4.Prevention and elimination methods

①Careful handling of steel coils;

②Set the winding tension reasonably, control the layer number of horizontal stacking, if necessary, use vertical stacking.

Rolling Equipment Supplier - Yushun

Wuxi Yushun Metallurgical Technology Co., Ltd. has a professional team composed of experienced engineers and technicians from design institutes and iron and steel enterprises, specializing in customizing high, medium and low configuration production lines or stand-alone equipment. Welcome new customers to come to consult us!