The heating of the ingot is not uniform, the heating temperature is too high or too low, the tube and bar extrusion tube or piercing needle is too smooth, the piercing needle is cracked or the extruded product is not cut clean, and delamination is formed after further stretching and rolling.
The surface of the product is in contact with the surrounding medium, chemical or electrochemical reaction takes place, and the process of forming a product film on the surface is called corrosion.
After corrosion, the surface loses its metallic luster and forms corrosion spots of different colors.
The causes of corrosion are: the surface of the product is not clean, there are residual liquid such as water and emulsion, or improper storage, wet climate or water droplets invade the surface; there is a corrosive atmosphere in the environment.
At higher temperatures, products come into contact with oxygen to form oxides called oxidation.
After oxidation, it shows different oxidation color, loses metal luster, and serious oxide scale appears.
The main causes of oxidation are: oxidizing atmosphere in annealing furnace, natural oxidation of surface due to high annealing temperature or long exposure time in air, and high residual temperature of rolled piece, oxidation is formed after coiling or stacking.
The local rupture on the surface of the product is called peeling. The appearance of a needle-like metal filament on the surface of the product is called prickling.
Peeling or prickling is generally distributed continuously or intermittently along the rolling direction, and there are often oxide scale or other dirt, inclusions and so on. The peeling of tube and bar generally forms tongue-like and fish-scale-like warping along the processing direction, which seriously runs through the whole product, and local serious scarring is formed. Prickling often occurs in the last process of rolled products.
The main reasons for peeling are: defects in ingots and uneven surface; surface defects caused by oxidation or previous process caused by high processing temperature; dirt such as water and oil on rolls, extruding cylinders and piercing needles; defects in processing tools and mechanical damage in the machining process.
The main causes of prickling are: roll cracking, uneven edge of billet, irregular depression and so on.
The surface of the product is uneven, with light microwave depressions and protuberances called wrinkling.
Wrinkling is generally consistent with the rolling direction or oblique distribution, showing a single or more uplift, feel more smooth, larger area.
The main causes of wrinkling are: uneven rolling piece, or poor unidirectional bending flatness; uneven tension (uneven tension roll or tension sleeve); poor plasticity and serious eccentricity of tube billet; uneven or excessive deformation of thick-walled tube; poor roll adjustment and other process defects.
The rough surface with tiny point-like depression and uneven surface is called hemp surface.
Hemp noodles are distributed locally or continuously, individual ones are called pockmarks, and serious ones are called pockmarks. The hemp caused by coarse grains is commonly known as orange peel.
The main causes of hemp surface are: too high annealing temperature, too long time, coarse grains; over pickling; too small processing rate, non-smooth surface; uneven roll surface hardness, serious wear, rolling tool corrosion, oxide scale or foreign metal.
The external force acts on the surface of the product or the dislocation between the plate and foil layers, resulting in strips, bundles, pits, sharp grooves and other shapes of scars, such as scratches, scratches, bruises and bruises.
The phenomenon that there are great differences in chemical composition in different parts of the product after rolling or annealing is called uneven composition. Uneven composition can cause differences in color or deformation characteristics, macroscopic examination can see the composition segregation point or segregation area, microstructure and properties are different, and even cracking.