01 overheating and overcooking
Metal in the heating or processing process, due to high temperature, long time, resulting in the organization and grain coarseness of the phenomenon known as overheating; when the metal is heated at a temperature close to the melting temperature or severe overheating, the intergranular local low melting point group element melting or grain boundaries of the phenomenon of weakening known as overcooking.
After overheating the surface appears rough pitting, orange peel, coarse grains and other phenomena. Overheating of the alloy strength is not much decline, but the impact toughness and plasticity at room temperature is greatly reduced. The material becomes brittle, the fracture shows coarse crystalline particles. High-power observation in addition to coarse isometric crystals, or coarse second phase, or coarse Weiss organization. Overheating is not absolute scrap, sometimes can be corrected or downgraded through the re-deformation, reprocessing and other methods to be used.
After overheating surface roughness, grain boundaries coarser, straighter, hairy, and even cracks, there will be easy to melt and oxidation of the film layer; overheating so that the metal bonding is greatly reduced; microstructure of the grain boundaries coarser, melting cavities or eutectic spheres, melting the liquid phase network, and even in the junction of several grains of melting appeared in the irregularities of the cavity and other phenomena; rolled or extruded after the emergence of cracks in the grain boundaries, the side of the plate cracks, the head of the rod Blossom, open mouth crack or cracked into pieces, cracked parts can be seen coarse dendrites and traces of melting.
The main reasons for overheating and overcooking are: high heating temperature, long time or local long time in the high temperature source; heat processing end temperature is too high or in the high temperature zone stay too long; alloy in the existence of low melting point group elements, or low melting point inclusions more.
02 Cracks and cracking
(1) Processing cracks: improper processing technology or process defects can cause processing cracks. Processing cracks can also be divided into two categories of hot and cold cracks, the difference lies in the microstructure around the crack, the former has no obvious changes and the latter has a serious deformation. In terms of morphology, there are longitudinal cracks, transverse cracks, side cracks, open mouth cracks, spiral cracks, periodic transverse cracks, fracture, 45 ° diagonal cracks, as well as irregular cracks and so on. According to the distribution can be divided into local cracks, head cracks, surface cracks, center cracks and intergranular cracks.
The causes of processing cracks should be analyzed from both the metal itself and the processing technology.
Belonging to the metal itself are the following factors: the composition of the alloy and impurity content; ingot there is a cold segregation, scarring and hemodialysis tumors and other surface defects, shrinkage, porosity, porosity, inclusions, segregation, and other internal defects, the processing of easy to produce cracks along the way; the developed columnar crystalline structure of the obvious weak surface of the easy to crack along the grain boundaries or the weak surface; the alloy in the previous process there are cracks, overcooking, overheating, or the second phase of poor distribution, tissue Uneven, as well as phase transition caused by micro-cracks and other defects.
(2) Heat treatment cracks
① When there is a large residual stress within the alloy, such as heating caused by thermal stress and residual stress in the same direction and superimposed over the strength of the metal will cause cracking.
② alloy in the heating process in the second phase along the grain boundary precipitation and the formation of the second type of additional stress, or due to phase change and the occurrence of obvious
03 inclusions
Processed products appear on the surface and inside the matrix with a clear interface, the performance difference between the metal or non-metallic material is called inclusions.
Processing products inclusions mainly from the ingot in the metal particles are not melted, the formation of large primordial crystals or heterogeneous metal into; or metal compounds and silicates, covering agents, and so on.
Its classification and characteristics and casting products inclusions are basically the same. Processing products inclusions are generally granular, long distribution along the processing direction, a certain form and color, interface is obvious, without erosion can be found under the metallurgical microscope.
04 foreign matter indentation
Metal or non-metal pressed into the surface of the product is known as foreign matter indentation.
Metal indentation and the substrate has a clear interface, clear contours, different metal luster, point, block, after peeling off the formation of pits; non-metallic indentation of different forms, different colors, more brittle, no metal luster, point, sheet, strip distribution along the processing direction, not easy to peel.
Sources of foreign matter: oxidized skin formed by heating, lubricant adhering to the surface of molds and products; fragments of molds and adherents; metal chips, burrs and fringes of cracked edges; furnace debris, oil; debris in the emulsion; foreign matter in the rolling channel and guide plate.
05 Bubble
Products after processing or annealing, the surface appears along the processing direction of the distribution of strip or bubble-shaped bulging, cut open for a cavity this bulging is known as bubbling.
Bubbles are mostly strip, smooth surface, along the processing direction of the elongated, cut open after the inner wall was bright metal color, individual with oxides or other inclusions. Most of the bubble is symmetrically distributed on both sides, in the thinner plate and strip or thin-walled tube is more obvious. The main reasons for the bubble are: the existence of ingot porosity, shrinkage holes and other defects; billet annealing, the furnace atmosphere is not properly controlled, the furnace temperature is too high; tube and bar extrusion ingot and extrusion cylinder, extrusion pads with poor or extrusion cylinder, piercing needle lubrication is excessive, the extrusion cylinder cleanup is not clean, piercing needle cracked and so on.
06 Lamination
The thickness of the product appears in the direction of the gap, corresponding to the processing direction of the separation into layers.
Between the layer and the layer of the bonding integration level, the area is larger, some have oxide or central impurity, often appear in the thin strip or thin strip after welding to show. Pipe bar material fracture inspection will also appear fracture delamination phenomenon.
The main reasons for delamination are: clank mirror in the air holes, shrinkage, shrinkage, central impurities, such as the continuation of the trap, the formation of delamination after processing; plate and strip hot rolling channel under the amount of improper distribution, under the amount of pressure is too large; special mirror heating is not uniform, the heating temperature is too high or too low; tube and bar extrusion of Jane or piercing needle lubrication is too much, piercing the needle has a crack or extruded products shrinkage tail is not cut the sea, after further stretching, rolling to form a delamination.
07 Corrosion
Product surface and the surrounding medium contact, chemical or electrochemical reaction, the formation of product film on the surface of the process is called corrosion.
After corrosion, the surface loses its metallic luster, forming corrosion stains of different colours.
The reasons for the formation of corrosion are: the product surface is not clean, residual water, emulsion and other residual liquid, or placed in the storage is not appropriate, the climate is humid or water droplets invade the surface; the environment has a corrosive atmosphere.
08 Oxidatio
Product surface west of the local rupture turned up called super skin. Products appear on the surface of the west needle tip-like metal filament warping is known as the starting system.
Super skin or up generally along the rolling direction is continuous or intermittent distribution, super skin parts often have oxide skin or other things, central impurities. Pipe and bar super skin is generally formed along the processing direction of tongue, fish Jiang-like warping, serious throughout the product, the local serious formation of knots and sores. Thorny more in the rolled products in the post-process.
The main reasons for super skin: clank shovel has a smile trap, the surface is not flat; processing temperature is too high to the products of the surface of the West oxidation or the previous process led to the surface of the West have performance traps; emulsion on the silver, extrusion Jane, perforation needle on the water, oil and other filth; processing tools have the town of traps, mechanical damage during processing.
The main reasons for the production of the system are: roll cracks; billet edge is not flat, there are irregular depressions and so on.
09 wrinkles
Product surface is not flat, a slight corrugated depression and raised called wrinkles.
Wrinkles are generally consistent with the rolling direction or diagonal distribution, a single or multiple bulges, feel more rounded, the area is larger. The main reasons for wrinkles are: uneven rolling, or one-way bending straightness; uneven tension (tension roll or tension sleeve uneven); pipe billet plasticity, eccentricity is serious; thick-walled pipe deformation is not uniform, or deformation is too large; poor roll adjustment and other process defects.
10 pitted surface
Products show a tiny point-like depression uneven rough surface known as pitting. Pockets of local or continuous distribution, individually known as pockmarks, seriously known as pockmarks. Coarse grain caused by pitting is commonly known as orange peel. The main reasons for pitting are: annealing temperature is too high, too long, coarse grain; over pickling; processing rate is too small, the surface is not smooth; roll surface hardness is not uniform, wear and tear is serious, rolling tool corrosion, oxidation or foreign metal.
11 mechanical damage
External force on the surface of the product or sheet and foil layers and layers of misalignment, caused by the surface of the strips, bundles, craters, sharp grooves and other shapes of the scar, common abrasions, scratches, bruises and pressure wounds.
13 Uneven composition, uneven organisation
Products after rolling or annealing, different parts of the chemical composition of the phenomenon of large differences is called uneven composition. Uneven composition can cause differences in colour or deformation characteristics, macro-inspection can be seen in the composition of segregation or segregation area, microstructure and performance differences, and even cracking.
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