Forging manufacturer: post-forging heat treatment of forgings
Forging Manufacturer: Forgings are usually forgings that need to be produced with a hydraulic press of 1000 tons or more. Most of them are the main basic parts of various large key equipment needed for national economy and national defense construction. For example: generator rotors of large steam turbines, working and supporting rolls of large rolling mills, barrels and heads of large high-pressure vessels, spindles, tail shafts and rudder stems of large ships, large artillery pieces, etc. These forgings are forged directly from ingots. Therefore, heat treatment should consider the impact of melting, casting and forging processes on the internal quality of forgings. The main influencing factors are.
1) Uneven chemical composition and various metallurgical defects.
2) These particles are rough and very heterogeneous.
3) More gases and inclusions.
4)High forging stresses and heat treatment stresses.
Forging mills: In general, the larger the size and weight of the forgings and the higher the alloy content of the steel, the more serious these problems will be. Large forgings usually require several heat treatments during the production process. Heat treatment immediately after forging is called post-forging heat treatment or pretreatment; heat treatment after cutting is called heat treatment.
Large forgings after forging heat treatment is to prevent white spots and hydrogen embrittlement, improve the internal organization of forgings, eliminate forging stress, reduce hardness, improve the machinability of forgings, refine grain, improve the ultrasonic flaw detection performance of forgings, so that forgings to obtain good mechanical properties or for the subsequent heat treatment process to prepare good organizational conditions. For the forgings no longer heat treatment, the need to ensure that the forgings through post-forging heat treatment to achieve the organization and performance of the technical conditions.
Forging manufacturer: large forgings in the white spot and hydrogen embrittlement is the internal cracking of steel. Round or oval silver-white spots appear on the longitudinal fracture of the forging with clear edges; on a low magnification of the transverse specimen, there is a tiny, fine line of cracks, a few millimetres long or tens of millimetres long. Under scanning electron microscopy, the microscopic morphology of the white spot is that of a crystal-piercing quasi-dissolution consisting of tearing ribs and dissociation surfaces.
Forging manufacturer: the appearance of white spots will lead to a sharp decline in the lateral properties of forgings (mainly plasticity and toughness), becoming a dangerous source of fracture and seriously reducing the performance and service life of the workpiece. Therefore, once white spots are found, forgings should be scrapped or forged into smaller forgings.
White spots are produced by the combined action of hydrogen and stress in the steel. The white spot formation temperature is about 200 to 50°C and basically does not change with the chemical composition of the steel. The formation of white spots requires a gestation period in order to create sufficient hydrogen deviation and metal embrittlement in the steel. Nucleation occurs at white grain boundaries, sub-grain boundaries, inclusions surfaces and other crystal defects.
Forging mills: In order to prevent the formation of white spots, the residual hydrogen in the steel should be limited to below the limiting hydrogen content for no white spots. The limiting hydrogen content of steel without white spots is controlled by the sensitivity to white spots and is related to the chemical composition of the steel, microstructure and other factors. Alloying elements such as nickel, manganese and nickel-chromium increase the white spot susceptibility of the steel. Zirconium, niobium, molybdenum, tungsten, vanadium, titanium, chromium and cerium reduce the white spot sensitivity of steel. Among the various tissues, the order of white spot sensitivity from highest to lowest is pearlite, bainite and martensite. Mixed tissues are more susceptible to white spotting than single tissues. Grain refinement, refinement and exfoliation of carbonaceous materials and increased dislocation density can increase the hydrogen trapping effect of structural defects and reduce the white spot sensitivity of steels.
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