The inspection of the surface quality of forgings is generally a non-destructive inspection. It is usually inspected with the naked eye or a low magnification magnifying glass, and the technique of nondestructive testing is also accepted when necessary. In the quality inspection, because of the requirements of the inspection content, some must accept the destructive test, that is, the anatomical experiments usually mentioned, such as low-power test, fracture test, high-structural test, chemical composition description and mechanical property test. Etc. Some can also accept non-destructive testing techniques, and in order to more accurately assess the quality of forgings, destructive experimental techniques and non-destructive testing techniques should be linked together for application. In order to explain the quality problems of forgings from the deep grades, the mechanism research is to be assisted by transmission or scanning electron microscopes, electron probes, and the like.
The quality inspection techniques in forgings can be summarized as follows: macroscopic structural test method, microstructural test method, mechanical property test, chemical composition description method and nondestructive test method.
The macroscopic structural test is a test that accepts a visual or low magnification magnifying glass (normal multiples below 30×) to investigate the low-fold structural characteristics of the forging. Common techniques for the macroscopic structural inspection of forgings are low-penetration methods (including thermal erosion, cold erosion and electrolytic erosion), fracture experiments and sulfur printing.
The low-frequency erosion method is used to search for cracks, folds, shrinkage holes, pore segregation, white spots, looseness, and forgings of materials such as steel, stainless steel, high-temperature alloy, aluminum and aluminum alloy, magnesium and magnesium alloy, copper alloy, and titanium alloy. Non-metal assimilation, segregation and convergence, distribution patterns of streamlines, grain size and distribution, etc. Only for differential materials, the difference in specifications of the etchant and etch received during the low-fold construction is shown.
The fracture test method is used to check the defects such as white spots, layered and internal cracks of the layout steel and stainless steel (excluding the austenitic type), the graphite carbon of the spring steel forgings, and the overheating and overheating of the above steel grades. For aluminum, magnesium, copper and other alloys used to check whether the crystal grains are finely symmetrical, whether there are defects such as oxide film and oxide assimilation.
The sulphur printing method is mainly used for large forgings of some layout steels, to check whether the distribution of sulfur is symmetrical and the sulfur content is a few.
Except for layout steel and stainless steel forgings, the test pieces for low-level inspection are not subjected to the final heat treatment, and the forgings of the other materials are generally subjected to the final heat treatment before the low-power test.
The section specimens are generally subjected to delineated heat treatment.
The microstructural test rule is to use an optical microscope to search the microstructure of various trademark forgings. The name of the inspection is generally of a quality grain size, or the grain size at the delineated temperature, that is, the actual grain size, the non-metal assimilates, the microstructure such as the decarburization layer, the eutectic carbide unevenness, Overheated, overfired structures and other required microstructures.
The test of mechanical properties and process performance is to apply the tensile test machine, the impact test machine, the forever test machine, the euphemism test machine, the hardness tester, etc. to the forged piece and the test piece which have been demarcated for the final heat treatment. The instrument is used to determine the mechanical properties and process performance values.
The chemical composition test is generally to accept the chemical description method or the spectral description method to explain and test the composition of the forging part. With the development of science and technology, both the chemical explanation and the spectrogram indicate the means of explanation. For the spectroscopic method, the spectroscopic and spectroscopic methods are not simply accepted for composition description. The emerging optoelectronic spectrometer not only shows that the rate is fast, but also the accuracy is greatly improved, and the appearance of the plasma photoelectric spectrometer is more The accuracy of the description has been greatly improved, and the accuracy of the description is up to 10-6. This is an effective technique for explaining the short and long-term harmful impurities such as Pb, As, Sn, Sb, Bi, etc. in the high-temperature alloy forgings.
The techniques mentioned above, whether it is macroscopic structural test, or microstructural test or performance and composition determination, are destructive experimental techniques. For some nervous, large forgings, the destructive skills are not complete. Adapting to the requirements of quality inspection, this aspect is because it is too uneconomical, and on the other hand, it is mainly to avoid the one-sidedness of destructive inspection. The development of non-destructive testing technology provides a better and more satisfactory means for forging quality inspection.
The non-destructive testing techniques accepted for the quality inspection of forgings are: magnetic particle test, penetration test, eddy current test, ultrasonic test, etc.
Magnetic particle inspection is widely used to detect defects on the surface or near surface of ferromagnetic metal or alloy forgings, such as cracks, hair lines, white spots, non-metal assimilation, delamination, folding, carbide or ferrite bands.
This technique is only suitable for the inspection of ferromagnetic material forgings, and forgings made of austenitic steel are not suitable for this technique.
In addition to the inspection of magnetic material forgings, the penetrant inspection method can also detect the surface defects of non-ferromagnetic material forgings, such as cracks, looseness, folding, etc., which are generally only used to check the surface defects of non-ferromagnetic forgings. The disadvantages hidden below the surface.
Eddy current testing is used to check for defects in the surface or near surface of conductive materials.