Test method for quality of precision castings
Macroscopical tissue examination is a kind of examination in which low power tissue characteristics of the forged tissue are observed by visual inspection or low power magnification. The commonly used methods for inspecting the macrostructure of precision castings include low-power corrosion method, including thermal corrosion method, cold corrosion method and electrolytic corrosion method, fracture test method and sulfur printing method.
Fracture test method is used to check the defects of structural steel and stainless steel, such as white spots, laminations and internal cracks, check the graphite and carbon of spring steel forgings and the overheating and overfiring of the above steel types, and for aluminum, magnesium, copper and other alloys, it is used to check whether the grain is fine and uniform, whether there is oxide film, oxide inclusion and other defects. In addition to structural steel, stainless steel forgings for low power inspection test pieces are not heat treated, the rest of the material forgings are generally heat treated before low power inspection.
The microscopic structure inspection rule is to use the light microscope to examine the microscopic structure of various material grades of forgings. The items examined generally have the essential grain size, or the grain size at a specified temperature, that is, the actual grain size, non-metallic inclusions, microstructure such as decarbonization layer, eutectic carbide inhomogeneity, overheating, overburning microstructure and other required microstructure.