1. chemical composition examination
General forgings do not carry out chemical composition inspection. Chemical composition is based on sampling analysis before smelting. But for important or suspicious forgings, some chips can be cut from the forgings, and chemical composition can be checked by chemical analysis or spectroscopic analysis.
2. size and shape check
(1) the visual inspection of the appearance is a common method of inspection between the processes. By observing the defects of the surface of the forgings, there are folds, cracks, bruising, scars, and surface burning. Defects hidden on the surface of the forgings are often observed after heat treatment and cleaning.
(2) size measurement includes: long, wide and high dimensions; parallelism and perpendicularity of the plane; the curvature of the axis; the ellipticity of the inner and outer circles; the radius of the circle; the concentricity; the angle and the error displacement. The inspection of forging size is regular. The tools used for measurement are divided into general-purpose and special ones. The general measuring tools are calipers, calipers, vernier calipers and so on. Special tools, such as calipers, plug gauges, templates, special fixtures, should be used when production is large. When the precision size test is required for the forgings, the inspection instruments that are controlled and analyzed by the computer, or the optical comparator and the optical projector can be used to check the size.
(3) die structure inspection should also check the die structure in order to ensure the size and shape of the die forging. Before the new forging die (or refurbished) the final die bore and the pre forging die bore, before the production is put into production, the lead sample should be cast, or the mixed metal salt castings of 2 parts of sodium nitrate and 1 parts of potassium nitrate are cast, and the shape of the sample and the state of the flying are checked, and the design of the mold chamber is judged reasonable. After the pickling, the first batch of forgings should be checked for filling and folding, so as to ascertain the correctness of the design of forging die rounded, flange, rib and so on. In addition, the trimming quality of precision forgings should be checked in order to determine the quality problems existing in the design and installation of trimming dies.
3. mechanical properties test
The inspection items are determined according to the importance and material properties of the forgings. The mechanical properties of the specimens must be cut from the forgings taken from the same smelting furnace and the same heat treatment furnace. Sample cutting, sample size and testing methods are carried out in accordance with national standards.
(1) hardness test is the easiest way to judge the mechanical properties of forgings in production. The purpose of the hardness test is to ensure the normal cutting performance of the forging parts, to judge the decarbonization of the forgings, and to understand the inhomogeneous degree of the internal structure of the forgings. Hardness test is usually carried out after forging heat treatment. Brinell hardness or Rockwell hardness tester can be used.
(2) tensile test is used to determine yield limit under uniaxial tension. The ultimate strength is CRB, elongation and shrinkage.
(3) impact test is used to check the toughness of materials or forgings. Shock tests are usually required for working parts, such as shock loads and vibration loads, or parts operating at high temperatures and high speeds, such as turbine discs and turbine blades.