The selection of the most reliable raw materials is a prerequisite for ensuring the quality of
forgings. We believe that the main link to determine the quality of raw materials is the melting of materials, ingot casting, semi-finished product processing. The technical requirements of raw materials for aviation forgings can be summarized in the following aspects.
The content of alloying elements, harmful impurity elements, gases and residual elements in the materials shall comply with the technical standards for aviation raw materials and the provisions of relevant technical conditions or technical agreements. If the production conditions permit, the content of harmful elements, gases and residual elements in the material should be controlled as far as possible. The uniformity of alloying element distribution should be required.
Ultra-high strength steel, titanium alloy and superalloy are produced by vacuum consumable remelting process, and titanium alloy and superalloy require no less than secondary vacuum consumable remelting. Alloy structural steel and stainless and heat-resistant steel are produced by electric arc furnace, electric arc furnace and electroslag remelting process or other better melting methods. Aluminum alloy is usually melted by flame furnace, resistance furnace and induction furnace, and high-quality aluminum alloy needs to take a series of process measures in strict control of impurity content and diversification of material heat treatment state.
Material variety specifications, surface quality and dimensional tolerances according to the
forging production process and quality requirements; The varieties and specifications of the materials are ingot, bar (rolled, forged, extruded), square billet, flat, cake (ring) and so on. When the forging has strict flow line distribution requirements, attention should be paid to choosing the flow line direction of the raw material to coordinate it with the flow line distribution specified in the forging. Surface defects of raw materials, such as cracks, folding, scarring, heavy skin, etc., can easily cause surface defects of forgings, so they should be limited. The dimensional tolerance of raw materials has an important impact on the precise forming of forgings, so it should be clearly required.
It should be ensured that the material has a sufficiently large degree of deformation, that is, the size of the forging ratio should be specified in an appropriate range to ensure that the material is sufficiently deformed and the casting structure in the material is reduced or eliminated. For aviation large forgings, the forging ratio of raw materials is generally required to be greater than 6 to 8.
The mechanical properties of raw materials include mechanical properties at room temperature and high temperature, such as strength indicators, plastic indicators, impact toughness, hardness, fracture toughness, lasting strength, creep limit, fatigue properties, stress corrosion resistance, etc., should be specified according to the forging and its use, and listed in the technical requirements for raw materials. Some mechanical performance indicators of large specifications of raw materials are low, and should be paid attention to when designing and selecting materials.
It is a requirement for the microstructure, grain size (for steel) and purity of the raw material in the final heat treatment state. The organization of the material has a decisive impact on its performance, some abnormal structures in the raw material organization, such as the excessive ferritic phase in austenitic and martensitic stainless steel, the eutectic compound phase in other steels and aluminum and magnesium alloys, the continuous thick β grain boundary in titanium alloy, the low melting point phase in superalloys, the carbide segregation, the strip structure and other microstructure defects. And the intrinsic grain of steel is too coarse and the purity is low, which not only seriously affects the performance of forgings but also increases the scrap rate of forgings. Therefore, there should be clear requirements for the high-throughput organization of raw materials, and it should be set out in the relevant technical standards.
It is used to check and limit various low metallurgical defects in raw materials. Low metallurgical defects of raw materials, such as white spots, white spots, shrinkage holes, shrinkage residue, bubbles, voids, peeling, delamination, cracks, inclusions, slag inclusions, dissimilar metal inclusions, point deviation, pinholes, severe dendrites, carbide accumulation (segregation), oxide film. The spot of titanium alloy. Serious porosity, etc., have a serious impact on the performance of forgings and forging process, should be strictly limited, and according to the relevant technical standards.
It refers to the supply state of raw materials before they are put into forging production, including whether heat treatment is required and whether the surface of raw materials needs to be skinned or processed to a certain roughness.
It refers to the provisions on raw material malleability, hardenability, machinability, weldability, etc. The malleability of raw materials has an important influence on forging forming and forging quality. The malleability is often measured by plasticity and deformation resistance. Hot top forging test is a way to show its malleability. The hardenability, machinability and weldability of materials are the necessary technological properties of forgings in their processing into parts. The manufacturability requirements of the materials shall be specified in the relevant technical standards.
Raw materials used in aviation important forgings, such as bars, cakes (rings), etc., should be provided for ultrasonic flaw inspection to prevent or avoid metallurgical defects within the material that are not found in destructive inspections to the forgings. The methods and standards of ultrasonic inspection, as well as the materials to be checked, shall be specified in the relevant technical conditions.
If the test results of each inspection item of raw materials do not meet the regulations, the problem of repeated tests should be differentiated and treated with caution. For the items that are unqualified due to the processing of the sample (including the heat treatment of the sample), the test method is inaccurate, or the items that are fully demonstrated that the unqualified inspection is not caused by the material defect, such as mechanical properties, chemical composition, hardness of supply state, hot forging test, etc., are allowed to repeat the test. Reinspection of metallurgical defects of raw materials at low magnifiers is not allowed in principle (except where specified if the raw material supplier has ultrasonic inspection methods or other effective methods to screen metallurgical defects of raw materials. And separate batch conditions, raw material receiving plant can consider acceptance and testing. However, in any case, for the white spots and white spots in the steel, once found, the whole furnace should be scrapped.
Test methods The test methods for inspecting the technical requirements of raw materials must be clearly specified and conform to the provisions of authoritative test method standards. Other technical requirements for the raw materials used as important forgings should be implemented head management or split number pipe transport; In the case of technical basis, according to the requirements of the demander, more stringent technical requirements can be put forward for raw materials, such as reducing the scope of chemical composition, more stringent low-power structure and high-power structure, hairless steel, higher mechanical properties, more stringent surface quality (depth of decoating layer, etc.) or other quality requirements.
In the production process of aviation forgings, through strict control of chemical composition, melting process, mechanical properties and microstructure, the quality and performance of forgings can be effectively improved to ensure its safety, reliability and long-term use in the aviation field. Therefore, for the aviation industry, always adhering to high standards of raw material selection and production management is a key step to ensure product quality and customer trust.
