Five technical requirements in flange forging process (part two)
Mechanical property
The mechanical properties of raw materials include properties at room temperature and high temperature, such as strength index, plasticity index, impact toughness, hardness, fracture toughness, permanent strength, fatigue properties, stress corrosion resistance, etc., which should be regulated based on flange forgings and their uses. The differences are specified separately according to the technical requirements for raw materials. Some mechanical properties of large-size raw materials are somewhat low, so be careful when choosing materials.
Microstructure
It is the requirement for the microstructure, grain size (for steel) and purity of the raw materials in the final heat treatment state. The organization of the material has a decisive influence on its properties. Some abnormal structures in the raw material, such as excess ferrite in austenitic and martensitic stainless steels, eutectic compounds in other steels and aluminum and magnesium alloys, the low melting point in the high temperature alloy, the microstructure defects such as carbide segregation and banded structure, and the excessive grain size and low purity will not only seriously affect the performance of forgings, but also will increase the reject rate of forgings. Therefore, there should be clear requirements for microstructure of raw materials and they should be stated in the relevant technical standards.
Macrostructure
It is used to inspect and limit various low-magnification metallurgical defects in raw materials, such as white spots, shrinkage holes and cavities, bubbles, delamination, cracks, slag inclusions, pinholes, segregation, oxide film, etc., which have a serious impact on the performance and processability of forgings, and should be strictly limited and treated according to relevant technical standards.
Supply conditions of raw materials
It refers to the state of raw materials before they are put into production, including whether it is necessary to prepare heat treatment and whether the surface of the raw material needs to be processed to a certain roughness.
Materials manufacturability
It refers to the regulations on the forgeability, hardenability, machinability, weldability, etc. of raw materials. The forgeability of raw materials has an important influence on the forging forming and quality, which is often measured by two indexes - one is plasticity and the other is deformation resistance. The hot forging test is a method of indicating the forgeability. The hardenability, machinability and weldability of the material are the process properties that the forging must have in the process of machining into parts. The technical requirements of the material should be stated in the relevant technical standards.
Regulations for special inspection projects
Raw materials for important aviation forgings should be inspected by ultrasonic flaw detection to prevent or avoid the internal metallurgical defects of materials not found in the destructive inspection. Ultrasonic flaw detection methods and standards, as well as materials to be inspected, should be specified in the relevant technical conditions.
Repeated tests
If there are inspection results of raw materials that are not in conformity with the regulations, their repeated test should be differentiated and treated with caution. For forgings that are unqualified due to problems in sample processing (including sample heat treatment) and inaccurate test methods, or not caused by material defects, such as mechanical properties, chemical composition, etc., repeated tests are allowed. Low-magnification metallurgical defects of raw materials are not allowed to be re-inspected in principle (except where required and the raw material supplier uses the ultrasonic flaw detection method or other effective methods to screen the metallurgical defects of raw materials. However, in any case, steel with white spots should be discarded once discovered.)
The mechanical properties of raw materials include properties at room temperature and high temperature, such as strength index, plasticity index, impact toughness, hardness, fracture toughness, permanent strength, fatigue properties, stress corrosion resistance, etc., which should be regulated based on flange forgings and their uses. The differences are specified separately according to the technical requirements for raw materials. Some mechanical properties of large-size raw materials are somewhat low, so be careful when choosing materials.
Microstructure
It is the requirement for the microstructure, grain size (for steel) and purity of the raw materials in the final heat treatment state. The organization of the material has a decisive influence on its properties. Some abnormal structures in the raw material, such as excess ferrite in austenitic and martensitic stainless steels, eutectic compounds in other steels and aluminum and magnesium alloys, the low melting point in the high temperature alloy, the microstructure defects such as carbide segregation and banded structure, and the excessive grain size and low purity will not only seriously affect the performance of forgings, but also will increase the reject rate of forgings. Therefore, there should be clear requirements for microstructure of raw materials and they should be stated in the relevant technical standards.
Macrostructure
It is used to inspect and limit various low-magnification metallurgical defects in raw materials, such as white spots, shrinkage holes and cavities, bubbles, delamination, cracks, slag inclusions, pinholes, segregation, oxide film, etc., which have a serious impact on the performance and processability of forgings, and should be strictly limited and treated according to relevant technical standards.
Supply conditions of raw materials
It refers to the state of raw materials before they are put into production, including whether it is necessary to prepare heat treatment and whether the surface of the raw material needs to be processed to a certain roughness.
Materials manufacturability
It refers to the regulations on the forgeability, hardenability, machinability, weldability, etc. of raw materials. The forgeability of raw materials has an important influence on the forging forming and quality, which is often measured by two indexes - one is plasticity and the other is deformation resistance. The hot forging test is a method of indicating the forgeability. The hardenability, machinability and weldability of the material are the process properties that the forging must have in the process of machining into parts. The technical requirements of the material should be stated in the relevant technical standards.
Regulations for special inspection projects
Raw materials for important aviation forgings should be inspected by ultrasonic flaw detection to prevent or avoid the internal metallurgical defects of materials not found in the destructive inspection. Ultrasonic flaw detection methods and standards, as well as materials to be inspected, should be specified in the relevant technical conditions.
Repeated tests
If there are inspection results of raw materials that are not in conformity with the regulations, their repeated test should be differentiated and treated with caution. For forgings that are unqualified due to problems in sample processing (including sample heat treatment) and inaccurate test methods, or not caused by material defects, such as mechanical properties, chemical composition, etc., repeated tests are allowed. Low-magnification metallurgical defects of raw materials are not allowed to be re-inspected in principle (except where required and the raw material supplier uses the ultrasonic flaw detection method or other effective methods to screen the metallurgical defects of raw materials. However, in any case, steel with white spots should be discarded once discovered.)
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