Forging is an important metal processing method that produces plastic deformation of metal billets by applying pressure, thereby obtaining forgings of the desired shape and size. According to the different tools used, production processes, temperatures, and forming mechanisms, forging methods can be divided into multiple types, each with its specific application scope.

Common defects in machined parts after forging include various types, which may be caused by multiple factors, including raw material problems, improper processing techniques, and unreasonable heat treatment. The following are some common defects in machined parts after forging and their causes:

1. Cracks and crack type defects

Cracks: including hot cracks, cold cracks, forging cracks, etc. Hot cracks are usually caused by excessive heating temperature or heating speed; Cold cracks may occur during the cooling process due to excessive internal stress; Forging cracks are caused by improper operation during the forging process or problems with the material itself.

Cracks: may be caused by defects in the raw material (such as pores, inclusions) that expand during the machining process, or by improper operation during the machining process (such as excessive cutting force, improper tool selection).

2. Non metallic inclusions

This type of defect mainly includes inclusions such as oxides and sulfides, which may enter the molten steel during melting or pouring and be retained in subsequent processing. These inclusions will seriously affect the mechanical properties and service life of forgings.

3. Surface defects

Pitts and dents: may be caused by improper operation during acid washing or cleaning, resulting in the appearance of pits or dents on the surface of the forging.

Scratches and abrasions: During the machining process, scratches or abrasions may occur on the surface of forgings due to unclean or sharp edges of cutting tools, fixtures, or workbenches.

4. Size and shape defects

Dimensional deviation: Due to insufficient machine precision, tool wear, or measurement errors, the size of the processed forging may exceed the tolerance range.

Shape deviation: It may be caused by improper adjustment of the machine tool, loose fixtures, or incorrect tool path settings, resulting in the shape of the processed forging not matching the expected shape.

5. Defects in heat treatment

Excessive or insufficient hardness: Improper heat treatment process may result in forging hardness not meeting the requirements. For example, excessive quenching temperature or holding time may lead to high hardness; However, a low quenching temperature or insufficient cooling rate may lead to low hardness.

Deformation: During the heat treatment process, uneven heating and cooling may cause deformation of the forging.

6. Other defects

Corrosion: If forgings are not properly protected during storage or transportation, they may be subjected to corrosion and cause surface damage.

Insufficient material performance: The inherent performance problems of raw materials, such as insufficient strength and poor toughness, may also be amplified and manifested as various defects during the processing.

In order to reduce the defect rate of machined parts after forging, it is necessary to start from multiple aspects such as raw material selection, processing technology optimization, heat treatment control, and quality control. Meanwhile, it is also crucial to strengthen monitoring and testing during the production process.

Article source: Non destructive welding

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