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Shortcomings when heating forgings
**Disadvantages of Heating Forgings**
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Shortcomings that occur during the heating process of forgings can significantly affect the quality and performance of the final product. Understanding these issues is essential for ensuring the durability and reliability of forged components.
1. **Antimony Oxide Formation**: Antimony oxide can lead to significant material loss and negatively impact the surface quality of the forging. If not properly removed, it may be embedded in the metal, causing defects and making the part unsuitable for use. Additionally, residual antimony oxide can interfere with machining processes, leading to further complications.
2. **Decarburization**: This occurs when carbon on the surface of the steel is burned off during heating. As a result, the outer layer of the workpiece becomes softer, reducing its hardness, wear resistance, and fatigue strength. This can ultimately compromise the performance and lifespan of the component.
3. **Overheating and Overburning**: Overheating happens when the steel is heated beyond the recommended temperature, causing coarse grain structures. This makes the material brittle and reduces its mechanical properties. However, overheating can often be corrected through normalizing or annealing after forging. Overburning, on the other hand, occurs when the material is exposed to excessive heat for too long, resulting in oxidation or partial melting. Unlike overheating, overburning cannot be reversed and leads to permanent damage.
4. **Thermal Stress Development**: During heating, differences in temperature within the metal can cause uneven expansion, leading to internal stress and thermal stress. These stresses can alter the microstructure of the metal and result in cracks or deformation after machining.
5. **Fracture Appearance in Cross-Section**: This issue disrupts the uniformity of the steel's chemical composition and structure, reducing its quenching hardness and overall mechanical properties. If the annealing temperature is too high, a graphite-like structure may form, making the material difficult to cut and prone to overheating during quenching. Conversely, if the temperature is too low, the pearlite may not fully transform, leading to poor machinability and difficulties in subsequent heat treatment.
6. **Hard and Brittle Reticular Carbides**: The presence of reticular carbides weakens the bonding between grains, significantly reducing the mechanical properties of the steel, especially its impact resistance. Normalizing can help improve or eliminate this condition. In cases of banded carbides, the hardness and microstructure after quenching and tempering become uneven, leading to distortion and reduced plasticity and toughness. This also affects the stability of the cutting process and increases tool wear.
By addressing these issues through proper heating techniques and post-processing treatments, manufacturers can enhance the quality and performance of their forged products.
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