What happens to metals during hot forging?

Hot forging is a metalworking process that involves shaping metal while it is heated to a temperature above its recrystallization point but below its melting point. During hot forging, metals undergo several changes and transformations due to the combination of high temperature and mechanical deformation. Here's what happens to metals during hot forging:

1. Softening and Plastic Deformation:

  - Heating the metal to an elevated temperature above its recrystallization point causes the material to soften and become more ductile. This allows the metal to undergo plastic deformation more easily without fracturing. As a result, the metal can be shaped into the desired form using forging dies and presses.

2. Grain Refinement:

  - The high temperature during hot forging promotes recrystallization and grain growth within the metal. As the metal is deformed through forging, the grains are broken down and rearranged, leading to a finer grain structure. A finer grain structure generally improves the mechanical properties of the metal, such as strength and toughness.

3. Reduction of Residual Stresses:

  - Hot forging can help reduce residual stresses that may be present in the metal due to previous manufacturing processes or thermal treatments. The plastic deformation and high temperature during forging allow the material to relax and redistribute internal stresses, resulting in a more uniform and stable microstructure.

4. Improved Material Homogeneity:

  - The uniform heating of the metal during hot forging promotes greater material homogeneity throughout the workpiece. This helps to minimize variations in mechanical properties and ensure consistent performance in the final forged product.

5. Enhanced Flow Properties:

  - Heating the metal to a high temperature increases its flow properties, allowing it to deform more easily under applied pressure. This facilitates the shaping of intricate and complex geometries during forging, resulting in a wider range of design possibilities for forged components.

6. Surface Scale Formation:

  - When metals are heated to high temperatures in the presence of oxygen, they can react with the atmosphere to form surface oxides or scale. This scale may need to be removed through subsequent machining or surface treatment processes to achieve the desired surface finish and dimensional accuracy in the final forged product.

Overall, hot forging is a highly effective manufacturing process for producing forged components with improved mechanical properties, dimensional accuracy, and material homogeneity compared to cold forging or other metalworking methods. It allows for the production of complex shapes and geometries while maximizing material utilization and minimizing waste.