The structure of forgings mainly includes two types: free forgings and die forgings. Each type has its own specific process and application scenarios.
Free forgings
Free forgings are to apply external force directly to the blank between the upper and lower anvils of the forging equipment to deform it and obtain the required geometric shape and internal quality. Free forgings are usually used to produce forgings with small batches, and are mainly formed by forging hammers, hydraulic presses and other equipment. The basic processes of free forgings include upsetting, drawing, punching, cutting, bending, twisting, displacement and forging.
Die forgings
Die forgings are forgings obtained by pressure deformation in a forging die with a specific shape. Die forgings are usually used to produce parts with small weight but large batches. Die forging can be divided into open die forging and closed die forging. The former has flash and the latter does not have flash. The specific types of die forgings include:
Hot die forging: The die and the blank are kept at a higher temperature for forging.
Warm forging: The metal deformation temperature is below the recrystallization temperature and above room temperature.
Cold die forging: Forging is performed at room temperature and is suitable for processing thin and small parts of low-carbon steel, non-ferrous metals and their alloys.
Specific application examples
For example, gears are usually formed by upsetting and slightly pressing, while universal joints and cross shafts are formed by extrusion and slightly upsetting. These structural differences determine the differences in forging processes and die designs.
Structure of forgings
Introduction
Forgings are metal components that have been shaped through a process of applying force to raw material in order to deform it into a desired shape. This process can be achieved through various methods such as hammering, pressing, rolling, or extrusion. The structure of forgings plays a crucial role in determining their mechanical properties and overall performance. In this article, we will discuss the different types of forging structures, their characteristics, and the factors that influence them.
Types of forging structures
There are three main types of forging structures commonly used in the industry:
1. Fibrous structure: Fibrous structure is characterized by long and continuous grains that follow the direction of metal flow during the forging process. This structure is typically found in forgings that have been heavily worked, such as those produced through hammering or pressing. Fibrous structure provides enhanced strength and toughness to the forging due to the alignment of grains along the load-bearing direction.
2. Equiaxed structure: Equiaxed structure consists of grains that are randomly oriented in all directions, resulting in a uniform distribution of grain boundaries throughout the forging. This structure is often found in forgings produced through processes like rolling or extrusion, where the metal is subjected to uniform deformation. Equiaxed structure provides good ductility and impact resistance to the forging.
3. Widmanstätten structure: Widmanstätten structure is characterized by the presence of elongated and interlocking grains that form when certain alloys undergo phase transformations at high temperatures. This structure is commonly found in forgings made from heat-treatable alloys, such as titanium or nickel-based superalloys. Widmanstätten structure provides excellent strength and creep resistance to the forging due to the formation of secondary phases within the grains.
Factors influencing forging structure
Several factors can influence the structure of forgings, including:
1. Temperature: The temperature at which forging is carried out plays a critical role in determining the final structure of the component. Higher forging temperatures promote grain growth and recrystallization, resulting in a finer and more uniform grain structure. Conversely, lower forging temperatures can lead to the formation of larger, more elongated grains.
2. Deformation rate: The rate at which the metal is deformed during the forging process can impact the resulting structure of the component. Higher deformation rates tend to produce a more refined grain structure, while lower deformation rates can lead to the formation of larger grains.
3. Alloy composition: The composition of the alloy used in the forging can significantly influence its structure. Elements such as carbon, nitrogen, and sulfur can form secondary phases that affect the grain boundaries and overall microstructure of the component. Additionally, the presence of alloying elements can alter the phase transformations that occur during forging, leading to the formation of specific structures like Widmanstätten.
4. Cooling rate: The cooling rate after forging also has a significant impact on the structure of the component. Rapid cooling can promote the formation of fine-grained structures, while slow cooling can result in coarser grains. Proper heat treatment processes are essential to control the cooling rate and achieve the desired structure in the forging.
Conclusion
The structure of forgings is a critical aspect that influences their mechanical properties and performance. Understanding the different types of forging structures, their characteristics, and the factors that influence them is essential for producing high-quality components with the desired properties. By carefully controlling the forging process parameters and selecting the appropriate alloy composition, manufacturers can achieve the desired structure in forgings to meet specific performance requirements.
