Forging is a very old method that involves rolling, pressing, or hammering to convert the metals into different shapes. Forging and casting are not the same; casting involves pouring melted metal into a mold.
Nickel superalloy forging is a process that also requires greater attention. When forging superalloys, a number of variables, including temperature, heating rate, and forging technique, must be taken into consideration because of their unique characteristics.
This article is very beneficial for you if you want to know more about the forging of nickel superalloys. It will go over the various forging techniques, as well as the features, challenges, and safety measures for forging superalloys.
What is Forging?
In general, it is the technique of heating and shaping heated metal to create designs or shapes appropriate for a certain usage. Many of the material’s characteristics, including structure, conductivity, and lifespan, are improved by working on it. Because the technique is cost-effective and produces certain mechanical qualities, forging provides a very practical and versatile medium for different industries.
Two main types of forging, hot forging, and cold forging, are given below:
Hot forging
In this process heated, the metal is heated to its plasticity and then changes its shape by hammering or rolling with pressure. This process increases the strength of the metal by rearranging its particle’s structure.
Cold forging
Cold forging is typically performed at or slightly above room temperature. Cold forging improves in the production of more precise and detailed pieces, but typically requiring greater force than hot forging. Additionally, cold forging can preserve a metal’s unique mechanical qualities while enhancing its strength.
Different Forging Methods
Open Die Forging
In open-die forging, a hot piece of metal is usually put on a stationary anvil and deformed by striking it with a hammer. Vehicle parts and other relatively basic, high-volume goods are usually manufactured using open-die forging. The dies continually hammer or press the metal, changing the material until it takes on the desired shape.
Closed Die Forging
Closed-die forging, or impression-die forging, is when heated metal is pressed between a pair of uniquely shaped dies to produce the desired shape. After being pressed or hammered, the metal flows and fills the shaped-die gaps. It is possible to produce more durable and stronger products with the help of this specific technique.
Characteristics of Nickel Superalloys
Low Hot Working Plasticity
Superalloys are more in strength and quality than stainless steel and carbon steel due to their chemical composition. Superalloys are made to improve the solid solution strengthening and precipitation strengthening. The performance of superalloys is good at high temperatures due to their composition therefore the plasticity of superalloys is lower than other type of carbon steel.
Narrow Hot Working Temperature Range
The hot working temperature range means the range between the initial melting point and recrystallization temperature of superalloys. Aluminum and titanium are two examples of elements found in superalloys that have lower melting points. They considerably reduce superalloys’ melting points. Furthermore, small amounts of elements like silicon, phosphorus, sulfur, and boron will also cause the alloy’s melting point to drop.
As a result, the majority of superalloys have lower initial melting temperatures. Superalloys also contain a lot of components that improve the solid solutions. These substances make it harder for atoms to spread by increasing the binding force between them. Thus, superalloys have an elevated recrystallization temperature.
The initial melting temrature of supperalloys is lower and recrystallization temperature is higher that’s why the range of hot working temperature is very narrow.
Low Thermal Conductivity
Superalloys with higher alloying elements have lower thermal conductivity, which results in uneven heating temperatures. The alloy becomes weaker as a result of this irregular crystal structure. More importantly, variations in temperature lead to uneven expansion stress, which raises the possibility of interior fractures. To maintain consistent interior temperatures, heating must be managed.
Precautions for Forging Nickel Superalloys
The following are some important precautions to be taken while forging superalloys.
Reasonable Temperature
Controlling the temperature during forging is crucial since the temperature range is very narrow. Furthermore, the alloy’s heating rate during forging and heating must be closely regulated to prevent cracks produced by the alloy’s uneven internal temperature. In order to achieve a more homogeneous structure, the material should cool as slowly as possible until forging is finished.
Deformation Degree
The superalloys are less malleable at high temperatures therefore Brittle fracture of the material can easily result from excessive deformation during the forging process.
The superalloy’s forging deformation should be kept within a range of 3% to 25%, depending on the grade.
Forging Pressure
Superalloys become harder to deform with the same forging pressure because of their high strength and poor plasticity. The higher pressure needed for superalloys means that they need higher-tonnage presses. The forging pressure is based on the tensile strength and yield strength, which are two of their referee values.
Deformation Speed
Deformation speed plays a vital role in forging. There are three cases of deformation speed.
- There is enough time for recrystallization to neutralize work hardening at very slow deformation speeds. In this instance, the material is weaker and more plastic.
- As the deformation speed increases, the material becomes stronger and loses plasticity because there is not enough time to minimize the effect of work hardening.
- As the deformation speed accelerates, internal heat effects occur, increasing the rate of recrystallization. As a result, the material’s qualities become more balanced.
FAQs
What is the difference between forging and casting?
Forging and casting are two different methods according to their processing techniques. Forging is a manufacturing technique in which metal is hammered, pounded, or squeezed under high pressure, whereas casting involves the melting and pouring of metal into a liquid condition before solidifying it into the structure.
What is the difference between forging and hot rolling?
Forging is the process of heating and shaping hot metal by hammering or pressing for a specific purpose, whereas hot rolling happens above the material’s recrystallization temperature, preventing the metal from work hardening.
In comparison to forging, hot rolling offers the advantages of being less expensive, more efficient, and capable of producing large-sized metal products.
When is it necessary to use the forging process?
When more strength, toughness, and high reliability are required, the forging process is best for metal parts such as automotive engines, shafts, and gears. Forging process is also necessary where improved mechanical properties and resistance to wear is required.
Conclusion
Many industries are using the forging process to obtain a wide variety of parts with better properties and finer grain structure.
There are two types of forging, which are mostly used: hot forging and cold forging. We have expertise in providing high-quality forged superalloys and custom forgings products with a variety of shapes. Feel free to contact us for further queries and orders.
