High-Temperature Alloy Steel Forging Processes

High-temperature alloy steel is a modern material. It has excellent corrosion resistance, high-temperature strength, and thermal stability. These materials can work reliably in environments with high temperatures, high pressure, and strong corrosion. They are used in aerospace, energy, and chemical industries. High-temperature alloy steel is especially important in the production of critical components like engine parts, gas turbine blades, and heat exchangers, which are exposed to high temperatures. High-temperature alloy steel maintains good mechanical properties and chemical stability at high temperatures. Therefore, it is an essential material in modern high-temperature engineering. The production process for high-temperature alloy steel is complex. The high-temperature alloy steel forging process requires strict control of various parameters to ensure the final product has excellent performance. Below is a detailed overview of the types of high-temperature alloy steel and the key points of their forging process.

Types of High-Temperature Alloy Steel

High-temperature alloy steel comes in many types. They are usually classified based on their base metal and alloying elements.

1. Iron-Based High-Temperature Alloy Steel

Iron-based high-temperature alloy steel is made by adding elements like chromium, nickel, and molybdenum to iron. This type of steel has good high-temperature oxidation resistance, but its strength is relatively low. Iron-based high-temperature alloy steel is divided into three types based on their microstructure after normalizing:

Pearlitic Type: This type is used in low to medium-temperature environments. It offers good toughness and tensile strength.

Martensitic Type: This type is suitable for higher temperatures and higher stress environments. It has higher strength and hardness.

Austenitic Type: This type shows excellent corrosion resistance and oxidation resistance at high temperatures. It is used in higher temperature applications.

2. Nickel-Based High-Temperature Alloy Steel

Nickel-based high-temperature alloy steel uses nickel as the base metal. It also contains elements like chromium, cobalt, and molybdenum. The main structure of nickel-based high-temperature alloy steel is austenitic, which provides excellent high-temperature performance and corrosion resistance. This type of steel is widely used in extreme high-temperature environments such as aerospace engines and gas turbines.

3. Cobalt-Based, Chromium-Based, and Copper-Based High-Temperature Alloy Steel

Apart from iron-based and nickel-based high-temperature alloy steel, there are special alloy systems like cobalt-based, chromium-based, and copper-based high-temperature alloy steel. These alloys have good thermal stability and can be used in environments above 1000°C. However, they have poor plasticity, which makes them difficult to shape. Therefore, they are used in specific high-temperature environments.

Forging Process of High-Temperature Alloy Steel

Forging high-temperature alloy steel is a technical process. It requires strict control of temperature, deformation, and other process parameters to ensure uniformity, density, and good mechanical properties. High-temperature alloy steels have low plasticity, and cracks can form easily during forging. Therefore, it is important to take various technical measures during the operation.

1. Forging Temperature and Deformation

The forging temperature must be carefully controlled. High-temperature alloy steel has a narrow forging temperature range, and its grain size is closely related to the amount of deformation. The grain size depends on the degree of deformation. High-temperature alloy steel has a large critical deformation range, usually between 0.5% and 20%. This means that the deformation degree for each pass must be above the critical value. If the deformation is below the critical value, the material may have poor properties.

High-temperature alloy steel has significant resistance to deformation. Therefore, the temperature must be high enough to achieve good deformation. To prevent cracks, temperature and deformation must be precisely controlled to avoid excessive deformation or low temperatures.

2. Forging Process Features and Methods

The forging process for high-temperature alloy steel is complex and requires strict operational standards. The key process requirements are as follows.

Material Preparation

For billets with a diameter smaller than 25mm, shearing can be used. For billets larger than 25mm, wheel cutting or mechanical processing is typically used. Wheel cutting can create thermal stress, which can lead to cracks at the ends of the billet. Therefore, mechanical processing is usually preferred.

Elongation

During elongation, V-shaped anvils are used. For alloys with low plasticity, a semi-circular arc shape should be used. This helps improve the stress distribution, reducing the risk of cracks. In the early stages of elongation, light hammering is applied to reduce stress concentration. The deformation is gradually increased until the desired shape is achieved.

Upsetting

To ensure even deformation during upsetting, paper pads coated with glass lubricant are used at both ends of the billet. For larger-diameter forgings, stacked forging is used with soft carbon steel pads at the ends to reduce deformation unevenness. Short rest periods (5–15 seconds) during upsetting help eliminate work hardening and improve plasticity.

3. Molds and Lubrication

The choice of molds and lubrication directly affects the quality of the forging. Billets should be preheated before each forging operation to meet the required temperature. Molds should be preheated to 250–300°C to reduce friction and heat loss. The surface of the mold should remain smooth, and appropriate lubricants, such as graphite colloids or glass lubricants, should be used. These lubricants help improve the mold's lifespan and ensure uniform deformation.

4. Post-Forging Cooling and Grain Control

The cooling process after forging is crucial for determining the final properties of high-temperature alloy steel forgings. Nickel-based high-temperature alloy steel forgings are usually air-cooled to prevent thermal cracking. Some alloys may require rapid cooling to prevent the precipitation of hardened alloys. During cooling, the forging can be heated to a temperature 50–100°C above the recrystallization temperature before cooling. It should then be held for 5–7 minutes to ensure uniform grain structure and achieve the desired mechanical properties.

Conclusion

High-temperature alloy steels are widely used in modern aerospace, energy, and other high-tech industries. They are known for their excellent resistance to high temperatures, corrosion, and high-temperature strength. The forging process for these steels is complex. It involves careful control of temperature, deformation, and cooling techniques. By controlling the forging process precisely, high-temperature alloy steel materials can maintain superior performance in harsh environments, ensuring reliable support for high-temperature applications. In actual operations, attention to detail and precise adjustments to the process are as important as basic technical requirements.