Eutectoid steel
Eutectoid steel refers to carbon steel with eutectoid composition containing 0.77% carbon. The following is a detailed explanation of eutectoid steel:
1. Definition and properties:
- Eutectoid steel is a carbon steel with a specific carbon content, which is exactly 0.77%. Under specific heat treatment conditions, this steel will slowly cool from the high-temperature austenite zone to 727℃ to generate polygonal pearlite structure.
- In this structure, ferrite and cementite are arranged in parallel in sheets, forming a unique microstructure.
2. Organization structure:
- The organization of eutectoid steel is mainly composed of ferrite and cementite, which coexist in a specific proportion (ferrite accounts for about 88% and cementite accounts for about 12%).
- This organization is represented as a eutectoid point on the iron-carbon equilibrium state diagram, that is, at this point, cementite and ferrite appear or disappear at the same time during phase transformation.
3. Performance and application:
- The strength and hardness of eutectoid steel can be controlled by adjusting the cooling rate. Generally speaking, the greater the cooling rate, the smaller the spacing between pearlite lamellae, which is conducive to improving strength and hardness.
- Due to its good mechanical properties and machinability, eutectoid steel is widely used in the manufacture of parts that require certain strength and hardness, such as gears, shafts, etc.
Pearlite steel
Pearlite steel, also known as pearlite heat-resistant steel or pearlite heat-resistant steel, refers to steel with pearlite and ferrite microstructures. The following is a detailed explanation of pearlite steel:
1. Definition and classification:
- Pearlite steel is a type of steel with pearlite and ferrite microstructures in the normalized state. This type of steel has a low content of alloy elements, good process performance, and an operating temperature of up to 600℃.
- Depending on the use, pearlite steel can be divided into boiler tube steel, air bag steel, fastener steel, rotor steel, etc.
2. Organization structure and performance:
- The organization of pearlite steel is mainly composed of a layered complex phase of ferrite and cementite arranged alternately, namely pearlite. This organization makes pearlite steel have mechanical properties between ferrite and cementite, that is, high strength and hardness, and moderate plasticity and toughness.
- Pearlite steel also has good heat resistance and oxidation resistance, and is suitable for parts working in high temperature environments.
3. Welding and heat treatment:
- Pearlite steel needs to pay special attention to the diffusion and migration of carbon during welding to avoid the formation of a decarburized layer in low-chromium steel and a carburized layer on the high-chromium steel side.
- Appropriate heat treatment may be required after welding to improve the performance of the welded joint.
In summary, there are obvious differences between eutectoid steel and pearlite steel in terms of definition, organization structure, performance and application.
Eutectoid steel is known for its specific carbon content and unique pearlite organization, while pearlite steel is widely used in many fields for its good heat resistance, oxidation resistance and process performance.