There are ten quenching methods commonly used in the heat treatment process, including single medium quenching (water, oil, air); the martensite-based quenching method below the Ms point; ; isothermal pre-cooling quenching method; delayed cooling quenching method; spray quenching method, etc.
1. Single medium quenching (water, oil, air)
Single-fluid quenching (water, oil, air): The part that has been heated to the quenching temperature is quenched in a quenching fluid to cool it completely. This is the simplest quenching method and is often used for carbon and alloy steel parts of simple shapes. The quenching medium is chosen based on heat transfer coefficient, hardenability, size, shape, etc. of the room.
2. Double medium quenching
Dual-medium quenching: The part heated to the quenching temperature is first cooled to near the Ms point in a quenching medium with high cooling capacity, and then transferred to a slowly cooling quenching medium to cool to room temperature in order to achieve different quenching cooling. temperature ranges and have a relatively ideal quench cooling rate. This method is often used for parts with complex shapes or large parts made of high carbon and alloy steel. Commonly used cooling media include water-oil, water-nitrate, water-air, and oil-air. Generally, water is used as a fast-cooling quenching medium, and oil or air is rarely used as a slow-cooling quenching medium. used.
3. Martensite graduated quenching
Martensitic graded quenching: the steel is austenitized, then immersed in a liquid medium (salt bath or alkaline bath) at a temperature slightly above or slightly below the upper martensitic point of the steel, and held for an appropriate time until what the interior and exterior surfaces of steel parts Once the layers have reached medium temperature, they are removed to be air cooled and the supercooled austenite is slowly transformed into martensite during the quenching process. It is generally used for small parts with complex shapes and strict deformation requirements. This method is also commonly used for quenching high-speed steel and high-alloy steel tools and molds.
4. Martensite graded quenching method below the Ms point
Graduated martensite quenching method below Ms point: When the bath temperature is lower than Ms of the workpiece steel and higher than Mf, the workpiece cools more quickly in the bath, and the same results as quenching Graduated can still be obtained when the size is larger. Commonly used for larger steel parts with low hardenability.
5. Isothermal bainite quenching method
Isothermal bainite quenching method: The workpiece is quenched in a bath with a lower bainite temperature of the steel and isothermal, so that the lower bainite transformation occurs, and is generally kept in the bath for 30 to 60 minutes. The bainite quenching process has three main steps: ① austenitization treatment; ② post-austenitizing cooling treatment; ③ bainite isothermal treatment, commonly used in alloy steels, high carbon steel small parts and ductile iron castings.
6. Compound quenching method
Compound quenching method: first quench the part below Ms to obtain martensite with volume fraction of 10%-30%, then isothermally in the lower bainite zone to obtain martensite and bainite structures for parts of larger section. It is commonly used. Alloy tool steel parts.
7. Precooling and isothermal quenching method
Pre-cooling isothermal quenching method: Also called heating isothermal quenching, parts are first cooled in a lower temperature bath (above Ms) and then transferred to a higher temperature bath to cause isothermal transformation austenite. It is suitable for steel parts with low hardenability or large parts that need to be hardened.
8. Delayed cooling and quenching method
Delayed cooling quenching method: parts are first pre-cooled in air, hot water or salt bath to a temperature slightly above Ar3 or Ar1, then single medium quenching is performed . It is often used for parts with complex shapes and very variable thicknesses in various parts and requiring low deformation.
9. Quenching and self-tempering method
Quenching and self-tempering method: the entire workpiece is heated, but during quenching, only the part that needs to be hardened (usually the working part) is immersed in the quenching liquid and cooled when the fire color is not submerged. The coin disappears, immediately take it out into the air. Medium cooling quenching process. The quench and self-temper method uses heat from the core that is not completely cooled to transfer it to the surface for quenching. Commonly used tools to resist impact such as chisels, punches, hammers, etc.
10. Spray quenching method
Spray quenching method: A quenching method in which water is sprayed onto the workpiece. The water flow can be high or low, depending on the depth of quenching required. The spray quenching method does not form a vapor film on the surface of the part, ensuring a deeper cured layer than water quenching. Mainly used for local surface quenching.
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