Ten commonly used quenching methods

Ten commonly used quenching methods

There are ten commonly used quenching methods in the heat treatment process, including single medium (water, oil, air) quenching; dual medium quenching; martensite graded quenching; martensite graded quenching method below the Ms point; bainite isothermal Quenching method; compound quenching method; precooling isothermal quenching method; delayed cooling quenching method; quenching self-tempering method; spray quenching method, etc.

1. Single medium (water, oil, air) quenching

Single-medium (water, oil, air) quenching: The workpiece that has been heated to the quenching temperature is quenched into a quenching medium to cool it completely. This is the simplest quenching method and is often used for carbon steel and alloy steel workpieces with simple shapes. The quenching medium is selected according to the heat transfer coefficient, hardenability, size, shape, etc. of the part.

2. Double medium quenching

Dual-medium quenching: The workpiece heated to the quenching temperature is first cooled to close to the Ms point in a quenching medium with strong cooling capacity, and then transferred to a slow-cooling quenching medium to cool to room temperature to reach different quenching cooling temperature ranges and have Relatively ideal quenching cooling rate. This method is often used for parts with complex shapes or large workpieces made of high-carbon steel and alloy steel. Carbon tool steels are also often used. Commonly used cooling media include water-oil, water-nitrate, water-air, and oil-air. Generally, water is used as the rapid cooling quenching medium, and oil or air is used as the slow cooling quenching medium. Air is rarely used.

3. Martensite graded quenching

Martensitic graded quenching: the steel is austenitized, and then immersed in a liquid medium (salt bath or alkali bath) with a temperature slightly higher or slightly lower than the upper Martensite point of the steel, and maintained for an appropriate time until the inner and outer surfaces of the steel parts After the layers reach the medium temperature, they are taken out for air cooling, and the supercooled austenite is slowly transformed into martensite during the quenching process. It is generally used for small workpieces 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 Ms point

Martensite graded quenching method below Ms point: When the bath temperature is lower than Ms of the workpiece steel and higher than Mf, the workpiece cools faster in the bath, and the same results as graded quenching can still be obtained when the size is larger. Often used for larger steel workpieces with low hardenability.

5. Bainite isothermal quenching method

Bainite isothermal quenching method: The workpiece is quenched into 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 austempering process has three main steps:

① austenitizing treatment;

② post-austenitizing cooling treatment;

③ bainite isothermal treatment; commonly used in alloy steel, high carbon steel small-size parts and ductile iron castings.

6. Compound quenching method

Compound quenching method: first quench the workpiece to below Ms to obtain martensite with a volume fraction of 10% to 30%, and then isotherm in the lower bainite zone to obtain martensite and bainite structures for larger cross-section workpieces. It is commonly used Alloy tool steel workpieces.

7. Precooling and isothermal quenching method

Pre-cooling isothermal quenching method: also called heating isothermal quenching, the parts are first cooled in a bath with a lower temperature (greater than Ms), and then transferred to a bath with a higher temperature to cause the austenite to undergo isothermal transformation. It is suitable for steel parts with poor hardenability or large workpieces that must be austempered.

8. Delayed cooling and quenching method

Delayed cooling quenching method: The parts are first pre-cooled in air, hot water, or salt bath to a temperature slightly higher than Ar3 or Ar1, and then single-medium quenching is performed. It is often used for parts with complex shapes and widely varying thicknesses in various parts and requiring small deformation.

9. Quenching and self-tempering method

Quenching and self-tempering method: The entire workpiece to be processed 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 of the unimmersed part disappears, immediately take it out in the air. Medium cooling quenching process. The quenching and self-tempering method uses the heat from the core that is not completely cooled to transfer to the surface to temper the surface. Tools commonly used to withstand 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 large or small, depending on the required quenching depth. The spray quenching method does not form a steam film on the surface of the workpiece, thus ensuring a deeper hardened layer than water quenching. Mainly used for local surface quenching.