There are ten common methods of quenching in the heat treatment process, which are single medium (water, oil, air) quenching; dual medium quenching; martensite graded quenching; martensite graded quenching method below Ms point; bainite isothermal Quenching method; compound quenching method; pre-cooling isothermal quenching method; delayed cooling quenching method; quenching self-tempering method; jet quenching method, etc.
1. Single medium (water, oil, air) quenching
Single medium (water, oil, air) quenching: quench the workpiece that has been heated to the quenching temperature with a quenching medium to make it completely cool. This is the simplest quenching method and is commonly used for carbon steel and alloy steel workpieces with simple shapes. The quenching medium is selected according to the heat transfer coefficient, hardenability, size and shape of the parts.
2. Dual medium quenching
Dual-media quenching: the workpiece heated to the quenching temperature is first cooled to the Ms point in the quenching medium with strong cooling capacity, and then transferred to the slow-cooling quenching medium to room temperature to achieve different quenching cooling temperature ranges, and there are The ideal quenching and cooling rate. It is used for large-scale workpieces with complex shapes or high-carbon steel and alloy steel. Carbon tool steel also uses this method. Commonly used cooling media are water-oil, water-nitrate, water-air, 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
Martensite graded quenching: steel is austenitized, and then immersed in a liquid medium (salt bath or alkaline bath) with a temperature slightly higher or slightly lower than the upper martensite point of the steel, and maintained for an appropriate time, waiting for the inside and outside of the steel After the layers have reached the medium temperature, they are taken out for air cooling, and the quenching process of supercooled austenite slowly transforming into martensite. It is generally used for small workpieces with complex shapes and strict deformation requirements. High-speed steel and high-alloy steel molds are also commonly used for this method of quenching.
4. Martensite grading quenching method below Ms point
Martensite graded quenching method below the Ms point: When the bath temperature is lower than the Ms of the workpiece steel and higher than Mf, the workpiece cools faster in the bath, and the same results as the graded quenching can be obtained when the size is larger. Commonly used for large-size low-hardenability steel workpieces.
5. Bainite isothermal quenching method
Bainite isothermal quenching method: the workpiece is quenched into the bath of the lower bainite temperature at the medium temperature of the steel, so that the lower bainite transformation occurs, and it is generally kept in the bath for 30 to 60 minutes. The bainite isothermal quenching process has three main steps: ① austenitizing treatment; ② austenitizing cooling treatment; ③ bainite isothermal treatment; commonly used in alloy steel, high carbon steel small size parts and ductile iron.
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 isothermally in the lower bainite zone to obtain a martensite and bainite structure for a larger cross-section workpiece, commonly used in Alloy tool steel workpiece.
7. Pre-cooling isothermal quenching method
Pre-cooling isothermal quenching method: also known as temperature-increasing 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, so that the austenite undergoes isothermal transformation. It is suitable for steel parts with poor hardenability or large-size workpieces that must be isothermally quenched.
8. Delayed cooling quenching method
Delayed cooling quenching method: parts are pre-cooled in air, hot water, salt bath to a temperature slightly higher than Ar3 or Ar1, and then single medium quenching. It is commonly used in parts with complex shapes and large thickness differences and small deformation.
9. Quenching and self-tempering method
Quenching self-tempering method: all the workpieces are heated, but during quenching, only the part that needs to be hardened (usually the working part) is immersed in the quenching liquid to cool, and when the fire color of the unimmersed part disappears, it is immediately taken out of the air Quenching process during cooling. The quenching self-tempering method uses the heat that is not completely cold in the core to transfer to the surface to temper the surface. Tools commonly used to withstand impacts such as chisel, punch, hammer, etc.
10. Jet quenching method
Jet quenching method: a method of quenching by jetting water to the workpiece. The water flow can be large or small, depending on the required quenching depth. The jet quenching method does not form a vapor film on the surface of the workpiece, which can ensure that a hardened layer deeper than the quenching in the water. Mainly used for local surface quenching.
