The heat treatment process of the latest methods have 10 different quenching, respectively is single medium (water, oil, air), quenching, quenching, martensite dual media grading quenching, below the Ms point of martensite step quenching method, bainite isothermal quenching method, composite quenching method, precooling isothermal quenching, delayed cooling quenching, quenching self backfires, spray quenching method, etc.
One, single medium (water, oil, air) quenching
Single-medium (water, oil, air) quenching: the workpiece heated to the quenching temperature is quenched into a quenching medium so that it is completely cooled. This is the simplest quenching method and is commonly used for carbon and alloy steel workpieces of simple shape. Quenching medium is selected according to the size of heat transfer coefficient, hardenability, size and shape of parts.
Two, double medium quenching
Dual medium quenching: the workpiece heated to the quenching temperature is first cooled in the quenching medium with the strong cooling capacity to close to the MS point, and then transferred to the slow cooling quenching medium to cool to room temperature, so as to achieve different quenching cooling temperature range, and has a relatively ideal quenching cooling speed. It is also used for large workpieces made of complex shape parts or high carbon steel and alloy steel. Commonly used cooling media are water-oil, water-nitrate, water-air, oil-air. Generally, water is used as a fast cold quenching medium, oil or air is used as a slow cold quenching medium, and the air is seldom used.
Three, martensite grading quenching
Martensite grading quenching: steel austenitizing, then immersed in the liquid medium (salt bath or alkali bath) with a slightly higher or lower temperature than the steel’s upper martensite point, keep the appropriate time, when the inner and outer layers of steel reach the medium temperature, take out air cooling, subcooled austenite slowly into martensite quenching process. Generally used in complex shape and deformation requirements of small workpiece, high speed steel, and high alloy steel die is also commonly used this method quenching.
Four. Martensite grading quenching method lower than MS point
Martensite grading quenching method below MS point: when the bath temperature is lower than MS of the steel used for the workpiece and higher than MF, the workpiece cools faster in the bath, and the same result as the grading quenching can be obtained when the size is larger. It is often used in large size steel parts with low hardenability.
Five, bainite isothermal quenching method
Bainite isothermal quenching method: the workpiece is quenched into the bath at the lower bainite temperature of the steel isotherm so that the lower bainite transformation occurs, generally in the bath for 30~60min insulation. There are three main steps in the isothermal quenching process of bainite: ① austenitizing treatment;② cooling treatment after austenitizing;③ isothermal treatment of bainite; Used for alloy steel, high carbon steel small size parts, and nodular cast iron.
Six, compound quenching method
Composite quenching method: the workpiece is rapidly cooled to MS below the volume fraction of 10%~30% martensite, and then the lower bainite region isothermal, so that the larger section of the workpiece martensite and bainite structure, commonly used in alloy tool steel workpiece.
Seven, precooling isothermal quenching method
Precooled isothermal quenching method: also known as heating isothermal quenching, the parts are cooled in the bath at a lower temperature (greater than MS), and then transferred to the bath at a higher temperature, so that the austenite isothermal transformation. It is suitable for steel parts with poor hardenability or large size which must be isothermal quenched.
Eight, delay cooling quenching method
Delayed cooling quenching method: parts are precooled in air, hot water, and salt bath to a temperature slightly higher than Ar3 or Ar1, and then single-medium quenching is carried out. It is often used for complex shape parts with different thicknesses and small deformation requirements.
Nine, quenching self-tempering method
Quenching self-tempering method: it is a quenching process in which all the processed workpiece is heated, but only the part that needs to be hardened (often the working part) is immersed in the quenching liquid to cool it, and the quenching process is immediately taken out in the air when the fire color of the unimmersed part disappears. The quenching self-tempering method uses heat that is not completely cold to the surface of the heart to make the surface tempering. Often used for impact bearing tools such as chisels, punches, hammers, etc.
Ten, jet quenching method
Jet quenching: A quenching process in which a jet of water, large or small, is injected into the workpiece, depending on the desired quenching depth. Jet quenching does not form a vapor film on the surface of the workpiece, which ensures a deeper hardened layer than quenched in water. Mainly used for local surface quenching.