●Single liquid quenching
It is a quenching operation method in which the austenitized workpiece is immersed in a certain quenching medium and cooled to room temperature. Single-liquid quenching media include water, brine, alkaline water, oil and specially prepared quenching agents.
Advantages: Simple operation, conducive to mechanization and automation.
Disadvantages: The cooling speed is limited by the cooling characteristics of the medium, which affects the quenching quality.
Application: Single liquid quenching is only suitable for workpieces with relatively simple shapes for carbon steel.
●Double liquid quenching
The austenitized workpiece is first immersed in a medium with strong cooling capacity, then taken out before the steel piece reaches the temperature of the quenching medium, and immediately immersed in another medium with weak cooling capacity for cooling, such as water first and then oil. , water first, then air, etc. Double-liquid quenching reduces the tendency of deformation and cracking, is difficult to operate, and has certain limitations in application.
● Martensite graded quenching
The austenitized workpiece is first immersed in a liquid medium (salt bath or alkali bath) with a temperature slightly higher or slightly lower than the martensitic point of steel, and maintained for an appropriate time until the inner and outer layers of the steel piece reach the medium After temperature, take out the air cooling to obtain the quenching process of martensite structure, also called graded quenching.
Advantages: Graded quenching can effectively reduce phase change stress and thermal stress, and reduce quenching deformation and cracking tendencies because the graded temperature remains until the internal and external temperatures of the workpiece are consistent and then air-cooled.
Application: Suitable for alloy steel and high-alloy steel workpieces with high deformation requirements. It can also be used for carbon steel workpieces with small cross-sections and complex shapes.
● Bainite austempering
It is a quenching process that austenitizes steel parts and quickly cools them to the bainite transformation temperature range (260 ~ 400°C) to maintain it isothermally to transform austenite into bainite. It is also sometimes called isothermal quenching, generally heat preservation. The time is 30~60min.
● Compound quenching
The workpiece is quenched to below Ms to obtain 10% to 20% martensite, and then isothermally maintained in the lower bainite temperature zone. This cooling method can make larger cross-section workpieces obtain M+B structure. The martensite formed during pre-quenching can promote bainite transformation and temper the martensite during isothermal process. Composite quenching is used for alloy tool steel workpieces to avoid the first type of temper brittleness and reduce the amount of retained austenite, that is, the tendency to deform and crack.