Quenching of steel is to heat the steel to a temperature above the critical temperature Ac3 (hypegmatized steel) or Ac1 (hyper-eutectoid steel), hold it for a period of time, make it all or part austenitized, and then cool it at a critical cooling rate. A rapid heat treatment process for martensite (or bainite) transformation below Ms (or isothermal near Ms). The solution treatment of materials such as aluminum alloys, copper alloys, titanium alloys, tempered glass, or the heat treatment process with a rapid cooling process is also referred to as quenching.
Quenching method
Single medium quenching
The workpiece is cooled in a medium such as water quenching and oil quenching. The advantages are simple operation, easy mechanization and wide application. The disadvantage is that the quenching stress in the water is large, the workpiece is easily deformed and cracked; the quenching in the oil, the cooling rate is small, the hardening diameter is small, and the large workpiece is not easily hardened.
Double dielectric quenching
The workpiece is first cooled to about 300 ° C in a medium with strong cooling capacity, and then cooled in a medium with weak cooling capacity. For example, oil quenching after water quenching can effectively reduce the internal stress of martensite transformation and reduce The tendency of workpiece deformation and cracking can be used for quenching workpieces with complex shapes and uneven sections. The shortcoming of the two-liquid quenching is that it is difficult to grasp the timing of the two-liquid conversion, the conversion is too early, the quenching is not hard, the conversion is too late and the quenching is easy. In order to overcome this disadvantage, a graded quenching method has been developed.
Graded quenching
The workpiece is quenched in a low temperature salt bath or an alkali bath furnace. The temperature of the salt bath or the alkali bath is near the Ms point, the workpiece stays at this temperature for 2 min to 5 min, and then the air cooling is taken out. This cooling method is called fractional quenching. The purpose of the staged cooling is to make the temperature inside and outside the workpiece more uniform and to perform martensite transformation, which can greatly reduce the quenching stress and prevent deformation and cracking. The grading temperature was previously set at a point slightly higher than the Ms point, and the temperature inside the workpiece was uniform after entering the martensite region. Improved to grade at temperatures slightly below the Ms point. Practice has shown that the grading effect below the Ms point is better. For example, a high carbon steel mold is quenched in an alkali bath at 160 ° C, which is hardened and has small deformation, so it is widely used.
Austempering
The workpiece is quenched in an isothermal salt bath, the salt bath temperature is in the lower part of the bainite zone (slightly higher than Ms), and the workpiece is isothermally held for a longer period of time until the end of the bainite transformation, and the air cooling is taken out. Austempering is used for steels with a medium carbon or higher in order to obtain lower bainite to improve strength, hardness, toughness and wear resistance. Low carbon steel generally does not use austempering.
Surface hardening
Surface quenching is a method of partial quenching in which the surface layer of a steel member is hardened to a certain depth while the core portion remains unquenched. When the surface is quenched, the surface of the rigid part is quickly heated to a quenching temperature by rapid heating. When the heat is too late to pass through the core of the workpiece, it is cooled immediately to achieve local quenching.
Induction hardening
Induction heating is the use of electromagnetic induction to generate eddy currents in a workpiece to heat the workpiece.
Cold
It is immersed in an ice-cold aqueous solution with a strong cooling capacity and quenched and cooled as a cooling medium.
Partial quenching
Quenching only on the part where the workpiece needs to be hardened.
Air quenching
Specifically refers to quenching cooling in vacuum and in neutral and inert gases at high pressure, negative pressure, atmospheric or high pressure.
Surface hardening
Quenching only on the surface of the workpiece, including induction hardening, contact resistance heating quenching, flame quenching, laser quenching, electron beam quenching, etc.
Air quenching
Quenching cooling with forced flow of air or compressed air as a cooling medium.
Brine quenching
Quenching cooling using an aqueous solution of a salt as a cooling medium.
Organic solution quenching
The quenching cooling is performed using an aqueous solution of an organic high molecular polymer as a cooling medium.
Spray quenching
Quenching cooling with a jet stream as a cooling medium.
Spray cooling
The workpiece is quenched and cooled in a mist of water and air mixed spray.
Hot bath cooling
The workpiece is quenched and cooled in a hot bath such as molten salt, molten alkali, molten metal or high temperature oil, such as salt bath quenching, lead bath quenching, alkali bath quenching, and etc.
Two-liquid quenching
After the workpiece is heated and austenitized, it is first immersed in a medium with a strong cooling capacity, and is immediately cooled into a medium having a weak cooling ability when the martensite transformation is about to occur.
Pressurized quenching
The workpiece is heated after austenitizing and then quenched and cooled by a specific clamp, and the purpose is to reduce the quenching and cooling distortion.
Extrusion
The workpiece is hardened from the surface to the core.
Austempering
After the workpiece is heated and austenitized, it is cooled to the bainite transformation temperature zone for isothermal maintenance, and the austenite is transformed into bainite quenching.
Graded quenching
After the workpiece is heated and austenitized, the immersion temperature is slightly higher or slightly lower than the M1 point in the alkali bath or the salt bath for a suitable time, and after the whole workpiece reaches the medium temperature, the air cooling is taken out to obtain quenching of martensite.
Sub-temperature quenching
The hypoeutectic steel workpiece is quenched and cooled after austenitizing in the Ac1-Ac3 temperature range to obtain quenching of martensite and ferrite structure.
Direct quenching
The process of direct quenching and cooling after the workpiece penetrates into the carbon.
Two quenching
After the workpiece is carburized and cooled, it is austenitized and quenched at a temperature higher than Ac3 to refine the core structure, and then austenitized at a temperature slightly lower than Ac3 to refine the quenching of the layered structure.
Self-cooling
After the local or surface layer of the workpiece is rapidly heated and austenitized, the heat in the heating zone is self-propelled to the unheated zone, thereby quenching the austenitizing zone for rapid cooling.
