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What are the quenching effects of quenching temperature on various steels?

The quenching temperature, also known as the quenching heating temperature, refers to the highest temperature at which the workpiece is heated. So what are the effects of quenching temperature on various steels? Can the optimization of quenching temperature improve the life of tooling?
I. Introduction Quenching temperature, also called quenching heating temperature, refers to the highest temperature reached by the workpiece that will be quenched, and the initial temperature at which it is cooled, which is above the critical temperature. Generally, the quenching temperature of the hypoeutectoid steel is 30 to 50 degrees above Ac3; the quenching temperature of the eutectoid steel or hypereutectoid steel is 30 to 50 degrees above Ac1.


Quenching temperature


Second, the impact of quenching temperature on various steels
1. Effect of quenching temperature on microstructure of high-boron high-speed steel In the ordinary high-speed steel material, a new type of high-boron high-speed steel material was designed by adding appropriate amount of boron to replace the expensive alloying elements in ordinary high-speed steel. The effect of quenching temperature on the microstructure of high boron high speed steel of 0.4% to 0.5% C and 1.0% to 1.5% B was investigated. The results show that the as-cast microstructure of high-boron high-speed steel consists of ferrite, pearlite and a small amount of martensite and boron-carbon compounds. The boron-carbon compound consists of M23(B,C)6, (W,Mo)2(B, C), composed of M3 (B1.5, C0.5) and M (B0.7, C0.3), distributed in the form of a network and a fishbone along the grain boundary. After quenching, the matrix structure is transformed into lath martensite containing 4% retained austenite. The type of boron carbon compound does not change, but the amount is reduced. Quenching at 950~1100 °C, local dissolution of boron-carbon compounds occurs, and the phenomenon of disconnection occurs. With the increase of quenching temperature, the phenomenon of disconnection is more and more obvious, thus reducing the splitting effect on the substrate.
Related conclusions:
(1) The as-cast microstructure of high-boron high-speed steel containing 0.3% to 0.5% C and 0.5% to 2.5% B consists of ferrite, pearlite and a small amount of martensite and boron carbon compound, boron-carbon compound It is distributed in the form of reticular and fishbone along the grain boundary; and, the boron-carbon compound consists of M23(B,C)6, (W,Mo)2(B,C), M3(B1.5,C0.5) and M (B0.7, C0.3) composition.
(2) After high-temperature quenching of high-boron high-speed steel, the matrix structure is transformed into lath martensite with good toughness and a small amount of retained austenite, and the content is about 4%;
(3) Quenching in the range of 950 ~ 1050 °C, the local dissolution of boron-carbon compounds occurs, and the phenomenon of disconnection occurs. As the quenching temperature increases, the phenomenon of disconnection becomes more and more obvious.
(4) After the high-boron high-speed steel is quenched, the type of the boron-carbon compound does not change, and the amount thereof decreases.
2. Effect of quenching temperature on mechanical properties of M2 high-speed steel With the increase of quenching temperature, the hardness and red hardness of M2 high-speed steel increase, but when it exceeds a certain limit temperature (about 1250 °C), the hardness and red hardness of steel begin again. decline. At the same time, as the quenching temperature increases, the toughness of M2 high-speed steel gradually decreases, especially when the temperature exceeds 1220 °C, the toughness decreases significantly. From the viewpoint of improving the hardness, wear resistance and red hardness of the tool, it is advantageous to use a high quenching temperature for the M2 high speed steel, but the quenching temperature is too high, the toughness of the high speed steel is remarkably lowered, and the excessively high quenching temperature enables the heat treatment. The consumption is increased, and the life of the heat treatment furnace is shortened, resulting in an increase in the production cost of the tool. Therefore, for tools with special requirements for hardness and red hardness, the quenching temperature of M2 high-speed steel should be 1230~1250 °C. For tools with special requirements for toughness, the quenching temperature of M2 high-speed steel should be between 1190~1220 °C. Adjustment.
3. Effect of quenching temperature on microstructure and toughness of medium carbon steel
(1) Increasing the quenching temperature can gradually reduce the number of flake martensite in the quenched structure of medium carbon steel, and obtain the structure mainly composed of lath martensite. Continued increase in quenching temperature will result in the formation of a significant amount of flaky retained austenite at the lath martensite boundary.
(2) tempering at 500 °C for 1.5h+4h, does not change the main characteristics of quenched martensite; there is cementite precipitation on the twin boundary of flaky martensite, but still retains the twin substructure; The cementite of the Wechs morphology in the strips of Martens is dissolved, and short strips of cementite are deposited at the slab boundary. The decomposition of retained austenite at the slab boundary during tempering promotes the continuous precipitation of cementite along the martensite boundary of the lath, forming a continuous distribution of cementite sheets.
(3) Appropriately increase the quenching temperature of medium carbon steel, and improve the fracture toughness under high temperature tempering condition by increasing the proportion of lath martensite in the quenched structure. As the number of lath martensite increases, the steel exhibits a fracture characteristic dominated by a plastic fracture mechanism.
(4) After quenching and tempering at a higher temperature, the cementite continuously distributed along the martensite boundary caused by the decomposition of retained austenite will greatly impair the fracture toughness of steel and cause a certain tendency of intergranular fracture.
(5) Extending the tempering time of 500 °C, the rupture of carbides and the gradual elimination of the twin structure of the martensite in the sheet, can improve the fracture toughness value under quenching and high temperature tempering, and increase the steel in The proportion of the plastic fracture mechanism at break greatly reduces the risk of intergranular fracture.


Quenching temperature


Third, optimize the quenching temperature to improve the life of the tooling Quenching temperature is an important process parameter of the quenching process of steel parts. The quenching temperature of common steel has data in the heat treatment manual and related technical books. In the production, it is generally selected as quenching. The basis of temperature is unobjectionable. However, with the recent in-depth study of the martensitic morphology and strengthening and toughening principles, as well as a large number of process experiments and practices, it provides a new basis and experience for us to more rationally choose the quenching temperature. Since the quenching temperature can be properly selected and the quenching temperature can be strictly controlled in the process or the actual operation, the service life of various tools can be significantly improved, and obvious economic benefits are obtained.

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