Steel is quenched and heat treated using a medium frequency induction quenching machine. What is the heating temperature and heating speed?

When steel is quenched and heat treated using a medium frequency induction quenching machine, its heat treatment quality is affected by many factors, such as heating temperature, heating speed, etc. Today, the editor will tell you how to determine the heating temperature and heating speed of different materials of steel?

(1) Heating temperature. The heating temperature for quenching hypoeutectoid steel is Ac3+30-50℃. Generally, heating in a medium-frequency induction quenching machine is 10-30℃ higher than heating in a salt bath. When using oil or nitrate salt quenching media, The quenching heating temperature should be about 20°C higher than that of water quenching.

The quenching heating temperature of eutectoid steel and hypereutectoid steel is Ac1+30-50℃, and the quenching heating temperature of general alloy steel is Ac1 or Ac3+30-50℃. High speed steel, high chromium steel and stainless steel should be selected according to the degree of required alloy carbide dissolution into austenite. For steels that are highly sensitive to overheating (such as manganese steel) and to steels that are highly sensitive to decarburization (such as molybdenum-containing steel), the upper limit temperature should not be set.

Low carbon martensitic steel has low hardenability. When using a medium frequency induction quenching machine for quenching heat treatment, the quenching temperature should be increased to increase the hardened layer. Medium carbon steel and medium carbon alloy steel should increase the quenching temperature appropriately to reduce the amount of quenching after quenching. The relative content of lamellar martensite is used to improve the toughness of the steel; low-temperature quenching or rapid heating of high carbon steel can limit the amount of austenite solid solution carbon, while increasing the content of lath martensite after quenching reduces the toughness of the quenched steel. brittleness. In addition, increasing the quenching temperature will also increase the amount of retained austenite after quenching of alloy steel.

(2) Heating speed. For large castings and forgings with complex shapes that require small distortion, or large castings and forgings made of alloy steel, the heating speed must be controlled to ensure that quenching distortion and cracking tendencies are reduced. Generally, the heating speed is limited to 30-70°C/s. 600-700℃, and then heat up at a speed of 50-100℃/s after equalizing the temperature for a period of time. Medium and low carbon steel with simple shapes and medium carbon alloy structural steel with a diameter less than 400mm can be heated directly in the furnace.

This article briefly introduces the heating temperature and heating speed when steel is heated and heat treated. When performing the heat treatment process, everyone should strictly follow the above operations to avoid defects.