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45 steel quenching heat treatment process

No. 45 steel quenching is the most common process in the heat treatment of steel. Quenching can improve the hardness and other properties of the metal surface. Below, Haituo Electromechanical will take a look at the quenching heat treatment process of No. 45 steel quenching. Friends come in and have a look.
1.1 preliminary heat treatment

No. 45 steel forgings are usually not annealed for two reasons:

First, if the annealing time is too long, it is easy to produce ferrite accumulation, resulting in tissue inhomogeneity;

Second, because the 45th steel forgings have a longer annealing cycle, the production efficiency is lower. For the 45th steel preparatory heat treatment, high temperature tempering and normalizing are generally used. No. 45 steel forgings are usually controlled within 724 °C, so that not only does the crystallization process not occur, but also the internal stress can be reduced, the hardness is greatly reduced, and the next cutting process is easy.

1.2 Low temperature spheroidizing annealing

The low temperature spheroidizing annealing is a heat treatment method in which the workpiece is heated to a temperature below the eutectoid transformation temperature Acl and then cooled and cooled to obtain a spheroidized structure. When the temperature of the No. 5 steel forging is close to 724 ° C, it takes a long time. In the heat preservation stage, the spheroidal spheroids will change and become spherical pearlite. Its hardness is within 145HB, and its toughness is good, which lays a foundation for cold extrusion.

1.3. Quenching

Quenching of No. 45 steel is to heat the steel to the temperature above Ac3 (hypoeutectoid steel) or Ac1 (hyper-eutectoid steel). After heat preservation, it is placed in various cooling mediums (V cold should be greater than V). Martensite structure is obtained. Since the austenite stability of the 45 steel is relatively poor, it is necessary to rapidly quench and cool the martensite structure to obtain a high hardness after heating. 45 steel has good thermal conductivity. When quenching, it can be directly used in the furnace. It does not need preheating. The temperature is selected according to the relevant technical requirements of the workpiece. The general heating temperature is controlled between 860 °C and 820 °C.

1.4 critical temperature quenching

A large number of experiments have shown that when 45 steel is quenched at a critical temperature of 780 ° C, it can obtain very fine austenite grains, which greatly improves the toughness and also significantly reduces the crack sensitivity. Some workpieces with widely different cross-sectional dimensions are prone to cracking during quenching, and the critical temperature quenching treatment can greatly reduce the probability of cracking.

1.5 induction hardening

High-frequency quenching is a method of heat treatment of metals by induction heating, inductive heating of the workpiece, rapid heating of the surface of the part, and rapid quenching. When the high-frequency heating speed control range is between 200 and 1 000 ° C, the critical temperature is also increased accordingly. Therefore, the quenching heating temperature of the 45-gauge steel forgings is between 880 and 920 ° C, generally compared with other types. The steel height is about 80 - 1000 ° C and sometimes higher. In this way, the No. 45 steel is heated at a high speed by quenching, the microstructure is small, the stress is increased, and the forging can reach a hardness of 62-66 HRC, which has high wear resistance, strong fatigue resistance and small notch sensitivity. specialty.
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