Heat Treatment of 45 Steel

Heat Treatment of 45 Steel

1.1 Preliminary heat treatment

The forging and rolling part of 45 steel is usually not annealed for two reasons:

First, if the annealing time is too long, it is easy to produce ferrite agglomeration, resulting in uneven structure; .

Second, the production efficiency is low because of the long annealing treatment period of 45 steel. The preparation heat treatment of 45 steel generally adopts high temperature tempering and normalizing. The forging and rolling part of 45 steel is usually controlled within 724℃, which not only does not produce crystallization process, but also can reduce its internal stress, the hardness is greatly reduced, and it is easy for the next cutting process.

1.2 Low temperature spheroidizing annealing

Low temperature spheroidizing annealing is to put the workpiece heated to eutectoid transformation temperature for thermal insulation under the Acl, and then slowly but grimly, and can achieve the spheroidizing organization heat treatment method, the temperature of the 5 steel forged parts in close to 724 ℃, must carry on the long time heat preservation stage, that slice the ball light body will change, become the spheroidal pearlite, its hardness is within 145 HB, its tenacity, which laid a foundation for cold extrusion.

1.3. Quenching

The quenching of 45 steel is to heat the steel to Ac3(subeutectoid steel) or Ac1(hypereutectoid steel) above the temperature, after the heat preservation into a variety of different cooling media (V cold should be greater than V), in order to obtain martensite structure. Due to the relatively poor austenite stability of 45 steel, it is necessary to quench and cool the martensite rapidly after heating in order to obtain the martensite structure with high hardness. 45 steel has good thermal conductivity, in the quenching, can be directly into the furnace, do not need to preheat, according to the relevant technical requirements of the workpiece to choose the temperature, the general heating temperature is controlled between 860℃ – 820℃.

1.4 Critical temperature quenching

A large number of experiments show that when 45 steel is quenched at 780℃ critical temperature, very small austenite grains can be obtained and toughened.

At the same time, the crack sensitivity was reduced significantly. Some work pieces with large cross section sizes are prone to crack during quenching, and the probability of crack can be greatly reduced when the critical temperature is quenched.

1.5 High-frequency quenching

High frequency quenching is through induction heating equipment, induction heating to the workpiece, quickly heating the surface of the parts, and then quickly quenching of a kind of gold.

Belongs to heat treatment method, the control range of high-frequency heating speed is between 200 ℃ and 1 000℃. The quenching heating temperature of 45 forged steel is between 880 ℃ and 920℃, generally higher than other types of steel about 80 ~ 1000℃ sometimes higher. In this way, 45 steel is heated at high frequency quenching very quickly, with fine structure and increased stress, which can make the forging reach the hardness of 62-66 HRC. It has the characteristics of high wear resistance, strong fatigue resistance and small notch sensitivity.