Residual Heat of Seamless Steel Tube Forgings

A large number of application examples show that the full use of the heat of forging heat treatment can serve two purposes, which not only saves energy, but also shortens the process. At the same time, it also plays an indirect role in protecting the environment.

Forging residual heat isothermal normalizing means that after the forging is formed, when the temperature is higher than that of Ar3 (for hypoeutectoid steel), it is rapidly cooled, cooled to an isothermal temperature, then kept warm for a while and then cooled to room temperature.

The main points of seamless steel tube control are:
1. Forging temperature control after forging. The forging temperature after forming must be above Ar3 (for hypoeutectoid steel), and direct quenching can be used when the temperature of the forged part is stable. When the temperature of the forged part is large or the cross-section of the forging changes, the temperature equalization process must be increased. Before quenching, make the temperature of the parts uniform, otherwise it will result in a large difference between the temperature of the forgings or different cross-sections after quenching, resulting in an abnormal microstructure (bainite or martensite).

2, Seamless steel tube quenching control
1) Cooling speed control. In the quenching process, the forgings are required to be rapidly cooled, and at the same time, the temperature of the same forging and the same batch of forgings is uniform (or similar) after cooling. At the same time, it is necessary to control the quenching speed, and the quenching speed that is too fast will produce Wei's structure in the forging structure. The general quench speed is controlled at 30 to 42°C/min.
2) Temperature control after quenching. After quenching, the forging temperature must be ensured in the pearlite transformation zone, and it must not be lower than the bainite transformation starting temperature (Bs), otherwise bainite (or granular bainite) structure will appear in the structure; if the temperature is too high after quenching, it will lead to the amount of pro-eutectoid ferrite increases, and the spacing of pearlite sheets after the tissue transformation is large, resulting in low hardness of the parts. The temperature of the forging after quenching is generally controlled at a temperature of 80 to 100°C above the temperature of the material Bs.

3, The choice of isothermal temperature seamless steel tube. The isothermal temperature directly affects the hardness of the forgings after isothermal normalization. The hardness is low when the isothermal temperature is high, and the hardness is high when the isothermal temperature is low. The isothermal temperature is usually 50 to 80°C above the temperature of the forging material Bs, and the specific temperature must be determined by testing according to the material and shape of the forging.

4. Determination of the isothermal holding time of seamless steel tubes. The pearlite transformation takes place during the isothermal process, so it must have sufficient holding time. If the isothermal time is too short, the undercooled austenite will not be completely transformed into pearlite. In the subsequent cooling process, it will transform into bainite or martensite. Body, causing unqualified tissue and high hardness after isothermal treatment. The isothermal time can be determined initially based on the isothermal transition curve of the material and adjusted according to the test conditions.