1 steel pipe heat treatment process is:

Quenching - After the medium frequency furnace heats the steel pipe to 930 °C, the workpiece is spray-cooled and quenched by water spray cooling at the exit of the induction furnace.

Tempering - After the medium frequency furnace heats the steel pipe to 600 °C ~ 650 °C, the steel pipe is cooled and tempered by natural cooling at the exit of the induction furnace.

2 quenching heat treatment medium selection:

The ideal cooling curve according to the material composition of the steel tube ( 20 埚) is shown in Fig. 1 . The quenching medium is generally oil quenched or water quenched. In order to inherit the advantages of oil quenching stability and rapid water quenching, but also to eliminate the large amount of smog pollution and cost defects caused by oil quenching and the quenching phenomenon due to excessive cooling rate during water quenching, I The company uses the latest gas mist cooling method to quench.

3 Description of problems in the water quenching process:

       Most workpieces are cracked by tap water quenching. The reason for quenching is well known: the low temperature cooling of tap water is too fast. This is a major drawback of tap water. Secondly, the effect of water temperature on the cooling characteristics is great. (See Figure 3. ) We have listed the cooling characteristics too sensitive to changes in liquid temperature as the second major drawback of tap water. The cooling characteristics of water are too sensitive to changes in water temperature, and the inadequacy of the change in oil temperature in Figure 2 compared to the cooling characteristics is obvious.

4 characteristics of gas mist medium:

The cooling process of gas mist quenching generally has three stages of membrane boiling, bubble boiling and convection. In the membrane boiling stage, the vapor film is formed between the quenching medium and the hot workpiece, which affects the affinity of the medium and the workpiece. Heat can only be carried out through the conduction of the vapor film, so the cooling rate is slow at this stage. When using steam-water mist medium spray quenching, the medium can be directly sprayed to the workpiece due to the aid of the soda water mist pressure, so that the cooling speed of the workpiece can be very stable, and the steam-water mist can not collect water during the cooling process. Effectively eliminate the problem of local softening point. In order to overcome the shortage of water temperature sensitive to changes in cooling characteristics during water quenching, the ideal cooling curve can be obtained by simply controlling the water temperature in the range of 20 to 40 °C (see Figure 3 ).

5 description of steam-water mist quenching process curve:

20 pots, Q345b , Q345c , 27 manganese, 37 manganese 5 , 15 manganese; steel is a medium hardenability quenched and tempered steel, the process is to heat the steel to Ac3 above 30 ~ 50 °C (ie 850 ~ 930 °C), then in the first slow cooling; the C curve 600 ~ 400 fast cooling between ℃; finally 350 ~ 200 and then slow cooling ℃, the thermal state austenite to martensite.

On the quenching line , after the front end of the workpiece exits the induction furnace,

The soda spray is cooled to a temperature below the phase transition point to obtain a quenched martensite.

On the tempering line , after the front end of the workpiece exits the induction furnace, natural cooling is performed to obtain tempered sorbite.

7 Determination of water vapor injection pressure flow data:

In order to ensure the hardenability of the workpiece, the pressure of the water and gas source must reach 0.6 to 0.8 MPa . The angle of the water spray is at an angle of 450 to the axial direction to prevent the effect of the rebounding water mist on the unquenched portion. The cooling rate of the water mist spray is generally 550 to 650 °C / sec. To ensure that the phase change point temperature of martensite is accurately reached in the effective quenching area of the workpiece, the pressure and flow rate of water and steam are required to be measured. The method of measurement can be obtained by using a computer to sample temperature, air pressure, water pressure, flow rate in a conventional manner, preferably experimental data, to finally obtain more accurate relevant data.