Pipe deformation during induction hardening and tempering
Steel pipe will have deformation during induction hardening and tempering process. If the steel pipe bending deformation is relatively large, which will bring difficulties to the pipe straightening as the pipe yield strength will be up to 100kg / mm2. Through experiments, we found the main reason for pipe bending during the process of induction hardening and tempering is ununiform heating and cooling, which results in uneven distribution of internal stress. That makes pipe deformed during pipe hardening and tempering induction heat treatment.
Please check the following reasons that effect pipe uniform heating and cooling.
1. The way of pipe going forward during heat treatment: When the pipe is heat treated, the pipe will be heated and cooled by horizontal and rotary forward.When the steel pipe goes forward horizontally, it is difficult to do concentric with the inductor.
There will be temperature difference even a slight deviation. Sometimes the temperature difference will be more than 100℃. Similarly, Concentric deviation between sprayer and pipe will also cause temperature difference.Therefore, the horizontal approach is not easy to ensure uniform heating and cooling of the steel pipe, while the rotation can overcome the above shortcomings. The pipe will have a very small deformation.
In order to achieve pipe rotating forward in the process pipe induction hardening and tempering, we set 18-20° angle between roller and transmission device. The pipe will rotate itself when it goes forward.
2. Warm-up speed when quenching heating
The warm-up speed of pipe heating for quenching has some effect for the pipe deformation. The heating speed of normal quenching is 15-20 ℃ / S. For pipes with a diameter of 51 mm and a wall thickness of 6 mm, the speed is 1-1.2 m / min.
3. Water pressure effects during spraying
Cooling condition will also have effect on the pipe when quenching. Internal stress difference caused by uneven cooling will result in pipe bending deformation. The uniformity of cooling during quenching depends mainly on the uniformity of the water jet pressure.
4.The degree of pipe bending before hardening and tempering heat treatment
Before hardening and tempering, the steel pipe undergoes a preliminary correction, and the general bending deformation is about 1.5mm / m. But sometimes more than this value. Bending deformation is too large, which will bring difficulties to rotation and change the speed. To ensure the pipe Min. bending deformation, the green pipe bending deformation should not be greater than 1.5mm / m before hardening and tempering.
5. Other factors
Among other factors, the cooling water is mainly prevented from entering the heated steel pipe from the end of the pipe during quenching,which will result in the difference of cooling conditions for pipe inside and outside, resulting in large deformation of the end. In the quenching and tempering treatment, user can use special plug to prevent quench water flowing into the tube
In summary, in order to reduce the bending deformation of steel pipe, the following measures should be taken in the production.
1. Do pre-straightening for green pipe before hardening and tempering.
2. The pipe should maintain the speed of 60-120RPM while going forward.
3. Inductors, sprinklers and pipes should maintain good concentricity.
4. Steel pipe end of the plug should be tightly packed.
After taking the above measures, the bending deformation of the small caliber steel pipe can all be controlled at ≦ 2.0 mm / m.
Any inquiry about Forever induction hardening and tempering equipment, welcome to contact with us.
Overseas manager: Tom Wang
Phone: 0086-13303078975(whatsapp, wechat,line)
Specialist of induction heating system in China; Glad to be your business partner in induction heating field.
Post time: 03-04-2018