Views: 73 Author: Site Editor Publish Time: 2018-05-28 Origin: Site
The quality defects of precision seamless steel pipe after heat treatment usually have a great relationship with technical operation. Now let's see what causes the defects of seamless steel tubes.
The microstructure overheating after quenching can be observed from the rough joint of the precision seamless steel tube. If there is coarse needle like martensite in quenching microstructure of precision seamless steel pipe, the overheated structure will be quenched. The cause may be the overheating of the overheating of the heating temperature or the long heat preservation time. It is also possible that the local superheat of the local martensite formed in the low carbon zone between the two bands is serious, and the local superheat caused by the local martensite formed in the low carbon zone between the two bands. Retained austenite increased and dimensional stability decreased in overheated structure. Because of the overheating of the quenched structure, the coarse crystal of the steel will cause the impact resistance of the high pressure alloy pipe to decrease, and the life of the high pressure alloy tube will also decrease. Overheating can even lead to quenching cracks.
2. Quenching crack
The crack of precision seamless steel pipe is quenched crack due to internal stress in the quenching process, which exceeds the tensile strength of the material instantly. The causes of this crack are as follows:
Because the quenching temperature is too high or the cooling is too urgent, the thermal stress and the mass volume change of the steel are more severe than those of the steel.
The original defects on the surface of the material are concentrated in the process of quenching.
Serious surface decarburization and carbide segregation;
Insufficient tempering or not timely tempering after the parts are quenched
In short, the reasons for quenching cracks may be one or more of the above, the existence of internal stress is the main reason for quenching cracks.
3. Heat treatment deformation
When the precision seamless tube is treated, there is thermal stress and tissue stress. This internal stress can be overlapped or partially offset. It is complex and changeable, because it can change with the change of heating temperature, heating speed, cooling rate, cooling mode, shape and size of parts and furnace mode, so its heat treatment deformation is difficult. It's free. Knowing and mastering its variation rule can make the deformation of bearing parts placed in a controllable range, which is conducive to normal production. Of course, mechanical collision during heat treatment will also cause deformation of parts, but this deformation can be reduced and avoided by improving operation.
In the heat treatment operation of the precision seamless steel pipe, there will be a lot of factors affecting the precision seamless tube, which requires the technician's technical level is very high, and the following needs to carry on the continuous summary of the operation experience.