Small diameter thick walled seamless steel pipe refers to a steel pipe with a small ratio of outer diameter to wall thickness. So, how to carry out heat treatment for small diameter thick walled steel pipes? Below, Yantai Steel Pipe Factory will take you to understand. I hope it will be helpful to you.

1. During the heat treatment process, the repaired parts require normalizing treatment. Normalizing is a heat treatment process where seamless steel pipes with small diameter and thick wall are heated to 45 ℃ above Ac3, insulated for an appropriate time, and cooled in still air. Structural parts that require mechanical performance indicators need to be normalized and tempered to meet the mechanical performance requirements. After normalizing, medium and high alloy steel and large forgings require high-temperature tempering to eliminate the internal stress generated during normalizing.

2. The annealing treatment of seamless steel pipes with small diameter and thick wall is a heat treatment process that heats the metal and alloy to an appropriate temperature, maintains it for a certain period of time, and then slowly cools down. After annealing, the microstructure of hypoeutectoid steel is ferrite with flake like pearlite; Eutectoid steel or hypereutectoid steel is granular pearlite. In short, the annealed microstructure is close to equilibrium state.

4. The normalizing heating knife of hypereutectoid steel is above Acm, allowing all the previously reticulated carbides to dissolve into austenite. Then, it is cooled at a faster rate to suppress the precipitation of carbides at the austenite grain boundaries, thereby eliminating the reticulated carbides and improving the microstructure of hypereutectoid steel. Weldments require parts with weld strength to be normalized to improve weld microstructure and ensure weld strength.

5. Some seamless steel pipes with small diameter and thick wall undergo partial martensitic transformation during forging, forming a hard structure. In order to eliminate this kind of bad tissue, when normalizing, the heating and insulation temperature should be about 20 ℃ higher than the normal normalizing temperature for normalizing. The normalizing process is relatively simple, which is conducive to using forging waste heat for normalizing, saving energy and shortening the production cycle. Improper normalizing process and operation can also cause structural defects, similar to annealing, and the remedial methods are basically the same.