Precautions for Austempering of Seamless Steel Pipes

Austempering is an important process in the production of seamless steel pipes. In the process of austempering, what are the precautions? The technical staff of the plain water pipe supplier made the following introduction for us.

Austempering is one of the effective quenching methods to reduce the deformation and cracking of seamless steel pipes, but how to correctly use this process should be carried out according to the requirements of the seamless steel pipe material, size, hardness, toughness, deformation, and specific working conditions. A reasonable choice, the following summarizes the issues that need attention during austempering:

1. If austempering is performed on steel grades with low hardenabilities, such as carbon seamless steel pipes, the quenching heating temperature should be appropriately increased. H is to increase the stability of austenite and to avoid and prevent the occurrence of high temperature in the isothermal process Bainite transformation.

2. Austempering is restricted by the steel grade and the size of the seamless steel pipe. When performing austempering, the basic principle is to ensure that seamless steel pipes will not undergo high-temperature changes during the cooling process. Therefore, the steel grade and size of seamless steel pipes directly affect the quality of austempering. Generally, carbon steel seamless steel pipes are required The effective thickness of alloy steel should be no more than 5mm, and the effective thickness of alloy steel should be less than 30mm. From the perspective of carbon content, 0.4% to 0.6% of carbon steel is not suitable for austempering, and only above 0.6% can be austempered.

3. The temperature and time of austempering should be determined according to the performance requirements of seamless steel pipes and with reference to the C curve of the steel. The principle is that all austenite is transformed into lower bainite. The cooling medium is usually a nitrate bath solution. In order to ensure the stability of the temperature, a cooling device should be added to the medium to prevent the increase of the medium temperature from affecting the quenching quality. In addition, the length of the isothermal time should be based on the completion of the seamless steel pipe structure transformation. If it is too long, it will reduce work efficiency, so it should be taken seriously.

4. Some seamless steel pipes subjected to austempering may not be tempered. However, for partially austenite-quenched workpieces, the internal retained austenite will be transformed into martensite in the subsequent air-cooling process, so it must be tempered in order to eliminate the brittleness and stability of seamless steel pipes. Pay attention The tempering temperature should be lower than the isothermal temperature.