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Quenching method for deformation and cracking of seamless steel pipe
Release time:
2023-02-27 14:26
Austempering is one of the effective quenching methods to reduce the deformation and cracking of seamed steel pipes (straight seam steel pipes, spiral steel pipes and erw steel pipes) and seamless steel pipes, but how to use the process correctly depends on the material. , size, hardness and toughness of steel pipe. Reasonable selection of deformation requirements, as well as specific working conditions, etc. The following is a summary of the problems that should be paid attention to in the austempering of seamless steel pipes, for reference by heat treatment operators.
For isothermal tempering of steels with low hardenability such as carbon seamless steel pipes, the quenching heating temperature should be appropriately increased to increase the stability of austenite and avoid and prevent high-temperature non-Bayesian body transformation during the isothermal process.
Austempering is limited by the steel and the size of the steel. The basic principle of austempering is to ensure that the seamless steel pipe does not undergo high-temperature transformation during the cooling process. Therefore, the steel type and size of seamless steel pipes directly affect the quality of austempering, and carbon steel seamless steel pipes are generally required. The effective thickness should not be greater than 5mm, and the effective thickness of alloy steel should be less than 30mm. From the perspective of carbon content, carbon steel with 0.4% to 0.6% is not suitable for austempering, and carbon steel with more than 0.6% can be austempered.
The temperature and time of austempering should be determined according to the performance requirements of the steel pipe and with reference to the C curve of the steel. The principle is that all austenite is transformed into lower bainite. For the cooling medium, a nitrate bath solution is usually used. In order to ensure the stability of the temperature, a cooling device should be added to the medium to prevent the medium temperature from rising and affecting the quenching quality. In addition, the length of the isothermal time should be determined according to the end of the structural transformation of the seamless steel pipe. Excessive time will reduce work efficiency and should be paid attention to.
Some seamless steel pipes that have been austempered can not be tempered. However, for partially quenched workpieces, the internal retained austenite will transform into martensite in the subsequent air cooling process, so tempering must be carried out to eliminate the brittleness and stability of seamless steel pipes. The fire temperature should be lower than the isothermal temperature.
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