Effective Quenching Method to Avoid Deformation and Crack of Seamless Steel Tube

Isotherm quenching is one of the effective quenching methods to reduce the deformation and cracking of seamless steel tubes. However, how to adopt this process correctly is to make reasonable selection according to the material, size, hardness, toughness, deformation and specific working conditions of seamless steel tubes. The following problems should be paid attention to under the condition of isothermal quenching. As follows, the heat treatment operator reference.

[1] if the steel with low carbon seamless steel pipe with low hardenability is quenched isotherm, the quenching temperature should be improved properly. H is to increase the stability of austenite and avoid and prevent the transition of high temperature non bainite during the isothermal process.

2. Austempering is limited by the size of steel and seamless steel tubes. In the process of isothermal quenching, the basic principle is to ensure that seamless steel pipe will not change during the cooling process, so the steel type and size of seamless steel pipe directly affect the quality of isothermal quenching. Generally, the effective thickness of carbon steel seamless steel pipe should not be more than 5mm, and the effective thickness of alloy steel should be below 30mm. From the point of view of carbon content, carbon steel of 0.4% to 0.6% is not suitable for austempering, and isothermal quenching is more than 0.6% carbon steel.

(3) the temperature and time of isothermal quenching should be determined according to the requirements of the performance of seamless steel pipe according to the C curve of the steel. The principle is that the austenite is completely converted to lower bainite. The cooling medium is usually used in the nitrate bath solution. In order to ensure the stability of the temperature, the cooling device should be added in the medium in order to prevent the temperature of the medium. The quality of quenching is affected by the improvement. In addition, the length of isothermal time should be based on the end of seamless steel tube structure transformation. Too long will reduce the operation efficiency, so we should take seriously.

[4] seamless steel tubes for isothermal quenching may not be tempered. However, for part of the hardened workpiece, its internal residual austenite will be transformed into martensite during the subsequent air cooling process. Therefore, tempering must be carried out to eliminate the brittleness and stability ruler of seamless steel tubes. It should be noted that the tempering temperature should be lower than the isothermal temperature.