Quenching refers to the transformation of the structure of the cs seamless pipe from austenite to martensite or bainite, heating the cs seamless pipe to the temperature above AC3 or AC1, and then heat preservation until the internal structure of the cs seamless pipe is all or part of the austenite It is a heat treatment process in which MS is transformed into martensite by rapid cooling at a temperature greater than the critical cooling temperature.
The quenching and tempering of cs seamless pipe is a very important and widely used process in the heat treatment process. Quenching can significantly increase the strength and hardness of steel. If it is matched with tempering at different temperatures, the internal stress of quenching can be eliminated (or reduced), and the combination of strength, hardness and toughness can be obtained to meet different requirements. Therefore, quenching and tempering are two inseparable heat treatment processes.
Process:
The cs seamless pipe is heated to the quenching temperature, kept for a period of time, and then rapidly cooled in water, brine or oil (individual materials in air).
Purpose:
1) Make the cs seamless pipe obtain higher hardness and wear resistance;
2) Make the cs seamless pipe get some special properties after tempering, such as higher strength, elasticity and toughness.
Common problems in the quenching of cs seamless pipes include deformation, cracking, air oxidation, carburizing, insufficient or asymmetrical strength, surface erosion, coarse grains, overheating, and poor alloy composition according to quality inspection standards. In specific production, corresponding preventive measures should be taken according to the causes of quenching deformation and quenching cracks to ensure that the cs seamless pipe is heated evenly and properly.
Quenching and insulation
CS seamless pipe quenching and holding time is determined by various factors such as equipment heating method, part size, steel composition, furnace loading and equipment power. For overall quenching, the purpose of heat preservation is to make the internal temperature of the steel pipe uniform and consistent. For various types of quenching, the holding time ultimately depends on obtaining a good quenching and heating structure in the area where quenching is required. Heating and heat preservation are important links that affect the quality of quenching. The microstructure obtained by austenitization directly affects the performance after quenching. Generally, the austenite grains of steel pipes are controlled at grades 5 to 8.
Quenching and cooling of CS seamless pipe
To make the high temperature phase in the steel pipe - austenite transform into the low temperature metastable phase - martensite during the cooling process, the cooling rate must be greater than the critical cooling rate of the steel tube. During the cooling process of the steel pipe, there is a certain difference in the cooling rate between the surface and the core. If this difference is large enough, it may cause the part above the critical cooling rate to transform into martensite, but the core part below the critical cooling rate cannot transform into martensite. In order to ensure that the entire section is transformed into martensite, it is necessary to select a quenching medium with sufficient cooling capacity to ensure a sufficiently high cooling rate at the core of the steel pipe. However, the cooling rate is high, and the internal stress caused by the uneven thermal expansion and contraction inside the steel pipe may deform or crack the steel pipe. Therefore, the above two contradictory factors should be considered, and the quenching medium and cooling method should be reasonably selected.
In the cooling stage, not only the parts can obtain a reasonable organization and achieve the required performance, but also the size and shape accuracy of the steel pipe must be maintained, which is the key link in the quenching process.
Precaution:
1) Use a cooling medium with good hardenability, formulate reasonable heat treatment and quenching process parameters, and select a reasonable cooling medium or control operation method;
2) Improve the heat treatment process, adopt vacuum heating, protective atmosphere heating and fully deoxidized salt bath furnace heating and graded quenching and isothermal quenching;
3) Fully tempered to obtain stable microstructure and properties; multiple tempering makes the retained austenite transformation fully and eliminates new stress
4) Improve the forging process or perform correct spheroidizing annealing and normalizing treatment to prevent local overheating or overburning, and take protective measures or pre-cooling measures;
5) Appropriately adjust the composition of steel grades, reduce the content of C element, refine the grains, and improve the crack growth resistance. The mass fraction of C and Mnv> should be strictly controlled for water-quenched steel grades. When w(C)+w(Mn)/3 ≥ 0.9%, there is a risk of cracking in the water-quenching process, and the oil-quenching process should be used. For high C and high Mn steels, reducing the quenching temperature and cooling rate is beneficial to prevent the occurrence of quenching cracks in the steel pipe.
TIPS: Quenching methods for CS seamless pipes include single-medium quenching, double-medium quenching, graded quenching, austempering, surface quenching, and induction hardening
The quenching and tempering of cs seamless pipe is a very important and widely used process in the heat treatment process. Quenching can significantly increase the strength and hardness of steel. If it is matched with tempering at different temperatures, the internal stress of quenching can be eliminated (or reduced), and the combination of strength, hardness and toughness can be obtained to meet different requirements. Therefore, quenching and tempering are two inseparable heat treatment processes.
Process:
The cs seamless pipe is heated to the quenching temperature, kept for a period of time, and then rapidly cooled in water, brine or oil (individual materials in air).
Purpose:
1) Make the cs seamless pipe obtain higher hardness and wear resistance;
2) Make the cs seamless pipe get some special properties after tempering, such as higher strength, elasticity and toughness.
Common problems in the quenching of cs seamless pipes include deformation, cracking, air oxidation, carburizing, insufficient or asymmetrical strength, surface erosion, coarse grains, overheating, and poor alloy composition according to quality inspection standards. In specific production, corresponding preventive measures should be taken according to the causes of quenching deformation and quenching cracks to ensure that the cs seamless pipe is heated evenly and properly.
Quenching and insulation
CS seamless pipe quenching and holding time is determined by various factors such as equipment heating method, part size, steel composition, furnace loading and equipment power. For overall quenching, the purpose of heat preservation is to make the internal temperature of the steel pipe uniform and consistent. For various types of quenching, the holding time ultimately depends on obtaining a good quenching and heating structure in the area where quenching is required. Heating and heat preservation are important links that affect the quality of quenching. The microstructure obtained by austenitization directly affects the performance after quenching. Generally, the austenite grains of steel pipes are controlled at grades 5 to 8.
Quenching and cooling of CS seamless pipe
To make the high temperature phase in the steel pipe - austenite transform into the low temperature metastable phase - martensite during the cooling process, the cooling rate must be greater than the critical cooling rate of the steel tube. During the cooling process of the steel pipe, there is a certain difference in the cooling rate between the surface and the core. If this difference is large enough, it may cause the part above the critical cooling rate to transform into martensite, but the core part below the critical cooling rate cannot transform into martensite. In order to ensure that the entire section is transformed into martensite, it is necessary to select a quenching medium with sufficient cooling capacity to ensure a sufficiently high cooling rate at the core of the steel pipe. However, the cooling rate is high, and the internal stress caused by the uneven thermal expansion and contraction inside the steel pipe may deform or crack the steel pipe. Therefore, the above two contradictory factors should be considered, and the quenching medium and cooling method should be reasonably selected.
In the cooling stage, not only the parts can obtain a reasonable organization and achieve the required performance, but also the size and shape accuracy of the steel pipe must be maintained, which is the key link in the quenching process.
Precaution:
1) Use a cooling medium with good hardenability, formulate reasonable heat treatment and quenching process parameters, and select a reasonable cooling medium or control operation method;
2) Improve the heat treatment process, adopt vacuum heating, protective atmosphere heating and fully deoxidized salt bath furnace heating and graded quenching and isothermal quenching;
3) Fully tempered to obtain stable microstructure and properties; multiple tempering makes the retained austenite transformation fully and eliminates new stress
4) Improve the forging process or perform correct spheroidizing annealing and normalizing treatment to prevent local overheating or overburning, and take protective measures or pre-cooling measures;
5) Appropriately adjust the composition of steel grades, reduce the content of C element, refine the grains, and improve the crack growth resistance. The mass fraction of C and Mnv> should be strictly controlled for water-quenched steel grades. When w(C)+w(Mn)/3 ≥ 0.9%, there is a risk of cracking in the water-quenching process, and the oil-quenching process should be used. For high C and high Mn steels, reducing the quenching temperature and cooling rate is beneficial to prevent the occurrence of quenching cracks in the steel pipe.
TIPS: Quenching methods for CS seamless pipes include single-medium quenching, double-medium quenching, graded quenching, austempering, surface quenching, and induction hardening
