Key Points of Annealing, Normalizing,Quenching and Tempering of Seamless Steel Pipes

1. Annealing operation method of seamless steel pipe: after heating the seamless steel pipe to AC3 + 30-50 degree or AC1 + 30-50 degree or below AC1, it generally cools slowly with the furnace temperature.
Objectives: 1. Reduce hardness, improve plasticity, improve cutting and pressure processing performance; 2. Refine grain, improve mechanical performance, and prepare for the next step; 3. Eliminate internal stress generated by cold processing.
Application focus: 1. It is applicable to the alloy structural steel, carbon tool steel, alloy tool steel, high-speed steel forgings, weldments and raw materials with unsatisfactory supply conditions; 2. It is usually annealed in blank state.




2. Normalizing operation method of seamless steel pipe: heat the seamless steel pipe to 30 to 50 degrees higher than AC3 or ACCM, and then cool it to a temperature slightly higher than annealing cooling rate.
Objectives: 1. Reduce hardness, improve plasticity, improve cutting and pressure processing performance; 2. Refine grain, improve mechanical performance, and prepare for the next step; 3. Eliminate internal stress generated by cold and hot processing.
Application points: normalizing is usually used as preheating process for forgings, welding parts and carburized parts. For low carbon and medium carbon structural steel and low alloy seamless steel pipes with low performance requirements, they can also be used as final heat treatment. For general medium and high alloy steels, air cooling can lead to complete or partial quenching, so it can not be used as the final heat treatment process.


3. Quenching operation method of seamless steel pipe: heat the seamless steel pipe to phase change temperature AC3 or AC1, keep it for a period of time, and then rapidly cool it in water, nitrate, oil or air.
Objective: quenching is usually used to obtain martensite with high hardness.  Sometimes, when some high alloy steels (such as stainless steel and wear-resistant steel) are quenched, a single uniform austenite structure is obtained to improve wear resistance and corrosion resistance.
The key points of application: 1. Generally used for carbon steel and alloy steel with carbon content greater than 0.3%; 2. Quenching can give full play to the strength and wear resistance of steel, but it will cause great internal stress at the same time. In order to reduce the plasticity and impact toughness of steel, it is necessary to temper to obtain better comprehensive mechanical properties.


4. Operation method for tempering of seamless steel pipe: heat the seamless steel pipe to the temperature below AC1 after quenching, and then cool it in air or oil, hot water and water after cooling.
Objective: 1. Reduce or eliminate the internal stress after quenching, reduce the deformation and cracking of the workpiece; 2. Adjust the hardness, improve the plasticity and toughness, and obtain the required mechanical properties; 3. Stabilize the workpiece size.
The main points of application are as follows: 1. Keep the high temperature and wear resistance of the steel after low temperature tempering; use medium temperature tempering to improve the elasticity and yield strength of the steel under the condition of maintaining certain toughness. When the strength is high enough, the high impact toughness and plasticity shall be maintained, and high temperature tempering shall be carried out; 2. Tempering between 230 and 280 degrees shall be avoided for ordinary steel, while tempering between 400 and 450 degrees shall be avoided for stainless steel, because tempering brittleness will occur.