The main points of annealing, normalizing, quenching and tempering of seamless carbon steel pipe

Posted by zora li on October 24th, 2022

Annealing operation method of seamless steel pipe:
After heating the seamless steel pipe to Ac3+30~50 degrees or Ac1+30~50 degrees or below Ac1, it is generally cooled slowly with the furnace temperature.

Purpose:
1. Reduce hardness, improve plasticity, and improve cutting and pressure processing performance;
2. Refine grains, improve mechanical properties, and prepare for the next step;
3. Eliminate the internal stress caused by cold working.

Application points:
1. It is suitable for alloy structural steel, carbon tool steel, alloy tool steel, high-speed steel forgings, welding parts and raw materials whose supply conditions are not ideal;
2. Generally annealed in billet state.

Normalizing operation method of seamless steel pipe: Heat the seamless carbon steel pipe to 30-50 degrees above Ac3 or Accm, and then cool it to a temperature slightly greater than the annealing cooling rate.

Purpose:
1. Reduce hardness, improve plasticity, and improve cutting and pressure processing performance;
2. Refine grains, improve mechanical properties, and prepare for the next step;
3. Eliminate the internal stress caused by cold and hot processing.

Application points: Normalizing is usually used as a preheat treatment process for forgings, welds and carburized parts. It can also be used as final heat treatment for low-carbon and medium-carbon carbon structural steel and low-alloy seamless steel pipes with low performance requirements. For general medium and high alloy steels, air cooling can lead to full or partial quenching and therefore cannot be used as a final heat treatment process.

Operation method of quenching seamless steel pipe: heat the seamless steel pipe to the phase transition temperature Ac3 or Ac1, keep it for a period of time, and then quickly cool it in water, nitrate, oil or air.
Purpose: Quenching is generally used to obtain martensitic structure with high hardness. Sometimes, some high alloy steels (such as stainless steel and wear-resistant steel) are quenched in order to obtain a single uniform austenite structure to improve wear and corrosion resistance.

Application points:
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 at the same time it will generate a lot of internal stress. In order to reduce the plasticity and impact toughness of the steel, tempering is required to obtain better comprehensive mechanical properties.

Tempering operation method of seamless steel pipe: reheat the quenched seamless steel pipe to a temperature below Ac1, and after cooling, cool it in air or oil, hot water and water.

Purpose:
1. Reduce or eliminate the internal stress after quenching and reduce the deformation and cracking of the workpiece;
2. Adjust the hardness, improve the plasticity and toughness, and obtain the mechanical properties required for the work;
3. Stable workpiece size.

Application points:
1. Maintain the high temperature and wear resistance of the steel after low temperature tempering and quenching; adopt medium temperature tempering to improve the elasticity and yield strength of the steel while maintaining a certain toughness; maintain high impact toughness and plasticity. Under high temperature tempering;
2. General steel should avoid tempering between 230 and 280 degrees, and stainless steel should avoid tempering between 400 and 450 degrees, because there will be temper brittleness.

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