What are the four fires of industry?

1. Annealing

Operation method: After heating the steel to Ac3+30~50 degrees or Ac1+30~50 degrees or the temperature below Ac1 (relevant information can be consulted), 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 process;

3. Eliminate the internal stress caused by cold and hot processing.

Application points:

1. It is suitable for alloy structural steel, carbon tool steel, alloy tool steel, high-speed steel forgings, welded parts and unqualified raw materials;

2. Generally, annealing is carried out in the rough state.

2. Normalizing

Operation method: Heat the steel to 30~50 degrees above Ac3 or Accm, and cool it at a cooling rate slightly greater than that of annealing after heat preservation.

Purpose:

1. Reduce hardness, improve plasticity, and improve cutting and pressure processing performance;

2. Refine grains, improve mechanical properties, and prepare for the next process;

3. Eliminate the internal stress caused by cold and hot processing.

Application points:

Normalizing is usually used as a pre-heat treatment process for forgings, weldments and carburized parts. For low-carbon and medium-carbon carbon structural steel and low-alloy steel parts with low performance requirements, it can also be used as the final heat treatment. For general medium and high alloy steels, air cooling can lead to complete or partial quenching, so it cannot be used as the final heat treatment process.

3. Quenching

Operation method: heat the steel to above the phase transition temperature Ac3 or Ac1, keep it for a period of time, and then rapidly cool it in water, nitrate, oil, or air.

Purpose: Quenching is generally to obtain a high-hardness martensite structure, and sometimes when quenching some high-alloy steels (such as stainless steel and wear-resistant steel), it is to obtain a single uniform austenite structure to improve wear resistance. 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 potential of steel, but at the same time it will cause great internal stress and reduce the strength of steel. Plasticity and impact toughness, so tempering is required to obtain better comprehensive mechanical properties.

4. Tempering

Operation method:

The quenched steel parts are reheated to a temperature below Ac1, and after heat preservation, they are cooled in air or oil, hot water, and water.

Purpose:

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 mechanical properties required by the work;

3. Stable workpiece size.

Application points:

1. Use low temperature tempering to maintain the high hardness and wear resistance of the steel after quenching; use medium temperature tempering to improve the elasticity and yield strength of the steel while maintaining a certain toughness; to maintain high impact toughness and plasticity Mainly, when there is sufficient strength, high temperature tempering is used;

2. Generally, steel should be tempered at 230~280 degrees and stainless steel should be tempered at 400~450 degrees, because a temper brittleness will occur at this time.