What are Normalizing, Tempering, Quenching, and Annealing Process

What are Normalizing Tempering Quenching and Annealing in Heat Treatment Process

1. Annealing

Operation method: Heat the steel part to a temperature of Ac3+30-50 degrees or Ac1+30-50 degrees or below (refer to relevant information), and then slowly cool it with the furnace temperature.

Purpose: 1. To reduce hardness, improve plasticity, and enhance cutting and pressure processing performance; 2. Refine grain size, improve mechanical properties, and prepare for the next process; 3. Eliminate the internal stress generated by cold and hot processing.

Application points: 1. Suitable for forgings, welded parts, and raw materials with unqualified supply status of alloy structural steel, carbon tool steel, alloy tool steel, high-speed steel; 2. Generally, annealing is carried out in the blank state.

2. Normalization

Operation method: Heat the steel part to 30-50 degrees above Ac3 or Accm, keep it warm, and cool it at a slightly higher cooling rate than annealing in furnace.

Purpose: 1. To reduce hardness, improve plasticity, and enhance cutting and pressure processing performance; 2. Refine grain size, improve mechanical properties, and prepare for the next process; 3. Eliminate the internal stress generated by cold and hot processing.

Application points: Normalization is usually used as a pre heat treatment process for forgings, welded parts, and carburized parts. For low-carbon and medium 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, and therefore cannot be used as the final heat treatment process.

3. Quenching

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

Purpose: Quenching is generally aimed at obtaining a high hardness martensitic structure. Sometimes, when quenching certain high alloy steels (such as stainless steel and wear-resistant steel), it is to obtain a single and uniform austenitic structure to improve wear resistance and corrosion resistance.

Application points: 1. Generally used for carbon steel and alloy steel with a carbon content greater than 0.3%; 2. Quenching can fully utilize the strength and wear resistance potential of steel, but at the same time, it can cause significant internal stress, reduce the plasticity and impact toughness of steel, so tempering is necessary to obtain better comprehensive mechanical properties.

4. Tempering

Operation method: Heat the quenched steel parts again to a temperature below Ac1, and after insulation, cool them in air, oil, hot water, or water.

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

Application points: 1. Low temperature tempering is used to maintain the high hardness and wear resistance of steel after quenching; When improving the elasticity and yield strength of steel while maintaining a certain toughness, medium temperature tempering is used; When maintaining high impact toughness and plasticity, and having sufficient strength, high-temperature tempering is used; 2. Generally, it is advisable to avoid tempering steel between 230~280 degrees Celsius and stainless steel between 400~450 degrees Celsius, as this can result in primary tempering brittleness.