1, annealing
Operation method: After the steel is heated to a temperature of Ac3+30~50°C or Ac1+30~50°C or Ac1 (available for related materials), it is usually cooled slowly with the furnace temperature.
Intent: 1. To reduce the hardness, improve the plasticity, improve the cutting performance; 2. To refine the grain, improve the mechanical properties, to prepare for the next step; 3. To eliminate the internal stress occurred in the cold and hot processing.
Key to use: 1. Suitable for alloy stainless steel, carbon structural steel, alloy structural steel, high-speed steel forgings, welding parts, and raw materials that are not qualified; 2. Annealing is usually performed in the rough condition.
2, normal fire
Operation method: The steel is heated to Ac3 or Accm above 30~50°C, and after cooling it is cooled at a slightly higher cooling rate than the annealing.
Intent: 1. To reduce the hardness, improve the plasticity, improve the machining performance; 2. To refine the grain, improve the mechanical properties, to prepare for the next step; 3. To eliminate the internal stress generated by the cold and hot processing.
Key to use: Normalizing is usually used as a pre-heat treatment process for forgings, weldments, and carburizing parts. Low-carbon and medium-carbon carbon stainless steels and low-alloy steels with low demand may also be used as the final heat treatment. With regard to the usual medium and high alloy steels, air cooling can cause thorough or partial quenching and cannot be used as a final heat treatment process.
3, quenching
Operation method: The steel is heated to the phase transition temperature Ac3 or Ac1 above, kept warm for a moment, and then rapidly cooled in water, salt, oil, or air.
Intent: Quenching is usually to obtain high hardness martensite structure. Sometimes when quenching certain 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.
Key to use: 1. Commonly used for carbon steel and alloy steel with carbon content greater than 0.3%; 2. Quenching can give full play to the steel's strength and wear resistance potential, but it will generate a great deal of internal stress and decrease. The plasticity and impact toughness of the steel are tempered to obtain better mechanical properties.
4, tempering
Operation method: The quenched steel piece is heated from the head to a certain temperature below Ac1, and after being warmed, it is cooled in air, oil, hot water, and water.
Intent: 1. To reduce or eliminate the internal stress after quenching, to prevent deformation and cracking of the workpiece; 2. To adjust the hardness, improve the plasticity and resistance, to obtain the required mechanical properties of the workpiece; 3. To stabilize the workpiece size.
The key to use: 1. In order to maintain high hardness and wear resistance of steel after quenching with low temperature tempering; in the maintenance of a certain degree of toughness to improve the elasticity and yield strength of steel with medium temperature tempering; to maintain high impact toughness Degree and plasticity are the main factors, and when the strength is satisfied, high-temperature tempering is used. 2. Normally, steel is not to be tempered between 230°C and 280°C, and stainless steel is tempered between 400°C and 450°C, because a temper brittleness occurs at this time.
5, conditioning
Operation method: Quenching after high temperature tempering after quenching, heating the steel to a temperature of 10 to 20 degrees higher than that during quenching, quenching after insulation, and tempering at a temperature of 400 to 720C.
Intent: 1. To improve the cutting performance, improve the appearance of smooth finish; 2. To reduce the deformation and cracking during quenching; 3. To achieve outstanding mechanical properties.
The key to use: 1. Suitable for high hardenability of alloy stainless steel, alloy structural steel and high speed steel; 2. Not only can be used as the final heat treatment of a variety of more important processes, but also can be used as some precision parts, such as screw, etc. The pre-heat treatment to reduce distortion.
6, aging
Operation method: Heat the steel to 80~200°C, keep it warm for 5~20 hours or more, then cool it in the air with the furnace.
Intent: 1. Stabilize the steel after hardening the organization, reduce the aging or long-term deformation; 2. Reduce the internal stress after quenching and grinding, stable shape and scale.
Key to use: 1. Applicable to various steels after quenching; 2. Commonly used in precision parts where the required shape no longer changes, such as precision screw, bed frame, etc.
7, cold treatment
Operation method: After quenching, the steel parts are cooled to -60--80°C or lower in a low-temperature medium (such as dry ice or liquid nitrogen), and the temperature is evenly taken out and the temperature is taken out to room temperature.
Intent: 1. Makes all or most of the remaining austenite in the hardened steel part convert to martensite, and then increases the hardness, strength, wear resistance and fatigue limit of the steel part; Stabilize the steel's structure to maintain the shape and dimensions of the steel.
Use the key: 1. After quenching, the steel parts should be cooled and then tempered at low temperature to eliminate the internal stress at low temperature cooling; Cold treatment is mainly applied to precision steel alloy tools, measuring tools and precision parts.
8, flame heating appearance quenching
Operation method: Using a flame of oxygen-acetylene gas mixture, it is sprayed on the surface of the steel part and rapidly heated. When it reaches the quenching temperature, it is sprayed and cooled immediately.
Intent: To improve the appearance hardness, wear resistance and fatigue strength of steel parts, and maintain a certain degree of toughness in the heart.
Use the key: 1. Mostly used for medium carbon steel parts, usually the depth of hardened layer is 2～6mm; 2. It is suitable for large workpieces that are produced in single or small batches and parts that require partial quenching.
9, induction heating appearance quenching
Operation method: Put the steel into the inductor to induce current on the surface of the steel, heat it to the quenching temperature in a very short time, and then spray water to cool it.
Intent: To improve the appearance hardness, wear resistance and fatigue strength of steel parts, and maintain a certain degree of toughness in the heart.
Use the key: 1. Used for medium carbon steel and medium carbon alloy stainless steel parts; 2. Because of the futile effect, the high-frequency induction quenched hardened layer is usually 1 to 2 mm, the intermediate frequency quenching is usually 3 to 5 mm, and the high-frequency quenching is usually greater than 10 mm.
10. Carburizing
Operation method: Put the steel pieces into the carburizing medium, heat it to 900-950°C and keep it warm, so that the steel piece will have a carburized layer with a certain concentration and depth.
Intent: To improve the appearance hardness, wear resistance and fatigue strength of steel parts, and maintain a certain degree of toughness in the heart.
Use the key: 1. For low carbon steel and low alloy steel parts with a carbon content of 0.15% to 0.25%, the depth of the carburized layer is usually 0.5-2.5mm; After the carburization, it is necessary to carry out quenching so that the desired martensite is obtained on the surface to achieve the intention of carburizing.
11. Nitriding
Operation method: The reactive nitrogen atoms differentiated from ammonia gas at 500-600°C are used to make the steel parts rich in nitrogen atoms to form a nitrided layer.
Intent: To increase the hardness, wear resistance, fatigue strength, and corrosion resistance of steel parts.
Key to use: It is mostly used for medium carbon alloy stainless steels rich in aluminum, chromium, molybdenum and other alloying elements, as well as carbon steel and cast iron. Usually the depth of nitrided layer is 0.025-0.8mm.
12, nitrocarburizing
Method of operation: Carburizing and nitriding together the appearance of the steel.
Intent: To increase the hardness, wear resistance, fatigue strength, and corrosion resistance of steel parts.
The use of key: (1) mostly used for low-carbon steel, low-alloy stainless steel and structural steel parts, usually 0.02~3mm depth of nitride layer; (2) quenching and low-temperature tempering after nitriding.