ROYCEO
Heat treatment process classification
1. Annealing
Operation method: After heating the steel temperature to Ac3+30~50 degree or Ac1+30~50 degree or below Ac1 degree, is general cooling slow with the furnace temperature.
Objectives: 1. To reduce the hardness, improve plasticity, improve the performance of cutting and pressure processing; 2. Grain refinement to improve the mechanical properties, to prepare for the next step; 3. To eliminate the internal stress of cold, thermal processing .
Application : 1. For alloy structural steel, carbon tool steel, alloy tool steel, high-speed steel forgings, welding parts and unqualified raw materials of the supply status; 2 generally annealed in the blank state.
2.Normalizing
Operation method: The steel is heated to 30 ~ 50 degrees higher than Ac3 or Accm , after insulation, cooling at a slightly larger speed than annealing cooling rate.
Objectives: 1. To reduce the hardness, improve plasticity, improve the performance of cutting and pressure processing; 2. Grain refinement to improve the mechanical properties, to prepare for the next step; 3. To eliminate the internal stress of cold, thermal processing .
Application: Normalizing is usually used as the pre-heat treatment process for forgings, welding parts and carburizing parts. And can also be used as the final heat treatment for Low-carbon and medium-carbon carbon structural steel and low-alloy steel parts, which are not required for performance. For medium and high alloy steels, air cooling can result in complete or partial quenching and therefore can not be used as a final heat treatment process.
3. Quenching
Operation method: The steel is heated above to the phase transition temperature Ac3 or Ac1, after insulation for some time, then quickly cooled in water, salt, oil, or air.
Objectives: Quenching is generally done to obtain a martensitic structure of high hardness, sometimes quenching some of the high-alloy steels (such as stainless steel, wear-resistant steels) in order to obtain a single homogenous austenitic structure for increasing wear resistance and corrosion resistance.
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 potential of steel strength and wear resistance, but at the same time will cause great internal stress, reduce the plasticity and impact toughness of steel, it is necessary to temper to get a better overall mechanical properties.
4. Tempering
Operation method: the quenched steel reheated to a temperature below Ac1, after insulation, cooling in the air or oil, hot water, water .
Objectives: 1. To reduce or eliminate the internal stress after quenching to reduce the deformation and cracking of the workpiece; 2. To adjust the hardness and improve the plasticity and toughness, get the mechanical properties required for the job; 3. Stable workpiece size.
Application: 1. To maintain the steel high hardness and wear resistance after quenching with low temperature tempering; to maintain a certain toughness conditions to improve steel elasticity and yield strength with medium temperature tempering; to maintain high impact toughness degree and plasticity, and have enough strength with high temperature tempering; 2 general steel try to avoid 230 ~ 280 degrees, stainless steel avoid 400 ~ 450 degrees tempering, because there will be a temper brittleness.
5. Quenching and tempering
Operation method: High temperature tempering after quenching is called quenching and tempering, heat the steel to 10 to 20 degrees higher than quenching temperature, after insulation,then quenching, and then tempering at a temperature of 400 ~ 720 degrees.
Objectives: 1. To improve the machinability, to improve the smoothness of the machined surface; 2. To reduce the deformation and cracking during quenching; 3. To obtain good overall mechanical properties.
Application: 1. For high hardenability of alloy steel, alloy tool steel and high-speed steel; 2. Not only as the final heat treatment of a variety of more important structure , but also can be used as the pre-heat treatment of some compact parts, such as screw Etc., to reduce the deformation.
6. Aging
Operation method: the steel is heated to 80 to 200 degrees, insulating for 5 to 20 hours or longer, and then removed with the furnace cooling in the air.
Objectives: 1. Stabilize the steel organization after quenching , to reduce the deformation during storage or use; 2. To reduce the internal stress after quenching and grinding, the shape and size stability.
Application: 1. For kinds of quenched steel species; 2. Commonly used in the compact workpiece which shape asked not to change, such as close screw, measuring tools, bed chassis and so on.
7. Cold treatment
Operation method: Put the quenched steel in low temperature medium (such as dry ice, liquid nitrogen) to cool to -60 ~ -80 degrees or lower, after the temperature was uniform and then remove the average temperature to room temperature.
Objectives: 1. Convert the remaining austenite of quenched steel parts all or most to martensite, thereby enhancing the hardness , strength, wear resistance and fatigue limit of steel;2. Stabilizes the organization of the steel to stabilize the shape and size of the steel.
Application : 1. Steel should do cold treatment immediately after quenching, and then tempering at low temperatures to eliminate the internal stress when cryogenic cooling; 2. Cold treatment is mainly applied to the compact alloy steel, measuring tools and tight parts.
8. Flame heating surface quenching
Operation method : Flame of oxygen - acetylene gas mixture combustion , sprayed onto the steel surface, rapid heating, reach quenching temperature immediately cooling with water.
Objectives: To improve the surface hardness of steel, wear resistance and fatigue strength, the heart still maintain a tough state.
Application : 1. Used for medium carbon steel parts, generally hardened layer depth is 2 ~ 6mm; 2. For single or small batch production of large parts and workpiece needs for partial quenching.
9. Induction heating surface quenching
Operation method: Put the steel pieces into inductor, the steel surface generates induction current, in a very short period of time heated to quenching temperature, and then spray cooling.
Objective: To improve the surface hardness of steel, wear resistance and fatigue strength, the heart to maintain the state of toughness.
Application: 1. Used for medium carbon steel and alloy steel structure parts; 2. Due to the skin effect, high-frequency induction quenching hardened layer depth is generally 1 ~ 2mm, medium frequency quenching depth is generally 3 ~ 5mm, power frequency quenching depth is generally greater than 10mm.
10. Carburizing
Operation method: Put the steel into the carburizing medium, heated to 900 ~ 950 degrees and insulation, the steel surface to obtain a certain concentration and depth carburized layer.
Objective: To improve the surface hardness of steel, wear resistance and fatigue strength, the heart still maintain a tough state.
Application: 1. For low carbon steel and low alloy steel parts which carbon content is 0.15% to 0.25%, the general carburized layer depth is 0.5 ~ 2.5mm; After carburizing must be quenched to make the surface martensite, in order to achieve the purpose of carburizing.
11. Nitriding
Operation method: Use the active nitrogen atoms which decomposes from ammonia , make the steel surface to be saturated with nitrogen to form nitride layer.
Purpose: To improve the hardness of the steel surface, wear resistance, fatigue strength and corrosion resistance.
Application: Used for medium-carbon alloy structural steel containing aluminum, chromium, molybdenum and other alloying elements, as well as carbon steel and cast iron, the depth of the general nitride layer is 0.025 ~ 0.8mm.
12. Nitrocarburizing
Operation method: carburizing and nitriding to steel surfaces simultaneously.
Objective: To improve the hardness of the steel surface, wear resistance, fatigue strength and corrosion resistance.
Application : 1. Used for low carbon steel, low alloy steel and tool steel parts, the general nitride layer depth is 0.02 ~ 3mm; 2. After nitriding needs quenching and low temperature tempering.