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Different processes of heat treatment

Feb 02, 2018

Different processes of heat treatment

 

1.Anneal

Operation method: The steel is heated to Ac3 + 30 ~ 50 degrees or Ac1 + 30 ~ 50 degrees or Ac1 the following temperature, the general slow cooling with the furnace temperature.

 

Purposes:

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 cold, thermal processing of internal stress.


Applications:

1. For alloy structural steel, carbon tool steel, alloy tool steel, high-speed steel forgings, welding parts and the supply of substandard raw materials;

2. generally annealed in the blank state.

 

 

2.Normalizing

Method of operation: The steel is heated to Ac3 or Accm above 30 ~ 50 degrees, after cooling slightly larger than the cooling rate of annealing cooling.

 

purposes:

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 cold, thermal processing of internal stress.

 

Applications: Normalizing is usually used as forgings, welding parts and carburizing parts preheat treatment process. For low-carbon and medium-carbon carbon structural steel and low-alloy steel, which have low performance requirements, can also be used as the final heat treatment. 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

Method of operation: The steel is heated to above the phase transition temperature Ac3 or Ac1, incubated for some time, and then quickly cooled in water, salt, oil, or air.

 

Purposes: 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 increased wear resistance And corrosion resistance.

 

Applications:

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

Method of operation: the quenched steel reheated to a temperature below Ac1, after insulation, in the air or oil, hot water, water cooling.

 

Purposes:

1. To reduce or eliminate the internal stress after quenching to reduce the deformation and cracking of the work piece;

2. To adjust the hardness and improve the plasticity and toughness, get the mechanical properties required for the job;

3. Stable work piece size.

 

Applications:

1. To maintain the steel after quenching high hardness and wear resistance with low temperature tempering; to maintain a certain toughness conditions to improve steel elasticity and yield strength with 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 between 400 ~ 450 degrees tempering, because then there will be a temper brittleness.

 

5. Quenching and tempering

Method of operation: Tempering after quenching, said tempering, tempering the steel is about to quench the temperature higher than 10 to 20 degrees, after quenching insulation, and then tempered at a temperature of 400 ~ 720 degrees.

 

Purposes:

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.

 

Applications:

1. For high hardenability of alloy steel, alloy tool steel and high-speed steel;

2. Not only as a variety of more important structure of the final heat treatment, but also can be used as some compact parts, such as screw Etc., to reduce the deformation.

 

 

6. Aging

Method of operation: the steel is heated to 80 to 200 degrees, incubated for 5 to 20 hours or longer, and then removed with the furnace in the air cooling.

 

Purpose:

1. Stabilize the steel after quenching the organization, to reduce the deformation during storage or use;

2. To reduce the internal stress after quenching and grinding, the shape and size stability.

 

Applications:

1. For quenched after the steel species;

2. Commonly used in the shape of the need to keep the work piece does not change, such as close screw, measuring tools, bed chassis and so on.

 

 

7. Cold treatment

Method of operation: the quenched steel, in low temperature medium (such as dry ice, liquid nitrogen) to cool to -60 ~ -80 degrees or lower, the temperature was uniform and then remove the average temperature to room temperature.

 

Purpose: 1. The hardened steel parts of the remaining austenite all or most converted to martensite, thereby enhancing the hardness of steel, strength, wear resistance and fatigue limit; Stabilizes the organization of the steel to stabilize the shape and size of the steel.

 

Applications:

1. Steel quenching immediately after the cold treatment, and then by tempering at low temperatures to eliminate the internal stress when cryogenic cooling;

2. Cold treatment is mainly applied to the close-knit alloy steel, measuring tools and tight parts.

 

 

8. Flame heating Surface hardening

Method of operation: Combustion with oxygen - acetylene gas mixture of flame, sprayed onto the steel surface, rapid heating, quenching temperature immediately after the water cooling.

 

Purpose:To improve the surface hardness of steel, wear resistance and fatigue strength, the heart still maintain a tough state.

 

Applications:

1. Used for medium carbon steel parts, generally hardened layer depth of 2 ~ 6mm; 2.For single or small batch production of large parts and the need for partial quenching of the work piece.

 

9. Induction heating surface hardening

Method of operation: the steel pieces into the sensor, the steel surface induction current, in a very short period of time heated to quenching temperature, and then spray cooling.

 

Purpose:To improve the surface hardness of steel, wear resistance and fatigue strength, the heart to maintain the state of toughness.

 

Applications:

1. Used for medium carbon steel and Zhongtang alloy structural steel parts;

2. Due to the skin effect, high frequency induction quench hardened layer is generally 1 ~ 2mm, IF quenching is generally 3 ~ 5mm, high frequency quenching is generally greater than 10mm.

 

 

10. Carburizing

Method of operation: The steel into the carburizing medium, heated to 900 ~ 950 degrees and heat, 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 points: 1. For carbon steel containing 0.15% to 0.25% of low carbon steel and low alloy steel parts, the general carburized layer depth of 0.5 ~ 2.5mm; Carburizing must be quenched to make the surface martensite, in order to achieve the purpose of carburizing.

 

11. Nitriding

Method of operation: use at 5. . ~ 600 degrees decomposition of ammonia from the active nitrogen atoms, the steel surface is saturated with nitrogen to form a nitride layer.

 

Purpose: To improve the hardness of the steel surface, wear resistance, fatigue strength and corrosion resistance.

 

Application points: 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

Method of operation: carburizing and nitriding steel surfaces simultaneously.

Purpose: To improve the hardness of the steel surface, wear resistance, fatigue strength and corrosion resistance.

 

Applications:

1. Used for low carbon steel, low alloy steel and tool steel parts, the general nitride layer deep 0.02 ~ 3mm;

2. After nitriding but also quenching and tempering.

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