Operation method, intention and application key of heat treatment process

Annealing

Method of annealing operation: after heating the steel to AC3 + 30 ~ 50c or AC1 + 30 ~ 50c or below AC1 (relevant materials can be consulted), it usually cools slowly with the furnace temperature.

Intention of annealing:

  • Reduce hardness, improve plasticity, improve machining and pressure machining functions;
  • Refine the grain, improve the mechanical function, and prepare for the next process;
  • Eliminate the internal stress caused by cold and hot working.

The key of annealing application:

  • (1) It is suitable for forging and welding parts of alloy structural steel, carbon structural steel, alloy structural steel and high-speed steel as well as raw materials with unqualified supply conditions;
  • (2) It is usually annealed in the rough condition.

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Normalizing

Normalizing operation method: heat the steel to 30-50 degrees above AC3 or ACCM, and cool it at a cooling rate slightly higher than annealing after heat preservation.
The intention of normalizing:

  • Reduce hardness, improve plasticity, improve machining and pressure machining functions;
  • Refine the grain, improve the mechanical function, and prepare for the next process;
  • Eliminate the internal stress caused by cold and hot working.

The key of normalizing application: normalizing is usually used as the pre heat treatment process of forgings, weldments and carburized parts. Low carbon and medium carbon carbon structural steel and low alloy steel with low functional requirements can also be used as final heat treatment. As for normal medium and high alloy steel, air cooling can cause complete or partial quenching, so it can not be used as the final heat treatment process.

Quench

Method of quenching operation: heat the steel piece to the transformation temperature above AC3 or AC1, keep it warm for a period of time, and then cool it quickly in water, nitrate, oil or air.
The purpose of quenching: usually, the purpose of quenching is to obtain martensite arrangement with high hardness. Sometimes, when quenching some high alloy steels (such as stainless steel and wear-resistant steel), it is to obtain single and uniform austenite arrangement to improve wear resistance and corrosion resistance.
Key points of quenching application:

  • (1) Generally used for carbon steel and alloy steel with carbon content more than 0.3%;
  • (2) Quenching can give full play to the strength and wear resistance potential of steel, but together it will form a great internal stress and reduce the plasticity and impact toughness of steel. Therefore, tempering should be carried out to obtain better inductive mechanical function.

Tempering

Tempering operation method: heat the quenched steel pieces from the beginning to a certain temperature below AC1, and cool them in air, oil, hot water and water after heat preservation.
Intention of tempering:

  • Reduce or eliminate the internal stress after quenching, reduce the deformation and cracking of workpiece;
  • Adjust the hardness, improve the plasticity and durability, and achieve the mechanical function required by the operation;
  • Stable workpiece scale.

Key points of tempering application:

  • The steel should be tempered at low temperature when it has high hardness and wear resistance after quenching;
  • Medium temperature tempering is used to improve the elasticity and yield strength of steel under the condition of certain toughness;
  • High temperature tempering is used when the impact toughness and plasticity are high and the strength is satisfied;
  • Generally, steel should be prevented from tempering between 230-280 ° C and stainless steel between 400-450 ° C, because one tempering brittleness will occur at this time.

Quenching and tempering

Method of tempering operation: after quenching, high temperature tempering is called tempering. The steel parts are heated to a temperature 10-20 degrees higher than that during quenching. After heat preservation, quenching is carried out, and then tempering is carried out at a temperature of 400-720 degrees.
Intention of tempering:

  • Improve the cutting function, improve the surface finish;
  • Reduce the deformation and cracking during quenching;
  • Excellent inductive mechanical function.

Key points of quality control:

  • (1) It is suitable for alloy structural steel, alloy structural steel and high speed steel with high hardenability;
  • (2) It can not only be used as the final heat treatment of various important parts, but also as the pre heat treatment of some tight parts, such as lead screw, to reduce the deformation.

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Prescription

Aging operation method: heat the steel pieces to 80-200 ℃, keep them warm for 5-20 hours or longer, and then take them out with the furnace and cool them in the air
Intention of prescription:

  • The arrangement after quenching can reduce the deformation of storage or operation time;
  • Reduce the internal stress after quenching and grinding, and stabilize the shape and size.

The key to time effective application:

  • (1) Suitable for all kinds of steel after quenching;
  • (2) It is often used for tight workpieces whose shape no longer changes, such as tight lead screw, measuring things, bed case, etc.

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Cold treament

The method of cold treatment operation: cool the quenched steel in low temperature medium (such as dry ice and liquid nitrogen) to – 60 ~ – 80 ℃ or lower, and take out the uniform temperature to room temperature after the temperature is uniform.
Intention of cold treatment:

  • The remaining austenite in the quenched steel is transformed into martensite, and then the hardness, strength, wear resistance and fatigue limit of the steel are improved;
  • The arrangement of stabilizing steel to stabilize the shape and dimension of steel parts.

Key points of cold treatment application:

  • (1) After quenching, the steel parts should be cooled immediately, and then tempered at low temperature to eliminate the internal stress during low temperature cooling;
  • (2) Cold treatment is mainly applicable to tight cutting tools, measuring tools and tight parts made of alloy steel.

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Surface quenching by flame heating

Operation method: use the flame burning with oxygen acetylene mixed gas, spray it on the surface of steel parts, heat it rapidly, and spray water to cool it when it reaches the quenching temperature.
Purpose: to improve the hardness, wear resistance and fatigue strength of the steel parts, and the core still adheres to the condition of resistance.
Key to application:

  • (1) Most of them are used in medium carbon steel, usually the depth of harden layer is 2-6mm;
  • (2) It is suitable for single or small batch production of large workpieces and parts requiring partial quenching.

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Induction hardening

Operation method: put the steel into the inductor, make the induced current on the surface of the steel, heat it to the quenching temperature in a very short time, and then spray water for cooling.
Purpose: to improve the hardness, wear resistance and fatigue strength of steel parts, and keep the plastic condition in the center.
Key to application:

  • (1) It is mainly used for medium carbon steel and alloy layout steel parts of the nave;
  • (2) Because of skin effect, the harden layer of high frequency induction quenching is usually 1-2mm, medium frequency quenching is usually 3-5mm, and high frequency quenching is usually more than 10 mm.

Carburization

Operation method: put the steel into the carburizing medium, heat it to 900-950 ℃ and keep it warm, so as to obtain a certain concentration and depth of carburizing layer on the steel surface.
Purpose: to improve the hardness, wear resistance and fatigue strength of steel parts, and the core part still adheres to the condition of resistance.
Key to application:

  • (1) For low carbon steel and low alloy steel parts with carbon content of 0.15% ~ 0.25%, the carburizing depth is usually 0.5 ~ 2.5mm;
  • (2) After carburizing, it is necessary to carry out quenching to obtain martensite on the surface, so as to finish carburizing.

Nitridation

Operation method: the active nitrogen atom differentiated from ammonia at 500-600 ℃ is used to make the steel surface full of nitrogen and form the nitriding layer.
Purpose: to improve the hardness, wear resistance, fatigue strength and corrosion resistance of steel parts.
The key of application: it is mainly used for medium carbon alloy layout steel, carbon steel and cast iron, which are rich in aluminum, chromium, molybdenum and other alloy elements. Generally, the nitriding layer depth is 0.025-0.8mm.

Nitrocarburizing

Method of operation: carburizing and nitriding to the surface of steel parts.
Purpose: to improve the hardness, wear resistance, fatigue strength and corrosion resistance of steel parts.
Key to application:

  • (1) It is mainly used for low carbon steel, low alloy structural steel and East steel parts, usually the nitriding layer is 0.02-3mm deep
  • (2) After nitriding, it needs to be quenched and tempered at low temperature.

Source: China Pipe Fitting Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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operation method intention and application key of heat treatment process - Operation method, intention and application key of heat treatment process
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Operation method, intention and application key of heat treatment process
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Method of annealing operation: after heating the steel to AC3 + 30 ~ 50c or AC1 + 30 ~ 50c or below AC1 (relevant materials can be consulted), it usually cools slowly with the furnace temperature.
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