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Steel pipe heat treatment process

Heat treatment process


Annealing

Method of operation: the steel heated to Ac3 +30 ~ 50 degrees or Ac1 +30 ~ 50 degrees or Ac1 below the temperature (you can consult the relevant information), the general slow cooling with the furnace temperature.

Objective: 1. Reduce the hardness, improve the plasticity, improve the cutting and pressure processing performance; 2. Refine the grain, improve the mechanical properties, prepare for the next step; 3. Eliminate the cold and hot work generated by the internal stress.

Application points: 1. Suitable 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 in the rough state of the annealing.

Normalizing

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

Objective: 1. Reduce the hardness, improve the plasticity, improve the cutting and pressure processing performance; 2. Refine the grain, improve the mechanical properties, prepare for the next step; 3. Eliminate the cold and hot work generated by the internal stress.

Application points: Normalizing is usually used as a preheating process for forgings, weldments and carburized parts. For low-carbon and medium-carbon carbon structural steels and low-alloy steels with low performance requirements, they can also be used as final heat treatment. For general medium and high alloy steels, air cooling can result in complete or local quenching and therefore can not be used as a final heat treatment process.

3. Quenching

Method of operation: the steel heated to the phase transition temperature Ac3 or Ac1 above, for a period of time, and then in water, salt, oil, or air in the rapid cooling.

Purpose: Quenching is generally done in order to obtain high hardness martensite, sometimes for some high alloy steels (such as stainless steel, wear-resistant steel) quenching, it is to get a single uniform austenite to improve wear resistance And corrosion resistance.

Application points: 1. Generally used for carbon content of more than 0.3 percent of the carbon steel and alloy steel; 2. Quenching can give full play to the strength of steel and wear resistance potential, but at the same time will cause a lot of internal stress, Reduce the plasticity of steel and impact toughness, it is necessary to temper to get better comprehensive mechanical properties.

4. Tempering

Method of operation: the quenching of the steel re-heated to Ac1 following a certain temperature, after insulation, in the air or oil, hot water, water cooling.

Purpose: 1. To reduce or eliminate the internal stress after quenching and reduce the deformation and cracking of the workpiece. 2. Adjust the hardness, improve the plasticity and toughness, get the mechanical properties required by the work; 3. Steady the workpiece size.

Application of the main points: 1. To maintain the steel after quenching in the high hardness and wear resistance with low temperature tempering; to maintain a certain toughness conditions to improve the elasticity and yield strength of steel with medium temperature tempering; to maintain high impact toughness Degree and plastic-based, but also have enough strength to use high-temperature tempering; 2. General steel as far as possible to avoid the 230 ~ 280 degrees, stainless steel in the 400 ~ 450 degrees between the tempering, because this time will produce a temper brittleness.

5. Temp

Method of operation: quenching after the high temperature tempering, said quenched and tempered, the steel will be heated to a higher than the quenching of 10 to 20 degrees when the temperature, heat quenching, and then 400 ~ 720 degrees temperature tempering.

Objective: 1. To improve the cutting performance, improve the degree of smooth surface processing; 2. To reduce the deformation and cracking during quenching; 3. To obtain a good comprehensive mechanical properties.

Application: 1. Suitable for alloy steel with high hardenability, alloy tool steel and high speed steel; 2. Not only can it be used as the last heat treatment of various important structures, but also as some tight parts, such as screw And so on to reduce the deformation.

6. Timely

Method of operation: the steel heated to 80 ~ 200 degrees, insulation 5 to 20 hours or more, and then with the furnace out in the air cooling.

Purpose: 1. Stabilize the steel after quenching the organization, reduce the storage or use during the deformation; 2. Reduce the quenching and grinding after the internal stress, stable shape and size.

Application points: 1. Applicable to the steel after quenching; 2. Commonly used in the requirements of the shape is no longer changing the tight parts, such as tight screw, measuring tools, bed chassis and so on.

7. Cold treatment

Method of operation: the quenched steel parts, in low-temperature medium (such as dry ice, liquid nitrogen) in the cooling to -60 ~ -80 degrees or less, the temperature is uniform after taking out the temperature to room temperature.

Purpose: 1. So that the quenched steel within the retained austenite all or most of the conversion to martensite, thereby enhancing the steel hardness, strength, wear resistance and fatigue limit; Stabilize the organization of the steel to stabilize the shape and size of the steel.

Application points: 1. Steel quenching should be immediately after the cold treatment, and then by low temperature tempering to eliminate the low temperature cooling of the internal stress; Cold treatment is mainly applied to alloy steel tight knives, measuring tools and tight parts.

8. Flame heating surface hardening

Method of operation: Oxygen-acetylene mixed gas combustion flame, spray to the steel surface, rapid heating, when the quenching temperature immediately after the water cooling.

Objective: To improve the surface hardness, wear resistance and fatigue strength of steel parts, the heart still maintain the toughness state.

Application points: 1. Used for medium carbon steel parts, the general hardened layer depth of 2 ~ 6mm; Suitable for single or small batch production of large parts and the need for local quenching of the workpiece.

9. Induction heating surface hardening

Method of operation: the steel into the sensor, so that the surface of the steel induced current, in a very short period of time heated to the quenching temperature, and then water cooling.

Objective: To improve the hardness, abrasion resistance and fatigue strength of steel parts, and to maintain the toughness state.

Application points: 1. Used for medium carbon steel and Zhongtang alloy structural steel parts; As the skin effect, high-frequency induction quenching hardening layer is generally 1 ~ 2mm, IF quenching is generally 3 ~ 5mm, high frequency quenching is generally greater than 10mm.

10. carburization

Method of operation: the steel into the carburizing medium, heated to 900 ~ 950 degrees and insulation, so that the steel surface to get a certain concentration and depth of the carburizing layer.

Objective: To improve the hardness, abrasion resistance and fatigue strength of steel parts, the core still retains the toughness state.

Application points: 1. For carbon content of 0.15% to 0.25% of low carbon steel and low alloy steel parts, the general depth of carburizing layer of 0.5 ~ 2.5mm; After carburizing must be quenched, so that the surface of martensite, in order to achieve the purpose of carburizing.

11. Nitriding

Method of operation: use in 5. The ~ 600 degrees ammonia decomposition of the active nitrogen atoms, so that the steel surface is nitrogen saturation, the formation of nitride layer.

Objective: To improve the hardness, abrasion resistance, fatigue strength and corrosion resistance of steel surface.

Application points: used for containing aluminum, chromium, molybdenum and other alloy elements in the carbon alloy structural steel, and carbon steel and cast iron, the general depth of the nitride layer 0.025 ~ 0.8mm.

12. Nitrocarburizing

Method of operation: to the steel surface at the same time carburizing and nitriding.

Objective: To improve the hardness, abrasion resistance, fatigue strength and corrosion resistance of steel surface.

Application points: 1. Used for low carbon steel, low alloy structural steel and tool steel parts, the general depth of nitriding layer of 0.02 ~ 3mm; Nitriding after quenching and low temperature tempering.


Example 1: Several kinds of commonly used steel heat treatment program

Q345: The steel for the construction, bridges and other steel, yield strength of 345MPa or so, generally use normalizing treatment, carbon 0.12-0.2% or so.

20Cr: carbon content of about 0.2%, can be used for construction steel, normalizing can; can also be used for carburizing steel, carburizing quenching.

GCr15: bearing steel, carbon content of about 1%, quenching temperature generally 860C, 180C low temperature tempering.

60Si2Mn: spring steel, carbon content of about 0.6%, quenching temperature of 860C, medium temperature tempering (450C or so).

0Cr18Ni9Ti: austenitic stainless steel, carbon content of less than 0.06%, generally about 1050C solution treatment (ie, heating water), improve the corrosion resistance.


Example 2: 45 #, 42CrMo, 20CrMo how to achieve 45HRC hardness requirements

45 # steel and 42CrMo can be directly quenched + tempered to meet the 45HRC hardness requirements;

20CrMo carburizing quenching + tempering treatment can meet the 45HRC hardness requirements.

With 40CrMo.45 # gear is usually normalized [or quenched and tempered] plus surface hardening .20CrMo is carburizing quenching. Not just to meet the hardness requirements. Such parts require a certain degree of contact fatigue strength.


Example 3: GCr15 steel heat treatment process parameters

GCr15 steel is a low alloy content, with good performance, the most widely used high-carbon chromium bearing steel. After quenching and tempering with high and uniform hardness, good wear resistance, high contact fatigue performance. The steel cold plastic processing medium, cutting performance in general, poor welding performance, the formation of white point sensitive performance, there are temper brittleness.

Chemical composition / element content (%)

C: 0.95-1.05 Mn: 0.20-0.40 Si: 0.15-0.35 S: <= 0.020 P: <= 0.027 Cr: 1.30-1.65

The heat treatment system: steel bar annealing, wire annealing or 830-840 degrees oil quenching.

Heat treatment process parameters:

1. Normal annealing: 790-810 degrees heating, the furnace cooled to 650 degrees, the air-cooled - HB170-207

2. Isothermal annealing: 790-810 degrees heating, 710-720 degrees isothermal, air-cooled - HB207-229

3. Normalizing: 900-920 degrees heating, air cooling - HB270-390

4. High temperature tempering: 650-700 degrees heating, air cooling - HB229-285

5. Quenching: 860 degrees heating, oil quenching - HRC62-66

6. Low temperature tempering: 150-170 degrees tempering, air cooling - HRC61-66

7. Carbonitriding: 820-830 degrees co-permeate 1.5-3 hours, oil quenching, -60 degrees to -70 degrees cryogenic treatment +150 degrees to +160 tempering, air cooling - HRRC67