30 Questions About Heat Treatment（1）

This is an article that answers 10 asked questions about heat treatment, here is the catalogue of these 10 questions.

1.What are the commonly used quenching methods, explain the principle of using different quenching methods?

2.What are the differences between chemical gas deposition and physical meteorological deposition technology, and their main applications?

3.Explain the micro appearance and macro appearance of fatigue breaks.

4.Point out the three quality problems that often occur in sensing heating and quenching, and try to analyze the reasons.

5.What are the characteristics of high-speed steel bottom high-temperature recovery new process?

6.What are the types of controllable atmosphere? Briefly describe the characteristics and application of each atmosphere.

7.What is the purpose of temperature quenching such as ball and ink cast iron? What are the tissues after the temperature and temperature quenching?

8.Briefly describe the main characteristics of commonly used chemical thermal treatment (carburizing, nitrogen exudation, carbon nitrogen penetration and nitrogen carbon coexistence). What materials or parts are mainly suitable for tissue and performance characteristics after thermal treatment?

9.Briefly describe the principles of thermal treatment process design.

10.What are the problems of the optimization design of the thermal treatment process?

1.What are the commonly used quenching methods, explain the principle of using different quenching methods?

Quenching method:

     1. Monochrome quenching——cooled to the end in a quenching medium, the stress thermal stress of monoclonal quenching tissue is relatively large, and the quenching deformation is large.

     2. Double liquid quenching——Purpose: Fitly cool between 650 ° C and ms, so that V>VC will slowly cool down below MS to reduce tissue stress. Carbon steel: water first and then oil. Alloy steel: Oil first and then air.

     3. Classified quenching——After removing the workpiece, stay at a certain temperature to make the temperature consistent on the inside and outside of the workpiece, and then the air-cooled process, the grading quenching occurs when the M phase becomes in the air, and the internal stress is small.

     4. Wait for temperature quenching——refers to the temperature of the bell temperature zone, the bainite transformation occurs, the internal stress decreases, and the deformation is small. The principle of the selection of quenching methods should consider not only considering the requirements of performance, at the same time reduce the quenching stress to avoid quenching deformation and cracking.

2.What are the differences between chemical gas deposition and physical meteorological deposition technology, and their main applications?

    The chemical meteorological deposition is mainly the CVD method. The reaction medium containing the element of coating material is gasized at a lower temperature. Then send it into a high-temperature reaction room and the surface of the workpiece to generate high-temperature chemical reactions. The coating is formed on the surface.

The main characteristics of the CVD method:

 1. You can deposit various crystal or amorphous inorganic film materials.

 2. High purity and strong collective combination.

 3. The sedimentation layers are dense, and the pores are very small.

 4. Good homogeneity, simple equipment, and craftsmanship.

 5. The reaction temperature is high.

 Application: Make a thin film with various uses on the surface of the steel, hard alloys, non-ferrous metals, inorganic non-metals, etc., mainly insulators, semiconductor film, conductor and superconductor film, and corrosion-resistant film.

 Physical meteorological deposition: The process of gaseous substances directly deposited into a solid film on the surface of the workpiece, called the PVD method. There are three basic methods, which are vacuum steaming, sputtering coating, and ion plating. Application: wear-resistant coating, heat-resistant coating, corrosion-resistant coating, lubricating coating, function coating decorative coating.

3.Explain the micro-appearance and macro-appearance of fatigue breaks.

     Micro: It is a stripe pattern observed under the microscopic, called fatigue strips or fatigue. Fatigue strips have two types: delay and brittleness. The fatigue strip has a certain distance. Under certain specific conditions, each stripe is corresponding to a stress cycle.

     Macro: In most cases, it has crispy fracture characteristics, and macro-deformation is visible to the naked eye. The typical fatigue breaks are composed of the crack source area, the crack expansion area, and the final instantaneous instant area. The area of fatigue is relatively flat, and sometimes it is a bright mirror. The crack expansion area is a pattern or shell pattern. There are some fatigue sources of varying distances. The character load and size of the characteristic loading method and size of the micro-appearance of the instant area may be a tough nest or a permitted separation, and the separation of the proof of the crystal is broken or mixed.

4.Point out the three quality problems that often occur in sensing heating and quenching, and try to analyze the reasons.

  1. Cracking: Excessive heating temperature and uneven temperature; improper selection of quenching medium and temperature; not timely ignition and insufficient recovery; material quenchtability, analysis of composition, defects, excessive amounts of mixed objects; parts design unreasonable.

  2. Unewal on surface hardness: unreasonable sensing structure; uneven heating; uneven cooling; poor material tissue (with tissue, local decarburization).

  3. Surface melting: The sensor structure is unreasonable; the parts have sharp corners, holes, and bad;

5.What are the characteristics of high-speed steel bottom high-temperature recovery new process?

   Take W18CR4V as an example. Why is it better than the mechanical properties after the average recovery? W18CR4V steel 1275 ℃ heated quenching+320 ℃*1h+540 ℃ to 560℃*1h*2 times to ignite.

   High-temperature recovery High-speed steel is more fully precipitated than the M2C carbonization substances of ordinary high-speed steel. M2C, V4C, and FE3C carbides are large and uniform, and there are about 5% to 7%of the bell welling. High-temperature recovery high-speed steel performance is better than important organizational factors for ordinary ignition.

6.What are the types of controllable atmospheres? Briefly describe the characteristics and application of each atmosphere.

    There are heat-absorbing atmospheres, dripping atmospheres, straight body atmospheres, other controllable atmospheres (atmosphere of nitrogen machines, ammonia decomposition atmosphere, heat-deducting atmosphere), and so on.

   1. The heat-absorbing atmosphere is to mix the raw materials at a certain percentage of the air. At high temperatures, the catalyst is generated. The reaction generation mainly contains the atmosphere of CO, H2, N2, and trace CO2, O2, and H2O. Because the reaction must be absorbed by heat, the heat is absorbed, so the heat is absorbed. Therefore Called endothermic atmosphere or RX gas. Used for carburizing and carbon-nitrogen.

   2. Dripping atmosphere is to directly point methanol into the furnace to crack, generate carriers containing CO and H2, and add richer agents for carburizing; carbon nitrogen penetration at lower temperatures, protecting heating light and quenching.

   3. Mix the penetrating agent, such as natural gas and air, and directly enter the furnace, reacting to a reaction at 900 ° C at a high temperature to directly generate the carburizing atmosphere. Ammonia lift gas is used for nitrogen exudation gas, steel, or non-ferrous metal in a low-temperature heating protection atmosphere. The nitrogen-based atmosphere is used in high-carbon steel or bearing steel. The heating atmosphere is used for decontamination annealing for low-carbon steel, bronze-ray heat treatment, or forging cast iron.

7.What is the purpose of temperature quenching such as ball and ink cast iron? What are the tissues after the temperature and temperature quenching?

Objective: After the gym-casting iron, the auscultation of the ball, the temperature quenching area is performed in the bearer transformation area to obtain good mechanical properties and small distortion. Waiting temperature: 260 ~ 300 ° C was obtained for the Belensitic tissue; 350 ~ 400 ° C was obtained for the Belish tissue.

8.Briefly describe the main characteristics of commonly used chemical thermal treatment (carburizing, nitrogen exudation, carbon-nitrogen penetration, and nitrogen- carbon coexistence). What materials or parts are mainly suitable for tissue and performance characteristics after thermal treatment?

    Carburizing: It is mainly the process of penetrating the carbon atoms to the surface of the workpiece. The surface layer recovers the maxis, residual A, and carbides. The purpose of the heart is to improve the carbon content of the surface layer. And high toughness, makes it bear a large impact and friction. Low-carbon steels such as 20CRMNTI, gears, and pistons are commonly used.

    Nitrogen exudation: penetrates the surface of nitrogen atoms on the surface. 38CRMOALA, 18CRNIW.

    Carbon nitrogen penetration: low carbon nitrogen penetration temperature, fast speed, and small deformation of parts. The surface tissue is a fine needle back to fire horse austenite+granular carbon nitroda compound FE3 (C, N)+a small amount of residual Olympic muscles. It has high abrasion resistance, fatigue strength, and compressive strength, and has a certain degree of corrosion resistance. It should be used for the heavy and medium load gear manufactured by low-medium carbon alloy steel.

    Nitrogen carbon coexistence: The co-penetration process of nitrogen carbon is faster, and the surface hardness is slightly lower than nitrogen exudation, but the anti-fatigue performance is good. It is mainly used for processing molds with small impact loads and requires a small amount of wear resistance, high fatigue limit, and small deformation. General steel parts, such as carbon structure steel, alloy structure steel, alloy tool steel, gray cast iron, ball ink cast iron, and powder metallurgy, can be penetrated by nitrogen carbon.

9.Briefly describe the principles of thermal treatment process design.

     1. Advanced craftsmanship.

     2. Reliable, reasonable, and feasible craftsmanship.

     3. Craft economy.

     4. Process safety.

     5. Try to use process equipment with high mechanization and automation procedures.

10.What are the problems of the optimization design of the thermal treatment process?

     1. Fully consider the connection between the hot and cold processing process, and the arrangement of the heat treatment process should be reasonable.

     2. Use new technologies as much as possible, briefly describe the heat treatment process, and shorten the production cycle. Under the condition of ensuring the organization and performance required by the parts, try to combine different processes or processes as much as possible.

     3. Sometimes to improve the quality of the product and extend the service life of the workpiece, the heat treatment process needs to be increased.