1. What are the commonly used quenching methods and explain the principles of selecting different quenching methods?
Quenching method 1. Single-liquid quenching — the process of cooling to the end in a quenching medium. The stress and thermal stress of the single-liquid quenching structure are relatively large, and the quenching deformation is large.2. Double liquid quenching — Purpose: To cool quickly between 650 and Ms to make V> Vc, cooled slowly below Ms to reduce tissue stress.Carbon steel: Water before oil.Alloy steel: oil first, air second.3. Graded quenching — the process of holding the workpiece at a certain temperature so that its internal and external temperatures are the same, and then air cooling. Graded quenching is a process in which M phase transition occurs during air cooling, and the internal stress is small.4. Isothermal quenching — bainite transformation occurs in the isothermal region of bainite temperature, resulting in reduced internal stress and small deformation.
In order to avoid quenching deformation and cracking, the quenching stress should be reduced as much as possible.
2. What are the differences between chemical vapor deposition and physical and meteorological deposition techniques, and their main applications?
A chemical meteorological deposition is mainly the CVD method. The reaction medium containing coating material elements is vaporized at low temperature, and then sent to the reaction chamber at high temperature to contact with the surface of the workpiece to produce high-temperature chemical reaction, and the alloy or metal and its compounds are precipitated and deposited on the surface of the workpiece to form a coating.
The main features of the CVD method are 1. It can deposit all kinds of crystalline or amorphous inorganic film materials.2.3. Dense sedimentary layer, few pores, good homogeneity, simple equipment, and technology.5 The reaction temperature is higher.
Application: To prepare various kinds of film on the surface of the steel, hard alloy, nonferrous metal, inorganic nonmetal, and other materials, mainly insulator film, a semiconductor film, conductor, and superconductor film, and corrosion-resistant film.
Physico-meteorological deposition: The direct deposition of gaseous material on the surface of a workpiece into a solid film.According to the PVD method. There are three basic methods: vacuum evaporation, sputtering and ion plating. Application: Wear-resistant coating, heat-resistant coating, corrosion-resistant coating, lubricating coating, functional coating decorative coating.,
3. Explain the micro-morphology and macro-morphology of the fatigue fracture.
Microscopic: A stripe pattern observed under a microscopic electron microscope, called a fatigue strip or fatigue stria. There are two kinds of fatigue strip, ductility, and brittleness. The fatigue strip has a certain spacing. Under certain specific conditions, each stripe corresponds to a stress cycle. Macroscopic: in most cases, it has the characteristics of brittle fracture, and no macroscopic deformation can be seen by the naked eye. The typical fatigue fracture is composed of the crack source area, the crack growth area, and the final transient fracture area. The fatigue source area is less flat and sometimes shows a bright mirror, the crack growth area shows a riverbank or shell pattern, and there are some parallel arcs with unequal spacing fatigue source as the center of the circle. The micromorphology of the transient fault zone takes the characteristic loading mode and size of the material, which may be dimple or quasi-dissociation, dissociation along the crystal fracture, or mixed shape.
4. Three kinds of quality problems often occur in induction heating quenching are pointed out, and the causes are analyzed.
1) Cracking: The heating temperature is too high and uneven; Improper choice of quenching medium and temperature; Slow tempering and insufficient tempering; The material has high hardenability, component segregation, defects and contains excessive inclusions; The design of the parts is not reasonable.2) Uneven surface hardness: unreasonable induction structure; Uneven heating; Uneven cooling; Poor material structure (banded structure, partial decarburization) 3,), surface melting: unreasonable sensor structure; The parts have sharp corners, holes, grooves, etc.Heating time is too long, workpiece surface cracks.
5. What are the characteristics of the new high-temperature tempering process for high-speed steel bottom?
(Take w18Cr4v as an example) Why is it better than ordinary tempered mechanical properties?W18Cr4v steel 1275, quenched +320*1h+540 to 560*1h* twice tempered.
1) The m2C type carbide of bottom high-temperature tempered HSS is precipitated more fully than that of ordinary tempered HSS. The carbide of M2C, V4c, and Fe3c types has high dispersion degree and good uniformity, and there is about 5% to 7% bainite. This is an important structural factor that the performance of bottom high-temperature tempered HSS is better than that of ordinary tempered HSS.
6. What kinds of the controllable atmosphere are commonly used?
Briefly describe the characteristics and applications of each atmosphere. There are suction type atmosphere, drip type atmosphere, straight type atmosphere, another controllable atmosphere (nitrogen machine atmosphere, ammonia decomposition atmosphere, exothermic atmosphere).
1) Endothermic atmosphere refers to the atmosphere in which raw gas is mixed with air in a certain proportion and reacts at high temperature through catalysts to produce an atmosphere mainly containing CO, H2, N2, and trace CO2, O2, and H2O. Since the reaction needs to absorb heat, it is called an endothermic atmosphere or RX gas.2) The dripping atmosphere is to directly point methanol into the furnace for cracking to generate carriers containing CO and H2, and then add enrichment agent for carburizing; At low temperature, carbonitriding, protective heating, bright quenching, etc.3) The percolating agent such as natural gas and air will be mixed in a certain proportion and then directly into the furnace, 900 reactions at high temperature to directly generate the carburizing atmosphere. Ammonia decomposing gas is used for nitriding, low temperature heating of steel or nonferrous metals to protect the atmosphere.The nitrogen-based atmosphere has a good protection effect for high carbon steel or bearing steel. The exothermic atmosphere is used for the bright heat treatment of low carbon steel and copper or decarburization of malleable cast iron.
7. What is the purpose of austempering ductile iron? What are the isothermal temperature and the isothermal quenching structure?
Objective: Good mechanical properties and small distortion of ductile iron can be obtained by isothermal quenching in the bainite transition zone after austenitizing.Isothermal temperature: 260~300℃ to obtain lower bainite tissue; The upper Bainite was obtained at 350~400℃.
8, briefly describes the commonly used chemical heat treatment (carburizing, carburizing, carburizing, and carburizing) the main characteristics of the process, the structure, and performance characteristics after heat treatment, mainly applicable to what materials or parts?
Answer: carburizing: mainly to the workpiece surface infiltration process of carbon atoms, surface tempered martensite, residual A and carbide, the core purpose is to improve the surface carbon content, high hardness, high wear resistance, the heart has A certain strength and high toughness, make it bear the impact and friction of large, low carbon steel, such as 20 cement, gear, and piston pin are commonly used.
Nitriding: to the surface infiltration of nitrogen atoms, is the surface hardness wearability fatigue strength and corrosion resistance and thermal hardness increase, the surface is nitride, core tempering soxhlet, gas nitriding, liquid nitriding, commonly used 38CrMoAlA, 18CrNiW.
Carbonitriding: Low temperature, high speed, small deformation of parts. The surface tissue was fine needle tempered Martensite + granular carbon nitrogen compound Fe3 (C, N) + a small amount of residual austenite.It has high wear resistance, fatigue strength, and compressive strength, and has certain corrosion resistance. It is often used in heavy and medium load gear made of low and medium carbon alloy steel.
Nitrocarburizing: The process of nitrocarburizing is faster, the surface hardness is slightly lower than nitrocarburizing, but the fatigue resistance is good. It is mainly used for parts and dies with small impact load, high wear resistance, high fatigue limit, and small deformation. General steel parts carbon structural steel, alloy structural steel, alloy tool steel, gray cast iron, nodular cast iron, and powder metallurgy can be nitrocarburized.
9. Briefly describe the principle of heat treatment process design
(1) Advanced technology (2) reliable, reasonable and feasible technology (3) economy of the process (4) safety of the process (5) adopt mechanized and automatic process equipment as far as possible
10. What should be considered in the optimal design of the heat treatment process?
1. Give full consideration to the connection between cold and hot processing technologies, and the arrangement of heat treatment procedures should be reasonable;2. Adopt new technology as far 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 technological processes;3. Sometimes, in order to improve the product quality and extend the service life of the workpiece, the heat treatment process needs to be added.
11. Briefly describe the principles of inductor design
The coupling distance between the inductor and the workpiece should be as close as possible. 2. The workpiece heated by the outer wall of the coil must be driven by the magnetic conductive body. 3.
12. What basic principles should designers consider when selecting materials?
1. Select materials according to the working conditions of parts, including load type and size, environmental conditions and main failure modes;2, considering the structure, shape, size and other factors of the parts, for easy to produce quenching distortion and cracking to choose the material with good hardenability, can be used oil quenching or water-soluble quenching medium treatment;3. Understand the structure and performance of materials after heat treatment. Some steels developed for various heat treatment processes and methods will have better structure and performance after treatment.4, under the premise of ensuring the service performance and life of parts, should try to choose can simplify the heat treatment process, especially can save the material.
13. What technological properties should be considered when choosing metal materials to make parts?
Casting performance 2, pressure machining performance 3, machining performance 4, welding performance 5, heat treatment process performance.
14. How many types of wear failure are there? How to prevent various wear and failure of parts?
Types of wear: adhesive wear, abrasive wear, corrosion wear, contact fatigue.Methods: To prevent the adhesive wear, select the friction pair matching material reasonably; Using surface treatment to reduce friction coefficient or improve surface hardness; Reduce contact compressive stress; Reduce surface roughness. For abrasive wear, in addition to reducing contact pressure and sliding friction distance in the design, the lubricating oil filter is improved to remove abrasive particles, and high hardness materials should be selected reasonably. The surface hardness of friction pair materials was improved by surface heat treatment and surface working hardening. For corrosion wear, choose antioxidant materials; Surface coating; Selection of corrosion-resistant materials; Electrochemical protection; The stress concentration of tensile stress is reduced when corrosion inhibitor is added. Stress relief annealing; Select materials that are not sensitive to stress corrosion. Change the medium conditions. To contact fatigue, improve the hardness of materials; Improve the purity of materials and reduce inclusions; Improve the core strength and hardness of parts; Reduce parts surface roughness; Increase the viscosity of the lubricating oil to reduce the oil wedge effect.
15.What is the basic process of chemical heat treatment of steel? What are the main ways to accelerate chemical heat treatment? What is the advantage of the “carburizing section control process”?Under normal circumstances low carbon steel carburizing quench after the surface and the heart of the tissue is what?
Decomposition, adsorption, and diffusion; Application of subsection control method, composite seepage treatment, high temperature diffusion, the use of new materials to accelerate the diffusion process, chemical penetration, physical penetration; Prevent the workpiece surface oxidation, conducive to diffusion, so that the three processes fully coordinated, reduce the workpiece surface forming carbon black process, accelerate the process of carburizing, to ensure that the transition layer is wider and more gentle quality layer; From the surface centriole, the sequence is hypereutectoid, eutectoid, hypereutectoid, and primordial eutectoid.
16. What is granular Bainite?
It is composed of massive (equiaxial) ferrite and A high carbon region A.
17. Describe the type, purpose, and purpose of the ball return?
Common ball retreat: increase hardness, improve machinability, reduce quenching distortion cracking.Isothermal ball retreat: for high carbon tool steel, alloy tool steel.Circular ball retreat: used in carbon tool steel, alloy tool steel.
18. The quenching temperature of subeutectoid steel is usually above Ac3, but why is the quenching temperature of hypereutectoid steel between AC1-ACM
(1) Due to the low content of subeutectoid steel and the original structure of P+F, if the quenching temperature is lower than Ac3, there will be undissolved F, and a soft point will appear after quenching. For hypereutectoid steel, if the temperature is too high and too much K ‘dissolves, the amount of flake M will increase, which is easy to cause deformation and cracking. If the amount of A’ increases, too much K ‘dissolves, and the wear resistance of the steel will also decrease.(2) As the temperature of hypereutectoid steel is too high, the tendency of oxidation and decarbonization increases, resulting in uneven surface composition of the steel and different MS height, leading to quenching cracking. (3) The selection of quenching temperature Ac1+ (30-50 degrees) can retain the undissolved K ‘to improve the wear resistance, reduce the carbon content of the matrix, and increase the strength plasticity, and toughness of the steel.
19. The new process of tempering at low temperature and high temperature will improve the life of quenched tempering parts of HIGH-SPEED steel.
Uniform precipitation of and M3C resulted in more uniform precipitation of M2C and MC within the range of secondary hardening temperature, which promoted partial conversion of residual austenite into bainite and improved strength and toughness.
20. Identify the following types of alloys
ZL104: Cast aluminum, MB2: Deformed magnesium alloy, ZM3: cast magnesium, TA4: type titanium alloy, H68: brass, QSN4-3: tin brass, QBe2: Beryllium brass, TB2: type titanium alloy.
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