At present, China can provide vacuum oil Quenching Furnace, Vacuum Tempering Furnace, vacuum pressurized gas quenching furnace (2bar), vacuum high pressure gas quenching furnace (6bar, 10bar), Vacuum Sintering Furnace and vacuum brazing furnace, etc., with an annual output of about 500 units. Domestic manufacturers still have considerable advantages in terms of price and service convenience. In the early 1990s, high-pressure gas quenching furnaces (20-40) × 105 Pa have been developed abroad, and the application is obviously further expanded. According to reports, high-temperature high-pressure vacuum furnaces with a pressure of 100×105Pa and a working temperature of 2200°C have been developed in foreign countries for high-temperature sintering, crystal production, gemstone manufacturing and some physical tests.
2.3.4 Laser heat treatment: The laser heat treatment is to irradiate the surface of the workpiece with a high energy density laser beam, so that the temperature of the part to be hardened on the workpiece rises sharply to form austenite, and then the self-excited quenching of the workpiece is extremely small. Heat treatment process for martensite microstructure. Laser heat treatment is divided into laser phase transformation hardening, laser melting, laser surface alloying, laser surface cladding and laser shock hardening. Here, laser phase transformation hardening is mainly introduced.
The main features of laser phase transformation hardening: (1) extremely fast heating and cooling rate, the heating speed of the workpiece surface can reach (104 ~ 106) ° C / S, the cooling rate can reach (106 ~ 108) ° C / S, so the laser heat treatment is A phase change hardening method for rapid heating and cooling ensures that a very fine structure can be obtained; (2) a local heat treatment method, which realizes self-paid quenching, does not require a cooling medium, and has a small heat affected zone, and generally has less deformation after processing (3) The hardness of the workpiece after treatment is higher than that of conventional quenching, and the wear resistance is good, especially for the cast iron such as the surface of the workpiece to melt, the fine-grained Leysite structure can be obtained, the wear resistance can be improved by 3 to 4 times; (4) the treated surface It has high residual compressive stress and improves the fatigue strength of parts. (5) The process is easy to automate and computer control; (6) It can be processed in the atmosphere, and the process is simple. The laser source commonly used in the industry is a CO2 continuous gas laser with a laser wavelength of 10.6 um, which is now produced in China. The laser beam mode is multimode. The main process parameters for laser phase transformation hardening are laser output power P, laser beam spot diameter D and laser scanning speed V. Other laser sources include excimer lasers and solid-state lasers, which typically operate in pulses, with pulse width and frequency added to the process parameters.
The laser beam spot has three kinds of circular, rectangular and linear shapes according to different lasers. The laser beam is scanned along the workpiece in a certain way, and there are three kinds of overlapping, connecting and spacing. Generally, the reflectivity of the metal to the laser is very high. In order to increase the absorption of the laser beam energy by the treated metal, the material is generally subjected to surface blackening. The blackening process can be phosphating or applying a black paint containing graphite powder and a coating of certain oxides such as SiO2.
After the laser treatment of 45 steel, the quenched layer is organized into fine martensite, and the excessive zone is martensite + troostite, and the surface hardness is 650-800 HV. The hardened layer of high carbon steel after laser quenching is fine needle martensite + retained austenite; the secondary surface layer is martensite + residual carbide + troostite structure, and the surface hardened layer reaches (850 ~ 1150) HV. The hardened layer of GCr15 steel is cryptocrystalline martensite + residual alloy carbide + retained austenite structure, and the excess zone is martensite + tempered troostite + alloy carbide structure, and the surface hardness is 900 ~ 1050 HV. After the laser is heat-treated by laser, the hardened layer is martensite + retained austenite + residual graphite (sheet or sphere, which varies according to the original gray cast iron or ductile iron), and the hardened layer is (700 ~ 900) HV, if the surface When melting occurs, the surface will obtain a Leysite structure, and a bivalve structure appears in the melting zone around the graphite: adjacent graphite is flake martensite + retained austenite, and the outer outer layer is a Leysite eutectic.
There are many examples of typical laser heat treatment, such as gears, crankshafts, and cylinder blocks. Generally, certain parts must be equipped with certain fixtures in order to be applied in large quantities. For small batch production, there are certain problems in the application of individual collaborative parts to production. In addition, the investment cost of lasers and processing machines is relatively large, which also limits the promotion of the technology to a certain extent.
Foreign lasers have high production quality and stable operation, but they are generally suitable for laser cutting and laser drilling.
2.3.5 Surface modification and composite treatment: In a broad sense, surface modification is a process of changing the surface properties of steel materials, changing the surface structure and changing the chemical composition of the surface, so carburizing, nitriding, carbonitriding Boronizing, infiltration of metals, etc. belong to the latter, induction heating, flame heating, laser phase transformation hardening, contact resistance heating, etc. belong to the former. However, the general surface modification is now focused on the surface coating technology, which is prepared by the method of vapor deposition.
Vapor deposition is a technique in which a vapor phase material is vaporized or deposited on a surface of a treated workpiece to form a film, and a special surface property is obtained. The film is divided into six categories according to the use of optical films, microelectronic films, optoelectronic films, integrated optical films and protective functional films. Closely related to mechanical parts are mainly high-strength and high-hardness films, referred to as hard films.
Vapor deposition can be divided into physical vapor deposition and chemical vapor deposition according to the manner of gas phase production, which is expressed as PVD and CVD.
Physical vapor deposition is the deposition of a vapor phase material that converts a plated solid material into an atomic, molecular or ionic state under vacuum to a surface of the workpiece. The deposited gas phase material can be further divided into the following three types according to the formation method: (1) vacuum evaporation, atomic or molecular deposition on the workpiece by thermal evaporation to form a thin film; (2) sputtering film formation: atomic or molecular deposition by sputtering Forming a film on the workpiece; (3) Ion plating: The plating material is deposited into a film in the form of ions and high-energy atoms or molecules.
Chemical vapor deposition is a method in which a gas containing one or more compounds of a constituent film is introduced into a reaction chamber, and a substance which forms a desired film by a chemical reaction on a substrate is deposited on a workpiece, and a general pressure of heating to promote a chemical reaction is used. CVD, low pressure CVD, plasma-assisted CVD using plasma to promote chemical reactions, and laser CVD using laser-assisted chemical reactions.
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