Laser quenching means that the laser generator produces high-efficiency energy particle beams. The laser directly hits the surface of the forging, and the surface of the forging digests and absorbs the kinetic energy of the laser and heats up rapidly. , the surface layer will undergo ferritization and austenite transformation in a short period of time, and a hardened bottom layer with a necessary depth of 1 is obtained, and only the laser scanner area is strengthened, and there is basically no harm to nearby areas. Because laser quenching is fast, precise, and easy to use, many of them are used for steel parts of various metal materials.
Laser Quenching Process of 30# Steel Forgings
Our company has undertaken the daily task of strengthening the first batch of 30# steel forgings, and stipulates that the strengthening strength is 45-46HRC. The traditional heat treatment method is used for heat treatment + ultra-low temperature quenching, and the strength after strengthening is 45-50HRC, and the strengthening regulations are considered; For the above problems, carry out scientific research and analysis to find the reason why laser quenching cannot be hardened.
Comparative Analysis of Heat Treatment Mechanisms
The heat treatment of steel is to heat the steel to the critical temperature of Ac3 (hypo-eutectoid steel) or Ac1 (hypereutectoid steel), heat insulation for a period of time, make all or part of it ferrite, and then exceed the critical temperature. The cooling rate of the value of the water cooling rate is fast cooling to the following Ms (or Ms surrounding isothermal) heat treatment method to carry out austenite (or bainite) changes.
The traditional heat treatment has a long heat preservation time, and the melting of martensite and the diffusion of aluminum alloy elements spreads evenly, and a relatively symmetrical ferrite can be obtained. Even if the initial structure is thick, it can be adjusted according to the heating temperature and insulation The heat preservation time obtains a relatively symmetrical heat treatment mechanism. The metallographic structure in the initial structure of 30# steel accounts for 56%. After the traditional quenching heat treatment, the water content of the metallographic structure decreases rapidly, and it is less than 10%.
Compared with traditional heat treatment, the ferritization time of laser quenching is very short, and the water cooling rate is very fast. When the laser is heated, the whole process of dissolving the martensite in the metal composite material and integrating into the ferrite is different, which is generally related to the initial situation before the laser is heated, and is related to the symmetry and diffusion of various mechanisms in the initial mechanism. There is an immediate correlation between the degree and the size of the complex martensite. The difference in the initial structure immediately affects the strength, the depth of the hardened layer and the symmetry of the structure obtained by the raw material after laser quenching.
There are many metallographic structures in the initial structure of 30# steel, and the asymmetry of ferritization during laser quenching makes the final structure very uneven after heat treatment. The carbon water content in the original ferrite area is relatively high, and the carbon atoms missed the outdiffusion during ferritization and are preserved in the ferrite body. After water cooling, the termination mechanism is high carbon steel austenite; The amount of water is very small, and austenite transformation cannot be produced. After heat treatment, the structure is still metallographic; at the junction of ferrite and metallographic structure, ferrite reduces carbon, metallographic structure increases carbon, and low carbon is produced after heat treatment. Environmentally friendly austenite. Therefore, the finishing mechanism of 30# steel after laser quenching is high carbon steel austenite + low carbon environmental protection austenite + metallographic structure.
Comparative Analysis of Macroeconomic Strength
In traditional quenching heat treatment, the mechanism is low-carbon environmental-friendly austenite + a small amount of metallographic structure. Although the low-carbon environmental-friendly austenite has low microscopic strength, its specific gravity is very large, and chemical reaction can obtain high macroeconomic strength; laser quenching, The mechanism is high carbon steel austenite + low carbon environmental austenite + metallographic structure. Although high carbon steel austenite has high microscopic strength, the proportion is small, and many metallographic structures lead to low macroeconomic strength.
Correlation between laser quenching intensity and main parameters of laser quenching process
The key to hardenability is related to the carbon content in the steel. More precisely, it is determined by the carbon water content dissolved in the ferrite of the steel during heat treatment. The higher the carbon water content, the higher the strength after heat treatment. higher.
The main parameters of the laser quenching process are the power of the laser generator, the speed of the scanner speed and the size of the light spot on the surface of the raw material. The three comprehensive functions immediately reflect the temperature of the whole process and the time of thermal insulation. The higher the ferrite temperature, the longer the thermal insulation time, the more sufficient the melting of carbon in the ferrite, the higher the microscope strength of the high carbon steel austenite, and the higher the actual effect of laser hardening. Therefore, the top priority of manipulating the main parameters of the laser quenching process is to increase the ferritization temperature and increase the thermal insulation time. The spot size will not change, increasing the laser output power or reducing the scanner speed can exceed the stated goals. In Table 2, comparing No. 1 and No. 2, it can be seen that increasing the laser output power can improve the heat treatment intensity; comparing 2 and 4, it can be seen that reducing the scanner speed can improve the heat treatment intensity.
However, for the metal material with a clear initial structure, with the increase of temperature and the increase of heat insulation time, the heating temperature will be close to the high-efficiency liquidus line of the metal material, and the surface layer will appear micro-melting, and then the heat treatment intensity will decrease. , with the intensification of the melting state, the heat treatment strength decreases rapidly. In Table 2, comparing 2 and 3, 4 and 5, it can be found that the heat treatment strength has just started to decrease. Laser quenching has the actual effect of extreme heat treatment. After this intensity is exceeded, the main parameters of the process are further adjusted, and the heat treatment intensity decreases. Beyond the limit heat treatment strength, if you want to comprehensively improve the heat treatment strength, you can only start from the initial mechanism position, optimize the initial mechanism, improve the uniformity of raw materials and the diffuseness of martensite, which can comprehensively improve the laser quenching strength.