Gear mold laser surface strengthening technology refers to the numerical control environment, the use of the laser beam of high energy density and coating or cladding material on the gear or mold surface processing, change its surface layer of the organization or composition, realization of surface phase transformation strengthening or enhance repair technology.
So-called laser phase transformation strengthening, is to use laser beam scanning artifacts, quick heat to Ac3 point above the surface layers of components, heating layer in spot removed, due to the effect of heat conduction of the workpiece substrate temperature between shun into martensite zone or bainite zone, martensite phase transformation or bainite phase transformation, phase transformation strengthening process.
Phase transformation strengthening technology had many advantages, such as good surface quality, according to different material, workpiece heat capacity of different sizes, and laser processing technology parameters, hardness, strengthening layer depth control. In the traditional heat treatment process factors influencing the reinforcement effect of the technology, in laser phase transformation strengthening the role of great changes have taken place.
1. Distortion strengthening and dispersion strengthening
Laser phase transformation strengthening austenite formation, when to stop the laser irradiation, the metal surface in martensitic transformation. In austenite formed in this process, whether it's surface layer, or layer, the austenitic grain size have no chance to grow up. Dispersion of the austenite grain size, form the bainite or martensite phase dispersion phase, the organization has a lattice strengthening and dispersion strengthening effect. And, under chilling conditions to form martensite lattice, have higher defect density than conventional quenching. Residual austenite, meanwhile, have extremely high dislocation density, the metal material has distortion strengthening effect, strength greatly increased.
2. No oxidation decarburization quenching
In a conventional heat treatment, the workpiece in the heating process such as no protection, oxidation and decarburization phenomenon will occur, the workpiece hardness, wear resistance, the use of performance and reduce the service life.
Laser phase transformation strengthening the use of light absorption performance of the coatings with surface protection against oxidation.
3. The fatigue mechanism of laser hardening
Impact of metal material fatigue performance is one of the reasons for the fatigue crack initiation time. Wear and promote interaction in the process of material damage, fatigue and wear the trench can become fatigue crack initiation points, accelerate the fatigue crack initiation, material surface fatigue cracks, surface roughness of serious deterioration, wear and tear will also increase.
Laser hardening layer has stronger ability to resist plastic deformation and adhesive wear resistance.
4. Strong working layer, etc
Cooling direction is situated in conventional heat treatment, surface cooling rate was the fastest, situated in cooling rate gradually reduced, so the decrease of hardness values received were situated in gradient distribution.
Laser phase transformation strengthening heating direction are the same, but the surface temperature is higher, and the heating time is relatively long, can reach 0.2 ~ 0.25 s, while the inner austenitizing is completed between shun, make the surface with a higher concentration of carbon in austenite, have stronger solid solution strengthening effect. Laser quenching cooling direction but, in contrast to the conventional heat treatment, and table is made, the inner temperature is low, but the cooling speed is the fastest, and the outer temperature is high, there are advantages of solid solution strengthening, but the cooling speed is the slowest, although slightly lower layer carbon concentration, but more intense deformation strengthening and dispersion strengthening. So almost unchanged was formed in the hardening layer hardness value distribution.
Such as pieces of laser hardening layer to avoid the strong work routine heat-treated pieces once surface wear, acceleration of its wear rate is.
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