In surface hardening using laser radiation, the material (carbonic steel) is heated above the austenization temperature for a short time. Through rapid cooling the steel reaches the martensitic material structure. Heat deposition is realized through the absorption of laser radiation at the surface of the material, whereas cooling occurs conductively within the remaining material. The thermal gradient is mainly defined by the laser spot geometry and the feed rate.
When compared with conventional hardening methods such as oven-, case-, flame or induction hardening, laser hardening is marked by a range of advantages such as the spatially and temporally limited energy deposition.
All conventional hardening methods require quenching with water, oil or salt bath. When using oven- or case hardening, the whole component is heated, resulting in very long heating times what is often combined with through hardening of the entire part. This is especially problematic with small and delicate parts. Flame hardening affects a large surface. However, this process is not very well defined and does not allow for temperature control of the process. Induction hardening enables selective hardening at specific places of a part. A thermal deposition in adjoining areas, however, cannot be avoided which often has detrimental effects on the mechanical properties of the part. When changing the part geometry, the geometry of the inductor is also necessary.
Laser hardening on the other hand allows for a highly defined zone of influence without affecting neighboring surfaces. High cooling rates make fine structures and high levels of hardness possible. Intricate contours are easily hardened using lasers due to robotic guidance possibilities. This also makes it possible to harden parts directly where it is required.
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