Softening is a process step for the transformation of steel components. At the softening process, the martensite formation hardened steel will be heated in predefined areas. Thereby, the steel microstructure is changed; depending on the temperature, the martensite is either annealed (softened) or transformed into a more flexible ferrite-pearlite via austenitization. For this heat treatment, lasers are the best tool because they guarantee a flexible and high-precision material treatment with little transition zone to the workpiece. Neither gas flames nor infrared radiators offer any comparable process quality.
The so-called annealing is a heat treatment that is typically applied after a hardening process. Here too, a material is heated in order to influence its properties, in particular to relieve tension. Hardened steel becomes softer the higher it is tempered. This reduces the hardness and increases the toughness. In addition to traditional steel-related processes, the compensation of internal stresses in materials and components also plays a role in non-metal-related production processes such as semiconductor production. Here, diode laser-based annealing processes are being tested to compensate for internal stresses in wafers during the production process.
Heat treatment with diode lasers does not only allow hardening but also the exact opposite, namely, the softening of materials. Here, the solidified structure is softened in certain zones by heat exposure (“tempered”) or is for instance turned back into a ferrite-pearlite structure by austenitization followed by slow cooling. The result is a better shapeable sheet that is easier to weld, form or cut. Here, diode laser is the better tool compared to other methods like induction, gas flames or infrared rays. On the one hand, material processing is highly flexible and precise, even with hardening; on the other hand, the created transition zone between the processed and unprocessed raw material is smaller than that created with other technologies. But in particular, diode lasers have a very homogeneous intensity distribution even at big spots, which makes the softening results specifically even.
Its application can actually save lives: In car body construction, soft deformation zones can be created at press-hardened areas by means of lasers, which absorb in case of crashes the impact energy and thus can protect the body. By this flexible material processing in the remaining zones, the total stiffness of the steel remains. A further application field is deep drawing, at which the circuit board is softened before pressing in the intended bending zones to avoid cracks or fractures during the forming process.
The process advantages of the diode lasers
Compared to other laser types, Laserline's diode lasers have a bigger spot and homogeneous intensity distribution. Together, both make an even softening all over possible. Thanks to a technology that was developed together with Fraunhofer ILT using double-sided radiation, process speeds of more than 10 meters per minute can be realized in the future.