Abstract
Laser surface hardening provides for many advantages in terms of flexible production due to very localized and controlled energy input into the material. Laser processing offers the possibility to treat surfaces in order to locally strengthen the areas that are prone to fatigue cracking. It is well known that laser energy absorption depends on many parameters, e.g., the surface structure and the surface orientation. The incident angle of the laser beam plays a key role in this regard. When complex geometries like crankshaft fillets are treated, the surface cannot be considered a series of flat surfaces. Obviously, this leads to locally varying degrees of energy absorption. In the present work, curved surface structures were chosen in order to analyze the impact of the geometrical characteristics on surface and subsurface material properties after laser treatment. Microstructure evolution generally was found to be similar for flat and curved geometries. However, even if higher absorption in the groove due to the illumination at larger incident angles was expected, the outer parts of the curved geometry were not fully hardened. Thus, the increased effective length of the complex geometry-treated and the larger heat-affected volume are expected to have a more dominant influence on the final appearance of the subsurface microstructure. Eventually, for austenitization of the complete illuminated surface volume, the energy density needs to be increased.
Highlights
IntroductionBesides well-known applications, e.g., welding, cutting, and drilling, where the material is heated to temperatures above the melting point, several processes are in operation, where the melting temperature is not reached, e.g., in laser hardening
Laser beam processing is widely used in many fields and for many applications today
In order to investigate the impact of the surface geometries on the characteristics of the heat-affected and hardened zones, laser hardening experiments were conducted in the present work using a laser beam emitted by an IPG fiber laser at a laser power of 2 kW and a round top-hat beam shape of 9 mm diameter
Summary
Besides well-known applications, e.g., welding, cutting, and drilling, where the material is heated to temperatures above the melting point, several processes are in operation, where the melting temperature is not reached, e.g., in laser hardening. In these cases, only solid to solid phase transformations induce changes of mechanical properties [1]. One of the possible applications of laser hardening is seen in crankshaft hardening, e.g., treatment of the fillet regions, where currently traditional surface treatments (e.g., induction heating, deep rolling) are used in order to prevent fatigue cracking. Microalloyed steels are used for crankshafts, such as 38MnSiVS5 [9,10,11,12] and 44MnSiVS6 [4], respectively
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