Diffusionsgesteuerte Umwandlungsfronten bei der Laserstrahlhärtung von Eisenwerkstoffen

Physical modells of microstructural processes in laser surface hardening and melting, resp., are proposed: Pearlite dissolution is performed at a transformation front running with a speed which is controlled by the carbon diffusion balance. The carbon diffusion path from the dissolving carbides to the front has large influence on the front propagation speed and on the shape of the interface between ferrite and austenite in a pearlite lamella, which may be observed by means of REM. In most ferrous materials this diffusion path is found to run through the austenite, in unalloyed pearlitic steels with low interlamellar spacing, however, it is running through the ferrite yielding a very large speed of the transformation front, which has been estimated. Furthermore, the remelting of ferritic cast iron is discussed to be controlled by the carbon diffusion balance at an austenitizing/melting double front system. Hence, the local maximum temperature at the melting zone boundary depends on carb on diffusion and laser interaction time.