Temperature fields in low carbon rimming steel with 2.5 and 0.45 mm thickness during surface treatment with pulsed
Nd:Glass laser have been simulated. Two models namely analytical and finite elements method (FEM) have been
applied for solving the one dimensional differential heat transfer equation. The analytical model is assuming constant
thermophysical properties, semi-infinite size of the treated material and no heat transfer with ambient atmosphere. For
the FEM the influence of the thermal dependence of the thermophysical properties and the finite size of the treated
material has been investigated. It has been shown that the one-dimensional analytical model could be successfully used
for the estimation of the temperature on the surface of both the thicker and the thinner steels, but is not suitable for the
characterization of the thermal field in the depth of the thinner material. The oxidation kinetics during laser treatment has
been simulated and the influence of the formed oxide film on the coefficient of absorption and thus on the temperature
field has been analyzed. For this purpose two models, namely the "smooth surface" and the "rough surface" model have
been applied. It has been found that the kinetics of the oxide film growth is defined only by the rate of the oxygen supply
to the treated surface and within the laser pulse duration (7ms) is linear in time. According to the "smooth surface"
model the consideration of the surface oxidation increases the optical absorption coefficient from 0.4 to 0.9 while
according to the "rough surface" model this increase is up to 1.0. The absorption coefficient increase is accompanied
with the same ratio increase of the temperature in respect to that when the oxidation has not been taken into account.
High chromium martensitic stainless steel has been surfacely treated by pulsed Nd:Glass laser. The temperature fields at the surface and in the bulk during the laser pulse and following cooling stage have been estimated with a numerical simulation. The modification of structure parameters has been analyzed by X-ray diffraction both in standard Bragg-Brentano and grazing incidence beam geometries. It has been found that the laser treatment modifies the surface parameters as follows: introduces residual macro-stresses, vacancies and dislocations, increases significantly (with 90%) Vickers micro-hardness at the surface and causes formation of a very thin oxide film.
Cold-rolled rimming steel has been surfacely treated by pulse Nd:YAG laser. The modification of structure parameters has been analyzed by X-ray diffraction. It has been found that the main consequences of the laser treatment are surface oxidation and formation of significant residual macrostresses.
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