Introduction: After laser melting during welding and heat treatment processes, the melted zone of the austenitic steel is characterized by a specific fine-grained microstructure formed as a result of the high heating and cooling rates. This causes additional difficulties when the microstructures of the molten zone and the base metal have to be investigated.
Aim: The aim of the present paper is to optimize the methodology for preparation of metallographic samples in order to study the microstructure of a laser-melted layer and of a base metal on the same sample.
Materials and Methods: Samples of AISI 321 austenitic stainless steel with laser-melted surface layers were ground and polished by a conventional procedure, but etched with aqua regia for different time periods.
Results and Discussion: It is found that the microstructure of the laser-melted layers is revealed after a shorter exposure time (2 min) of the reagent, as longer exposure time leads to over-etching. A longer exposure time (5 min) is required to reveal the microstructure of the base metal. Subsequent polishing of the sample results in more obscure structural features.
Conclusion: An optimized procedure of a two-stage etching process is proposed. In the first stage, the microstructure of the laser-melted layer is revealed in 2 min exposure time, followed by metallographic studies. After that the second stage continues with additional etching of 3 min to reveal and study the microstructure of the base metal.
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