Experimental investigation on dissimilar pulsed Nd:YAG laser welding of AISI 420 stainless steel to kovar alloy

Abstract

This paper presents the results of an investigation on autogeneous laser welding of AISI 420 stainless steel to kovar alloy using a 100W pulsed Nd:YAG laser. The joints had a circular geometry and butt welded. The joints were examined by optical microscope for cracks, pores and for determining the weld geometry. The microstructure of the weld and the heat affected zones were investigatedby scanning electron microscope. The austenitic microstructure was achieved in the weld. The morphology of weld zone solidification was basically cellural, being influenced by the temperature gradient. It was found that the start of solidification in the kovar side of weld zone occurred by means of epitaxial growth. When the temperature gradient was high, the columnar grains were created in the fusion boundary of 420 stainless steel side toward weld zone. Measurements taken by X-ray spectrometry for dispersion of the energy in the weld zone indicated a significantly heterogeneous distribution of chromium element. The variations in chemical compositions and grains morphologies significantly alter the Vickers microhardness values in the weld zone.