Interference Phenomena on Infrared Thermography during a Mushy Solidification Zone

Abstract

This research aims to investigate the interference phenomena on a mushy zone during weld solidification using infrared thermography. Stationary heating source was carried out on a low carbon steel through GTAW process. The different spot-heating sequences were studied, namely, single and double melting steps. Surface preparation of a specimen was divided into two (2) cases, firstly a non-grinded surface and secondly a grinded surface. Thermocouples of three (3) points were attached nearby liquid-solid state region in order to verify an appropriate emissivity coefficient of a high-temperature mushy zone. As the result, in the case of non-grinded surface specimen with immediately spot-melting double steps exhibited that the infrared images were strongly interfered from an oxide film formation. Such an oxidized surface moved randomly around the molten pool margin. As for the grinded surface specimen with spot-melting double steps, it revealed the first-spot melting step was notably clear infrared images. However, the second-spot melting step exhibited the interference phenomena from the first-melted surface region. Such the surface region affected on the proper heat transfer emissivity coefficient of high temperature. The grinded surface with single melting step was able to attain clear infrared images. Therefore, the corrected temperature of a mushy zone was determined by approximate constant emissivity coefficient of 0.23. Additionally, more accurate temperature measurement of entire region was done with emissivity coefficient depended on temperature.