Interference Phenomena on Infrared Thermography during a Mushy Solidification Zone

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.