Thermite Welding Metallurgy
Metallurgical structures that are present in thermite welds depend on the chemical composition of the weld metal and on
the cooling rate of the joint after pouring is completed.
Figure 1 shows a typical macrostructure of a carbon steel rail thermite weld and the microstructure of the fusion zone, the
fusion line, the end of the heat-affected zone (HAZ), and the unaffected rail. Typically, the weld is 100% pearlite with
varying degrees of coarseness. This is due to the slow cooling rate that completes transformation before reaching the
martensite start temperature and the formation of untempered martensite.