Welding and Brazing Metallographic examination is a powerful technique for studying weld failures. In the case below, the polished and etched section revealed the incorrect use of medium carbon 1040 steel without preheat and post heat. This lead to the formation of a hardened zones in the fillet welds of the bar stock. The bar stock, which was part of a support structure, was replaced with fully weldable A-36 steel.
Weld Failure Analysis
Heat affected zone of 1040 bar stock showing the formation of a hardened zone of martensite. Brittle fracture occurred in this hardened zone. 2% nital etch. X100 
Microstructure of normalized 1040 bar stock showing large areas of high carbon pearlite. 2% nital etch X200
Brittle, untempered martensite at weld fracture. Carbon contents in the range of 0.40% favor martensite formation. 2% nital etch X200
