Mechanical properties and microstructures in the Heat Affected Zone (HAZ) of SA 106 Gr.C piping steel were studied using weld thermal simulations. The test results showed that in the most of HAZ regions mechanical properties were better than those in the base metal. The weak properties appeared in the simulated Sub-Critical HAZ, where the value of impact toughness and tensile strength and microhardness were lower than those of other regions of the HAZ and the base metal. Main causes of the poor properties in that region were regarded as the carbide coarsening of the pearlite due to overtempering effect by repeated weld thermal cycle and post weld heat treatment. Further, there was an area site where the yield strength changes abruptly. The finite element analysis was carried out to prove that this strength mismatch brings an additional stress concentration, which in turn may induce an easier crack formation.
