Study on Weldability of High Strength Steel for Structural Applications

Welding conditions of steel tubes for structural applications have to be carefully designed because of their effect on strength and toughness of the welded joints, and then on the performance of the complete structure. In this sense the study of microstructure in the heat affected zone (HAZ), basically its dependence on thermal treatment, is of great importance for the design of optimum welding procedures.

Welding energy (HI) can be expressed in terms average cooling rate between 800°C and 500°C (t85) which is one of the parameters of Hannerz equation. Different regions of the HAZ were simulated, including the coarse grain HAZ (CGHAZ) and the sub-critical HAZ (SCHAZ). Furthermore, dual treatments were designed and simulate, to study the effect of a multi-pass welding procedure.

In this work a Gleeble 3500 thermo-mechanical simulator is used to reproduce, by using Hannerz equation, the thermal cycles in the heat affected zone of a medium carbon Cr-Mo steel. Simulations were performed on different kind of samples to evaluate hardness, toughness and tensile strength. Resulting mechanical properties combined with microstructural analysis allowed to determine proper ranges for welding parameters.

Numerical modeling was also performed to evaluate the macroscopic effect of these thermal treatments on complex welding geometries.