Effect of galvanizing heat treatments on the microstructure and properties of Al-Si TRIP assisted steels during plastic deformation

Galvanizing is essential for the use of TRIP assisted steels in automotive manufacturing. This requires that heat treatments compatible with the galvanizing process produce not only surfaces with excellent wettability by molten zinc, but also the appropriate microstructure and mechanical properties. Two galvanizable Al-Si TRIP assisted steels were heat treated using the McMaster Galvanizing Simulator. The resulting phase constituents and their evolution during straining were investigated using SEM and XRD. Within the overall work hardening of the investigated steels, the relative contribution of the kinematic component increased with the increasing strain. The development of additional back stresses due to the formation of strain-induced martensite counterbalanced the plastic relaxation, with the net result that the back stress increased parabolically up to a large strain during plastic deformation. © 2008 MS&T08®.