Non-Oxidizing Water Quench to Tailor UHSS for Excellent Zinc Wettability

Recently, Fives Stein has developed a non-oxidizing wet cooling process dedicated to high strength steel quenching in continuous galvanizing lines to freeze desired bainite and martensite phases, triggering Tata Steel R&D to collaborate in an innovative project together with Fives Stein. They have demonstrated that this promising technology could improve metallurgy and coatability. This technology can be implemented for galvanizing 3rd generation Advanced High Strength Steel (AHSS) / Ultra High Strength Steel (UHSS) grades of Tata Steel. The pickling effect of wet cooling agent (water containing an acid) on steel surface after annealing prior to dipping into the Zn bath according to the wet cooling concept developed by Fives Stein was assessed by a metallurgy driven set of experiments on a Non-Oxidizing-Water-Quench (NOWQ) cooling test bench simulation. Selected samples were further preheated to required temperature in 5%H₂/N₂ and subsequently dipped in liquid zinc by a hot dip zinc simulator HDAS (Heat to Coat heated, i.e., without annealing). Results of experiments along with X-ray Photoelectron Spectroscopy (XPS)/Glow Discharge Optical Emission Spectroscopy (GDOES) analyses demonstrated that the NOWQ technology significantly improved pickling efficiency of Mn, Si, and Al selective oxides to secure good Zn wetting of exposed metallic strip surface.