Heat treated galvannealed steel material and a method for its manufacture

摘要

A galvannealed heat-treated steel material is provided which has excellent corrosion resistance after coating and high strength and is suitable for use as an automotive member. Also provided is a process for producing the material. The galvannealed heat-treated steel material is one obtained by galvannealing at least one side of a steel material and subjecting at least part of the resultant galvannealed steel material to a heat treatment in which the material is heated to a temperature in a range which enables quench-hardening. At least part of the part which has undergone the heat treatment has a residual deposit adherent to the surface in an amount of 20-80 g/m per side. The deposit has an iron concentration of 15-35% and includesηphase. The deposit has a center-line average surface roughness (Ra) of 1.5 µm or less.