摘要：From the perspective of crashworthiness and passenger safety, martensitic and complex phase Ultra High Strength Steels (UHSS) are ideal candidates for automotive anti-intrusion components. However, these steels must be protected from corrosive environments in order to maintain the longterm integrity of the structures involved for which continuous galvanizing is a cost-effective solution. Several challenges have to be overcome in order to process the above steels in the continuous galvanizing line (CGL) while achieving the minimum target tensile strength of 1250 MPa. Steel chemical compositions should be selected in such a way that maintaining a suitable cooling rate produces martensite or bainite, and also provides a substrate surface with sufficient reactive wetting suitable for galvanizing. In the present study, steel chemistries were designed around relatively lean compositions based on carbon, manganese and silicon with additional hardenability being provided by molybdenum or chromium additions. Annealing cycles were determined based on the continuous cooling transformation behaviour of the steels. For both steel compositions the target tensile strength of 1250 MPa was achieved using austenitic annealing for 120s followed by cooling to room temperature at 50°C/s. The steels were successfully reactively wet by the Zn(Al,Fe) bath using a 95%N2-5%H2, -30°C dew point process atmosphere. From scanning electron microscopy, X-ray photoelectron spectroscopy and scanning Auger microscopy it was determined that oxides of manganese, silicon and chromium formed during annealing. However, these oxides did not have an adverse effect on coatability and both steels formed high quality, adherent coatings.
