摘要：From the perspective of crashworthiness andpassenger safety, martensitic and complexphase Ultra High Strength Steels (UHSS) areideal candidates for automotive anti-intrusioncomponents. However, these steels must beprotected from corrosive environments in orderto maintain the longterm integrity of thestructures involved for which continuousgalvanizing is a cost-effective solution. Severalchallenges have to be overcome in order toprocess the above steels in the continuousgalvanizing line (CGL) while achieving theminimum target tensile strength of 1250 MPa.Steel chemical compositions should be selectedin such a way that maintaining a suitablecooling rate produces martensite or bainite,and also provides a substrate surface withsufficient reactive wetting suitable forgalvanizing. In the present study, steelchemistries were designed around relativelylean compositions based on carbon,manganese and silicon with additionalhardenability being provided by molybdenumor chromium additions. Annealing cycles weredetermined based on the continuous coolingtransformation behaviour of the steels. For bothsteel compositions the target tensile strength of1250 MPa was achieved using austeniticannealing for 120s followed by cooling to roomtemperature at 50°C/s. The steels weresuccessfully reactively wet by the Zn(Al,Fe) bathusing a 95%N2-5%H2, -30°C dew pointprocess atmosphere. From scanning electronmicroscopy, X-ray photoelectron spectroscopyand scanning Auger microscopy it wasdetermined that oxides of manganese, siliconand chromium formed during annealing.However, these oxides did not have an adverseeffect on coatability and both steels formed highquality, adherent coatings.
