12th International Conference on Zinc & Zinc Alloy Coated Steel Sheet - GALVATECH 2021

Medium-Mn TRIP steels are promising candidates amongst the third generation advanced high strength steels (3G-AHSSs) for meeting automotive weight reduction demands without compromising passenger safety. However, the thermal processing of these steels should be compatible with the continuous galvanizing line (CGL) as it provides cost-effective, robust corrosion protection for autobody parts. Recently, it has been shown that CGL-compatible thermal processing of two prototype medium-Mn TRIP steels of approximate composition 0.2C-6Mn-1.5Si-0.5Al-0.5Cr-xSn (wt.%) can produce 3G-AHSS target mechanical properties (i.e. UTS × TE ≥ 24,000 MPa%). In the present study, these prototype medium-Mn steels were subjected to a range of CGL-compatible two-stage annealing heat treatments with two process atmosphere dew points (-30°C and -10°C). The external and internal selective oxides formed during the annealing treatment were analyzed across a variety of length scales. This contribution will evaluate the selective oxide chemistry and morphology as a function of process atmosphere oxygen partial pressure, intercritical annealing parameters and minor surface active element (Sn) addition within the context of developing CGL-compatible process parameters which will produce thin and dispersed external oxides and promote reactive wetting during the continuous hot-dip galvanizing process.