Effects of Alloying Elements on Surface Oxides of Hot-Dip Galvanized Press Hardened Steel

TL;DR

This study investigates how different alloying elements influence the formation and composition of surface oxide layers on hot-dip galvanized press hardened steel, revealing the roles of ZnO, Mn-Zn spinels, and Cr-enriched films.

Contribution

It provides detailed insights into the effects of alloying elements on oxide layer composition and structure, highlighting the role of chromium in strengthening and regenerating Al2O3 layers.

Findings

ZnO and Mn-Zn spinels are primary oxides on galvanized steel surfaces.

Cr enrichment can form a protective Cr2O3 layer at high concentrations.

Secondary ion mass spectrometry distinguishes ZnO from Zn(OH)2 effectively.

Abstract

Effects of steel alloying elements on the formation of the surface oxide layer of hot-dip galvanized press hardened steel after austenitization annealing were examined with various advanced microscopy and spectroscopy techniques. The main oxides on top of the original thin Al2O3 layer, originating from the primary galvanizing process, are identified as ZnO and (Mn,Zn)Mn2O4 spinel. For some of the investigated steel alloys, a non-uniform, several nanometer thick Cr enriched, additional film was found at the Al2O3 layer. At a sufficiently high concentration, Cr can act as a substitute for Al during annealing, strengthening and regenerating the original Al2O3 layer with Cr2O3. Further analysis with secondary ion mass spectrometry allowed a reliable distinction between ZnO and Zn(OH)2.