Selective Oxidation of a CMnSi Steel during Heating to 1000 °C: Reversible SiO2 Oxidation

Abstract

Many multiphase cold-rolled high-strength steels require complex thermal processing, including a (partial) austenitization to reach the desired microstructure. However, of importance for their galvanizability, the selective oxidation of these steels in the austenitic region has not been studied extensively. The present work aims at characterizing the selective oxidation of a CMnSi steel during heating up to 1030°C by X-ray photoelectron spectroscopy (XPS) surface analysis. A phenomenological description of the evolution of the surface composition during heating and soaking in a N 2 -5 pct H 2 atmosphere with a dew point of -50°C is presented. Four distinct stages of selective oxidation were identified during heating; manganese oxidation, SiO 2 film growth, a transition stage, and a steady state with boron nitride (BN) passivation. During the transition stage, the previously formed SiO 2 film disappears, resulting in increased iron concentration at the surface. Simultaneously, a BN film forms on the uncovered metallic iron, inhibiting any further oxidation of the surface. It is demonstrated that the SiO 2 oxidation is reversible and temperature controlled.

Effect of Surface Microstructure on Oxidation of a CMnSi Advanced High Strength Steel

“…4,10,[12][13][14][15][16][17] The method most relevant to this study is the promotion of internal oxidation over external oxidation. This transition can be induced by raising the dewpoint of the annealing furnace atmosphere.…”

“…27) Glow discharge optical emission spectroscopy (GDOES) and EDS results indicated manganese enrichment at the surface was greatest at low temperatures or when the matrix was entirely ferritic. 7,13,27) Grain size has also been shown to impact oxidation behavior, influencing overall coverage as well as surface oxide chemistry and morphology. 28) Coarse-grained samples from the study by Thorning et al tended to form a continuous network of manganese-rich oxides along the grain boundary, but sparse oxidation on grain interiors.…”

Effects of Surface Microstructure on Selective Oxidation Morphology and Kinetics in N₂ + 5%H₂ Atmosphere with Variable Dew Point Temperature

“…Several methods have been developed to overcome the galvanization challenges posed by AHSS with varying degrees of success for many first-generation grades. 4,7,[13][14][15][16][17][18] Development of new AHSS grades are still underway and a fundamental understanding of the thermodynamics and kinetics of selective oxidation is paramount to designing and developing strategies to hot-dip galvanize new alloys. To enable prediction of oxidation behavior, all contributing factors need to be identified and accounted for.…”

“…To enable prediction of oxidation behavior, all contributing factors need to be identified and accounted for. The effect of certain parameters such as atmospheric dewpoint [6][7][8]15,[17][18][19][20] and microstructure 10,14,[21][22][23] have been studied but many questions remain.…”

Effects of Oxygen Partial Pressure on Oxidation Behavior of CMnSi TRIP Steel in an Oxidation-Reduction Scheme

“…Therefore, extensive work has been performed to suppress the external oxidation of the alloying elements in AHSSs during intercritical annealing by controlling the dew point (DP) and composition of the annealing gases [6][7][8][9][10][11][12][13]. Increasing the DP in the annealing furnace could promote the alloying elements to shift from undergoing external oxidation to internal oxidation, and thus improve the galvanizability of AHSS sheets.…”