Effect of Dew Point on the Selective Oxidation of Advanced High Strength Steels

Abstract:

The effect of the dew point (and therefore oxygen partial pressure) on the selective oxidation of Advanced High Strength Steels was investigated. Steels with different Si contents, 0.2 wt% Si, 0.8 wt% Si and 1.5 wt% Si were used. The steel samples were annealed at 840 °C for 60 s and various gas atmospheres prior to hot-dip galvanized at 460 °C. The dew point of the 5 % H₂-N₂ annealing atmosphere was lowered from-30 °C (equivalent to 380 ppm H₂O) to-58 °C (equivalent to 14 ppm H₂O) in order to investigate surface segregation of alloying elements Si, Mn and Cr. These conditions are reducing for Fe, but oxidizing the oxygen-affine elements. Oxide morphology changed from a complete covering surface at high dew point to separated oxide spots at grain boundaries at low dew point. At the low dew point Cr was not oxidized. Oxides with a low Mn/Si-ratio seems to be amorphous. The Si-oxides are especially located at grain boundaries, Mn-oxides tend to cover the surface. Oxides covering the steel surfaces are detrimental for subsequent procedures as hot dip galvanizing, painting and welding.

• Periodical: Materials Science Forum (Volume 891)
• Pages: 292-297
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.891.292
• Online since: March 2017
• Authors: Magdalena Maderthaner*, Alexander Jarosik, Gerhard Angeli, Roland Haubner
• Keywords: Advanced High Strength Steels (AHSS), Dew Point, Hot-Dip-Galvanizing, Selective Oxidation

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