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

Abstract

The work presented here demonstrated that changes to the near-surface microstructure could promote internal oxidation in a CMnSi advanced high strength steel (AHSS) grade. The starting material was industrially-supplied cold-rolled sheet. Samples with this microstructure were compared against two other conditions: annealed at 1 200°C and 850°C prior to oxidation. The surface regions of both annealed samples were decarburized. All samples were then oxidized at 850°C in an argon atmosphere with approximately 10 − 20 atm oxygen for 5-90 minutes. The oxidation treatments were performed in a high-temperature confocal scanning laser microscope (CSLM) setup that enabled in-situ visualization of surface oxide formation. Analysis of CSLM and scanning electron microscopy (SEM) images of sample surfaces indicated there were differences in oxide morphology and coverage between samples with different starting microstructures. Cold-rolled samples showed little internal oxidation but extensive external oxidation. Samples annealed prior to oxidation exhibited both internal and external oxidation. The differences in behavior were attributed to the formation of a decarburized surface layer during the pre-anneal, which led to ferritic iron near the surface. Another result of the pre-anneal was a reduction in dislocation density, which potentially led to fewer preferential nucleation sites for oxides very close to the sample surface.

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

“…Oxidation occurred for 120 s in forming gas atmospheres (N 2 + 5%H 2 ) with con- trolled DPTs of − 30°C and 0°C. A second set of samples was annealed for 1 800 s to examine effects of hold time and to compare with previous results 23) where gaseous oxygen at very low partial pressures was the only oxidant. SEM images of external surfaces showed differences in coverage with both DPT and starting microstructure.…”

“…Parameters used to achieve each microstructure and results from Vickers hardness tests to assess changes to near-surface microstructure are reported elsewhere. 23) Grain size measurements were collected from pre-annealed specimens in the decarburized zone near the surface. Measured grain sizes per ASTM standard E112 were 52.8 ± 8 μm for 1 200 A samples and 7.0 ± 1 μm for 850 A samples.…”

“…For the scope of this report, improvements included reducing external oxidation or increasing internal oxidation. Prior work by the current authors suggested steel microstructure can influence selective oxidation behavior, 23) however this work was conducted under conditions that were not industrially relevant. In this report, the effect of microstructure was tested under anneal-ing conditions that were more industrially relevant.…”

“…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.…”

Surface morphology analysis of oxide layers formed on 10CrMo9-10 steel used in the power industry

“…Therefore the topic of materials oxidation is still a current issue. Many research centers performs research related to the oxidation of materials [7][8][9][10][11][12][13][14][15][16][17][18][19][20], especially metallic materials [21][22][23][24]. Corrosion is an issue of high interest to scientists [25][26][27][28][29][30].…”