Investigation of Microstructure, Nanohardness and Corrosion Resistance for Oxi-Nitrocarburized Low Carbon Steel
Abstract
:1. Introduction
2. Materials and Methods
3. Results and Discussion
3.1. Microstructure and Phase Analysis
3.2. Nanohardness of the Surface Hardened Layer
3.3. Corrosion Resistance
4. Conclusions
- EPMA and EBSD methods are useful techniques for analysis of microstructure including the oxide layer of magnetite and compound layer of ε-phase and γ′-phase for oxi-nitrocarburized low-carbon steel.
- Though the nanohardness measured by nanoindentation method is not precise enough, it is worth measuring the nanohardness to understand the cross-sectional microstructure for the surface hardened layer.
- Regardless of the oxidation conditions, the corrosion resistance of the oxi-nitrocarburized specimens showed superior performance when compared to the untreated-specimens. This means that oxi-nitrocarburizing is a potential method for improving the corrosion resistance because of the formation of a thicker magnetite oxide layer.
Author Contributions
Acknowledgments
Conflicts of Interest
References
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Fe | C | Mn | P | S | Cu |
---|---|---|---|---|---|
Bal. | 0.0018 | 0.206 | 0.092 | 0.004 | 0.051 |
Notation | Gas Nitrocarburizing | Oxidation | ||||
---|---|---|---|---|---|---|
Temp. (°C) | Input Gas Ratio (NH3:N2:CO2) | Time (min) | Temp. (°C) | Input Gas | Time (min) | |
Untreated-specimen | - | - | - | - | - | - |
Air-specimen | 560 | 5:4:1 | 100 | 550 | Air | 5 |
Steam-specimen | 550 | Steam (H2O) | 30 |
Classification | Air-Specimen | Steam-Specimen |
---|---|---|
Thickness of Hardened Layer | Thin [8–12 μm] | Thick [14–16 μm] |
Thickness of Oxide Layer | Thin [1.5–2.5 μm] | Thick [4–6 μm] |
Microstructure of Oxide Layer | Dense | Porous |
Thickness of Compound Layer | Thin [6.5–9.5 μm] | Thick [10–12 μm] |
Microstructure of ε-Phase | Massive, continuous | Small and isolated in the γ′-phase |
Specimen | Corrosion Potential (V) | Current Density (mA/cm2) |
---|---|---|
Untreated | −0.97 | 0.184 |
Air | −0.77 | 0.087 |
Steam | −0.75 | 0.071 |
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Cho, Y.-W.; Kang, Y.-J.; Baek, J.-H.; Woo, J.-H.; Cho, Y.-R. Investigation of Microstructure, Nanohardness and Corrosion Resistance for Oxi-Nitrocarburized Low Carbon Steel. Metals 2019, 9, 190. https://doi.org/10.3390/met9020190
Cho Y-W, Kang Y-J, Baek J-H, Woo J-H, Cho Y-R. Investigation of Microstructure, Nanohardness and Corrosion Resistance for Oxi-Nitrocarburized Low Carbon Steel. Metals. 2019; 9(2):190. https://doi.org/10.3390/met9020190
Chicago/Turabian StyleCho, Young-Wook, Young-Joon Kang, Ju-Hwan Baek, Jeong-Ho Woo, and Young-Rae Cho. 2019. "Investigation of Microstructure, Nanohardness and Corrosion Resistance for Oxi-Nitrocarburized Low Carbon Steel" Metals 9, no. 2: 190. https://doi.org/10.3390/met9020190