| WANG Xu,HE Ding-yong,SHAO Wei,ZHOU Zheng,WU Xu,ZHANG Tie-jun.Effect of Boron Content on High-temperature Oxidation Resistance of NiCrB Surfacing Alloy[J],52(8):247-254, 300 |
| Effect of Boron Content on High-temperature Oxidation Resistance of NiCrB Surfacing Alloy |
| Received:August 16, 2022 Revised:September 20, 2022 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.08.019 |
| KeyWord:NiCrB alloy cored wire surfacing high-temperature oxidation CrBO3 hardness |
| Author | Institution |
| WANG Xu |
Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing , China |
| HE Ding-yong |
Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing , China;Beijing Engineering Research Center of Eco-Materials and LCA, Beijing , China |
| SHAO Wei |
Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing , China |
| ZHOU Zheng |
Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing , China |
| WU Xu |
Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing , China |
| ZHANG Tie-jun |
Pipe Technology Service Center, Sinopec Shengli Petroleum Engineering Co., Ltd., Shandong Dongying , China |
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| Abstract: |
| Ni-based surfacing alloys have the reliable oxidation resistance in protecting the steel tubes of coal-fired boilers operating in power plant. However, these conventional surfacing alloys are not hard enough to bear the wear from the sand particles in circulating fluidized bed boiler. Therefore, the protective surfacing alloys should possess both good oxidation resistance and high hardness. Researchers have shown that chromium (Cr) can enhance the oxidation resistance of Ni-based surfacing alloys while boron (B) can improve the hardness of the surfacing alloys. Thus, NiCrB surfacing alloys with different boron contents were designed in this work for tube protection. The oxidation resistance and hardness of the surfacing alloys were investigated. Five NiCrB (Cr:24.0%, B:0~3.5% in mass) cored wires with different boron contents were produced, and then these cored wires were used to manufacture surfacing alloys by TIG process. The high-temperature oxidation behavior of the surfacing alloys was investigated after 200 hours of oxidation at 800 ℃. An electronic scale with an accuracy of 0.01 mg was used to measure the mass of the samples during the high-temperature oxidation tests. The high-temperature oxidation kinetic curves were plotted based on the per unit area mass gain of the samples and the oxidation time. The hardness, phase compositions and microstructures of the surfacing alloys were analyzed by Vickers hardness tester, XRD and SEM-EDS, respectively. Compared to NiCr surfacing alloy, the hardness of NiCrB surfacing alloys was significantly increased. The rise in boron content increased the boride content in the alloy, and thus the hardness was improved. In addition, the hardness of the alloys before and after oxidation changed slightly. The NiCrB surfacing alloys possessed NiCr solid solution and borides, which were was mainly CrB and Cr5B3. After oxidation tests, NiCr surfacing alloys showed the best oxidation resistance due to the formation of dense Cr2O3 oxide scale. The oxidation products of NiCrB surfacing alloys were composed of Cr2O3 and CrBO3. CrBO3 was the reaction product of B2O3 and Cr2O3. The results showed that the oxidation resistance of NiCrB surfacing alloys was affected by the content of the CrBO3. When the boron content was 0.8 wt.%, the oxide scale formed was thin and adhered well to the NiCrB surfacing alloy. Therefore, the alloys had a similar oxidation resistance to the NiCr surfacing alloy. When the boron content was ≥1.6 wt.%, the oxide scale gradually became loose and presented a multi-layer structure. With the further increase in boron content, the oxide scale tended to peel off in the tests. CrBO3 was formed in large quantities in the oxide scale, which led to the loosening of the scale. B2O3 was in liquid state at 800 ℃ when B2O3 reacted with Cr2O3 to form CrBO3, resulting in a change in the volume of the oxide scale. As a result, the cracks and pores generated within the oxide scale, which contributed to the formation of a multi-layer structure of oxide scale. Moreover, the discontinuous formation of Cr2O3 and CrBO3 also facilitated the loosening of the scale. Additionally, selective oxidation of CrB and Cr5B3 was happened prior to chromium, resulting in the internal oxidation of NiCrB surfacing alloy with the boron content of 3.5 wt.%. |
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