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Effect of trace magnesium on mechanical properties of Incoloy825 corrosion resistant alloy
- Qiuhan LI Wei GONG Zhouhua JIANG Pengfei WANG
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The Chinese Journal of Process Engineering. 2023, 23(3):
451-459.
DOI: 10.12034/j.issn.1009-606X.222126
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As a corrosion-resistant alloy, Incoloy825 alloy is used in marine engineering, LPG, and other industries. Due to the harsh environment of such industries, it is necessary not only for the material to have excellent corrosion resistance, but also to have high mechanical properties. In this work, 4 furnaces of Incoloy825 alloy with Mg content of 0wt%, 0.0012wt%, 0.0030wt%, and 0.0065wt% were smelted in a 25 kg vacuum induction furnace. Utilizing a metallographic microscope, scanning electron microscope, and energy dispersive spectrometer, the size and quantity of non-metallic inclusions were counted, the morphology and composition were observed and analyzed, and the microstructure and carbide were observed. Room temperature tensile test and room temperature impact test were carried out on the alloy. Combined with the experimental results, the influence mechanism of magnesium on the mechanical properties of Incoloy825 was revealed. The results showed that the addition of magnesium reduced the content of oxygen and sulfur in the alloy, reduced the number of inclusions, improved the composition of inclusions, improved the cleanliness of the alloy, reduced the influence of inclusions on mechanical properties, and refined the grains of the alloy. The yield strength, tensile strength, reduction of area and elongation of the alloy were improved to a certain extent, that was, the improvement of inclusions and microstructure improved the strength and plasticity of the alloy. It was also found that the addition of magnesium can expel Cr, Fe and Mo from the grain boundary of the alloy, thus reducing the precipitation of hard and brittle carbide M23C6 at the grain boundary and significantly improving the impact toughness of the alloy. Compared with the alloy without magnesium addition, when the Mg content increased to 0.0065wt%, the sulfur content and oxygen content in the alloy decreased by 37.19%, 15.71%, number density of inclusions decreased from 75 to 53 pcs, the large-sized bulk Al2O3 was transformed into small-sized MgO?Al2O3 and MgO with nearly circular 2D morphology, and the impact absorbing energy was increased from 262.5 J to 384.7 J, with an increase range of 46.55%. The mechanical properties of the alloy were improved by the comprehensive effects of the reduction of impurity elements, the number of inclusions, grain refinement, the size of carbides and the number of carbides at grain boundaries.