Abstract
The effect of calcium treatment on inclusions in H08A welding rod steel was studied by industrial experiment and using thermodynamics theory. The effects of inclusion composition, morphology, quantity, and size in H08A welding rod steel before and after calcium treatment were studied by metallographic microscope, scanning electron microscope (SEM), and energy dispersive spectrometer (EDS). Thermodynamic studies show that the addition of calcium can form various forms of xCaO·yAl2O3, under the condition that the composition of molten steel remains unchanged, the control of calcium content is the key to generate low melting point calcium-aluminate complex non-metallic inclusions and improve the quality of molten steel. The production practice in steel plant shows that for welding rod steels, the calcium content in a suitable range can meet the requirements of calcium treatment. Effective calcium treatment can not only transform the high melting point Al2O3 inclusions into the low melting point complex non-metallic inclusions between 3CaO·Al2O3 and 12CaO·7Al2O3, but also make the original shape-diversified inclusions into the spherical calcium-aluminate complex non-metallic inclusions. Meanwhile, the total number of inclusions and large-scale inclusions in welding rod steel are reduced, and the inclusions tend to disperse in the steel, which is very conducive to the improvement of steel quality. The results show that the modification path of magnesium aluminate spinel in steel is as follows: Al2O3 → MgO-Al2O3 → MgO-CaO-Al2O3. In addition, calcium treatment can modify MgO-Al2O3 spinel in steel into liquid MgO-CaO-Al2O3 complex non-metallic inclusions with low melting point.
Highlights
With the rapid development of global infrastructure, the demand for steel in various countries is increasing; welding rod steels are the most consumed steel in the welding material industry [1]
By adding metallic calcium to the H08A welding rod steel, it was found that MnS, Al2O3, and MnS-Al2O3 were the main inclusions in H08A welding rod steel before calcium treatment
The inclusions in the steel begin to transform into CaOAl2O3 complex non-metallic inclusions, MgO-CaO-Al2O3 complex non-metallic inclusions, and MgO-Al2O3-MnS complex non-metallic inclusions, and the inclusions morphology presents a spherical shape
Summary
With the rapid development of global infrastructure, the demand for steel in various countries is increasing; welding rod steels are the most consumed steel in the welding material industry [1]. The type, quantity, size, morphology, and distribution of non-metallic inclusions in steel have great influence on the quality of metal products. For H08A welding rod steel, the type, quantity, and size of inclusions in the steel are important factors to determine whether cracks, folds, scabs, and other defects occur in the steel. The research of welding rod steels mainly focuses on crack resistance, fatigue, microstructure, and mechanical properties [7]. Aluminum deoxidation will produce large size and cluster alumina inclusions, which will cause nozzle clogging, and affect the steel properties during steel processing [19]. This paper studies the main source, quantity, and size distribution of inclusions in H08A welding rod steel, and the evolution and deformation of inclusions in H08A welding rod steel before and after calcium treatment. By deepening the understanding of inclusions in welding rod steels, the theoretical basis for the inclusion conditioning is provided, and the production quality of welding rod steels is improved
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