Effect of Ti content on solidification organization and non-metallic inclusions in 0Cr25Al5 electrothermal alloy

Alloy microalloying is one of the most important means of improving the performance of ingots. In order to further investigate the effect of Ti element on the solidification organization and non-metallic inclusions of 0Cr25Al5 electric heating alloy ingots on their properties, the thermodynamic software Thermo Calc was first used to calculate the behavior of AlN and TiN precipitates in the solidification front of Fe-Cr-Al-Ti-N-C hexagonal system with different Ti contents (mass fractions, the same below, 0.08%, 0.10%, and 0.12%, respectively) and different N contents (mass fractions, the same below, 0.009%, 0.012%, 0.017%, and 0.020%, respectively), and the control level of N content corresponding to different Ti contents was given. The results of experiments show that the isometric crystal rate obviously reduces for the solidification organization of this alloy with increasing Ti content, and when the content of Ti is 0.082%, the equiaxed crystal rate of lengthwise section reaches the maximum value of 69.56%, on the contrary, the average grain size is the minimum value of 1.96 mm. Thus, the appropriate addition of Ti elements for micro-alloying can improve the solidification organization for this alloy. Meanwhile, automatic inclusion analysis systems were used to detect inclusions in three different Ti content metallographic samples. The results indicate that when Ti content is 0.082%, the number, size, area fraction, and quantity density of inclusions are all at their minimum values. In addition, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to observe and analyze the metallographic samples after erosion. It is found that Ti containing inclusions mainly exist in the form of Ti (C, N), TiO_x, TiN rare earth composite inclusions, and Ti containing rare earth oxides in the steel ingot. In addition, when the content of Ti is 0.110%, it is also found that a large number of non-metallic inclusions TiN, the size is about 1-2 µm, are found to be enriched at grain boundaries, which causes greater harm to the fatigue properties and mechanical properties for this alloy. In summary, adding 0.082% Ti to the ingot significantly improves the solidification structure and reduces the negative impact of Ti inclusions present in the ingot on the ingot properties.