Investigation on Porosity Formation With Pressure Drop Between Dendrite Tip and Root During Pressurized Solidification of 30Cr15Mo1N Ingot

This paper presents a method based on Darcy's law to determine the pressure drop between the dendrite tip and root during the formation of porosity. After verification by the measurement result of the porosity region in 30Cr15Mo1N ingot, this method is employed to investigate the change in the pressure drop with solidification pressure, considering various factors such as the second dendrite arm spacing, solid fraction, cooling rate, temperature gradient, density, liquidus temperature, and solidus temperature. The relationship between the pressure drop and solidification pressure determines the formation of porosity. The results demonstrate that as the solidification pressure increases from 0.3 to 0.7 MPa, the pressure drop decreases from 1.572 to 0.676 MPa. When the solidification pressure is below 0.6 MPa, the pressure drop consistently exceeds the solidification pressure, leading to inadequate interdendritic feeding of the molten steel and subsequent porosity formation. Conversely, when the solidification pressure ranges between 0.6 and 0.7 MPa, the pressure drop undergoes minimal change and is approximately equal to the solidification pressure, which leads to sufficient interdendritic feeding. Consequently, increasing the solidification pressure effectively suppresses the formation of porosity by reducing the hindrance to molten steel feeding and enhancing its feeding capacity. Furthermore, a more accurate determination of the constant kC was obtained to calculate the pressure drop in 30Cr15Mo1N ingot, within the range of 2.77 to 3.11.