Elimination Mechanism of Shrinkage Porosity During Pressurized Solidification Process of 19Cr14Mn4Mo1N High-Nitrogen Steel Ingot

Elimination mechanism of shrinkage porosity during pressurized solidification process of 19Cr14Mn4Mo1N high-nitrogen steel ingot was systematically investigated by experimental and calculational methods. According to the formation mechanism and morphological characterization, there are three types of shrinkage porosity in the 19Cr14Mn4Mo1N ingots, namely conventional shrinkage porosity, gas-shrinkage porosity, and gas-induced shrinkage porosity. It is shown that with increasing solidification pressure from 0.3 to 0.4 MPa, the dominant type of shrinkage porosity transfers from gas-shrinkage porosity to conventional shrinkage porosity, and the size of gas-shrinkage porosity under 0.3 MPa is larger than that of under 0.4 MPa. Under 0.6 MPa, the shrinkage porosity virtually disappears completely. The results demonstrate that increasing solidification pressure can eliminate shrinkage porosity. Since there are only a few variations in the cooling rate at the center of ingots with increasing solidification pressure from 0.3 to 0.6 MPa, increasing the solidification pressure cannot eliminate shrinkage porosity defects by changing the cooling rate of 19Cr14Mn4Mo1N ingot. Therefore, increasing the solidification pressure eliminates shrinkage porosity mainly by inhibiting the nucleation and growth of nitrogen pore and promoting the feeding flow.