Cause of formation
During the solidification process, the steel fails to be welded during the hot working process due to the final solidification shrinkage of the low melting point material and the voiding of the evolved gas. According to its distribution, it can be divided into two categories: center and general porosity.
On the lateral hot acid immersion surface, the pores are irregular polygons and narrow bottom pits, and such pits usually appear in the segregation spots. In severe cases, there is a tendency to become spongy.