Distribution law of casting defects of multi branch cast steel joints:
(1) Cracks mainly appear in the R zone of cast steel joints. The reason is that the thickness of the branch pipe is only half of that of the main pipe, resulting in different cooling conditions between the branch pipe and the main pipe. The thin branch pipe cools faster and the main pipe cools slower. The solidification time and shrinkage rate of the two are different. However, the main pipe and the branch pipe are a whole, which is easy to release stress through cracks at the junction, which is also consistent with the test results;
(2) The probability of shrinkage cavity and porosity defect near the R zone is very high. The reason is that the intersection area between the branch pipe and the main pipe is a hot joint, which solidifies late. The solidification in other areas blocks the feeding of the hot joint by the riser, so it does not solidify according to the cooling route, resulting in shrinkage defects near the branch pipe;
(3) Shrinkage cavity and porosity defects mainly appear in the middle of the wall thickness of cast steel joints, and inclusion defects mainly appear on the outside and inside of the wall thickness. The probability of appearing in the middle is very low, and most of the porosity defects appear on the outside of cast steel joints;
(4) Delamination defects mainly appear in the uppermost part of cast steel joints.