First, it is cheaper than the price. The francs in the market are cheaper to cast, and the next is pure forging.
Secondly, destructive tests are made to separate flanges. The cast flanges have trachoma and the pure forged ones do not. Sometimes the cast-forged flanges have cracks.
Third, from the flange tolerance and surface finish, the forged flange will generally have a negative tolerance of 1-5mm, edge chamfering irregular, a burr in the hole is not smooth, and forged flange tolerance is smaller.
Purchase of carbon steel flange, according to its use environment to select, not only greedy price but to use as a prerequisite.