Brittle fracture of thick carbon steel forgings for low temperatures rapture de fragilite des pieces en acier au carbone forgees epaisses pour basses temperatures

摘要

Growing plant unit capacities have to date caused equipment size to become larger. In a project, thick (130 mm) forgings for heat exchanger tube sheets suffered brittle fracture during flattening after explosion-cladding. This brittle fracture was caused by the use of raw materials highly containing phosphorus/sulfur and inappropriate heat treatment/forging. 24 tube sheets of 12 exchangers were newly manufactured; the raw materials were refined by vacuum degassing, and their chemical composition was adjusted to a pinpoint level. The raw materials were then forged to a forging ratio of 50s or more and were heat treated accurately. As a result, properly strong and tough tube sheets were manufactured. We should note that the manufacture of thick carbon steel forgings for low temperatures requires very high steel manufacturing/forging technologies. It appears necessary to evaluate the technology of forgers and raw material manufacturers, as well as equipment manufacturers.