Investigation of the causes of destruction of heat-resistant molded pallets

Pallets are used as bases for storage and handling of products from the furnace to the quenching bath, and for loading of products into the furnace. In the manufacture of pallets special attention is paid to the choice of steel grade, preference being given to high-temperature steel grades. Pallets are produced from heat-resistant steel by casting methods. Violation of the manufacturing technology reduces the duration of pallet operation. At the considered plant the pallets broke down after four months of operation. Warpage, formation of longitudinal and transverse cracks, and destruction of the individual elements occurred. The paper analyzes the causes of the destruction of pallets made of heat-resistant steel 20Kh25N19S2L. It was shown that despite the use of pallet material according to operating conditions fracture occurs for several reasons. The first one was the abscence of heat treatment of large cast pallets at the manufacturing enterprise. A carbide network was observed in the structure which caused embrittlement of the metal. The second cause were thermal stresses due to quenching which are unevenly distributed in the pallet construction. The areas of occurrence of tensile and compressive stresses were identified on the basis of measurement of the temperature of different parts of the pallet. The third reason was the incomplete combustion of fuel that formed carburizing atmosphere in the furnace.