Relaxation stability of high-strength cast irons with spheroidal graphite

Abstract

1. The resistance of cast irons to relaxation is due to the structure of the matrix. At 450° C iron of pearlitic structure has the greatest resistance to relaxation and ferritic iron the least. At 525° C, during the initial stage of the relaxation process, the process proceeds in the same way, but over the second stage the relaxation process is slower in a cast iron with a ferritic structure. This is apparently connected with the increase in the diffusional mobility of the atoms and the increased role of diffusional processes in relaxation. 2. All the unalloyed high-strength cast irons with spheroidal graphite that have been studied have only a slight resistance to relaxation at 450° C, and especially at 525° C, regardless of the structure of the base metal. Their resistance to relaxation, however, is still higher than that of gray cast irons [4]. 3. The alloying of high-strength cast iron with spheroidal graphite with molybdenum and copper sharply increases the resistance to relaxation strength. For a resistance to relaxation greater than 0.5%, however, it is apparently inadvisable for a cast iron designed for operation at up to 450° C to contain any molybdenum. 4. The alloying of high-strength pearlitic cast irons with spheroidal graphite may be employed for parts operating under conditions causing stress relaxation.