Abstract
The mechanical properties of En 39 steels with Mn contents ranging from 0·02 to 0·5% which have been preheated at temperatures within the range 1200°-1400°C and cooled at different rates have been determined after the steels have been subsequently fully heat treated. It has been found that a severe loss of ductility and a decrease in the impact energy can occur with steel containing 0·34%Mn and 0·008%S. Increasing the Mn content to 0·5% brings about an improvement, as does decreasing the Mn content to 0·02%. The reasons for these changes are discussed in relation to the influence of Mn on the solubility of S in austenite. Even with a Mn content of 0·02% and a S content of 0·007%, intergranular failures are found after high-temperature treatment. These have been found to be associated with a mixed MnS-CrS precipitation at the austenite grain boundaries. For low-alloy steels to be used for large forgings it is suggested that the Mn specification should be reduced to 0·05% or less and this should be linked with a S specification within the range 0·001–0·004%. Steels with a composition within the range 0·2–0·4%Mn and 0·008–0·010%S are likely to embrittle severely by overheating during forging. For small forgings where there is no risk of inducing temper embrittlement the Mn content should be above 0·5%.
Get full access to this article
View all access options for this article.