Effect of minor alloying element variation on the properties of alloy 800

Application of Alloy 800 in steam generator tubing of fast reactors, where continuous service temperature of the order of 550° is experienced, has been analyzed with respect to small variations in its chemical composition. Several laboratory melts of Alloy 800 have been prepared and their microstructural and mechanical property changes during simple aging and creep tests at 500 to 600° have been studied. It has been found that in the above temperature range precipitation of M₂₃C₆on the grain boundaries is independent of the Ti : C ratio generally specified for Alloy 800. Gamma prime precipitation occurred in alloys containing as low as 0.5 pct Ti+ Al after 1000 h of aging and was accompanied with a creep ductility decline. Upon γ precipitation creep rate was retarded and its reacceleration for test times up to 8500 h at 550° was not observed. Based on the findings, increased Ti concentration at the expense of Al within the specified chemical composition range with carbon content of 0.030 to 0.050 has been suggested. A. A. Tavassoli is on sabbatical leave from the Arya-Mehr University of Technology, Tehran, Iran.