Effect of rare-earth metals on the composition of nonmetallic inclusions and the heat resistance of austenitic steel

Abstract

1. REM have a large effect on the quantity, dispersity, and composition of nonmetallic inclusions and also on the heat resistance of Cr−Ni austenitic steel. 2. With the addition of up to 0.1% REM the total quantity of nonmetallic inclusions changes little, with replacement of the usual sulfides and oxide inclusions by REM sulfides and oxides. Larger amounts of REM lead to a substantial increase in the number of nonmetallic inclusions of another type consisting of REM, phosphorus, and nonferrous impurities. The concentration of sulfur in these inclusions is much smaller than in REM oxysulfides. 3. REM increase the ductility of the steel in long-term tests. With increasing amounts of REM the time to failure first increases considerably, reaching a peak with 0.1% REM, and then decreases to the original value. The creep rate changes little with up to 0.1% REM and then increases sharply, in conformity with the larger quantity of nonmetallic inclusions in the steel.