Study on Behaviour of Carbides and Knife Line Attack Phenomenon in Stabilized Austenitic Stainless Steels (Report VII)

Improvement of Knife Line Attack Sensitivity by Addition of the Rare Earth Metals

Abstract

The mechanism of knife line attack phenomena in SUS 321 and SUS 347 were already investigated in detail up to this report.
In this report, effects of addition of rare earth metals (REM) on the improvement of knife line attack sensitivities in SUS 321 and SUS 347 were studied based on the results obtained in the previous reports. At the same time, the mechanical properties and the corrosion resistances of REM bearing SUS 321 and SUS 347 were examined.
The results obtained in this reports are as follows;
1) The knife line attack sensitivities of SUS 321 and SUS 347 were improved by addition of REM. The optimum quantities of REM were about 0.15% in SUS 321 and about 0.11% in SUS 347.
2) By addition of REM, the quantities of M₂₃C₆ precipitated in HAZ of both SUS 321 and SUS 347 decreased.
This fact was considered to be the cause of improvement of knife line attack sensitivities in these steels.
3) Tensile properties at elevated temperature of REM bearing steels were almost same as ones in basesteels, and corrosion resistances of REM bearing steels were slightly improved.