The authors have made a study of some effects of rare earths adlition to steel for theseseveral years. In this report, the influences of addition of the RE (rare earth)-Ca-Si complexalloys (of domestic commercial product) to stainless steels (AISI type 201, 202, 304 and 430), stainless alloy (20 series, equivalent to Carpenter 20) and heat resistant alloys (Iron-base Ni-Cr-Mo, equivalent to Timken 16-25-6; Ni-base, to Nimonic 90; and Fe-Cr-Al alloys) aresummarized. The ingot weights of type 304 and 20-series alloy were 30-50 kg, and those ofother laboratory-made ones were about 4kg, and 0'l5'-06 wt% of RE-alloys were added in thefurnace just before casting. Besides, to check up the influence of calcium and silicon containedin RE alloy, comparative specimens (added 02-05 wt% of Ca-Si alloy) of type 201, 202 and 430 steels were melted, respectively.
The authors investigated mainly the effects of RE-alloys upon microstructure, mechanicalproperties, ductility at high temperature, anticorrosion and oxidation properties: particularly, on the subject of ductility at high temperature, sub-size impact, impact-bending, torsion, bending and tensile tests were carried out elaborately.
Main results of experiments obtained are as follows:
(1) Treatment with RE-Ca-Si decreased the non-metallic inclusions in alloys, especiallyA-series (ductile sulphides and silicates) and B-series (alumina), and it appears better touse RE-Ca-Si than to use RE metals or Ca-Si alloy alone.
(2) Microstructure was not markedly influenced, but RE treatment arrested the precipitationof impurities and harmful carbides at grain boundaries, so that the corrosion resistance, particularly to the intergranular corrosion, was improved. Moreover Ca-Si treatmentdelayed the coarsening of ferritic grain-size of Fe-Cr-Al steel at high temperature.
(3) As RE elements tend to stabilize sulphides in steel, the hot-workability and hightemperature ductility were improved remarkably.
(4) In an oxidation test of heat-resisting alloy series, RE-Ca-Si alloy treated specimensshowed an increase in the scaling resistance because their oxide films were fine and hard tospall.