| ‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘ KAWASAKI STEEL TECHNICAL REPORT No.40 ( May 1999 ) Steinless Steel and Steel Platel ‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘ |
| Effect of La and Zr Addition on High-Temperature
Oxidation Resistance of 20%Cr-5%Al Steel
Foil Kazuhide Ishii, Masaaki Kohno, Susumu Satoh |
| Synopsis: River Lite 20-5USR(20%Cr-5%Al) stainless steel foil, which contains small amounts of La and Zr, possesses excellent oxidation resistance, and has been widely applied to catalytic converters of automobiles. To clarify the mechanism of improvement in oxidation resistance by La and Zr addition, the oxidation behavior of 50 Κm thick 20%Cr-5%Al steel foils containing small amounts of La, La + Ti and La + Zr was examined. The addition of La decreased the growth rate of both Al2O3 layer, which grew until Al in the foil had been depleted, and Cr2O3 layer, which formed between the Al2O3 layer and the substrate after the depletion of Al. The addition of an adequate amount of Zr to alloys containing La made the growth rate of both oxide layers still lower, while the addition of Ti did not. The segregation of La and Zr at grain boundaries in the Al2O3 was observed with TEM. However, Ti segregation was little detected. The reduction in the growth rate of the Cr2O3 layer indicates that the oxygen diffusion rate in the Al2O3 layer is reduced. It is considered that La and Zr segregation suppresses oxygen diffusion via the Al2O3 grain boundaries with the result of decreasing the growth rate of the Al2O3 and Cr2O3 layers. |
| TextiPDF: 6P/276kbj |