Abstract
Recently variable nozzle type turbocharger market grows up rapidly in the environmental issues because it improves the fuel efficiency and cope with the exhaust gas regulation. The environment of the variable nozzle type turbocharger becomes severe than before. The exhaust gas temperature will go up to 1323K in the close future. In the result the high Cr cast steel mainly used as turbocharger parts won´t always meet durability. The material with better heat resistance and wear resistance at high temperature becomes necessary. In addition, the cost reduction of parts is also always required. In the respect, the powder metal method takes advantage for it because of near net shape process. This report introduces sintered alloy EW- 50 with higher performance and lower cost than the high Cr cast steel to be suitable for the turbocharger parts.
The basic material design of EW-50 is to disperse a larger amount of carbide than high Cr cast steel on the high Cr alloy matrix. EW-50 achieved superior heat temperature oxidation resistance and wear resistance to high Cr cast steel. Sintered alloy makes it possible to disperse a larger amount of Cr carbide uniformly and finely without carbide growth that is avoided in the cast steel. Though sintered alloy usually has internal pore and it brings internal oxidation, EW-50 prevents the oxidation due to pore closing by liquid sintering.
As a result of the oxidation resistance test, EW-50 has more excellent oxidation resistance than the high Cr cast steel in all the temperature up to 1323K because of the prevention of internal oxidation by the liquid phase sintering as mentioned above. And EW-50 has better wear resistance than the high Cr cast steels. Wear amount of EW-50 in sliding test at high temperature was half of the high Cr cast steels because a larger amount of Cr carbide than the high Cr cast steel prevent the plastic deformation on sliding. EW-50 is superior to the high Cr cast steel on the cost side because the fabrication amount and the material yield can be largely decreased by the near net shape process in the powder metal.
As the mentioned above, EW-50 is a proper material for the variable nozzle type turbocharger parts, especially nozzle ring because EW-50 is more excellent than the high Cr cast steel on both sides of high-temperature properties and the cost. It means that EW-50 has great possibility to give solutions for various problems in variable nozzle type turbocharger parts.
Keywords: Turbocharger, wear resistance, oxidation-resistance, high Cr stainless steel, high-temperature strength