Turbocharger can improve the power of automobile engine, reduce fuel consumption, reduce noise and pollution, effectively improve engine power, economy and environmental protection performance, and is increasingly widely used. Due to the gradual increase of exhaust emission temperature, the high temperature performance requirements of turbochargers are increasingly high. At present, the shell materials suitable for this demand are mainly:

1. Grey cast iron

Cast iron has good casting process performance. Most of the volutes are made of cast iron. Gray cast iron has excellent casting and molding properties, but its mechanical properties are relatively low. Therefore, it is generally used in the lower load supercharger shell after adding Cr, Ni, Si and other alloy elements to improve the properties.

2. Nodular cast iron

Ductile iron not only has good casting process properties, but also has good mechanical properties and oxidation resistance, especially the thermal fatigue strength is much higher than gray iron. It is a good material for manufacturing supercharger shell, and is the main material for automobile supercharger and high-performance engine supercharger at present. Ordinary nodular cast iron has lower manufacturing cost and better heat resistance than gray cast iron, but it can only be used for diesel engines with lower heat load.

3. Medium silicon molybdenum nodular cast iron

The addition of alloying elements such as Si and Mo in nodular cast iron can improve the mechanical properties and oxidation resistance of nodular cast iron at high temperature. The amount of Si added shall be controlled at 3 5-4 5%. Mo is generally controlled at 0 3 - 0 7%. The medium silicon molybdenum nodular cast iron thus formed has good high temperature mechanical properties, high temperature stability and oxidation resistance, and is suitable for diesel engines with higher thermal load (600-700 ℃).

4. Heat resistant cast steel

The heat-resistant austenitic cast steel has high creep resistance and good resistance to temperature change. Heat resistant steel and high nickel ductile iron volute can make the heat resistant temperature of turbocharger reach above 1150 ℃, which is the mainstream development direction of turbocharger volute in the future.

The shape of turbocharger shell is complex, which requires good casting performance and high temperature performance. At present, the turbochargers on the market are mainly made of ordinary nodular iron or high silicon molybdenum nodular iron, and the heat-resistant temperature is only about 900 ℃, which has gradually failed to meet the requirements of modern cars, especially the gasoline engine of cars. Therefore, the heat-resistant cast steel with higher high-temperature performance has gradually become the preferred material for the turbochargers of automobiles.