ABSTRACT
Conventional austenitic stainless steel (ASS) with nickel (Ni) content in the range of 20 to 40 Wt% are primarily used for the Turbine Housing component of turbochargers for gasoline applications. Due to the increase in cost of the nickel in the global commodity market, has become imperative to develop alternative cost-effective material solution. Therefore, few potential options were evaluated, and Nitrogen has been identified as one of the strong austenitic stabilizers, which can reduce Nickel content while simultaneously enhancing mechanical properties and crack resistance under severe Thermo-Mechanical Fatigue (TMF) loading conditions. The “Integrated Computational Materials Engineering” (ICME) methodology was developed to explore new options of material composition for low Ni steel. The optimum chemical composition of low Ni steel was down selected by performing a wide range of kinetics and thermodynamic studies under equilibrium & non-equilibrium conditions, and optimum nitrogen solubility limit. The impact of various undesirable phase formations during solidification was systematically addressed without compromising the manufacturability of the alloy. The sensitivity of various casting process parameters was systematically evaluated with the selected alloy composition. Large casting trials were conducted to minimize casting defects and achieve optimum microstructure features. The turbine housing component was tested up to 1050°C gas temperature under severe thermal shock loading conditions and compared with existing high Ni conventional steels. The overall development of this new material with a well-integrated development process, encompassing both computational and experimental techniques, proves it is a promising alternative solution providing both better performance and lower cost for high temperature turbocharger applications.
