Design of stainless steel automotive exhaust manifolds

Abstract

The paper deals with the design of stainless steel exhaust manifolds, focusing on the development of high temperature ferritic grades and their forming capabilities related to the new forming processes, like bending and hydroforming. In particular, it is shown along the presentation, how a niobium stabilized 14%Cr grade can be used in replacement of austenitic grades in many situations of complex shaped manifolds thanks to its combined improved formability and its high temperature resistance up to 950°C. Finally, the authors present a “virtual” thermomechanical fatigue design approach, using a dedicated post processor, which would permit to optimize the design of the fabricated exhaust manifolds, and would lower the development cost and time by limiting both the number of prototype and motor bench tests and, finally, would reduce the risk of failure.