Use of Ferritic SS444 in Exhaust Gas Cooling for Gasoline Engine

Abstract

<div class="section abstract"><div class="htmlview paragraph">With the introduction of CAFÉ norms (Corporate Average Fuel Economy or Efficiency) in automobile industries, gasoline engines must improve their fuel economy by reducing overall CO₂ footprints. To fulfil this demand many OEMs have adopted the use of exhaust gas circulation coolers (EGR)</div><div class="htmlview paragraph">Most of the gasoline engines are having exhaust gas temperatures ranging from 650-850°C, these gases could also be highly corrosive in nature. It’s very important to select the right grade of stainless steel which should have high corrosion resistance and oxidation properties. It should also withstand high temperatures and should have low sensitization at high temperatures.</div><div class="htmlview paragraph">Most of grades stainless steel offers high resistance against corrosion, high temperature properties. But good sensitization at high temperature is not always associated with all grades of steel.</div><div class="htmlview paragraph">To compare corrosion resistivity, PREN number (Pitting Resistance Equivalent Number) plays important role. Highest the PREN number highest is the resistance to corrosion. Based on initial screening SS316L and SS444 grade are selected to undergo various test to demonstrate and compare corrosion, oxidation, and sensitization properties.</div><div class="htmlview paragraph">These materials have gone under various tests like condensate corrosion test as per VDA 230-214 K-1.2 standard, for 1000 hours. After each test, material microstructure properties have been analysed and results are compared. This technical paper includes advantage of material grade in terms of austenitic vs ferritic, manufacturing process, joining process (weldability or brazing), cost and the application where is it most suitable to use.</div></div>