In a recently issued patent (US 10,619,950 April 14, 2020) researchers at the Toyota Motor Company have demonstrated that the corrosion resistance of stainless steel exhaust systems for cars and trucks can be substantially improved by heat treatment in high vacuum. Stainless steel is a complex metal alloy of iron, nickel, chrome and other elements. It is known to be a very durable metal but even this robust material can be corroded by exposure to chloride ions, sulfuric and hydrochloric acids, soot and other artifacts of the exhaust from an internal combustion engine. Reaction with these aggressive gases causes pits in steel which eventually lead to premature failure. The use of low-grade fuels speeds the degradation of exhaust systems.
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