Stainless future for manifolds

As engine temperatures rise to make harmful emissions fall, automakers are turning to cast stainless exhaust manifolds to prevent thermal fatigue.

“Because engines are running much hotter, some applications require stainless steel,” says William LeVan, vice-president of Wescast Industries of Brantford, Ont., the world’s largest supplier of exhaust manifolds for passenger cars and light trucks. “These include heavier truck engines that are frequently under full load.”

General Motors recently chose Wescast to supply fully cast machined nickel stainless steel manifolds for the car-maker’s 2500/3500 truck series. The deal represents Wescast’s first major contract to supply this type of manifold since the company began developing the technology five years ago.

The manifolds for GM will be cast out of CN12 stainless steel, which contains about 13% nickel. The steel has superior thermal fatigue resistance, a minimum tensile strength of 370 megapascals and a minimum yield strength of 240 megapascals.

Most exhaust manifolds are made of conventional ductile iron alloys strengthened by 4-6% silicon and up to 2% molybdenum.

But since the 1970s, engine temperatures have soared by as much as 500C and this is hotter than some manifolds can handle. Future engines are expected to run even hotter, not only for improved performance but for better emission control. The faster the engine gases heat up, the more efficient the catalytic converter that controls the emissions.

As a result, LeVan sees a growing market for Wescast’s stainless steel product, even though cast stainless manifolds are four times more expensive than conventional cast-iron manifolds. The main competition for the high-performance market is a fabricated manifold made of tubular stainless steel, but they are more expensive and not as durable as the cast manifolds.

At 7 kg, the cast manifolds are lighter than conventional cast-iron and last for up to 1.5 million km. Spent manifolds can be sold as scrap metal to steel mills.

LeVan believes the market for Wescast’s cast stainless steel manifolds could grow to 1-2 million units annually, out to a total North American market of 23-24 million units.

The company operates three casting and three machining plants, and produces about 10 million iron manifolds per year. A joint-venture foundry is under construction in Hungary to service the European market.

— The preceding is from Nickel, a publication of the Toronto-based Nickel Development Institute.