Traditionally, automakers have used mild carbon steel in car and truck fasteners. As conventional engines evolve to newer, hotter-running, more fuel-efficient engines, fasteners with improved high-temperature strength and creep resistance are required compared to carbon steel. Most of these high-temperature automotive fasteners use A286, a hot-selling aerospace alloy that operates at temperatures up to 700 degrees Celsius (1,300 degrees Fahrenheit).
In recent years, regulatory requirements and fuel emissions requirements for cars and trucks have become increasingly stringent. In response to these regulations, original equipment manufacturers (OEMs) have added more turbocharged engines to their vehicles. A turbocharger is an air pump driven by exhaust gases, which pressurizes the intake. This allows more air and fuel to enter the cylinders, which increases the horsepower of the engine. This technology has resulted in smaller, hotter-running, more efficient engines with power and responsiveness previously only seen in larger displacement engines. Single or twin turbine engines are sometimes paired with direct-injection engines, resulting in some of the most efficient engines available today.
Because these high-efficiency engines improve fuel economy, lower emissions, and increase horsepower, nearly all car and diesel truck manufacturers are adopting this new technology. It is expected that most engines produced in the future will feature this technology. However, these new clean-burning engines operate at higher temperatures, typically at or near 649 degrees Celsius (1200 degrees Fahrenheit), thus challenging the ability of fasteners (fittings, bolts, shafts, studs, etc.) to provide leak-free venting and proper sealing surfaces. This is important because any gas leakage from the sealing system can compromise the integrity of the connection, significantly impacting the efficiency gains that OEMs are seeking.
Carbon steel cannot operate at temperatures above 371 degrees Celsius (700 degrees Fahrenheit) without undergoing performance degradation. As a result, the use of carbon steel in these higher temperature operating environments increases the likelihood of fastener creep. When creep occurs, it can lead to a gap between the exhaust manifold and the engine block, which can lead to exhaust system failure, reduced fuel efficiency, and increased gas emissions.
As a result, many automotive and truck designers have turned to similar aerospace high-temperature steel alloys, such as alloy A286, for their exhaust fasteners. Unlike conventional carbon steel, these alloys are unaffected at temperatures up to 704 degrees Celsius (1300 degrees Fahrenheit) and do not lose their properties when they return to room temperature. As a result, they are able to maintain the integrity of the joint during the cycle of expansion and contraction.
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