The demands on modern automobile manufacturers are twofold: in addition to the material verification that has always been necessary, they must comply with increasing regulatory pressures to build more fuel-efficient cars. The National Highway Traffic Safety Administration, for example, has recently increased Corporate Average Fuel Economy (CAFE) standards. Car manufacturers are meeting CAFE requirements by using lighter-weight, higher-strength steel components that provide improved fuel economy. These new steel grades, called advanced high-strength steels (AHSS), make the car body structures stronger but lighter in weight. According to the American Iron and Steel Institute, AHSS not only increase safety and fuel economy, but compared to other materials, they help reduce CO2 emissions over the life cycle of the vehicle.
Advanced high-strength steels add to the already numerous grades of steel and stainless steel used to make different automotive components. Some examples of the variety of steels and their applications include the following:
- Low-carbon, or mild steel, is composed of carbon, manganese, silicon, and traces of other elements. Low-carbon steel is used to make clutch housings, bushings and suspension components such as brackets and control arms. Because it improves weldability, low carbon steel is also used in decorative applications such as automotive wheel covers, and as fasteners such as nuts, bolts, screws and washers.
- Aluminum-killed draw-quality (AKDQ) steel is deoxidized with aluminum and sometimes silicon. These alloys are processed to be exceptionally resistant to thinning and as such are used to make inner door panels and guardrails.
- High-strength low-alloy (HSLA) steels are strong but lightweight and weldable. HSLA steel is used in seating components, body-in-white and suspension assemblies, and chassis components.
- Ferritic grades of stainless steel, which derive their properties from high percentages of chromium and little or no nickel, are commonly found in automotive exhaust systems because they have better corrosion, heat, and cracking resistance.
Each grade is made from designated percentages of different elements and undergoes refining processes to have the appropriate properties for specific automotive components. Even slight variations in the recipe can render the parts defective. With the above list representing just a few of the many types of steel, it’s easy to see why PMI is so important. Portable XRF Analyzers are indispensible tools for performing PMI of incoming raw materials, work in progress, and final quality assurance of finished parts because they can determine the elemental composition of a sample within seconds. Today’s best practices include testing 100% of critical materials as part of a quality assurance/quality control (QA/QC) program.
In fact, tune in for the next article to see how Chip Ganassi Racing, makers of Nascar racing cars, take this practice to heart.
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