Mazda, Competitors Use More High-Strength Steel

(MoneyWatch)  The world's automakers are using more high-strength steel than ever before.

The redesigned Mazda3, for instance, contains twice as much high-strength steel as the model it replaces, according to Ruben Archilla, group manager, research and development for Mazda North American Operations.

As the name implies, high-strength steel is made of alloys that are stronger and more crush-resistant than ordinary steel. That makes for stronger performance for parts that are critical for passenger safety, like the beams inside the doors designed to resist side impacts.

Pound for pound, high-strength steel is more costly than regular steel, but since it's stronger, you can use less of it. The net effect is either more strength for the same weight, or less weight with no sacrifice in strength. Saving weight is an especially desirable characteristic nowadays, with the U.S. government hiking the required Corporate Average Fuel Economy.

BNET Auto Analyst Jim Henry interviewed Archilla about high-strength steel last week at a press introduction for the new Mazda3. The following are edited excerpts:

BNET: What are some of the trade-offs associated with using high-strength steel? Ruben Archilla: From a process standpoint, it's more difficult to work with. For instance, it requires more robust stamping equipment (to bend it to the desired shape). And it's more expensive.

BNET: So why use it, other than the fact that it's stronger? R.A.: The motivation for applying it is how to increase the envelope of performance without sacrificing anything -- The use of CAD (computer aided design) tools has kind of optimized the improvement you can make by changing the structural design. In other words, it's hard to improve rigidity and weight efficiency by design alone. That sort of leaves improving the material itself.

BNET: How much weight do you save in the new car by using high-strength steel? R.A.: On the one hand, there's thicker sheet metal around the suspension, for instance. That improves NVH (noise, vibration and harshness) but there are weight penalties associated with that. It's more a case of the high-strength steel making up for those penalties than it is a net weight improvement overall.

BNET: You said earlier (in a separate presentation) that the body-in-white (of the Mazda3) was 11 kilograms lighter than the car it replaced. (The body-in-white is the car's empty body, without the doors, hood, trunk lid, suspension, wheels, drivetrain or any of the interior appointments, like seats.) How much lighter is the new car overall? R.A.: The curb weight (that is, the weight of the fully assembled car, with a full tank of gas) is actually up slightly on the new car versus the old car. But the new car has more features, and that adds weight. We also added suspension reinforcement. The overhangs are slightly larger. In the rear, the fuel tank is a little bigger. And in the front, there's more of an overhang, to do with pedestrian safety regulations, mostly for European regulations.

BNET: So the car would have been a lot heavier instead of only a little heavier, without the high-strength steel. Is there a simple way to express how much more high-strength steel is in the new car, like the number of parts, or the weight? R.A.: It was about 18 percent (high-strength) on the previous car, and the new one is about 35 percent ?€" roughly twice as much. It's probably the highest percentage of any of our cars, except maybe the Mazda6, which is also new. Image: Mazda