It's Tensile War! Who Has The Stronger Steel?
A day after Mazda had announced that the company “has become the first automaker to successfully develop vehicle components using 1,800 MPa ultra-high tensile steel,” Nissan announced “the world’s first Ultra High Tensile Strength Steel rated at 1.2 gigapascals (GPa).” So who’s on first?
5 minutes of in-depth research revealed that 1,800 MPa equal 1.8 GPa. In the heavy metal business, those Gs are similar to gigahertz or gigabytes in computers: The more, the merrier. Whether Mazda has outdone Nissan or v.v. is also a bit like Pentium and Athlon: It depends. What matters is that cars get both stronger and lighter
Three topics give a car engineer sleepless nights:
Ever since Newton, weight became the enemy of fuel economy. You want to make the car as light as possible. Less mass, less gas. Safety is a complicated matter. You want to build a car that crushes like a beverage can in just the right places, while protecting the passengers in a safe house built into the car. Using modern materials such as magnesium alloy or carbon fiber can make the life of an engineer easier in both cases, but it also can cause meetings with the controller or failures in the marketplace. Who says designing cars is a glamorous job?
Ultra-high tensile steel is one answer. High tensile steel starts somewhere around 400 MPa. Which compares to ultra high tensile steel something like a 400 Mhz computer to a 1.4 GHz computer.
Together with Nippon Steel, Nissan developed a 1.2 GPa ultra high tensile steel that will make its cars both lighter and stronger. Nissan is especially proud that theirs can be used in cold pressing. Before, high tensile steel above 980 MPa needed complex and expensive presses. Mazda developed its 1.8 GPa ultra high tensile steel together with Sumitomo Metal Industries.
Making steel strong helps, but opens another can of worms. As Mazda explains:
“The use of high tensile steel enables vehicle parts to be thinner yet still retain the same degree of strength. This leads to significant savings in vehicle weight … However, stronger materials are less pliant and therefore absorb less energy in a collision.”
Nissan basically says the same, but from the standpoint of a production engineer:
“Until now, high tensile strength steel involved a critical trade-off: increased strength came with increased rigidity and a consequent reduction in press formability.”
The Nissan steel trades a few megapascals for being able to use their cold presses around the world. Both Mazda and Nissan agree that proper welding becomes even more important as tensile strength of steel goes up.
Mazda is using its ultra high tensile steel very sparingly, only in the front and rear bumpers. Nissan is using its ultra high more generously, for center pillar reinforcements, front and side roof rails and other key structural components.
Nissan will save up to 15 kilograms with this technology. Mazda will save 4.8 kilograms. Don’t watch your bodyweight, or leave junk in the trunk, and you negate all that expensive research and material.
Bertel Schmitt comes back to journalism after taking a 35 year break in advertising and marketing. He ran and owned advertising agencies in Duesseldorf, Germany, and New York City. Volkswagen A.G. was Bertel's most important corporate account. Schmitt's advertising and marketing career touched many corners of the industry with a special focus on automotive products and services. Since 2004, he lives in Japan and China with his wife <a href="http://www.tomokoandbertel.com"> Tomoko </a>. Bertel Schmitt is a founding board member of the <a href="http://www.offshoresuperseries.com"> Offshore Super Series </a>, an American offshore powerboat racing organization. He is co-owner of the racing team Typhoon.
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Makes me wonder what was the ratio of 1965 Rambler Classic 770 to toaster-oven broilers used by Chevy on my Avalanche.
Time to fire the Mazda engineers. They're 180 degrees wrong. High strength steel is the same stiffness as regular steel. It just keeps on bending more than regular steel before it eventually takes a permanent set. It therefore absorbs more energy for a given shape and mass before it takes that permanent set. I've written about this before, and the message has apparently not sunk in. An engineer would be fired for saying what Mazda has said. It's just wrong. Google "high strength steel stiffness" if you don't believe me. Below I've stolen a Q and A from Car and Driver, which explains HSS in everyday terms: "Why does Car and Driver (and every other magazine) insist on saying that a car has gotten stiffer due to increased usage of high-tensile or high-strength steel? Those terms only refer to the strength of the steel, which doesn’t impact the stiffness. All carbon steel has pretty much the identical stiffness, or Young’s modulus, of 30 million psi. The only way to make a steel structure stiffer is through design geometry or increasing its thickness. The strength of the steel improves crashworthiness. Please help spread the word. Adam Silverstein Oxford, Michigan You’re right, but Kafka thinks you must be confusing C/D with some other magazine, as we’ve been spreading the word for years. Think of a steel rod clamped to a table and extending over the edge, with a weight hanging on its end. Stiffness is a measure of how far the rod will bend relative to the weight hanging on it. Of course, if you hang enough weight on the bar, it will eventually either break or bend so far that it won’t return to its original straight shape. The point where the bar bends permanently, or breaks, defines the strength of the steel. As you mentioned, the cheapest steel water pipe and the finest tool steel have basically the same stiffness (or Young’s modulus), so changing the grade of steel alone won’t change the stiffness of any part or structure. High-strength steel does improve crash performance, though, because the steel is able to absorb more energy before and during its deformation."