By on October 5, 2011

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: Fuel economy, safety, and cost.

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.

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17 Comments on “It’s Tensile War! Who Has The Stronger Steel?...”

  • avatar

    Despite all the advanced materials hype, steel still has a lot of life left in it.

  • avatar

    There are two key words missing in all this – low alloy.

    You can’t have high strength without adding alloying elements; and when you do that, there goes your ductility, weldability, yield strength, and so on (I’m talking strictly non-heat treat, non-reduced steel, forming steel here)
    So basically they may have started with a HSLA (high strength low alloy) steel “formula” and made some microalloying changes then declared a “breakthrough” in high tensile strength steel. I’m not buying it, all you got at the end of the day is another alloyed steel that Mazda and Nissan are using in a very limited application. Metallurgy is a Science not sorcery.

    • 0 avatar

      Exactly. Look at how sparingly Mazda is using that 1800 Mpa steel- then see how much more Nissan is using of its 1200 Mpa. And Nissan wins out, saving over 30 pounds to Mazda’s 12 or so.

      The higher strength the steel is, the more places you want to use it…but the fewer things you can actually do to it. Catch 22. Eventually they’ll have steel you can cut diamonds with, but you won’t be able to weld it, form it, or machine it.

      Long live 1020!

      • 0 avatar

        I’m not a mechanical engineer, but I did see some interesting articles about engineering tradeoffs of different alloys when applied to bicycle frames. For alloys and composites that can’t be welded, new bonding or construction techniques will need to be applied to make it practical in the real world. The future will have some really interesting manufacturing techniques, automotive and elsewhere.

  • avatar

    I thought not watching your body weight is how you get junk in the trunk?

  • avatar

    It takes about 6900 pascals to equal 1 psi. When the French came up with the metric system, the pascal was defined as the overpressure caused by one butterfly farting.

  • avatar

    If that means slimmer pillars, I’m all for it!

    • 0 avatar

      Maybe not. I don’t know how auto body engineers deal with buckling of the pillars, but in general, you want an appropriate cross section regardless of the strength of the particular grade of steel (or any other selected material). Cross section meaning not only the area but also the moment of inertia. Moment varies with the cube of a circular section (an analogy for the pillar shape) for a given thickness and weight varies with thickness times radius, so you may be better off with a little larger radius and less cross section area. The actual trade offs are probably a lot more complicated because the damage occurs in milliseconds – in high speed loading the steel has a higher strength and the engineer needs to decide how much to exceed the standards to account for variation in material, manufacturing and etc, etc. Not surprising a new body design can cost a few Solyndra units of money.

    • 0 avatar

      I hear ya! I sat in a `73 DeVille recently and was stunned: I had forgotten how thin the A-pilars on those old tanks used to be! And the hardtop made the absence of B-pilars an utter joy.
      My dad`s `66 Chrysler 300 rolled 3 times down an embankment and he walked away (wearing no seatbelts!) so I know those old roofs were solid. I never understood the A-pilars on modern cars are the size of Rita MacNiel’s waist!

  • avatar

    I wonder how repairable this stuff is compared to lower strength steels. For bumpers, this is obvious; what about important structural bits? Can this stuff safely be repaired by the many corner body shops in this country?

  • avatar

    Interesting development. This will especially be important for small cars.

  • avatar

    Without some more technical information, this really isn’t much news. For example – when are those strengths reached (before or after pressing or processing)? Are the quoted numbers the ultimate points or the yield points, in an “engineering” or a “true” stress diagram? Usually one would quote yield points in an engineering diagram (if my mechanical engineering knowledge hasn’t completely left me ;)), but since the purpose of this sort of announcement is PR, I wouldn’t bet on it.

    Audi announced the use of steels with up to 1600MPA in the A4 back in ’08 (even more so in the Q5 and new A6), using boronic alloys and hot forming processes. The fact that the Nissan steel apparently can be used in cold pressing does seem impressive, the rest of the announcements imho is missing critical information to truly judge the “newness” and advantages of those new steels…

  • avatar

    I can think of one very good reason to keep the use of this steel to parts above the midpoint of the car. RUST.

    What I mean is that it may not be a good idea to use a thinner-section steel in places like rocker panels. This is because losing 0.5mm of steel to rust makes a much bigger difference to a 1mm section than it does to a 2mm section. So the safety of the car could be reduced much more by corrosion than with old-fashioned materials.

    I wonder how that will go for Mazda’s bumpers. They are in a fairly well protected location, I suppose. But rear bumpers can get rocks and salt spray kicked up by the rear tires.

  • avatar
    cRacK hEaD aLLeY

    Makes me wonder what was the ratio of 1965 Rambler Classic 770 to toaster-oven broilers used by Chevy on my Avalanche.

  • avatar

    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.”

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