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.