Nissan: Lighter, stronger steel will cut weight, boost mpg
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YOKOHAMA, Japan -- As part of a drive to shed weight and boost fuel economy, some Nissan brand vehicles will get the ultra-high-strength, lightweight steel that debuted in the Infiniti Q50 in January at the Detroit auto show.
Nissan Motor Co. says that by 2017, it aims to use so-called advanced high-tensile-strength steel, including this ultra-high-strength kind, in a quarter of all new-vehicle body parts.
The goal is to use lighter steel that can shave vehicle curb weight -- thereby improving fuel efficiency and reducing emissions -- while delivering the same performance as ordinary steel.
In general, a 15 percent reduction in vehicle weight cuts carbon dioxide emissions 5 percent, says Shinsuke Suzuki, Nissan's general manager for body engineering.
Automakers are racing to lighten their fleets in an attempt to meet increasingly stringent emissions standards.
Nissan, for instance, cut 73 pounds from the Nissan Altima when it redesigned the mid-sized sedan for the 2013 model year. And engineers cut 176 pounds from the Nissan Leaf electric vehicle with its 2012 redesign.
"In order to comply with these regulations, we are working hard to reduce weight," Suzuki said. "This is increasingly urgent."
A key strategy for Nissan is the use of more advanced high-tensile-strength steel.
Today, the company uses such steel in 9 percent of its new body parts, by weight. Nissan aims to raise that to 25 percent in 2017. The figures are measured as a ratio of overall component weight. The target applies only to new or redesigned vehicles.
Advanced high-tensile-strength steel is generally considered steel with tensile strength of more than 780 megapascals, a measure of pressure, stress and tensile strength. Tensile strength measures the force required to pull something until it breaks.
Ultra-high-tensile steel, which has tensile strength of about 1.2 gigapascals, is strong but normally too brittle to be stamped into intricately shaped components.
Nissan has developed a new grade of ultra-high-tensile steel and a new manufacturing process that allows its use in complicated parts. That allows Nissan to use ultra-high-tensile steel for parts that had been off limits, such as roof pillars. The result is weight loss without strength loss.
The Infiniti Q50, the successor to the G series sedan, was the first vehicle from the automaker to get the new steel, which reduced the car's weight by 24 pounds.
The steel will first be used through the luxury Infiniti lineup but migrate to the volume Nissan brand before 2017, said Masahito Katsukura, manager of materials engineering.
Nissan declined to identify future nameplates to use the steel. But engineers said they are even looking at small cars.
"We are pushing the limits of steel," Suzuki said.
The newly developed steel, with a tensile strength of 1.2 gigapascals, uses special additives to improve its ductility.
Nissan developed the steel with Nippon Steel & Sumitomo Metal Corp. and Kobe Steel Ltd., which hold the metal patents. Nissan holds patents on the process of molding and joining the steel.
Nissan says using the new steel costs less than high-tensile alternatives because it is much thinner. That allows the company to use less of it.
Nissan can use its stamping technology to mold the extremely hard steel but it has had to adjust the timing of its welding process when joining the steel to other parts.
Nissan sees weight loss as a key weapon in its fight to boost fuel economy.
Under CEO Carlos Ghosn's Green Program 2016 environmental plan, Nissan aims to lift fleetwide fuel economy 35 percent by the fiscal year ending March 31, 2017, compared with 2005 levels.
You can reach Hans Greimel at hgreimel@crain.com. -- Follow Hans on 
