A New Automotive Body In Light
A recent study shows nanostructured steels can mean lighter vehicles
with less manufacturing risk than other materials
By Bruce Morey, Contributing Editor
Automakers need to deliver lighter future vehicles to get better fuel economy. While exotic materials, from magnesium to carbon-fiber reinforced plastics, are creating a lot of buzz, the case for advanced steels is strong.
A study commissioned by NanoSteel (Providence, RI) and conducted by EDAG (Auburn Hills, MI), showed the potential for the company’s Advanced High Strength Steels (AHSS) to offer a 30% (100 kg/220 lb) reduction in Body-In-White weight from a 2011 Honda Accord. EDAG’s assessment for NanoSteel leveraged a previous study conducted for NHTSA which generated a Light Weight Vehicle (LWV) design using the 2011 Honda Accord as the baseline vehicle. When compared to the NHTSA Light Weight Vehicle design, EDAG’s analysis of NanoSteel materials showed a 10.5% (27 kgs/60 lb) reduction in BIW weight. The study was released August 5 and is available from NanoSteel’s website at www.nanosteelco.com/EDAG. A video on the topic is available at http://tinyurl.com/biwvideo.
AHSS means less risk, according to Craig Parsons, President-Automotive for NanoSteel. There is a vast body of steel expertise with current body structure engineers and that expertise remains valid for AHSS. The company aims to deliver AHSS steels that may be processed using existing manufacturing methods. “Manufacturing engineers are not afraid of the impact of steel on their operations because they have been using it for 100 years” said Parsons. There is also less disruption to the existing supply chain, since NanoSteel’s business model is to provide a royalty-free license of their advanced formulations through existing steel mills at a price expected to be at a moderate premium to traditional steels.
Why call it Nano? “Nano refers to the grain structure of the material,” replied Parsons. “Most alloy steels have grain structures that are 10-6 meters while our steels are engineered with grain structures at 10-9 meters.” NanoSteel’s AHSS materials will be offered in three different categories according to strength and elongation performances:1) 950 MPa tensile strength with 35% elongation; 2) 1200 MPa tensile strength with 20% elongation; and 3) 1600 MPa tensile strength with 15% elongation. With these properties, NanoSteel’s AHSS would be classified as a Third Generation AHSS according to criteria developed by the Steel Market Development Institute. Second generation AHSS steels, such as austenitic stainless steel or twinning-induced plasticity (TWIP), were both high-strength (> 1200 MPa) and high elongation (> 50%), but were comparatively expensive. They also exhibited some unwelcome properties, such as hydrogen-embrittlement according to Parsons.
Elongation means formability, an essential element of a successful AHSS. Why? Although high strength means reducing the gauge, simply using thinner gauges usually leads to unpleasant NVH side effects. Parts must be redesigned to increase stiffness through geometry changes to adequately achieve both performance and lighter weights.
“The most likely parts to manufacture with NanoSteel AHSS are high strength, structural components such as pillars, rails, or cross-members,” said Parsons “Also, medium strength parts will also find advantages such as floor pans or dash panels.”
Parsons reports that the company is conducting full scale production trials. “The goal of what we are doing now is completing our production trials and then getting approvals [from automakers].” , Parsons believes the timing for these approvals may be as little as a few months to much longer, depending on the part and the OEM.