Whether they're used in steel wagons or station wagons, high-strength steels (HSS) are gaining more and more acceptance from customers. Well, OK, not many station wagons are among North American automobile lines—people prefer minivans or smaller, more environmentally friendly cars that weigh less and have les overall impact on the environment.
But other customers are responding. A Swedish manufacturer of steel wagons for the transport of iron ore, for example, has seen great success with the use of high-strength steels manufactured by Svenskt Stal AB (SSAB), Stockholm.
The new steel wagons are in service between Lulea, Sweden, and Narvik, Norway, where the highest permissible axle load is 30 tonnes, which means that every wagon could weigh a maximum of 120 tonnes when fully laden.
Sweden's LKAB, which manufactures the wagons, has raised its delivery capacity substantially in recent years, and the trend will continue in the immediate future, according to a case study on SSAB's Web site. In order to succeed, transport must take place without disturbances and at high efficiency. The designers have outfitted the wagons for rapid loading and unloading, which takes place while the train is rolling.
"We had to put to use everything possible within the framework set by the authorities for railway wagons," said Jonas Finn, LKAB's project leader for the development of the new wagon bodies. "In the design work, we also had to take into consideration that the wagons must be more efficient and simpler to maintain." The lighter wagons have led to more profitable transport, since the payload capacity of the wagons has been increased by 20 percent in terms of weight and around 25 percent in terms of volume.
General Motors Corp., Detroit, has got into the act in a more traditional way, working with steel producers through the American Iron and Steel Institute's Steel Market Development Initiative to increase the use of high-strength steels in the vehicles it manufactures.
Curt Horvath, GM's technical fellow of materials and corrosion engineering, global technology engineering, body structure and closure materials, advanced vehicles and global programs, said the automaker sees numerous advantages in the use of high-strength steels and is having good success using the products in many vehicles and applications.
"Depending on the type and strength of the steel, we can engineer vehicle components to absorb energy from crash events and significantly reduce the amount of energy transfer to the occupants and, where necessary, we can select the steel grade to resist deformation and prevent intrusion into the passenger compartment, such as in side impacts and rollover events," Horvath said. "There is a lot of engineering and materials science involved in vehicle design. We routinely use a wide range of high-strength steels, and the newer advanced high-strength and ultra high-strength steels."
It isn't uncommon to have a body structure mass with 60 to 70 percent high-strength steel content, he said. "The real key is to use the steels where they provide the most benefit, and then select the proper material for the application. Almost every major structural member uses some form of HSS. I guess it would be easier to identify non-high-strength steel parts floor and compartment pans and dash panels are generally low-carbon steel."
But Detroit has to do a better job of informing the car-buying public of the use and benefits of high-strength steels, Horvath said. "Consumers benefit from high-strength steels in the safety and improved fuel economy of the vehicles they purchase. However, for the most part, I don't think consumers recognize how much high-strength steels are used in the vehicles they purchase. In fact, I am not even sure that they really care. Today's consumers are largely driven by reported safety ratings from federal government crash tests. As a group, I don't think consumers understand how much material technology is commonplace in the vehicles they are purchasing. As long as a vehicle meets their expectations for safety and other needs, such as fuel economy, they are happy.
"I don't think that the auto industry as a whole has really educated the consumer about the advantages of high-strength steel usage," Horvath said.
Based on the performance requirements for each part, Chrysler LC uses a material application plan, which is a detailed strategy of which materials make best sense for every part in the body structure, to determine the best material for each application, David Reed, lightweight body supervisor at Chrysler, said, noting that increased costs of materials can be minimized.
"High-strength steels are typically more expensive per pound than traditional steel, so they do incur a cost penalty," he said. "In some applications, the increased strength of the steel will allow a thickness down-gauge of the material, resulting in a weight reduction. If enough weight is reduced, the cost increase is minimized. It is often not efficient to add numerous reinforcements when higher-strength materials are increasingly available."
Chrysler was the first North American automaker to use high-strength, low-alloy steel on its vehicles in 1974 and the first to use "interstitial-free rephosphate" steel in 1990, Reed said. The Chrysler Sebring today rides with more than 40 percent high-strength steel grades on board, and the current Chrysler 300 uses almost 50 percent HSS. Future models will contain even more high-strength steels.
The environmental benefits of increased use of high-strength steels are significant, he said. "Improvements in fuel economy directly correlate to reductions in CO2 emissions. A 10-percent reduction in mass can result in a 6- to 8-percent reduction in fuel consumption, with commensurate reduction in emitted pollutants." SCOTT ROBERTSON