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LONDON (Reuters) - New high-tech products mean steel is now winning battles in a long war to defend its share of the auto sector against lighter aluminium, as car makers have to shed weight to meet emissions standards.
But aluminium is set for further gains over the next decade as the United States slashes the weight of bulky pick-up trucks and SUVs, while high-strength steel grades are likely to dominate in Europe.
Conventional steel will be the big loser in both areas.
The amount of aluminium - which is more expensive but a third of the weight of conventional steel - in autos has shot up, tripling in North American and European cars over the past two to three decades.
Steel, long dominant in the industry, has been fighting back and has scored a string of successes as many top car makers opt for new grades of high strength steel over aluminium to trim the weight of new models.
"The steel industry has been on the march with this over the last seven to eight years and it's really catching on now," said Dick Schultz, managing director of consultants Ducker Worldwide in Michigan and an expert on materials used in autos.
The world's third biggest carmaker, Volkswagen (VOWG_p.DE), used thinner sheets of the material, which is up to six times as strong as conventional steel, to help reduce the weight of its latest Golf model by about 100 kg (220 lb).
Ford (F.N) opted for high strength steels, including an alloy using boron, for more than half of the Fiesta's body structure while Nissan (7201.T) plans to deploy a new ultra-strong steel this year across its line-up of models to cut at least 15 kg (33 lb) of weight from each vehicle.
The use of advanced high strength steel in North America nearly doubled between 2005 and 2009 to 150 lb (68 kg) per vehicle and is due to more than double again to 365 lbs (166 kg) by 2025, according to Ducker.
But the gains are cannibalising conventional steel's market share, which is due to shrink further in coming years.
"Our customers are rooting for steel to win this competition because of our cost structure," said Jody Shaw, director of technical marketing and Product Research at United States Steel Corp. (X.N)
"If they have to go to aluminium they will, but they would love to have a steel solution," added Shaw, also chairman of automotive group of the World Steel Association.
Cutting one lb of car weight with advanced high strength steel costs about 50 cents while using aluminium costs four times as much.
"It is a very cost-effective way of reducing weight," said Armin Plath, VW's head of materials research and manufacturing.
Graphic on changing material mix for autos:
Graphic on aluminium prices and stocks:
Graphic on world steel production:
The stakes are high for both materials, the world's top two metals in terms of output volume.
Steel is keen to defend its dominance as about one of every eight tonnes produced by the global steel industry goes into cars, totalling around 185 million tonnes a year.
Aluminium has been steadily taking away market share, but still accounts for only about 8 percent of the weight of a typical car versus nearly 60 percent for steel.
The aluminium sector, weighed down by overproduction, surpluses and weak prices, views autos as a key growth area.
At the heart of this contest are demands by governments to slash emissions, notably by cutting the weight of vehicles.
Fuel efficiency in the United States must roughly double by 2025 to 54.5 miles per gallon and in Europe CO2 emissions must tumble to 95 grams per km by 2020 from 142 gm/km.
To achieve this, car makers are targeting the car body, the main future battleground between the two metals.
Aluminium has already made inroads in autos with extensive use in engine blocks, heat exchangers, transmissions and wheels, but scant presence in the body - doors, bonnets and wings.
To counter aluminium, the steel industry has designed a prototype vehicle targeted at 2025 regulations, which it argues cuts the body mass by 35 percent with special steel products.
But the aluminium sector and many experts say there is a limit to how much steel can be strengthened and made thinner.
"If you want to take a first step in light-weighting, you can do it with advanced steels, but there are limits to that. If you want big weight savings, you need to go for a different solution, such as aluminium," said Bernard Gilmont, automotive and transport director at the European Aluminium Association.
Schultz agrees: "In North America where we have to double our fuel economy by 2025, you have to take drastic measures. If you really want to save a lot of weight, you have to use aluminium."
He added: "There's more of the new steel used in Europe today than in North America, and Europe is probably more typical of what could happen in the rest of the world."
Ducker forecasts that global aluminium use in passenger vehicles is likely to surge 65 percent to 28-30 billion lb (12.7-13.6 million tonnes) by 2020 from about 17-18 billion lb in 2009.
More extensive use of aluminium in North America is also due to the way emissions regulations have been crafted.
The United States and Canada base emissions criteria on size, which benefits aluminium and other materials such as carbon fibre, while the rest of the world uses weight, giving an advantage to high-strength steels, Schultz said.
The two sides are also tussling over how to measure emissions as governments consider assessing not only what comes out of the tailpipe, but also the greenhouse gases emitted during the production process.
The steel industry says it would benefit from life-cycle measurement, which would probably not take place until 2020, because production of energy-intensive aluminium creates about six times as much greenhouse gases as steel.
The aluminium camp says its material is comparable in life-cycle emissions if end-of-life recycling is taken into account.
Both sides accept future cars will contain both traditional and exotic materials, including magnesium and carbon fibre.
"The future is the best material at the right place, and as long as all materials continue to take their future in their hands and be innovative, there will be a place for all of them," said Gilmont at the European Aluminium Association.
Reporting by Eric Onstad; Editing by Veronica Brown and Anthony Barker