The 1943 Steel Cent was created as a consequence of the shortage of copper during World War II. The Mint produced cents with a composition of zinc plated steel, rather than the usual 95% copper. Collectors sometimes refer to these Steel Cents as “steelies”.
The new composition did cause some problems in circulation. Because the zinc coating did not cover the edges of the coins, they were susceptible to rust. The coins could also be picked up by a magnet, causing problems with some vending machines. The Steel Cents were only produced for one year before the Mint was able to resume the copper based composition after developing a process to salvage bullet casings to augment their copper supply.
During the single year of production, the Philadelphia Mint produced 684,628,670 Steel Cents, while the San Francisco and Denver Mints produced 217,660,000 and 191,550,000 coins.
The composition change did result in the creation of some rare error coins. The 1943 Copper Lincoln Cent was created when some planchets with the previous composition accidentally made their way into the press machines after the composition change over. Just 12 of these errors are confirmed to exist. The last example offered for sale in 2004 sold for over $200,000. Counterfeits of this rare error do exist, so professional authentication is recommended.
taken from: http://lincolncents.net/