Complex sentence: In 2004, Outokumpu bought the shares owned by Corus, so AvestaPolarit became a wholly owned subsidiary of the Outokumpu Group, delisted from the Helsinki and Stockholm stock exchanges, and only Outokumpu remained, headquartered in Espoo.
Split into simpler sentences: In 2004, Outokumpu bought the shares owned by Corus, so AvestaPolarit became a wholly owned subsidiary of the Outokumpu Group. AvestaPolarit was delisted from the Helsinki and Stockholm stock exchanges, and only Outokumpu remained, headquartered in Espoo.