<SHARON STEEL CORP> EXTENDS EXCHANGE OFFER Sharon Steel Corp said it extended from March six to March 31 the expiration date for its debt exchange offer to allow time to complete the sale of its Mueller Brass Co unit and to meet other conditions of the offer. The exchange offer covers Sharon's outstanding 13.5 pct subordinated sinking fund debentures due 2000 and its 14.25 pct subordinated sinking fund debentures due 1990. Sharon said that as of March six, 31.6 pct of the 13.5 pct notes and 20.9 pct of the 14.25 pct notes were tendered. The Mueller sale is conditioned on receipt of 80 pct of the notes.