May. 1978 Osaka Steel Co., Ltd. was established in preparation for the merger of Daitetsu Steel Industrial Co., Ltd. and Yamato Steel Co., Ltd.
Oct. 1978 Osaka Steel acquired the two companies and commenced operation.
Oct. 1980 Acquired Nittetsu Koki Co., Ltd. and relocated its plant to Tsumori Works as a processing plant.
Nov. 1980 Established Osaka Bussan Trading Co., Ltd. as a subsidiary.
Feb. 1981 Established Osaka Shin Unyu Co., Ltd. as a subsidiary.
Sep. 1987 Established Nihon Steel Co., Ltd. as a subsidiary.
Mar. 1989 Acquired the management rights to Nishi-Nippon Steel Co., Ltd.
Mar. 1990 Reorganized as a subsidiary of Nippon Steel Corporation (presently Nippon Steel & Sumitomo Metal Corporation) following capital increase by allotment of new shares to third parties.
Dec. 1994 Listed on the Second Section of the Osaka Stock Exchange.
Jun. 1995 Merged with Nishi-Nippon Steel Co., Ltd., naming its plant Nishi-Nippon Works (presently Nishi-Nippon Kumamoto Works); acquired Nishikou Transport Service Co., Ltd. as a subsidiary as a result of the merger.
Nov. 1996 Listed on the Second Section of the Tokyo Stock Exchange.
Sep. 1997 Listing transferred to the First Section of the Tokyo Stock Exchange and the Osaka Stock Exchange.
Oct. 1998 Commenced the operation of a rolling mill at Sakai integrating Tsumori and Dai-ni rolling mills.
Oct. 1999 Acquired Kansai Billet Center Co., Ltd. and named its steelmaking plant Sakai Works.
Mar. 2002 Acquired ISO9001 certification for Osaka Steel's Okajima Works (presently Osaka Plant Okajima Works) and Sakai Works (presently Osaka Plant Sakai Works).
Apr. 2003 Acquired ISO9001 certification for Osaka Steel's Nishi-Nippon Works (presently Nishi-Nippon Kumamoto Works).
Nov. 2003 Acquired ISO14001 certification for Osaka Steel Co., Ltd.
Jan. 2005 Reorganized Nihon Steel Co., Ltd. as a wholly-owned subsidiary.
Dec. 2012 Jointly established PT. Krakatau Osaka Steel (KOS) with state-run PT. Krakatau Steel (Persero) Tbk. in Indonesia.
Sep. 2014 Concluded a final agreement on the joint manufacturing and sales operation of medium/small steel and iron reinforcing bars and flat bars with PT. Krakatau Tbk.
Feb. 2016 Liquidated SHIN-HOKKAI STEEL CO., LTD.
Mar. 2016

Acquired TOKYO KOHTETSU CO., Ltd as a subsidiary in the Tender Offer.
Suspended production of a steelmaking process of Osaka Okajima Works (presently Osaka Plant Okajima Works), and transferred its production to a steelmaking process of Sakai Works (presently Osaka Plant Sakai Works).

Jan. 2017 PT. KRAKATAU OSAKA STEEL started commercial production.
Apr. 2017 Set up the Osaka plant, which supervises Osaka Okajima Works and Sakai Works, and renamed Osaka Okajima Works as Osaka plant Okajima Works, and Sakai Works as Osaka plant Sakai Works.