SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d)

OF THE SECURITIES EXCHANGE ACT OF 1934

DATE OF REPORT – September 8, 2014

(Date of Earliest Event Reported)

AK STEEL HOLDING CORPORATION

(Exact name of registrant as specified in its charter)

Commission File No. 1-13696

Registrant’s telephone number, including area code: (513) 425-5000

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

AK Steel Holding Corporation (the “Company”) is filing this Current Report on Form 8-K to provide certain financial information with respect to Severstal Dearborn, LLC (“Dearborn”) and the pending acquisition of Dearborn by AK Steel Corporation (the “AK Steel”), a wholly-owned subsidiary of the Company. As previously disclosed in its Current Report on Form 8-K filed on July 22, 2014, AK Steel entered into a Membership Interest Purchase Agreement, dated as of July 18, 2014 (the “Purchase Agreement”), by and among Severstal Columbus Holdings, LLC, Dearborn and AK Steel. Pursuant to and subject to the terms and conditions of the Purchase Agreement, the Company will acquire all of Severstal’s membership interests in Dearborn (the “Dearborn Acquisition”).

Included in this filing as Exhibit 99.1 are the audited consolidated financial statements of Dearborn for the periods described in Item 9.01(a) below, the notes related thereto and the Independent Auditors’ Report, and included in this filing as Exhibit 99.2 are the unaudited consolidated financial statements of Dearborn for the periods described in Item 9.01(a) below and the notes related thereto and the Independent Auditors’ Review Report.

Also included in this filing as Exhibit 99.3 is Management’s Discussion and Analysis of Financial Condition and Results of Operations of Severstal Dearborn, LLC for the periods indicated therein and included as Exhibit 99.4 is the pro forma financial information described in Item 9.01(b) below.

The following unaudited pro forma condensed consolidated financial information of the Company, giving effect to the Dearborn Acquisition, the relating financing therefor, which includes an offering of senior notes and an offering of common stock, and the application of the proceeds from the offerings, including any remainder from such offerings, after the financing of the Dearborn Acquisition, to repay outstanding borrowings under the Company’s asset-backed revolving credit facility, is included in Exhibit 99.3 hereto:

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Dated: September 8, 2014

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