UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): March 21, 2016

Horsehead Holding Corp.

(Exact name of registrant as specified in its charter)

4955 Steubenville Pike, Suite 405

Pittsburgh, Pennsylvania 15205

(Address of principal executive offices, including zip code)

724-774-1020

(Registrant’s telephone number, including area code)

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:

On March 21, 2016, Horsehead Holding Corp. (the “Company”) filed a monthly operating report for the period from February 2, 2016 to February 29, 2016 (the “Monthly Operating Report”) with the United States Bankruptcy Court for the District of Delaware (the “Bankruptcy Court”). The Bankruptcy Court has had jurisdiction over the reorganization proceedings under Chapter 11 of the United States Bankruptcy Code for the Company and certain of its direct and indirect wholly-owned subsidiaries since February 2, 2016. A copy of the Monthly Operating Report is attached as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated herein by reference.

The information set forth in this Item 7.01 of this Current Report on Form 8-K is being furnished pursuant to Item 7.01 of Form 8-K and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that Section, nor shall it be deemed incorporated by reference into any of the Company’s filings under the Securities Act of 1933, as amended, or the Exchange Act, whether made before or after the date hereof and regardless of any general incorporation language in such filings, except to the extent expressly set forth by specific reference in such a filing. The filing of this Item 7.01 of this Current Report on Form 8-K shall not be deemed an admission as to the materiality of any information herein that is required to be disclosed solely by reason of Regulation FD.

SIGNATURE

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.