[Signature on FollowingPage]

EXHIBIT 4.1

GUARANTEE AGREEMENT

GUARANTEE AGREEMENT dated as of August 7, 2003 made by AKS Investments, Inc., an Ohio corporation (the “Guarantor”), in favor of the holders from time to time of the Notes referred to below (collectively the “Obligees”).

WHEREAS, AK Steel Corporation, a Delaware corporation (the “Company”), and AK Steel Holding Corporation, a Delaware corporation, have entered into several Note Purchase Agreements dated as of December 17, 1996 (as amended or otherwise modified from time to time, collectively the “Note Agreements” and terms defined therein and not otherwise defined herein are being used herein as so defined) with the institutional purchasers listed in Schedule A thereto, pursuant to which the Company issued previously and sold to such purchasers $250,000,000 aggregate principal amount of its Senior Secured Notes due 2004 (the “Notes”); and

WHEREAS, it is a requirement of the Note Agreements that the Guarantor shall execute and deliver this Guarantee Agreement;

NOW, THEREFORE, in consideration of the premises the Guarantor hereby agrees as follows:

SECTION 1. Guarantee. The Guarantor unconditionally and irrevocably guarantees, as primary obligor and not merely as surety,

A. the punctual payment when due, whether at stated maturity, by acceleration or otherwise, of all obligations of the Company arising under the Notes and the Note Agreements, including all extensions, modifications, substitutions, amendments and renewals thereof, whether for principal, interest (including without limitation interest on any overdue principal, premium and interest at the rate specified in the Notes and interest accruing or becoming owing both prior to and subsequent to the commencement of any proceeding against or with respect to the Company under any chapter of the Bankruptcy Code of 1978, 11 U.S.C. §101 et seq.), any successor statute thereto or any similar state law, Make-Whole Amount, fees, expenses, indemnification or otherwise, and

B. the due and punctual performance and observance by the Company of all covenants, agreements and conditions on its part to be performed and observed under the Notes and the Note Agreements;

(all such obligations are called the “Guaranteed Obligations”); provided that the aggregate liability of the Guarantor hereunder in respect of the Guaranteed Obligations shall not exceed at any time the lesser of (1) the amount of the Guaranteed Obligations and (2) the maximum amount for which the Guarantor is liable under this Guarantee Agreement without such liability being deemed a fraudulent transfer under applicable Debtor Relief Laws (as hereinafter defined), as determined by a court of competent jurisdiction. As used herein, the term “Debtor Relief Laws” means any applicable liquidation, conservatorship, bankruptcy, moratorium, rearrangement, insolvency, reorganization or similar debtor relief laws affecting the rights of creditors generally from time to time in effect.

The Guarantor also agrees to pay, in addition to the amount stated above, any and all reasonable expenses (including reasonable counsel fees and expenses) incurred by any Obligee in enforcing any rights under this Guarantee Agreement or in connection with any amendment of this Guarantee Agreement.

Without limiting the generality of the foregoing, this Guarantee Agreement guarantees, to the extent provided herein, the payment of all amounts which constitute part of the Guaranteed Obligations and would be owed by any other Person to any Obligee but for the fact that they are unenforceable or not allowable due to the existence of a bankruptcy, reorganization or similar proceeding involving such Person.

SECTION 2. Guarantee Absolute. The obligations of the Guarantor under Section 1 of this Guarantee Agreement constitute a present and continuing guaranty of payment and not of collectability and the Guarantor guarantees that the Guaranteed Obligations will be paid strictly in accordance with the terms of the Notes and the Note Agreements, regardless of any law, regulation or order now or hereafter in effect in any jurisdiction affecting any of such terms or the rights of any Obligee with respect thereto. The obligations of the Guarantor under this Guarantee Agreement are independent of the Guaranteed Obligations, and a separate action or actions may be brought and prosecuted against the Guarantor to enforce this Guarantee Agreement, irrespective of whether any action is brought against the Company or any other Person liable for the Guaranteed Obligations or whether the Company or any other such Person is joined in any such action or actions. The liability of the Guarantor under this Guarantee Agreement shall be primary, absolute, irrevocable, and unconditional irrespective of:

A. any lack of validity or enforceability of any Guaranteed Obligation, any Note, the Note Agreements or any agreement or instrument relating thereto;

B. any change in the time, manner or place of payment of, or in any other term of, all or any of the Guaranteed Obligations, or any other amendment or waiver of or any consent to departure from any Note, the Note Agreements or this Guarantee Agreement;

C. any taking, exchange, release or non-perfection of any collateral, or any taking, release or amendment or waiver of or consent to departure by the Guarantor or other Person liable, or any other guarantee, for all or any of the Guaranteed Obligations;

D. any manner of application of collateral, or proceeds thereof, to all or any of the Guaranteed Obligations, or any manner of sale or other disposition of any collateral or any other assets of the Company or any other Subsidiary;

E. any change, restructuring or termination of the corporate structure or existence of the Company or any other Subsidiary; or

F. any other circumstance (including without limitation any statute of limitations) that might otherwise constitute a defense, offset or counterclaim available to, or a discharge of, the Company or the Guarantor.

This Guarantee Agreement shall continue to be effective or be reinstated, as the case may be, if at any time any payment of any of the Guaranteed Obligations is rescinded or must otherwise be returned by any Obligee, or any other Person upon the insolvency, bankruptcy or reorganization of the Company or otherwise, all as though such payment had not been made.

SECTION 3. Waivers. The Guarantor hereby irrevocably waives, to the extent permitted by applicable law:

A. promptness, diligence, presentment, notice of acceptance and any other notice with respect to any of the Guaranteed Obligations and this Guarantee Agreement;

B. any requirement that any Obligee or any other Person protect, secure, perfect or insure any Lien or any property subject thereto or exhaust any right or take any action against the Company or any other Person or any collateral;

C. any defense, offset or counterclaim arising by reason of any claim or defense based upon any action by any Obligee;

D. any duty on the part of any Obligee to disclose to the Guarantor any matter, fact or thing relating to the business, operation or condition of any Person and its assets now known or hereafter known by such Obligee; and

E. any rights by which it might be entitled to require suit on an accrued right of action in respect of any of the Guaranteed Obligations or require suit against the Company or the Guarantor or any other Person.

SECTION 4. Waiver of Subrogation and Contribution. The Guarantor shall not assert, enforce, or otherwise exercise (A) any right of subrogation to any of the rights, remedies, powers, privileges or liens of any Obligee or any other beneficiary against the Company or any other obligor on the Guaranteed Obligations or any collateral or other security, or (B) any right of recourse, reimbursement, contribution, indemnification, or similar right against the Company, and the Guarantor hereby waives any and all of the foregoing rights, remedies, powers, privileges and the benefit of, and any right to participate in, any collateral or other security given to any Obligee or any other beneficiary to secure payment of the Guaranteed Obligations, until such time as the Guaranteed Obligations have been paid in full.

SECTION 5. Representations and Warranties. The Guarantor hereby represents and warrants as follows:

A. The Guarantor is a corporation duly organized, validly existing and in good standing under the laws of its jurisdiction of incorporation. The execution, delivery and performance of this Guarantee Agreement have been duly authorized by all necessary action on the part of the Guarantor.

B. The execution, delivery and performance by the Guarantor of this Guarantee Agreement will not (i) contravene, result in any breach of, or constitute a default under, or result in the creation of any Lien in respect of any property of the Guarantor or any Subsidiary of the Guarantor under, any indenture, mortgage, deed of trust, loan, purchase or credit agreement, lease, corporate charter or by-laws, or any other material agreement or instrument to which the Guarantor or any Subsidiary of the Guarantor is bound or by which the Guarantor or any Subsidiary of the Guarantor or any of their respective properties may be bound or affected, (ii) conflict with or result in a breach of any of the terms, conditions or provisions of any order, judgment, decree, or ruling of any court, arbitrator or Governmental Authority applicable to the Guarantor or any Subsidiary of the Guarantor or (iii) violate any provision of any statute or other rule or regulation of any Governmental Authority applicable to the Guarantor or any Subsidiary of the Guarantor.

C. The Guarantor and the Company are members of the same consolidated group of companies and are engaged in related businesses and the Guarantor will derive substantial direct and indirect benefit from the execution and delivery of this Guarantee Agreement.

SECTION 6. Amendments, Etc. No amendment or waiver of any provision of this Guarantee Agreement and no consent to any departure by the Guarantor therefrom shall in any event be effective unless the same shall be in writing and signed by the Required Holders, and then such waiver or consent shall be effective only in the specific instance and for the specific purpose for which given; provided that no amendment, waiver or consent shall, unless in writing and signed by all Obligees, (i) limit the liability of or release the Guarantor hereunder, (ii) postpone any date fixed for, or change the amount of, any payment hereunder or (iii) change the percentage of Notes the holders of which are, or the number of Obligees, required to take any action hereunder.

SECTION 7. Addresses for Notices. All notices and other communications provided for hereunder shall be in writing and (A) by telecopy if the sender on the same day sends a confirming copy of such notice by a recognized overnight delivery service (charges prepaid), or (B) by registered or certified mail with return receipt requested (postage prepaid), or (C) by a recognized overnight delivery service (with charges prepaid). Such notice if sent to the Guarantor shall be addressed to it at the address of the Guarantor provided below its name on the signature page of this Guarantee Agreement or at such other address as the Guarantor may hereafter designate by notice to each holder of Notes, or if sent to any holder of Notes, shall be addressed to it as set forth in the Note Agreements. Any notice or other communication herein provided to be given to the holders of all outstanding Notes shall be deemed to have been duly given if sent as aforesaid to each of the registered holders of the Notes at the time outstanding at the address for such purpose of such holder as it appears on the Note register maintained by the Company in accordance

with the provisions of Section 13.1 of the Note Agreements. Notices under this Section 7 will be deemed given only when actually received.

SECTION 8. No Waiver; Remedies. No failure on the part of any Obligee to exercise, and no delay in exercising, any right hereunder shall operate as a waiver thereof; nor shall any single or partial exercise of any right hereunder preclude any other or further exercise thereof or the exercise of any other right. The remedies herein provided are cumulative and not exclusive of any remedies provided by law.

SECTION 9. Continuing Guarantee. This Guarantee Agreement is a continuing guarantee of payment and performance and shall (A) remain in full force and effect until payment in full of the Guaranteed Obligations and all other amounts payable under this Guarantee Agreement, (B) be binding upon the Guarantor, its successors and assigns and (C) inure to the benefit of and be enforceable by the Obligees and their successors, transferees and assigns.

SECTION 10. Jurisdiction and Process; Waiver of Jury Trial. The Guarantor irrevocably submits to the non-exclusive in personam jurisdiction of any New York State or federal court sitting in the Borough of Manhattan, The City of New York, over any suit, action or proceeding arising out of or relating to this Guarantee Agreement. To the fullest extent permitted by applicable law, the Guarantor irrevocably waives and agrees not to assert, by way of motion, as a defense or otherwise, any claim that it is not subject to the in personam jurisdiction of any such court, any objection that it may now or hereafter have to the laying of the venue of any such suit, action or proceeding brought in any such court and any claim that any such suit, action or proceeding brought in any such court has been brought in an inconvenient forum.

The Guarantor consents to process being served in any suit, action or proceeding of the nature referred to in this Section by mailing a copy thereof by registered or certified mail, postage prepaid, return receipt requested, to the Guarantor at its address specified in Section 7 or at such other address of which you shall then have been notified pursuant to said Section. The Guarantor agrees that such service upon receipt (i) shall be deemed in every respect effective service of process upon it in any such suit, action or proceeding and (ii) shall, to the fullest extent permitted by applicable law, be taken and held to be valid personal service upon and personal delivery to the Guarantor. Notices hereunder shall be conclusively presumed received as evidenced by a delivery receipt furnished by the United States Postal Service or any recognized courier or overnight delivery service.

Nothing in this Section 10 shall affect the right of any holder of a Note to serve process in any manner permitted by law, or limit any right that the holders of any of the Notes may have to bring proceedings against the Guarantor in the courts of any appropriate jurisdiction or to enforce in any lawful manner a judgment obtained in one jurisdiction in any other jurisdiction.

THE GUARANTOR WAIVES TRIAL BY JURY IN ANY ACTION BROUGHT ON OR WITH RESPECT TO THIS GUARANTEE AGREEMENT OR ANY OTHER DOCUMENT EXECUTED IN CONNECTION HEREWITH.

SECTION 11. Governing Law. This Guarantee Agreement shall be construed and enforced in accordance with, and the rights of the Guarantor and the Obligees shall be governed by, the laws of the State of New York excluding choice-of-law principles of the law of such State that would require the application of the laws of a jurisdiction other than such State.

[Signature on Following Page]

IN WITNESS WHEREOF, the Guarantor has caused this Guarantee Agreement to be duly executed and delivered as of the date first above written.