As filed with the Securities and Exchange Commission on September 30, 1999
                                                      Registration No. 333-82035
================================================================================

                      SECURITIES AND EXCHANGE COMMISSION
                            WASHINGTON, D.C. 20549

                                   FORM S-8
                  POST-EFFECTIVE AMENDMENT NO. 1 ON FORM S-8
                                      TO
                                   FORM S-4
                            REGISTRATION STATEMENT
                                     UNDER
                          THE SECURITIES ACT OF 1933*


                         AK STEEL HOLDING CORPORATION
            (Exact Name of Registrant as Specified in its Charter)


          Delaware                                           31-1401455
(State or Other Jurisdiction                              (I.R.S. Employer
of Incorporation or Organization)                        Identification No.)

                               703 Curtis Street
                            Middletown, Ohio 45043
                                (513) 425-5000
              (Address, Including Zip Code, and Telephone Number,
       including Area Code, of Registrant's Principal Executive Offices)


                  1993 LONG-TERM INCENTIVE PLAN OF ARMCO INC.
              AMENDED 1993 LONG-TERM INCENTIVE PLAN OF ARMCO INC.
                       1996 INCENTIVE PLAN OF ARMCO INC.
              ARMCO INC. AND SUBSIDIARIES 1988 STOCK OPTION PLAN
                             (FULL TITLE OF PLANS)


                              JAMES L. WAINSCOTT
             VICE PRESIDENT, TREASURER AND CHIEF FINANCIAL OFFICER
                         AK STEEL HOLDING CORPORATION
                               703 CURTIS STREET
                            MIDDLETOWN, OHIO 45043
                                (513) 425-5000
                    (NAME AND ADDRESS, INCLUDING ZIP CODE,
       AND TELEPHONE NUMBER, INCLUDING AREA CODE, OF AGENT FOR SERVICE)




                          CALCULATION OF REGISTRATION FEE
============================================================================================
TITLE OF SECURITIES TO BE          AMOUNT TO BE REGISTERED       PROPOSED MAXIMUM OFFERING
 REGISTERED                                                        PRICE PER SHARE(2)
                                                           
COMMON STOCK, $.01 PAR VALUE PER        2,695,959(1)                    $17.0625
 SHARE
============================================================================================
============================================================
  PROPOSED MAXIMUM AGGREGATE   AMOUNT OF REGISTRATION FEE
       OFFERING PRICE
                            
         $11,755,295                    3,268(3)

============================================================


(1)  ALSO INCLUDES AN INDETERMINATE NUMBER OF ADDITIONAL SHARES OF THE
     REGISTRANT'S COMMON STOCK AS MAY BE ISSUED (A) PURSUANT TO SECTION 12 OF
     THE 1996 INCENTIVE PLAN OF ARMCO INC. AND SECTION 15 OF THE 1993 LONG-TERM
     INCENTIVE PLAN, OR (B) TO PREVENT DILUTION RESULTING FROM STOCK DIVIDENDS,
     STOCK SPLITS OR SIMILAR TRANSACTIONS IN ACCORDANCE WITH RULE 415 UNDER THE
     SECURITIES ACT OF 1933.

(2)  ESTIMATED SOLELY FOR THE PURPOSE OF COMPUTING THE REGISTRATION FEE PURSUANT
     TO RULE 457 (C) AND (H) UNDER THE SECURITIES ACT OF 1933 ON THE BASIS OF
     THE AVERAGE OF THE HIGH AND LOW SALES PRICE OF THE REGISTRANT'S COMMON
     STOCK ON THE NEW YORK STOCK EXCHANGE ON SEPTEMBER 28, 1999.

(3)  THE FILING FEE WITH RESPECT TO 2,007,004 OF THE 2,695,959 SHARES OF THE
     REGISTRANT'S COMMON STOCK TO BE REGISTERED HEREUNDER HAS BEEN PREVIOUSLY
     PAID IN CONNECTION WITH THE FILING OF THE REGISTRANT'S REGISTRATION
     STATEMENT ON FORM S-4 (FILE NO. 333-82035) WITH THE SECURITIES AND EXCHANGE
     COMMISSION. ACCORDINGLY, THE REGISTRATION FEE HAS BEEN CALCULATED BASED ON
     THE ADDITIONAL ESTIMATED 688,955 SHARES BEING REGISTERED.


     *FILED AS A POST-EFFECTIVE AMENDMENT ON FORM S-8 TO SUCH FORM S-4
     REGISTRATION STATEMENT (NO. 333-82035) PURSUANT TO THE PROCEDURE DESCRIBED
     HEREIN. SEE "INTRODUCTORY STATEMENT".


                             INTRODUCTORY STATEMENT

        AK Steel Holding Corporation amends its registration statement on Form
S-4 (Registration No. 333-82035) by filing this post-effective amendment no. 1
on Form S-8 relating to the sale of shares of common stock of AK Steel Holding
Corporation issuable upon the exercise of options granted under the following
Armco Inc. stock option plans:


        .  1993 Long-Term Incentive Plan of Armco Inc.
        .  Amended 1993 Long-term Incentive Plan of Armco Inc.
        .  1996 Incentive Plan of Armco Inc.
        .  Armco Inc. and Subsidiaries 1988 Stock Option Plan


        On September 30, 1999, Armco Inc., an Ohio corporation, merged with
and into AK Steel Corporation, a Delaware corporation, which is the surviving
corporation in the merger and is a wholly-owned subsidiary of AK Steel Holding
Corporation.  As a result of the merger, each outstanding share of Armco common
stock was converted into .3829 shares of AK Steel Holding Corporation common
stock.  Each option to purchase Armco common stock outstanding under Armco's
stock option plans was converted into an option to purchase the number of shares
of AK Steel Holding Corporation common stock equal to the number of shares of
Armco common stock subject to such option multiplied by the exchange ratio for
the merger, and the associated exercise price was adjusted accordingly, subject
to additional adjustments relating to the change of control provisions in
certain of the Armco stock option plans.

        The designation of the post-effective amendment as Registration No.
333-82035 denotes that the post-effective amendment relates only to the shares
of AK Steel Holding Corporation common stock issuable on the exercise of options
under the Armco stock option plans and that this is the first post-effective
amendment to the Form S-4 filed with respect to these shares.



                                       i


                                     PART I

              INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

          The documents containing the information specified in Part I of Form
S-8 and the statement of availability of information required by Item 2 of Form
S-8 and information relating to the Armco stock option plans and other
information required by Item 2 of Form S-8 have previously been, or will be,
sent or given to plan participants as specified by Rule 428(b)(1) of the
Securities Act of 1933, as amended.  Such documents are not required to be and
are not filed with the Securities and Exchange Commission either as part of this
registration statement or as prospectuses or prospectus supplements pursuant to
Rule 424.  These documents and the documents incorporated by reference in this
registration statement pursuant to Item 3 of Part II of this Form S-8, taken
together, constitute a prospectus that meets the requirements of Section 10(a)
of the Securities Act.

                                      I-1


                                    PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.  Incorporation of Documents by Reference.

          The following documents filed with the Securities and Exchange
Commission by AK Steel Holding Corporation pursuant to the Securities Exchange
Act of 1934, as amended, are incorporated by reference in this document:

        .  Annual Report on Form 10-K, as amended by Form 10-K/A, for the year
           ended December 31, 1998;

        .  Current Reports on Form 8-K dated February 3, 1999, February 16,
           1999, February 17, 1999, March 25, 1999, April 15, 1999, April 28,
           1999, May 24, 1999, June 2, 1999, July 20, 1999, August 31, 1999 and
           September 23, 1999;

        .  Quarterly Reports on Form 10-Q, as amended by Form 10-Q/A, for the
           quarter ended March 31, 1999 and June 30, 1999; and

        .  the description of AK Steel Holding Corporation common stock
           contained in AK Holding Corporation's Registration Statement on Form
           8-A filed on March 23, 1994, including any amendment or report filed
           for the purpose of updating such description.

        References within this document to:

        .  the Form 10-K for the year ended December 31, 1998, refer to that
           Form 10-K as amended by the Form 10-K/A, and

        .  the Form 10-Q for the quarter ended March 31, 1999, refer to Form 10-
           Q as amended by the Form 10-Q/A.

          All documents subsequently filed by AK Steel Holding Corporation with
the Securities and Exchange Commission pursuant to Sections 13(a), 13(c), 14 or
15(d) of the Exchange Act, prior to the filing of a post-effective amendment to
this registration statement which indicates that all securities covered by this
registration statement have been sold or which deregisters all of the shares
then remaining unsold, will be deemed to be incorporated by reference in this
registration statement and to be a part of this document from the date of filing
of those documents.  Any statement contained in a document incorporated or
deemed to be incorporated by reference in this document will be deemed to be
modified or superseded for purposes of this post-effective amendment no. 1 to
the registration statement to the extent that a statement contained in this
document or in any other subsequently filed document which also is or is deemed
to be incorporated by reference in this document modifies or supersedes such
statement.  Any

                                      II-1


such statement so modified or superseded will not be deemed, except as so
modified or superseded, to constitute a part of this post-effective amendment
no. 1.

Item 4.  Description of Securities.

          Not applicable.

Item 5.  Interests of Named Experts and Counsel.

          Not applicable.

Item 6.  Indemnification of Directors and Officers.

          AK Steel Holding Corporation is a Delaware corporation.  Subsection
(b)(7) of Section 102 of the Delaware General Corporation Law (the "DGCL")
enables a corporation in its original certificate of incorporation or an
amendment thereto to eliminate or limit the personal liability of a director to
the corporation or its stockholders for monetary damages for violations of the
director's fiduciary duty, except (i) for any breach of the director's duty of
loyalty to the corporation or its stockholders, (ii) for acts or omissions not
in good faith or which involve intentional misconduct or a knowing violation of
law, (iii) pursuant to Section 174 of the DGCL (providing for liability of
directors for unlawful payment of dividends or unlawful stock purchases or
redemptions) or (iv) for any transaction from which a director Corporation
derived an improper personal benefit.  The Certificate of Incorporation of AK
Steel Holding Corporation has eliminated the personal liability of its directors
to the fullest extent permitted by law.

          Subsection (a) of Section 145 of the DGCL empowers a corporation to
indemnify any director or officer, or former director or officer, who was or is
a party or is threatened to be made a party to any threatened, pending or
completed action, suit or proceeding, whether civil, criminal, administrative or
investigative (other than an action by or in the right of the corporation) by
reason of the fact that such person is or was a director or officer of the
corporation, or is or was serving at the request of the corporation as a
director, officer, employee or agent of another corporation, partnership, joint
venture, trust or other enterprise, against expenses (including attorneys'
fees), judgments, fines and amounts paid in settlement actually and reasonably
incurred in connection with such action, suit or proceeding provided that such
director or officer acted in good faith in a manner reasonably believed to be
in, or not opposed to, the best interests of the corporation, and, with respect
to any criminal action or proceeding, provided further that such director or
officer has no reasonable cause to believe his conduct was unlawful.

          Subsection (b) of Section 145 empowers a corporation to indemnify any
director or officer, or former director or officer, who was or is a party or is
threatened to be made a party to any threatened, pending or completed action or
suit by or in the right of the corporation to procure a judgment in its favor by
reason of the fact that such person acted in any of the capacities set forth
above, against expenses (including attorney's fees) actually and reasonably
incurred in connection with the defense or settlement of such

                                      II-2


action or suit provided that such director or officer acted in good faith and in
a manner he reasonably believed to be in, or not opposed to, the best interests
of the corporation, except that no indemnification may be made in respect of any
claim, issue or matter as to which such director or officer shall have adjudged
to be liable to the corporation unless and only to the extent that the Court of
Chancery or the court in which such action or suit was brought shall determine
upon application that, despite the adjudication of liability but in view of all
of the circumstances of the case, such director or officer is fairly and
reasonably entitled to indemnity for such expenses which the Court of Chancery
or such other court shall deem proper.

          Section 145 further provides that to the extent a director or officer
of a corporation has been successful in the defense of any action, suit or
proceeding referred to in subsections (a) or (b) or in the defense of any claim,
issue or matter therein, he shall be indemnified against expenses (including
attorneys' fees) actually and reasonably incurred by him in connection
therewith; that indemnification and advancement of expenses provided for, by, or
granted pursuant to, Section 145 shall not be deemed exclusive of any other
rights to which the indemnified party may be entitled; and empowers the
corporation to purchase and maintain insurance on behalf of any person who is or
was a director or officer of the corporation, or is or was serving at the
request of the corporation as a director, officer, employee or agent of another
corporation, partnership, joint venture, trust or other enterprise against any
liability asserted against him or incurred by him in any such capacity, or
arising out of his status as such, whether or not the corporation would have the
power to indemnify him against such liabilities under Section 145.

          Article Eighth of the Certificate of Incorporation of AK Steel Holding
Corporation states that the corporation shall indemnify any person who was or is
a party or is threatened to be made a party to, or testifies in, any threatened,
pending, or completed action, suit or proceeding, whether civil, criminal,
administrative or investigative in nature, by reason of the fact that such
person is or was a director, officer, employee or agent of the corporation, or
is or was serving at the request of the corporation as a director, officer,
employee or agent or in any similar capacity of another corporation,
partnership, joint venture, employee benefit plan, trust or other enterprise,
against expenses (including attorneys' fees), judgments, fines and amounts paid
in settlement actually and reasonably incurred by him in connection with such
action, suit or proceeding to the full extent permitted by law, and the
corporation may adopt by-laws or enter into agreements with any such person for
the purpose of providing such indemnification.

Item 7.  Exemption from Registration Claimed.

          Not applicable.

                                      II-3


Item 8.  Exhibits.


Exhibit
Number                                     Description
- ---------------     ------------------------------------------------------------

4.1                 Certificate of Incorporation of AK Steel Holding
                    Corporation, filed with the Secretary of State of the State
                    of Delaware on December 20, 1993, as amended (incorporated
                    herein by reference to Exhibit 3.1.1 to AK Steel Holding
                    Corporation's Current Report on Form 8-K, filed on May 27,
                    1998).

4.2                 By-laws of AK Steel Holding Corporation (incorporated herein
                    by reference to Exhibit 3.2 to AK Steel Holding
                    Corporation's Registration Statement on Form S-1
                    (Registration No. 33-74432)).

4.3                 Rights Agreement, dated as of January 23, 1996, between AK
                    Steel Holding Corporation and the Bank of New York as
                    predecessor to the Fifth Third Bank, as Rights Agent, with
                    respect to AK Steel Holding Corporation's Stockholder Rights
                    Plan (incorporated herein by reference to Exhibit 1 to AK
                    Steel Holding Corporation's Registration Statement on Form
                    8-A, as filed on February 5, 1996).

4.4(a)              1993 Long-Term Incentive Plan of Armco Inc. (incorporated
                    herein by reference to Exhibit 10 to Armco Inc.'s Quarterly
                    Report on Form 10-Q for the quarter ended March 31, 1993).

*4.4(b)             Amendment to the 1993 Long-Term Incentive Plan of Armco Inc.


 4.5                Amended 1993 Long-term Incentive Plan of Armco Inc.
                    (incorporated herein by reference to Exhibit 10 to Armco
                    Inc.'s Quarterly Report on Form 10-Q for the quarter ended
                    March 31, 1998).

*4.6(a)             1996 Incentive Plan of Armco Inc.

*4.6(b)             Amendment to the 1996 Incentive Plan of Armco Inc.

4.7                 1988 Stock Option Plan of Armco Inc. (incorporated herein by
                    reference to Exhibit 10(h) to Armco Inc.'s Annual Report on
                    Form 10-K for the year ended December 31, 1988).

*5.1                Opinion of John G. Hritz, Executive Vice President and
                    General Counsel of AK Steel Holding Corporation, as to the
                    legality of the securities being registered.

*23.1               Consent of Deloitte & Touche LLP, Independent Auditor.

                                      II-4


*23.2               Consent of General Counsel of AK Steel Holding Corporation
                    (filed as part of Exhibit 5.1 hereto).

**24.1              Powers of Attorney.


- ----------------
*      Filed herewith.
**     Previously filed.


Item 9.  Undertakings.

     (a)  The undersigned registrant hereby undertakes:

          (1) To file, during any period in which offers or sales are being
made, a post-effective amendment to this registration statement to include any
material information with respect to the plan of distribution not previously
disclosed in the registration statement or any material change to such
information in the registration statement; and

          (2) That, for the purpose of determining any liability under the
Securities Act, each such post-effective amendment shall be deemed to be a new
registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof; and

          (3) To remove from registration by means of a post-effective amendment
any of the securities being registered which remain unsold at the termination of
the offering.

     (b) The undersigned registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
registrant's annual report pursuant to section 13(a) or section 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to section 15(d) of the Exchange Act) that is
incorporated by reference in this registration statement shall be deemed to be a
new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

     (c) The undersigned registrant hereby undertakes that insofar as
indemnification for liabilities arising under the Securities Act may be
permitted to directors, officers and controlling persons of the registrant
pursuant to the foregoing provisions, or otherwise, the registrant has been
advised that in the opinion of the Securities and Exchange Commission such
indemnification is against public policy as expressed in the Securities Act and
is, therefore, unenforceable.  In the event that a claim for indemnification
against such liabilities (other than the payment by the registrant of expenses
incurred or paid by a director, officer or controlling person of the registrant
in the successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the registrant will, unless in the opinion of its counsel the matter
has been settled by

                                      II-5


controlling precedent, submit to a court of appropriate jurisdiction the
question whether such indemnification by it is against public policy as
expressed in the Securities Act and will be governed by the final adjudication
of such issue.

                                      II-6


                                   SIGNATURES

          Pursuant to the requirements of the Securities Act of 1933, as
amended, AK Steel Holding Corporation certifies that it has reasonable grounds
to believe that it meets all of the requirements for filing on Form S-8 and has
duly caused this post-effective amendment to the registration statement to be
signed on its behalf by the undersigned, thereunto duly authorized, in the City
of Middletown, State of Ohio, on September 30, 1999.

                                 AK STEEL HOLDING CORPORATION

                                 By:    /s/  James L. Wainscott
                                        -----------------------
                                 Name:  James L. Wainscott
                                 Title: Vice President, Treasurer and Chief
                                        Financial Officer

          Pursuant to the requirements of the Securities Act of 1933, this post-
effective amendment to the registration statement has been signed by the
following persons in the capacities and on the date indicated.



                                            

                  SIGNATURE                                              TITLE
- ---------------------------------------------  ---------------------------------------------------------

                      *                             Chairman and Chief Executive Officer (Principal
- ---------------------------------------------       Executive Officer)
             Richard M. Wardrop

                     *                              Vice President, Treasurer and Chief Financial
- ---------------------------------------------       Officer (Principal Financial Officer)
             James L. Wainscott

                     *                              Controller (Principal Accounting Officer)
- ---------------------------------------------
             Donald B. Korade

                     *                              Director
- ---------------------------------------------
                 Allen Born

                                                    Director
- ---------------------------------------------
               John A. Georges

                     *                              Director
- ---------------------------------------------
              Dr. Bonnie Hill

                     *                              Director
- ---------------------------------------------
             Robert H. Jenkins

                     *                              Director
- ---------------------------------------------
             Lawrence A. Leser

                                                    Director
- ---------------------------------------------
             Robert E. Northam

                     *                              Director
- ---------------------------------------------
                Cyrus Tang

                     *                              Director
- ---------------------------------------------
           James A. Thomson, Ph.D.



*By:    /s/  James L. Wainscott                     Date:  September 30, 1999
    -------------------------------
    James L. Wainscott
    Attorney-in-fact

                                      II-7


Exhibit
Number                                     Description
- ----------      ----------------------------------------------------------------

4.1             Certificate of Incorporation of AK Steel Holding Corporation,
                filed with the Secretary of State of the State of Delaware on
                December 20, 1993, as amended (incorporated herein by reference
                to Exhibit 3.1.1 to AK Steel Holding Corporation's Current
                Report on Form 8-K, filed on May 27, 1998).

 4.2            By-laws of AK Steel Holding Corporation (incorporated herein by
                reference to Exhibit 3.2 to AK Steel Holding Corporation's
                Registration Statement on Form S-1 (Registration No. 33-74432)).

4.3             Rights Agreement, dated as of January 23, 1996, between AK Steel
                Holding Corporation and the Bank of New York as predecessor to
                the Fifth Third Bank, as Rights Agent, with respect to AK Steel
                Holding Corporation's Stockholder Rights Plan (incorporated
                herein by reference to Exhibit 1 to AK Steel Holding
                Corporation's Registration Statement on Form 8-A, as filed on
                February 5, 1996).

4.4(a)          1993 Long-Term Incentive Plan of Armco Inc. (incorporated herein
                by reference to Exhibit 10 to Armco Inc.'s Quarterly Report on
                Form 10-Q for the quarter ended March 31, 1993).

*4.4(b)         Amendment to the 1993 Long-Term Incentive Plan of Armco Inc.

4.5             Amended 1993 Long-term Incentive Plan of Armco Inc.
                (incorporated herein by reference to Exhibit 10 to Armco Inc.'s
                Quarterly Report on Form 10-Q for the quarter ended March 31,
                1998).

*4.6(a)         1996 Incentive Plan of Armco Inc.

*4.6(b)         Amendment to the 1996 Incentive Plan of Armco Inc.

4.7             1988 Stock Option Plan of Armco Inc. (incorporated herein by
                reference to Exhibit 10(h) to Armco Inc.'s Annual Report on Form
                10-K for the year ended December 31, 1988).

*5.1            Opinion of John G. Hritz, Executive Vice President and General
                Counsel of AK Steel Holding Corporation, as to the legality of
                the securities being registered.

*23.1           Consent of Deloitte & Touche LLP, Independent Auditor.


*23.2           Consent of General Counsel of AK Steel Holding Corporation
                (filed as part of Exhibit 5.1 hereto).

**24.1          Powers of Attorney.

- -----------
*      Filed herewith.
**     Previously filed.