Document:

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                                                                EXHIBIT 10.1a(1)

                     FIRST AMENDMENT TO CREDIT AGREEMENT

      THIS FIRST AMENDMENT TO CREDIT AGREEMENT (this "Amendment"), dated as
of May 4, 1998, by and among STEEL DYNAMICS, INC., an Indiana corporation
(the "Borrower"), the lenders listed on the signature pages hereof and
MELLON BANK, N.A., a national banking association, as agent for the Lenders
under the Credit Agreement (Amended and Restated) referred to below (the
"Agent").

                                  RECITALS:

      WHEREAS the Borrower, certain lenders, the Agent, Mellon Bank, N.A.,
as Issuing Bank, and certain Co-Agents entered into a Credit Agreement
(Amended and Restated), dated as of June 30, 1994 and amended and restated
as of June 30, 1997 (as so amended and restated, the "Original Agreement"),
pursuant to which the Lenders have extended credit to the Borrower;

      WHEREAS, the Borrower and the Lenders (as defined in the Original
Agreement) desire to amend the Original Agreement to make certain changes
therein;

      WHEREAS, capitalized terms not otherwise defined herein shall have
the meanings assigned thereto in the Original Agreement.

      NOW, THEREFORE, the parties hereto, in consideration of their mutual
covenants and agreements hereinafter set forth and intending to be legally
bound hereby agree as follows:

      Section 1.  Amendments.  (a)  Section 6.03 of the Original Agreement
is hereby amended by deleting the word "and" appearing at the end of
paragraph (g) thereof, by replacing the period at the end of paragraph (h)
thereof with "; and", and by adding at the end thereof, as a new paragraph
(i), the following:

                  (i)  Indebtedness of IDI (x) pursuant to, or otherwise
            permitted under Section 6.03 of, the Credit Agreement, dated as
            of December 31, 1997, among IDI, the Lenders party thereto and
            Mellon Bank, N. A., as agent, as the same may be amended or
            modified from time to time, (y) pursuant to lending
            arrangements with General Electric Capital Corporation or
            another lender arranged by American Electric Power Company in

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            a principal amount not exceeding $6,500,000 and (z) to the Borrower
            in a principal amount not exceeding $75,000,000.

      (b)  Section 6.05(g) of the Original Agreement is hereby amended to
read in its entirety as follows:

                  (g)  An equity investment in IDI in an aggregate amount
            of $30,000,000, to be made prior to the funding of indebtedness
            of IDI pursuant to its Credit Agreement referred to in Section
            6.03(i) and additional investments in IDI, not to exceed
            $75,000,0000 in the aggregate, which may be either equity
            investments or loans (which loans may be subordinated to other
            Indebtedness of IDI) and which shall include any extraordinary
            legal costs paid by SDI for the benefit of IDI under the
            Administration Agreement between SDI and IDI.

      (c)  Section 6.10 of the Original Agreement is here amended by
deleting the word "and" at the end of paragraph (b) thereof, by replacing
the period at the end of paragraph (c) thereof with "; and" and by adding
at the end thereof a new paragraph (d) to read as follows:

                  (d)  The Borrower may transfer to IDI a tract of real
            property, constituting a portion not exceeding approximately
            seventy-five acres of the Borrower's premises in Butler,
            Indiana, together with easements, rights of way and other
            property rights over the remainder of such premises, which the
            Borrower deems appropriate for the construction and operation
            of IDI's iron making facilities.

      (d)  Section 6.12(c) of the Original Agreement is hereby amended to
read in its entirety as follows:

                  (c)  The Borrower may enter into with IDI, and perform,
            the Tax Sharing Agreement dated as of December 31, 1996, the
            Administration Agreement dated on or about May 4, 1998 and the
            Offtake Agreement dated on or about May 4, 1998 and, so long as
            IDI is a wholly-owned Subsidiary of the Borrower, the Borrower
            may enter into such other transactions (not prohibited by other
            provisions of this Agreement) with, or for the benefit of, IDI
            as the Borrower deems necessary or desirable for the interests
            of the Borrower; and

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      (e)  Section 6.15 of the Original Agreement is hereby amended by
replacing the period at the end of paragraph (b) thereof with "; and" and
by adding at the end thereof a new paragraph (c) to read as follows:

                  (c)  Restrictions applicable to IDI pursuant to IDI's
            Credit Agreement referred to in Section 6.03(i) hereof or
            pursuant to documentation governing the Indebtedness of IDI
            referred to in clause (y) or Section 6.03(i) hereof.

      Section 2.  Consents and Directions to Agent.  By execution of this
First Amendment, the Lenders hereby (i) consent to the release from the
Mortgage of the real property and interests therein to be transferred by
the Borrower to IDI as contemplated by the amendment made by Section 1(c)
of this First Amendment (it being understood that easements and other
rights in real property being retained by the Borrower will remain subject
to the Mortgage); (ii) consent to the release of the IDI Guaranty and the
IDI Security Agreement; and (iii) authorize and direct the Agent to execute
and deliver the releases referred to in the foregoing clauses (i) and
(ii).

      Section 3.  Miscellaneous.  (a) This First Amendment shall become
effective upon execution and delivery hereof by all of the Lenders, the
Borrower and the Agent.

      (b) The Original Agreement, as amended by this Amendment, is in all
respects ratified, approved and confirmed and shall, as so amended, remain
in full force and effect.  From and after the date hereof, all references
to the "Agreement" in the Original Agreement and in the other Loan
Documents shall be deemed to be references to the Original Agreement as
amended by this Amendment.

      (c)  This Amendment shall be deemed to be a contract under the laws
of the State of New York and for all purposes shall be governed by and
construed and enforced in accordance with the laws of said State.

      (d)  This Amendment may be executed in any number of counterparts and
by the different parties hereto on separate counterparts, each of which,
when so executed, shall be deemed an original, but all such counterparts
shall constitute but one and the same instrument.

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      IN WITNESS WHEREOF, the parties hereto, by their officers thereunto
duly authorized, have executed and delivered this Amendment as of the date
first above written.

                                       STEEL DYNAMICS, INC.

                                       By /s/ Tracy L. Shellabarger
                                          ----------------------------
                                       Title:

                                       MELLON BANK, N.A., as Lender
                                         and as Agent

                                       By /s/
                                          ----------------------------
                                       Title:

                                       KREDITANSTALT FUR WIEDERAUFBAU

                                       By /s/
                                          ----------------------------
                                       Title:

                                       BANQUE NATIONALE DE PARIS

                                       By /s/
                                          ----------------------------
                                       Title:

                                       COMERICA BANK

                                       By /s/
                                          ----------------------------
                                       Title:

                                      -4-
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                                       NBD BANK, N.A.

                                       By /s/
                                          ----------------------------
                                       Title:

                                       THE INDUSTRIAL BANK OF JAPAN,
                                         LIMITED

                                       By /s/
                                          ----------------------------
                                       Title:

                                       BANK AUSTRIA AKTIENGESELLSCHAFT

                                       By /s/
                                          ----------------------------
                                       Title:

                                       By /s/
                                          ----------------------------
                                       Title:

                                       THE CHASE MANHATTAN BANK

                                       By /s/
                                          ----------------------------
                                       Title:

                                       HARRIS TRUST AND SAVINGS BANK

                                       By /s/
                                          ----------------------------
                                       Title:

                                      -5-
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                                       NATIONAL CITY BANK, INDIANA

                                       By /s/
                                          ----------------------------
                                       Title:

                                       WESTDEUTSCHE LANDESBANK
                                         GIROZENTRALE, NEW YORK BRANCH

                                       By /s/
                                          ----------------------------
                                       Title:

                                       By /s/
                                          ----------------------------
                                       Title:

                                       SUNTRUST BANK, CENTRAL FLORIDA, N.A.

                                       By /s/
                                          ----------------------------
                                       Title:

                                       NORTHERN TRUST COMPANY

                                       By /s/
                                          ----------------------------
                                       Title:

                                       FORT WAYNE NATIONAL BANK

                                       By /s/
                                          ----------------------------
                                       Title:

                                      -6-
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                                       ENRON CAPITAL & TRADE RESOURCES
                                         CORP.

                                       By /s/
                                          ----------------------------
                                       Title:

                                       FIRST UNION NATIONAL BANK

                                       By /s/
                                          ----------------------------
                                       Title:

                                       THE HUNTINGTON NATIONAL BANK

                                       By /s/
                                          ----------------------------
                                       Title:

                                      -7-<PAGE>   1
                                                                EXHIBIT 10.1b(4)

                    FOURTH AMENDMENT TO CREDIT AGREEMENT

            THIS FOURTH AMENDMENT TO CREDIT AGREEMENT (this "Agreement"),
dated as of December 21, 1999, by and among IRON DYNAMICS, INC., an Indiana
corporation (the "Borrower"), the lenders listed on the signature pages
hereof and MELLON BANK, N.A., a national banking association, as agent for
the Lenders under the Credit Agreement referred to below (the "Agent").

                                  RECITALS:

            WHEREAS the Borrower, certain lenders, the Agent and Mellon
Bank, N.A., as Issuing Bank, entered into a Credit Agreement, dated as of
December 31, 1997, as amended by the Amendment and Waiver, dated as of June
10, 1998 and by the Second Amendment to Credit Agreement, dated as of March
15, 1999, and the Third Amendment and Waiver to Credit Agreement, dated as
of June 30, 1999 (as so amended, the "Credit Agreement"), pursuant to which
the Lenders have extended credit to the Borrower;

            WHEREAS, the Borrower has requested the Lenders to effect
certain amendments and waivers to the Credit Agreement and the Required
Lenders are willing to do so to the extent provided herein;

            WHEREAS, capitalized terms not otherwise defined herein shall
have the meanings assigned thereto in the Credit Agreement.

            NOW, THEREFORE, the parties hereto, in consideration of their
mutual covenants and agreements hereinafter set forth and intending to be
legally bound hereby agree as follows:

            Section 1.  Amendment to Section 6.03(h) of the Credit
Agreement.  Section 6.03(h) of the Credit Agreement is hereby amended by
changing the words "Unsecured Indebtedness of the Borrower to SDI in an
aggregate principal amount not exceeding $25,000,000 at any time
outstanding" to read "Unsecured Indebtedness of the Borrower to SDI in an
aggregate principal amount not exceeding $55,000,000 at any time
outstanding".

            Section 2.  Directions to Agent.  The Required Lenders hereby
direct the Agent to execute and deliver this Agreement.

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            Section 3.  Miscellaneous.  (a) This Agreement shall become
effective, as of its date, upon (i) the execution and delivery hereof by
the Required Lenders, the Borrower and the Agent and (ii) the delivery to
the Agent of a fully executed copy of an SDI Subordination Agreement in the
form of Exhibit GG to the Credit Agreement (or an amendment to the existing
SDI Subordination Agreement in such form) covering the full amount of the
$55 million referred to in Section 1 above, to which there has been
attached a copy of a Subordinated Promissory Note in the principal amount
of $55 million delivered by IDI to SDI in the form of Exhibit FF attached
to the Third Amendment to the Credit Agreement.

            (b) The Credit Agreement, as amended or modified by this
Agreement, is in all respects ratified, approved and confirmed and shall,
as so amended and modified, remain in full force and effect.  From and
after the date hereof, all references to the "Agreement" in the Credit
Agreement and in the other Loan Documents shall be deemed to be references
to the Credit Agreement as amended and modified by this Agreement.

            (c)  This Agreement shall be deemed to be a contract under the
laws of the State of New York and for all purposes shall be governed by and
construed and enforced in accordance with the laws of said State.

            (d)  This Agreement may be executed in any number of
counterparts and by the different parties hereto on separate counterparts,
each of which, when so executed, shall be deemed an original, but all such
counterparts shall constitute but one and the same instrument.

            IN WITNESS WHEREOF, the parties hereto, by their

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officers thereunto duly authorized, have executed and delivered
this Agreement as of the date first above written.

                                       IRON DYNAMICS, INC.

                                       By /s/ Tracy L. Shellabarger
                                          ----------------------------
                                       Title:

                                       MELLON BANK, N.A., as Lender,
                                         as Issuing Bank and as Agent

                                       By /s/
                                          ----------------------------
                                       Title:

                                       KREDITANSTALT FUR WIEDERAUFBAU

                                       By /s/
                                          ----------------------------
                                       Title:

                                       By /s/
                                          ----------------------------
                                       Title:

                                       COMERICA BANK

                                       By /s/
                                          ----------------------------
                                       Title:

                                       NATIONAL CITY BANK, INDIANA

                                       By /s/
                                          ----------------------------
                                       Title:

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                                       NATIONAL CITY BANK, INDIANA, f/n/a
                                       FORT WAYNE NATIONAL BANK

                                       By /s/
                                          ----------------------------
                                       Title:

                                       LASALLE BANK NATIONAL
                                           ASSOCIATION

                                       By /s/
                                          ----------------------------
                                       Title:

                                      -4-

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                         [BARRETT & MCNAGNY LETTERHEAD]

March 29, 2000

VIA EDGAR

Securities & Exchange Commission
450 Fifth Street, NW
Washington, D.C.  20549

RE:         Steel Dynamics, Inc.
            Annual Report on Form 10-K
            (Securities Exchange Act of 1934 - Commission file #0-21719)

Gentlemen/Ladies:

Transmitting herewith via EDGAR is the Form 10-K Annual Report of Steel
Dynamics, Inc. If there are any questions please contact the undersigned at
219-423-8905.

Sincerely,

Barrett & McNagny

/S/ ROBERT S. WALTERS

Robert S. Walters

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