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                                                                    Exhibit 8.1

[Letterhead of Sidley Austin Brown & Wood LLP]


Steel Dynamics, Inc.                                              March 7, 2003
6714 Pointe Inverness Way
Suite 200
Fort Wayne, Indiana 46804
                            Re: Steel Dynamics, Inc.
                                4% Convertible Subordinated Notes due 2012
                                ------------------------------------------
Ladies and Gentlemen:

                  We have acted as special tax counsel to Steel Dynamics, Inc.,
an Indiana corporation (the "Company"), in connection with the preparation and
filing with the Securities and Exchange Commission under the Securities Act of
1933, as amended, of the Company's Registration Statement on Form S-3 (the
"Registration Statement"), of which the preliminary Prospectus forms a part (the
"Prospectus"). The Registration Statement relates to $115,000,000 aggregate
principal amount at maturity of the Company's 4% Convertible Subordinated Notes
due December 15, 2012 (the "Notes") and shares of the Company's common stock
issuable upon conversion thereof and certain additional shares of the Company's
common stock. The Notes were issued pursuant to an Indenture, dated as of
December 23, 2002 (the "Indenture"), between the Company and Fifth Third Bank,
Indiana as trustee.

                  As special tax counsel to the Company, we have made such legal
and factual examinations and inquiries and obtained such advice, assurances, and
certificates as we have deemed necessary and advisable under the circumstances
in order to render this opinion, including, but not limited to, an examination
of originals or copies of the following:

                  (a)      the Registration Statement and Prospectus;

                  (b)      the Purchase Agreement, dated as of December 17,
                           2002, between the Company and Morgan Stanley & Co.
                           Incorporated and Goldman, Sachs & Co. (the "Initial
                           Purchasers");

                  (c)      the Indenture;

                  (d)      the form of the Notes, as attached as an exhibit to
                           the Indenture; and

                  (e)      the Registration Rights Agreement, dated as of
                           December 23, 2002, between the Company and the
                           Initial Purchasers.

The term "Documents" as used in this opinion letter refers to the documents
listed in paragraphs (b) through (e) above.

                  In our examinations, we have assumed the legal capacity of all
natural persons, the genuineness of all signatures, the authenticity of original
and certified documents, and the conformity to original or certified documents
of all copies submitted to us as conformed or reproduced copies. As to various
questions of fact relevant to the opinions expressed herein, we have relied
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upon, and assume the accuracy of, the representations and warranties contained
in the Documents and certificates and oral and written statements and other
information of or from representatives of the Company, its subsidiaries, and
others and assume compliance on the part of all parties to the Documents with
their covenants and agreements contained therein. To the extent it may be
relevant to the opinions expressed herein, we have assumed that parties to the
Documents other than the Company have the power to enter into and perform such
agreements and that such agreements have been duly authorized, executed, and
delivered by such other parties and constitute legal, valid, and binding
obligations of such other parties, enforceable against such parties in
accordance with their terms, and that such parties will comply with all other
obligations under the Documents and all laws applicable thereto.

                  On the basis of the foregoing, the Company's representation
that, as of the issue date of the Notes, the likelihood of a contingent interest
payment being made on the Notes during the term of the Notes is not remote, the
Company's representation that, as of the issue date of the Notes, the likelihood
of a contingent interest payment not being made on the Notes during the term of
the Notes is not remote, and certain estimates made by the Company and the
Initial Purchasers regarding the present value of contingent payments, and in
reliance thereon, and subject to the assumptions, qualifications, and
limitations set forth herein, we are of the opinion that:

                  The Notes will be treated as indebtedness of the Company that
are subject to the regulations governing contingent payment debt instruments
that are contained in Treasury Regulation section 1.1275-4(b); the term
"comparable yield" means the annual yield the Company would pay, as of the
initial issue date, on a noncontingent, nonconvertible, fixed-rate debt
instrument with terms and conditions otherwise comparable to those of the Notes;
and the statements in the Prospectus under the caption "Certain United States
Federal Income Tax Considerations", insofar as such statements constitute a
summary of the United States federal tax laws referred to therein, accurately
summarize in all material respects the United States federal tax laws referred
to therein.

                  We express no opinions other than those expressed herein. The
opinions expressed herein are given as of the date hereof, and we undertake no
obligation to supplement this letter if any applicable laws change after the
date hereof or if we become aware of any facts that might change the opinions
expressed herein after the date hereof or for any other reason. This opinion is
provided to you as a legal opinion only and not as a guaranty or warranty of the
matters discussed herein.

                  We hereby consent to the filing of this opinion as an exhibit
to the Registration Statement and to the reference to our name under the caption
"Legal Matters" in the Prospectus. In giving such consent, we do not thereby
admit that we are in the category of persons whose consent is required under
Section 7 of the Securities Act of 1933.

                                             Very truly yours,


                                             Sidley Austin Brown & Wood LLP

                                             /S/  Sidley Austin Brown & Wood LLP


