-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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<SEC-DOCUMENT>0001229452-06-000003.txt : 20060418
<SEC-HEADER>0001229452-06-000003.hdr.sgml : 20060418
<ACCEPTANCE-DATETIME>20060418154140
ACCESSION NUMBER:		0001229452-06-000003
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20060411
FILED AS OF DATE:		20060418
DATE AS OF CHANGE:		20060418

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			STEEL DYNAMICS INC
		CENTRAL INDEX KEY:			0001022671
		STANDARD INDUSTRIAL CLASSIFICATION:	STEEL WORKS, BLAST FURNACES  ROLLING MILLS (COKE OVENS) [3312]
		IRS NUMBER:				351929476
		STATE OF INCORPORATION:			IN
		FISCAL YEAR END:			1204

	BUSINESS ADDRESS:	
		STREET 1:		6714 POINTE INVERNESS WAY
		STREET 2:		SUITE 200
		CITY:			FORT WAYNE
		STATE:			IN
		ZIP:			46804
		BUSINESS PHONE:		2604593553

	MAIL ADDRESS:	
		STREET 1:		6714 POINTE INVERNESS WAY
		STREET 2:		SUITE 200
		CITY:			FORT WAYNE
		STATE:			IN
		ZIP:			46804

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			CRAWFORD THOMAS J
		CENTRAL INDEX KEY:			0001229452

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-21719
		FILM NUMBER:		06764749

	MAIL ADDRESS:	
		STREET 1:		P O BOX 13948
		CITY:			ROANOKE
		STATE:			VA
		ZIP:			24038-3948
</SEC-HEADER>
<DOCUMENT>
<TYPE>3
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2006-04-11</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001022671</issuerCik>
        <issuerName>STEEL DYNAMICS INC</issuerName>
        <issuerTradingSymbol>STLD</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001229452</rptOwnerCik>
            <rptOwnerName>CRAWFORD THOMAS J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>P.O. BOX 13948</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>ROANOKE</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>24038-3948</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Vice President</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>16010</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Stock option - right to buy</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>11.42</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2006-04-11</value>
            </exerciseDate>
            <expirationDate>
                <value>2007-12-04</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4433</value>
                    <footnoteId id="F2"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock option - right to buy</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>14.02</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2006-04-11</value>
            </exerciseDate>
            <expirationDate>
                <value>2009-02-02</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4433</value>
                    <footnoteId id="F2"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The 16,010 shares of Steel Dynamics (SDI) common stock were received by Mr. Crawford as part of the merger consideration, in exchange for 40,025 shares of Roanoke Electric Steel Corporation (&quot;Roanoke&quot;) common stock formerly held by Mr. Crawford, regarding the merger of Roanoke with and into a wholly-owned subsidiary of SDI, effective April 11, 2006. Mr. Crawford's disposition of his Roanoke shares in accordance with the terms of the merger agreement was approved in advance of closing by the Roanoke board of directors, and Mr. Crawford's acquisition of his SDI shares in exchange therefor, was approved in advance of closing by the board of directors and Compensation Committee of SDI, all in accordance with the requirements of the exemption described by SEC Rule 16b-3(d), as interpreted by the SEC in Skadden, Arps, Slate, Meagher &amp; Flom LLP (January 12, 1999), from the short-swing profits rules of Section 16(b) of the Exchange Act.</footnote>
        <footnote id="F2">The stock option to purchase 4,433 shares of common stock of SDI at $11.42 per share, expiration December 4, 2007, and the option to purchase 4,433 shares at $14.02 per share, expiration February 2, 2009, were received by Mr. Crawford, incident to the merger of Roanoke with and into a wholly-owned subsidiary of SDI, effective April 11, 2006. Mr. Crawford's former Roanoke options, for 6,000 shares each, were assumed by and exchanged for stock options of SDI, as required by the merger agreement. Mr. Crawford's disposition of his Roanoke stock options was approved in advance by the board of directors of Roanoke, and the issuance of SDI stock options (and the underlying SDI shares) in exchange was likewise approved in advance by SDI's Board in accordance with the exemption from Section 16(b) described by SEC Rule 16b-3(d), as interpreted by the SEC in Skadden, Arps, Slate, Meagher &amp; Flom LLP (January 12, 1999).</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>T. Joe Crawford</signatureName>
        <signatureDate>2006-04-17</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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