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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
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 iAAL7bP0jnsvYQaCQG/JqQ==

<SEC-DOCUMENT>0001229467-06-000002.txt : 20060418
<SEC-HEADER>0001229467-06-000002.hdr.sgml : 20060418
<ACCEPTANCE-DATETIME>20060418154521
ACCESSION NUMBER:		0001229467-06-000002
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:			DUKE TIMOTHY R
		CENTRAL INDEX KEY:			0001229467

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-21719
		FILM NUMBER:		06764769

	MAIL ADDRESS:	
		STREET 1:		P O BOX 2547
		CITY:			HUNTINGTON
		STATE:			WV
		ZIP:			25726-2547
</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>0001229467</rptOwnerCik>
            <rptOwnerName>DUKE TIMOTHY R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>P.O. BOX 2547</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>HUNTINGTON</rptOwnerCity>
            <rptOwnerState>WV</rptOwnerState>
            <rptOwnerZipCode>25726-2547</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>13813</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The 13,813 shares of Steel Dynamics (SDI) common stock were received by Mr. Duke as part of the merger consideration, in exchange for 34,532 shares of Roanoke Electric Steel Corporation (&quot;Roanoke&quot;) common stock formerly held by Mr. Duke, regarding the merger of Roanoke with and into a wholly-owned subsidiary of SDI, effective April 11, 2006. Mr. Duke'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. Duke'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>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Timothy R. Duke</signatureName>
        <signatureDate>2006-04-17</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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