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<?xml version="1.0" encoding="windows-1252"?> |
<ownershipDocument> |
| <schemaVersion> X0306 </schemaVersion> |
| <documentType> 4/A </documentType> |
| <periodOfReport> 2020-01-10 </periodOfReport> |
| <dateOfOriginalSubmission> 2020-01-14 </dateOfOriginalSubmission> |
| <issuer> |
| | <issuerCik> 0001022671 </issuerCik> |
| | <issuerName> STEEL DYNAMICS INC </issuerName> |
| | <issuerTradingSymbol> STLD </issuerTradingSymbol> |
| | </issuer> |
| <reportingOwner> |
| | <reportingOwnerId> |
| | | <rptOwnerCik> 0001335987 </rptOwnerCik> |
| | | <rptOwnerName> Sonnenberg Steven Alan </rptOwnerName> |
| | | </reportingOwnerId> |
| | <reportingOwnerAddress> |
| | | <rptOwnerStreet1> 7575 W. JEFFERSON BLVD. </rptOwnerStreet1> |
| | | <rptOwnerStreet2></rptOwnerStreet2> |
| | | <rptOwnerCity> FORT WAYNE </rptOwnerCity> |
| | | <rptOwnerState> IN </rptOwnerState> |
| | | <rptOwnerZipCode> 46804 </rptOwnerZipCode> |
| | | <rptOwnerStateDescription></rptOwnerStateDescription> |
| | | </reportingOwnerAddress> |
| | <reportingOwnerRelationship> |
| | | <isDirector> 1 </isDirector> |
| | | <isOfficer> 0 </isOfficer> |
| | | <isTenPercentOwner> 0 </isTenPercentOwner> |
| | | <isOther> 0 </isOther> |
| | | <officerTitle></officerTitle> |
| | | <otherText></otherText> |
| | | </reportingOwnerRelationship> |
| | </reportingOwner> |
| <nonDerivativeTable> |
| | <nonDerivativeTransaction> |
| | | <securityTitle> |
| <value> Common Stock </value> |
| </securityTitle> |
| | | <transactionDate> |
| <value> 2020-01-10 </value> |
| </transactionDate> |
| | | <transactionCoding> |
| <transactionFormType> 4 </transactionFormType> |
| <transactionCode> A </transactionCode> |
| <equitySwapInvolved> 0 </equitySwapInvolved> |
| </transactionCoding> |
| | | <transactionAmounts> |
| <transactionShares> |
| <value> 38 </value> |
| <footnoteId id="F1"/> |
| <footnoteId id="F2"/> |
| </transactionShares> |
| <transactionPricePerShare> |
| <value> 33.54 </value> |
| </transactionPricePerShare> |
| <transactionAcquiredDisposedCode> |
| <value> A </value> |
| </transactionAcquiredDisposedCode> |
| </transactionAmounts> |
| | | <postTransactionAmounts> |
| <sharesOwnedFollowingTransaction> |
| <value> 7788 </value> |
| <footnoteId id="F3"/> |
| </sharesOwnedFollowingTransaction> |
| </postTransactionAmounts> |
| | | <ownershipNature> |
| <directOrIndirectOwnership> |
| <value> D </value> |
| </directOrIndirectOwnership> |
| </ownershipNature> |
| | | </nonDerivativeTransaction> |
| | </nonDerivativeTable> |
| <derivativeTable></derivativeTable> |
| <footnotes> |
| | <footnote id="F1"> Represents the number of shares of common stock underlying additional deferred stock units (DSUs) issued to the reporting person as a dividend equivalent, in connection with this person's retainer as a director under the the Company's Amended and Restated 2015 Equity Incentive Plan (the "Plan"). This transaction is exempt from both the reporting requirements of Section 16(a), including Rule 16a-11, and the provisions of Section 16(b), by virtue of this dividend reinvestment feature of the Plan and the Company's existing Dividend Reinvestment Plan, as well as being exempt from Section 16(b) independently by virtue of Rule 16b-3(d)(1) and (3). </footnote> |
| | <footnote id="F2"> Reportable as directly owned shares of common stock, rather than as a derivative security in Table II, because any and all underlying DSUs are payable, at such time as they are to be settled, solely in shares of common stock. (See Lincoln National Corp. (March 20, 1992) (Q.3). </footnote> |
| | <footnote id="F3"> Includes shares resulting from reinvestment of dividends on any underlying DSUs included in this total. </footnote> |
| | </footnotes> |
| <remarks> Line 2 in the original Form 4 filed on January 14, 2020, was an error and should not have been entered on the form. </remarks> |
| <ownerSignature> |
| | <signatureName> Theresa E. Wagler by Power of Attorney </signatureName> |
| | <signatureDate> 2020-01-14 </signatureDate> |
| | </ownerSignature> |
| </ownershipDocument> |