-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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<SEC-DOCUMENT>0000276889-05-000249.txt : 20051208
<SEC-HEADER>0000276889-05-000249.hdr.sgml : 20051208
<ACCEPTANCE-DATETIME>20051208170840
ACCESSION NUMBER:		0000276889-05-000249
CONFORMED SUBMISSION TYPE:	5
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20051031
FILED AS OF DATE:		20051208
DATE AS OF CHANGE:		20051208

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			BAYLES MICHAEL R
		CENTRAL INDEX KEY:			0001232445

	FILING VALUES:
		FORM TYPE:		5
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-05725
		FILM NUMBER:		051253265

	BUSINESS ADDRESS:	
		STREET 1:		QUANEX
		STREET 2:		1900 WEST LOOP SOUTH
		CITY:			HOUSTON
		STATE:			TX
		ZIP:			77027

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			QUANEX CORP
		CENTRAL INDEX KEY:			0000276889
		STANDARD INDUSTRIAL CLASSIFICATION:	ROLLING DRAWING & EXTRUDING OF NONFERROUS METALS [3350]
		IRS NUMBER:				381872178
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1031

	BUSINESS ADDRESS:	
		STREET 1:		1900 W LOOP S STE 1500
		STREET 2:		ATTN BRENT KORB
		CITY:			HOUSTON
		STATE:			TX
		ZIP:			77027
		BUSINESS PHONE:		713-877-5328

	MAIL ADDRESS:	
		STREET 1:		1900 WEST LOOP SOUTH
		STREET 2:		SUITE 1500
		CITY:			HOUSTON
		STATE:			TX
		ZIP:			77027
</SEC-HEADER>
<DOCUMENT>
<TYPE>5
<SEQUENCE>1
<FILENAME>doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>5</documentType>

    <periodOfReport>2005-10-31</periodOfReport>

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    <form4TransactionsReported>0</form4TransactionsReported>

    <issuer>
        <issuerCik>0000276889</issuerCik>
        <issuerName>QUANEX CORP</issuerName>
        <issuerTradingSymbol>NX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001232445</rptOwnerCik>
            <rptOwnerName>BAYLES MICHAEL R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1900 WEST LOOP SOUTH</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 1500</rptOwnerStreet2>
            <rptOwnerCity>HOUSTON</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>77027</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Senior VP-Building Prod. Group</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
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                <value></value>
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                <transactionShares>
                    <value>5.111</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>53.32</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
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                <sharesOwnedFollowingTransaction>
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                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                <sharesOwnedFollowingTransaction>
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                    <value>66.22</value>
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                    <value>A</value>
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                    <value>16172.6961</value>
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                <directOrIndirectOwnership>
                    <value>D</value>
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        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
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                <footnoteId id="F14"/>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F6"/>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3.861</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>68.57</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
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            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>16176.5571</value>
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                <directOrIndirectOwnership>
                    <value>D</value>
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        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F6">Shares acquired with dividend reinvestment through the Quanex 401(k) Plan.</footnote>
        <footnote id="F2">Shares acquired through Quanex 401 (k) Plan.</footnote>
        <footnote id="F13">Due to the upgrade and transition of the Transcentive software, the Transaction Date is 9/8/05.</footnote>
        <footnote id="F9">Due to the upgrade and transition of the Transcentive software, the Transaction Date is 7/7/05.</footnote>
        <footnote id="F8">Due to the upgrade and transition of the Transcentive software, the Transaction Date is 2/7/05.</footnote>
        <footnote id="F1">Due to the upgrade and transition of the Transcentive software, the Transaction Date is 5/5/05.</footnote>
        <footnote id="F14">Due to the upgrade and transition of the Transcentive software, the Transaction Date is 12/31/04.</footnote>
        <footnote id="F11">Due to the upgrade and transition of the Transcentive software, the Transaction Date is 8/5/05.</footnote>
        <footnote id="F4">Due to the upgrade and transition of the Transcentive software, the Transaction Date is 4/6/05.</footnote>
        <footnote id="F7">Due to the upgrade and transition of the Transcentive software, the Transaction Date is 3/31/05.</footnote>
        <footnote id="F5">Due to the upgrade and transition of the Transcentive software, the Transaction Date is 6/30/05.</footnote>
        <footnote id="F12">Due to the upgrade and transition of the Transcentive software, the Transaction Date is 10/5/05.</footnote>
        <footnote id="F3">Due to the upgrade and transition of the Transcentive software, the Transaction Date is 6/3/05.</footnote>
        <footnote id="F10">Due to the upgrade and transition of the Transcentive software, the Transaction Date is 3/2/05.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Terry M. Murphy, Power of Attorney</signatureName>
        <signatureDate>2005-12-08</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----