<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2020-07-27</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000055242</issuerCik>
        <issuerName>KENNAMETAL INC</issuerName>
        <issuerTradingSymbol>KMT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001332652</rptOwnerCik>
            <rptOwnerName>Rossi Christopher</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O KENNAMETAL INC.</rptOwnerStreet1>
            <rptOwnerStreet2>525 WILLIAM PENN PLACE, 33RD FLOOR</rptOwnerStreet2>
            <rptOwnerCity>PITTSBURGH</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>15219</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President and CEO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2020-07-27</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>28120</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>135011.094</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Represents 28,120 shares deemed to have been earned by the Compensation Committee on July 27, 2020, with respect to the third tranche of the Performance Unit Award granted to the reporting person on August 1, 2017, under the Kennametal Inc. Stock and Incentive Plan of 2016 (the &quot;2017 Performance Unit Award&quot;.) The vesting and payout of these shares remains subject to the reporting person's continued employment with the Company through August 1, 2020.</footnote>
        <footnote id="F2">Includes a total of 81,893 shares of Performance Unit shares not yet distributed.</footnote>
        <footnote id="F3">Includes 1,428.752 shares acquired through Kennametal Inc.'s dividend reinvestment plan, meeting the requirements of Rule 16a-11 of the Securities and Exchange Act of 1934, as amended, since the reporting person's last Form 4 filing.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Michelle R. Keating</signatureName>
        <signatureDate>2020-07-29</signatureDate>
    </ownerSignature>
</ownershipDocument>
