<SEC-DOCUMENT>0000045876-19-000100.txt : 20190515
<SEC-HEADER>0000045876-19-000100.hdr.sgml : 20190515
<ACCEPTANCE-DATETIME>20190515134837
ACCESSION NUMBER:		0000045876-19-000100
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20190513
FILED AS OF DATE:		20190515
DATE AS OF CHANGE:		20190515

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			EVERITT DAVID C
		CENTRAL INDEX KEY:			0001196652

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-03970
		FILM NUMBER:		19826931

	MAIL ADDRESS:	
		STREET 1:		DEERE & COMPANY
		STREET 2:		ONE JOHN DEERE PLACE
		CITY:			MOLINE
		STATE:			IL
		ZIP:			61265

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			HARSCO CORP
		CENTRAL INDEX KEY:			0000045876
		STANDARD INDUSTRIAL CLASSIFICATION:	FABRICATED STRUCTURAL METAL PRODUCTS [3440]
		IRS NUMBER:				231483991
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		350 POPLAR CHURCH ROAD
		CITY:			CAMP HILL
		STATE:			PA
		ZIP:			17011
		BUSINESS PHONE:		7177637064

	MAIL ADDRESS:	
		STREET 1:		350 POPLAR CHURCH ROAD
		CITY:			CAMP HILL
		STATE:			PA
		ZIP:			17011
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_155794250262759.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2019-05-13</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000045876</issuerCik>
        <issuerName>HARSCO CORP</issuerName>
        <issuerTradingSymbol>HSC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001196652</rptOwnerCik>
            <rptOwnerName>EVERITT DAVID C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>350 POPLAR CHURCH ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CAMP HILL</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>17011</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Restricted Stock Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2019-05-13</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>4737</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F1"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4737.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>27276</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Represents restricted stock units granted under the 2016 Non-Employee Directors' Long-Term Equity Compensation Plan. Each restricted stock unit shall vest at the close of business on the earlier of (i) the first anniversary of the grant date or (ii) the annual meeting of the Issuer's stockholders in the year immediately following the year of the grant date.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ David C. Everitt</signatureName>
        <signatureDate>2019-05-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
