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  <xs:element id="ati_DebtCovenantUndrawnAvailabilityRequirementAmount" abstract="false" name="DebtCovenantUndrawnAvailabilityRequirementAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ati_DebtCovenantUndrawnAvailabilityRequirementPercentOfTotalAvailableLiquidity" abstract="false" name="DebtCovenantUndrawnAvailabilityRequirementPercentOfTotalAvailableLiquidity" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ati_NickelMember" abstract="true" name="NickelMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ati_NaturalGasContractsMember" abstract="true" name="NaturalGasContractsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ati_PercentageOfRawMaterialUsageHedged" abstract="false" name="PercentageOfRawMaterialUsageHedged" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ati_PercentageOfForecastedNaturalGasUsageHedgedforYear1" abstract="false" name="PercentageOfForecastedNaturalGasUsageHedgedforYear1" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ati_PercentageOfForecastedNaturalGasUsageHedgedforYear2" abstract="false" name="PercentageOfForecastedNaturalGasUsageHedgedforYear2" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ati_NickelAndOtherRawMaterialContractsMember" abstract="true" name="NickelAndOtherRawMaterialContractsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ati_EffectiveIncomeTaxRateReconciliationDiscreteTaxBenefitExpenseAmount" abstract="false" name="EffectiveIncomeTaxRateReconciliationDiscreteTaxBenefitExpenseAmount" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ati_StartUpCostsAndTransactionCostsMember" abstract="true" name="StartUpCostsAndTransactionCostsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ati_TransformationCostsMember" abstract="true" name="TransformationCostsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ati_LossesOnTheSaleOfCustomerAccountsReceivableMember" abstract="true" name="LossesOnTheSaleOfCustomerAccountsReceivableMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ati_RevenueFromInternationalSales" abstract="false" name="RevenueFromInternationalSales" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalForeignCustomersAttributedToEntitiesCountryOfDomicile" abstract="false" name="EntityWideDisclosureOnGeographicAreasRevenueFromExternalForeignCustomersAttributedToEntitiesCountryOfDomicile" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ati_InternalCustomersMember" abstract="true" name="InternalCustomersMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ati_AllocatedCorporateOverhead" abstract="false" name="AllocatedCorporateOverhead" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ati_SegmentEarningsBeforeIncomeTaxesDepreciationAmortizationEBITDA" abstract="false" name="SegmentEarningsBeforeIncomeTaxesDepreciationAmortizationEBITDA" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ati_CorporateExpenses" abstract="false" name="CorporateExpenses" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ati_CashCashEquivalentsAndOther" abstract="false" name="CashCashEquivalentsAndOther" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ati_OtherCountriesMember" abstract="true" name="OtherCountriesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount" abstract="false" name="EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ati_ShareRepurchaseProgramAdditionalAuthorizedAmount" abstract="false" name="ShareRepurchaseProgramAdditionalAuthorizedAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ati_ShareRepurchaseProgramUtilizedAmount" abstract="false" name="ShareRepurchaseProgramUtilizedAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ati_AccumulatedDeferredTaxAssetValuationAllowanceAttributableToParentMember" abstract="true" name="AccumulatedDeferredTaxAssetValuationAllowanceAttributableToParentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ati_AccumulatedDeferredTaxAssetValuationAllowanceAttributableToNoncontrollingInterestMember" abstract="true" name="AccumulatedDeferredTaxAssetValuationAllowanceAttributableToNoncontrollingInterestMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ati_EnvironmentalRemediationObligationFederalSuperfundSites" abstract="false" name="EnvironmentalRemediationObligationFederalSuperfundSites" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ati_EnvironmentalRemediationObligationForFormerlyOwnedSites" abstract="false" name="EnvironmentalRemediationObligationForFormerlyOwnedSites" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ati_EnvironmentalRemediationObligationForOwnedOrControlledSitesWithClosedOperations" abstract="false" name="EnvironmentalRemediationObligationForOwnedOrControlledSitesWithClosedOperations" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ati_EmployeeRetentionCredits" abstract="false" name="EmployeeRetentionCredits" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
</xs:schema>
