<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2023 Workiva-->
<!--r:56259b2d-3d1f-4ac9-96ea-4ee0aef957a5,g:5740c4c4-b37d-4831-a4df-5c1544f34a5f-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2022q4/ecd-2022q4.xsd#PvpAdjustmentsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllAdjToCompMember" xlink:href="https://xbrl.sec.gov/ecd/2022q4/ecd-2022q4.xsd#ecd_AllAdjToCompMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmt_EquityAwardsCurrentYearRestrictedStockGrantsMember_2a2bd37e-57e7-4883-812f-d6c9684dd4ab" xlink:href="cmt-20230407.xsd#cmt_EquityAwardsCurrentYearRestrictedStockGrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllAdjToCompMember" xlink:to="loc_cmt_EquityAwardsCurrentYearRestrictedStockGrantsMember_2a2bd37e-57e7-4883-812f-d6c9684dd4ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmt_EquityAwardsGrantedDuringTheYearUnvestedMember_1c657e56-8b42-4cbe-bee4-787f297d3675" xlink:href="cmt-20230407.xsd#cmt_EquityAwardsGrantedDuringTheYearUnvestedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllAdjToCompMember" xlink:to="loc_cmt_EquityAwardsGrantedDuringTheYearUnvestedMember_1c657e56-8b42-4cbe-bee4-787f297d3675" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmt_EquityAwardsChangeInMarketValueUnvestedRestrictedStockMember_b6a8adf4-1c04-4160-be9d-9a296eabb47d" xlink:href="cmt-20230407.xsd#cmt_EquityAwardsChangeInMarketValueUnvestedRestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllAdjToCompMember" xlink:to="loc_cmt_EquityAwardsChangeInMarketValueUnvestedRestrictedStockMember_b6a8adf4-1c04-4160-be9d-9a296eabb47d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmt_EquityAwardsChangeInMarketValueUnvestedSARSMember_ba4d8f75-5864-4536-936c-be5b9ae5032b" xlink:href="cmt-20230407.xsd#cmt_EquityAwardsChangeInMarketValueUnvestedSARSMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllAdjToCompMember" xlink:to="loc_cmt_EquityAwardsChangeInMarketValueUnvestedSARSMember_ba4d8f75-5864-4536-936c-be5b9ae5032b" xlink:type="arc" order="4"/>
  </link:definitionLink>
</link:linkbase>
