The　extreme　high-speed　laser　material　deposition　(EHLA)　process　has　the　potential　to　enable　additive　manufacturing　for　mass　production　by　overcoming　the　limitations　of　slow　scanning　speed　in　conventional　laser　material　deposition　(LMD)　processes.　Thermal　features　are　the　key　factors　to　link　process　and　properties.　A　sound　understanding　of　process-thermal-property　relationships　is　essential　for　performance　control　and　process　optimization　of　a　deposited　component.　In　this　study,　we　studied　the　thermal　characteristics　within　a　single　layer　and　among　layers　for　continuous　processing　using　the　numerical　method,　and　reveal　the　mechanism　of　microstructure　and　hardness　changes　of　AISI　4140　material　formed　by　EHLA　and　LMD　processes　through　the　analysis　of　thermal　properties　and　temperature　history　results.　The　grain　size　and　hardness　evolution　for　both　processes　during　single-layer　cladding　and　continuous　forming　processes　were　investigated.　The　results　revealed　that　the　grain　refinement　effect　in　continuous　LMD　processing　is　stronger　than　that　in　EHLA　process　(from　30.0　μm　for　single　layer　to　3.2　μm　for　multi　layers　vs.　from　18.6　μm　for　single　layer　to　2.2　μm　for　multi　layers).　Similar　hardness　values　were　obtained　by　LMD　and　EHLA　processes,　with　mean　values　of　511　HV　and　472　HV,　respectively.　The　yield　and　tensile　strengths　of　EHLA　were　superior　to　the　conventional　cast　material,　but　inferior　to　those　of　the　conventional　material　quenched　and　tempered　at　lower　temperatures.　The　enhanced　tensile　results　of　EHLA　process　were　found　similar　to　those　prepared　through　conventional　method　with　quench　and　tempering　at　600　°C.　©　2024　The　Society　of　Manufacturing　Engineers