Deposited　metals　were　submerged　arc　welded　with　F69A4-ECM4-M4　metal-cored　wire　under　different　heat　inputs　18.67,20.57,22.56,24.63　kJ/cm,　respectively.　Their　microstructure　and　impact　toughness　were　investigated　by　optical　microscope,　scanning　electron　microscope　and　impact　testing.Results　showed　that　the　morphology　of　microstructure　and　their　percentage　of　deposited　metal　had　significant　differences　under　different　heat　inputs.　With　the　increase　of　heat　input,　the　width　of　columnar　crystal　of　deposited　metal　increased,　impact　toughness　at　-40　decreased,　and　radical　zone　ratio　of　fracture　surface　increased.　When　heat　input　was　18.67　kJ/cm,　microstructure　consisted　mainly　of　fine　acicular　ferrite,　impact　absorbed　energy　reached　the　maximum　value　139　J.　The　reason　of　decrease　of　impact　toughness　was　that　deposited　metal　stayed　longer　at　high　temperature,　thus　acicular　ferrite　grains　grew　bigger　quickly　with　the　increase　of　heat　input.　©　2018,　Editorial　Board　of　Transactions　of　the　China　Welding　Institution,　Magazine　Agency　Welding.　All　right　reserved.