Mechanical properties and grain refinement by acicular ferrite in high strength high toughness weld metal

The volume fraction and morphology of acicular ferrite evolution in a high strength high toughness weld metal were studied and the mechanical properties of weld metal under heat input of 21 kJ/cm with and without fast cooling were tested.The results show the weld metal can obtain a large proportion of acicular ferrite during a wide range of cooling rate and the sizes of acicular ferrite in length and thickness decrease with cooling rate increasing.The weld metal exhibited high tensile strength（895 MPa and 870 MPa） and good low temperature toughness(average A_KV-30℃ 104 J and 79.2 J).The higher tensile strength and better low temperature toughness of the weld metal under fast cooling are due to the more refined grain of acicular ferrite.