In this study; QSTE 420TM quality steel sheet plate material, which is widely used in sectors such as defense industry, automotive industry, oil transmission lines, has fine-grained and micro-alloy structure are combined separately. Different heat inputs are applied to the filler wires of different diameters. Thus, mechanical and metallurgical changes occurring on the welded area (base material, heat affected zone and weld metal) were examined by tensile, bending, notch - impact, hardness tests and macrographic and micrographic examinations. As a result of the tests performed; It has been observed that the 1.6 mm additional wire provides the mechanical and metallurgical properties expected of the welded joint. In the tensile tests of welded joints made with 2.0 mm additional wire with 44% higher heat input, breakage from weld metal was realized. With these results, negative effects of high heat input on mechanical and metallurgical properties of materials such as QSTE420TM were also investigated.