High-strength steels can be effectively utilized for strengthening existing structures or to improve highly stressed elements or structural details fabricated from lower grade steel. When used together with traditional grades of steel, the favourable mechanical properties of high-strength steels open up a wide range of applications in the steel constructions of civil and engineering structures, both in primary structural elements and in individual parts. The paper is concerned with butt and fillet welded joints of components made of high-strength steel with a yield strength of 700MPa and elements made of traditional grade S355 and S235 steel. The technique for welding materials with different strengths and the choice of additive materials for welding are presented in the experimental research.