Investigations on the impact strength of constructional high-strength Weldox steel at lowered temperature

Purpose: The paper presents the results of investigations concerning the impact strength of thick steel plates at lowered temperature obtained by industrial smelting of micro-alloyed steel of the type S1100QL (Weldox 1100) and S1300QL (Weldox 1300) with a yield strength of 1100-1300 MPa. Design/methodology/approach: The main methods used for these researches were the impact test Charpy V at lower temperatures, and metallographic observations. The tested samples at lower temperature have also been analyzed fractographically. Findings: The influence of the chemical composition and technology of production on the structure and mechanical properties of the investigated kinds of steels have been determined, as well as their ductility temperature of transition into the brittle state. Research limitations/implications: A large dispersion of intermetallic precipitated phases restricted considerably the possibility of their metallographic identification. This latter one will be done in the next stage of basic investigations. Practical implications: A wide range of practical applications of Weldox 1100 and Weldox 1300 sheet plates is warranted by both their high impact strength, especially at lower temperatures, and lower ductility transition temperature. Originality/value: It has been found that the degree of refinement of the martensitic structure and dispersion of secondary precipitations, mainly carbides and niobium nitrocarbides affect considerably the change of the impact strength within the investigated range of temperature from ambient temperature to minus 150°C.