Resistance to fracture of carbon weldable structural steel with ferrite-pearlite and widmanstaetten structure

Consideration is given to mechanical properties of St3 steel with varying ferritic-peartilic and widmanstaetten structures typical of a weld seam and adjacent zones. It has been found that mechanical properties determined at static tension are sensitive to structure variation in the limits under study. A considerable difference has been detected during impact tests CT50, asub(p)). The highest resistance to breakage is observed for the steel with a fine-grain ferritic-pearlitic structure (T50=-10 deg C, asub(p)=4.3 kgxm/cm2). The enlargement of such a structure enhances transition temperature (T50=+20 deg C) and reduces resistance to crack development (asub(p)2.4 kgxm/cm2). The appearance of widmanstaetten zones in the fine-grain structure leads also to a higher T50, up to +10 deg C, and at a completely widmanstaetten structure T50=+25 deg C. An especially unfavorable effect on the resistance of steel to breakage is produced by structure nonuniformity, i.e. accumulation of loop-like pearlitic and ferritic zones