Manufactured by the end of the 80s in the last century steel structures were made of
steel which contain significant amounts of non-metallic inclusions. As a result of many
years of intensive use of the structures made of steel, structural discontinuity material
combine to form internal cracks called lamellar cracks.
These cracks are formed in rolled sheets with non-metallic inclusions. Studies of
lamellar cracks began in the 1960s, but there is still no satisfactory theory explaining