Review of weakness mechanism of grain boundaries cohesion by segregati
on of impurities is given in present paper. Grain boundaries segregati
on of impurities in steels leads to the changes of bonding energy in t
his locality. Grain boundary cohesion energy reducing by impurities se
gregation leads to corresponding lowering of applied local stress requ
ired for grain boundary brittle fracture occurrence. In the paper some
cohession strength measurement methods are discussed.