Small Crack Effect on Threshold Stress Intensity KTH for High Strength Steel with Internal Hydrogen

摘要

The size effect of the threshold stress intensity KTH for hydrogen-precharged specimens of SAE52100 were investigated.Four types of tensile specimens were used: (i) smooth specimens and (ii) specimens having various shapes of artificial defects with sizes of about 35 ～ 500 μm.In the smooth specimens,fracture origins were nonmetallic inclusions with the size of 10 ～ 30 μm (e.g.Al2O3·(CaO)x,TiN and TiC).The fracture toughness determined for the small defects at fracture origin,i.e.the KTH calculated from the defect size (area) and the fracture tensile stress σf,showed a defect size dependence,where,area denotes the area of the domain defined by projecting the defect on a plane normal to the cylindrical axis of the specimen.The values of KTH for both the nonmetallic inclusions and artificial defects were much smaller than those for large cracks measured by the standard WOL and CT specimens.