Fatigue Crack Growth of AISI 1020 Steel Grade in Pre-Deformed Condition

In the present research, the fatigue crack growth (FCG) of AISI 1020 steel with and without pre-deformation were characterized by using MTS Landmark 100 kN under fatigue loading at ratio (R) = 0.3, Pmax = 0.7 and f = 10 Hz at room temperature. Tensile test results show that 6.25% pre-deformation given on the steel increases of yield strength. In contrast, the ultimate tensile strength, elastic modulus and elongation decrease. The FCG rate (da/dN) of AISI 1020 steel without pre-deformation determined at stage II is 6.12´10-11ΔK2.94 m/cycle and steel with 6.25% pre-deformation is 8.03´10-10ΔK2.02 m/cycle. According to microstructural observation for the pre-deformation steel, plastic deformation formed on the steel in the axial direction affects the FCG rate of the steel, leads to crack retardation for certain period of time. SEM fractographic observation on the fracture surface of the steel shows that a transgrannular crack length of 12 mm for 42,000 cycles occurs at ferrite grains. The steel failed when the crack length reached ~18.1 mm within 43,500 cycles and continuing up to 43,549 cyles, the steel experienced static failure.