Effect of Surface Crack Size on Residual Strength and Apparent Fracture Toughness of 15CDV6 Steel Parent Metal and Weldment

Abstract The effect of surface crack size on the strength of 15CDV6 steel parent metal and weldments has been studied in hardened and tempered conditions. Residual strength (σr) and apparent fracture toughness (KIe) in the presence of surface cracks are important inputs to the designers to prevent catastrophic failure during service. A surface crack tension (SCT) test has been carried out by introducing different crack sizes on the parent metal and weldments of 6-mm-thick 15CDV6 steel plates and compared with defect-free material. The maximum reduction in strength was found to be 5.5 % when compared with the ultimate tensile strength (UTS) of the parent metal. Similarly, for weldment, it was found to be 3.6 % for crack sizes up to 7 × 2.4 mm. It was also found that in the parent metal, with a range of a/B ratios from 0.23 to 0.44, the σr was found to vary from 1,074 MPa to 1,018 MPa. Similarly, for a/B ratios varying from 0.23 to 0.47, σr ranges from 1,031 MPa to 964 MPa for weldments. This indicates that 6-mm-thick 15CDV6 steel is not prone to brittle fracture for surface crack sizes up to 8.2 × 2.2 mm in the case of the parent metal and 7.5 × 2.1 mm for weldment. The range of KIe values obtained for parent metal varies from 50 MPa√m to 82 MPa√m and for weldments from 47 MPa√m to 78 MPa√m. The fractography of SCT test specimens reveals the presence of fine dimples, which are indicative of ductile fracture. The obtained results were compared with high-strength steels like Maraging (M250) and 0.3C-CrMoV(ESR) in the parent metal and welded conditions.