Friction-Stir-Processing Effect on Fracture Toughness of Oil Pipelines in ST 37 Group Before/After Nano ZrO2-Coating

Herein, Compact-Testing (CT ) and Charpy V-Notch (CVN) testing have been done on four Friction-Stir-Processed (FSPed) samples: BM (Base-Metal), FS (FSPed-Sample), FN5 (FSP Nano-ZrO2-coated/560 rpm rotational speed) and FN9 (FSP Nano-ZrO2-coated/900 rpm), to investigate the KIC and the dominant parameters on it for St 37 steel. Experiments are also surveyed and validated by ABAQUS. Results showed the greatest KIC value for BM (CT: 110.40 /CVN: 98.72 MPa√m) and the least for FN9 (CT: 72.20/CVN: 60.08 MPa√m). FSP caused brittle behavior but not as much as FSP Nano-coating. The calculation of CT samples was done in Gerson theory by using of LEFM formulas. Investigations showed more reliability for CVN obtained results. The KIC and ductile fracture decreased after FSP for both CVN and CT.