13th International Conference on Fracture June 16–21, 2013, Beijing, China Table 1. Main characteristics of the investigated materials and used welding technologies Steel type Grade/Mark Welding method Shielding gas Filler material micro-alloyed 37C gas metal arc 100 CO2 VIH-2 low-alloyed DP DP-25156 – – – micro-alloyed E420C gas metal arc 80 Ar + 20 CO2 Union K56 high strength TRIP TRIP-28670 – – – high strength X80TM gas metal arc 82 Ar + 18 CO2 X-90 IG high strength QStE690TM – – – high strength S960QL under development (see 5. Conclusions, too) high strength XABO 1100 – – – The measured mechanical properties (Ry, Rm, A5) and the therefrom calculated values (Ry/Rm, Rm*A5) of the investigated base materials and weld metals are summarized in Table 2. Table 2. Mechanical properties and characteristic calculated values of the investigated materials Grade/Mark Ry (1) N/mm2 Rm N/mm2 Ry/Rm – A5 % Rm * A5 N/mm2 * % 37C base material 270 405 0,666 33,5 13567 VIH-2 weld metal 410-485 535-585 0,766-0,829 22,0-24,8 ≥11770 DP-25156 base material 350-380 790-820 0,427-0,481 12,5-19,8(2) ≥9875(2) E420C base material 450 595 0,756 30,7 18266 Union K56 weld metal ≥500 560-720 0,694-0,893 ≥22,0 ≥12320 TRIP-28670 base material 430-490 730-745 0,577-0,671 24,2-28,6(2) ≥17666(2) X80TM base material 540 625 0,864 25,1 15687 QStE690TM alapanyag 780 850 0,918 18,3 15555 Böhler X90-IG weld metal ≥890 ≥940 ≈0,947 ≥16,0 ≥15040 S960QL base material 1007 1045 0,964 16,0 16112 XABO 1100 base material 1125 1339 0,840 11,0(3) 14729(3) (1) Ry means ReH or Rp0,2. (2) For these material A80 instead of A5. (3) For these material A97 instead of A5. Fig. 1 shows the ultimate tensile strength vs. elongation (fracture strain) diagram [12] and the location of the investigated base materials based on the data can be found in Table 2. 2.2. Fatigue crack growth examinations Compact tension (CT), three point bending (TPB) and single edge notched tension (SENT) specimens were tested for base materials and welded joints, while for testing of weld metal TPB type specimens were used. CT and TPB type specimens were cut from the sheets parallel and perpendicular to the rolling direction, so the directions of fatigue crack propagation were the same. For testing of weld metals cracks, which propagate parallel or perpendicular to the axis of the joint were also distinguished. Compact tension shear (CTS) specimens were used for tests under mixed mode I + II loading condition. The specimens were cut parallel to the rolling direction; the ratio of the two loading modes (I and II) was varied using a special specimen holder [13], so the cracks were propagated in different angles according to the rolling direction. Tests were carried out according to the ASTM prescription [14] by an universal electro-hydraulic MTS testing machine. Experiments were performed by ΔK-decreasing and constant load amplitude methods, at room temperature, in air, following sinusoidal loading wave form. Stress ratio was constant (R = 0,1), and the crack propagation was registered by compliance and/or optical method. -2-
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