accurately control loading during the test. The design of the OSU-MITS ensures the implant specimen is free of bending, torsion, or shock loading. It has the capability of providing tensile loads of up to 10,000 lb (4500 kg), and the entire system is easily moved. The times to failure for a series of tests performed at various stress levels were recorded by a computer equipped with a data-acquisition system connected to the OSU-MITS. The load (stress) applied is then plotted against the time to failure. The highest stress at which no failure occurs after 24 h loading is defined as the lower critical stress (LCS), which is taken as an index to determine susceptibility to HIC. Flux cored arc welding (FCAW) was used to deposit the weld bead on the top surface of the specimen plates. The welding consumable used was the 0.047 in. (1.2 mm) Pipeliner®111M (AWS E111T1- GM) provided by The Lincoln Electric Co. Welding parameters were as follows: 25 V, current 225–235 A, travel speed 12 in./min (5.1 mm/s), and wire feed speed 300 in./min (127 mm/s). This corresponds to a heat input in the range of 28.1 to 29.4 kJ/in. (1.11 to 1.16 kJ/mm). Ar + 25%CO2 is the recommended shielding gas for this consumable; however, in order to minimize the hydrogen loss, pure argon at a flow rate of 45 ft3/h (21.2 L/min) was used instead. Welding with this consumable can produce diffusible hydrogen content in the range of 4–5 mL/100 g for typical performance as stated in the product specification. Previous tests show that cracking did not occur without intentional introduction of diffusible hydrogen. Then, in order to introduce sufficient diffusible hydrogen to cause HIC in HAZ, a thin film of lubricating oil was applied evenly on the specimen plate surface before welding, and the amount of oil was carefully controlled each time. This produced an average diffusible hydrogen content of 8.1 mL/100 g (four samples were tested with a standard deviation of 0.2 mL/100 g), which was measured using the gas chromatograph method in accordance with AWS A4.3. Metallographic samples were sectioned perpendicular to the welding direction through the axis of the implant specimens. Then they were mounted, polished, and etched with 5% nital and examined using an optical microscope. The TEM samples were evaluated in a Philips CM200 TEM operated at 200 kV. Vickers hardness measurements were conducted WELDING JOURNAL 21-s WELDING RESEARCH Fig. 1 — Schematic drawing of the implant test. Fig. 2 — The OSU Modified Implant Testing System (OSU-MITS) and implant specimen. A — Full view of the testing system; B — close-up view showing an implant specimen under loading and an unloaded one on the top right corner; C — the implant specimen. Table 1 — Chemical Composition of the Test Steels Element (wt-%) HY-100 HSLA-100 HSLA-65 C 0.18 0.051 0.074 Mn 0.28 0.90 1.35 Si 0.21 0.25 0.24 P 0.008 0.008 0.011 S 0.002 0.002 0.006 Cu 0.15 1.17 0.25 Ni 2.32 1.58 0.34 Cr 1.37 0.60 0.14 Mo 0.26 0.37 0.06 V <0.01 <0.01 0.058 Nb <0.01 0.017 0.018 Ti <0.01 <0.01 0.012 A B C
Welding Journal | January 2013
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