ture toughness, as well as high strength. The microconstituents and inclusions are examined using a combination of optical and SEM microscopy, and the fracture properties are studied using instrumented impact testing followed by fractography. Experimental The weld metal chemistry is summarized in Table 1, and has a calculated CEIIW carbon equivalent of 0.62, and Pcm value of 0.21 (Ref. 26). The welds were completed using a flux cored arc welding (FCAW) consumable that conforms to AWS specification A5.29, with CO2 shielding gas, using a current of 200 A, voltage of 24 V in direct current electrode negative (DCEN) polarity, and 0.0625-in. (1.6 mm) wire with a feeding rate of 200 in./min (84 mm/s). The details of the consumable design and flux chemistry have been reported elsewhere; however, C it should be noted that the flux contains MgO, which provides an opportunity to introduce Mg content into the weld metal (Ref. 27). Welding was conducted in the flat (1G) position on a 0.75-in.-thick ASTM A514 steel plate with a 45-deg bevel angle, a 0.5-in. root opening and a backing plate, similar to other studies (Ref. 28). The travel speed was approximately 8 in./min during each welding pass, and the heat input was an average of 1.8 kJ/mm. During welding, the preheat or interpass temperature was 350°F (177°C), and no postweld heat treatment was applied. Charpy impact testing was conducted between –73° to 20°C on material extracted from the middle of the weld region. Additional welds were produced on a 75-mm-thick plate using the same conditions as above in order to facilitate extraction of 10 × 10 mm Charpy coupons along the transverse direction of the weld. These were obtained from approximately 2 mm below the surface of the root, as well as 2 mm below the surface of the crown of the weld, in order to obtain mainly reheated or as-deposited weld metal, respectively, from these two regions. These top and bottom portions of the weld were also tested by instrumented impact testing in which the force and displacement were recorded during impact. Instrumented impact testing was used in order to provide a comparison of the relative fracture initiation energy values in these top and bottom regions of the weld. The microstructures were analyzed using a combination of optical and SEM microscopy after etching with 2% nital. Microhardness indentation was used to determine the hardness of the reheated and as-deposited material. In order to determine the chemistry of fine inclusions, Auger electron spectroscopy (AES) was used to map elemental distributions. Further analysis of the inclusions was also conducted by JANUARY 2014, VOL. 93 16-s WELDING RESEARCH Fig. 1 — A — Macroscopic section of the joint; B — optical micrograph of the as-deposited weld metal; C — optical micrograph of the reheated weld metal. A Table 1 — Weld Metal Chemistry (wt-%, balance Fe) C Mn P S Si Cu Cr V Ni Mo Al Ti 0.059 1.219 0.006 0.003 0.123 0.044 0.264 0.005 3.511 0.212 0.557 0.002 Nb Co B W Sn Pb Zr Ce As O N Mg 0.003 0.005 0.0005 0.005 0.005 0.001 0.028 0.001 0.0034 0.012 0.0064 0.03 B
Welding Journal | January 2014
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