Russell J. Steel

Friction Stir Welding of Carbon Steel for Application in Used Fuel Containers

Friction Stir Welding (FSW) is being investigated as a method to fabricate a partial penetration closure weld of the steel vessel of a copper-coated used fuel container. The hemi-head is made of A516 Grade 70 steel and the cylinder body is made of A106 Grade C steel. In this initial feasibility study, the objective is to use FSW to demonstrate the merits of FSW using flat steel plate in concert with a closure weld joint designed specifically for a cylindrical container. To complete this objective, there are two initial feasibility demonstrations. First, demonstrate the capability of FSW to create defect free welds in a corner joint design with specific dimensions (10 mm deep weld nugget). Subsequently, verify the weld quality by ultrasonic inspection and metallography. Further, characterize weld zone properties by establishing mechanical properties and hardness at room temperature, and impact toughness at-5°C. Second, demonstrate the ability to use FSW to repair defects that might occur in the initial friction stir weld. Weld repair was accomplished by intentionally creating tunnel defects by FSW, performing metallography and ultrasonic inspection to characterize the morphology of the defects, performing a second friction stir weld repair over the defects, and verifying the subsequent weld integrity by repeating the metallography and ultrasonic inspections. Results on these initial two phases of this program are presented herein.

Microstructure and Properties of Friction Stir Processed HY80 Steel

Microstructures and mechanical property changes associated with Friction Stir Processing (FSP) of HY-80 steel both dry and under seawater were examined. FSP on HY-80 plates employed a PCBN / tungsten rhenium tool operating at 400 rpm and 2 ipm. Micro structural characterization of the as-received HY-80 plate emphasized the differences in the distribution of constituent phases and inclusions in the rolling, transverse and normal planes using optical and scanning electron microscopy. Micro structural details of transverse sections as well as the plan section at the tool extraction sites of processed plates were also evaluated. Mechanical properties of these samples were evaluated by tensile tests, microhardness tests and Charpy V-notch impact tests. Residual hydrogen content was also evaluated. Stir zones exhibited untempered bainitic / martensitic micro structure s with minimal hydrogen pick up but distinct property gradients from stir zone to base metal. The influence of a post-FSP tempering treatment also is summarized.

Friction Stir Welding of Pipeline Steels

In prior FSW studies, consistent full penetration in pipeline steel has proved to be a difficult goal when using a portable FSW system capable of operation in the field [1]. In a previous study, metallography, mechanical testing (tensile and Charpy impact), and workmanship testing (root bend) demonstrated that full penetration can be achieved through much of the weld length, and when full penetration is achieved, mechanical properties are excellent. However, at times there remained sections of the weld that did not exhibit full penetration. As an example, metallography and root bend tests of the weld root have shown full penetration at many locations around the pipe circumference while from the same weld, locations are identified where remnant faying surfaces remain and full penetration was not achieved. Further, some welds exhibit full penetration accompanied by a continuous oxide path that remains at the weld root. Conversely, if the FSW tool penetrates into the support anvil, anvil material is drawn into the weld nugget. Thus, different approaches need to be developed to assure consistent full penetration without anvil contact.

Friction Stir Welding of API Garde 65 Steel Pipes

Friction stir welding (FSW), a novel solid-state joining process, was applied to girth weld API 5L Grade 65 steel pipes with an outer diameter of 12.75″ (324 mm) and a wall thickness of 0.25″ (6.35 mm). Fully consolidated single pass butt welds were obtained using a specially designed mechanized portable FSW system suitable for on-site pipe construction welding. The friction stir girth weld shows a slightly overmatched strength and superior impact toughness in comparison with the base metal, a very desirable combination of properties for pipeline weld that can be attributed to the wrought microstructure with refined grains in the stir zone (SZ), the thermal-mechanically affected zone (TMAZ), and the heat-affected zone (HAZ).Copyright

Friction Stir Welding in Pipeline Applications

Friction stir welding (FSW) is a relatively new joining process which has exhibited many advantages over traditional arc welding processes such as the elimination of solidification defects and reduced distortion. With the introduction of new tool material technology such as the use of polycrystalline cubic boron nitride, materials such as steels, stainless steels, and nickel base alloys have successfully been FSW. Though there are many advantages to friction stir welding, there has been very little work in applying the process to out of position welds, such as those found in pipelines. This study outlines the progression from linear friction stir welding to initial work consisting of the rotation of pipe coupons on a turn table and finally to the design of a portable FSW machine able to weld 305 mm (12 inches) diameter line pipe. A brief summary of FSW weld characteristics are given for API grades X65, X80, and X100 steels.Copyright