BACKGROUND: ASM International presented an historic award to the Phoenix Iron Works, Phoenixville, PA in October, 2006. The principal accomplishment was the wide use of a rolled structural segment. These contoured segments were configured in 4, 6, 8 and 10 section columns in various lengths exceeding 20 feet long. A rivet flange on each side of each segment was upset to form a solid flanged/riveted column. These were used to assemble bridges and structural columns for modern buildings of the period from 1850 through 1890. The segment which was examined, tested and analyzed as subject here was cast and rolled in 1863 according to the roll marker. It is comprised of alpha iron and an assortment of oxide, sulfide, and silicate inclusions.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

A client requested ESI to examine several sections removed from a failed cooling tower. The client was particularly interested in determining if corrosion was the root cause of the failure.Specimens were saw cut from the received sections, and mounted in epoxy cold mount material. The specimens were ground with silicon carbide grinding paper starting at 60 grit and progressing to 600 grit with tap water as a coolant. Rough polishing was performed with 1 µm paste and lapping oil on a nylon cloth. Final polishing was conducted with .06 µm alumina/water slurry on a napped cloth.The resulting polished surface was un-identifiable. The surface was tarnished, pitted and scratched. Subsequent attempts at polishing with the above techniques resulted in more scratches and pits. Several other specimens from the cooling tower were examined in the SEM. EDS results indicated that the contents of typical alloy elements, Cu, Mg, Mn, and Si, were low, less than 0.5% each, while the Al content was very high. The specimen appeared to be 1100 Al.Several resources, along with personal experience of the analysts, were consulted for appropriate grinding and polishing techniques. The grinding and polishing techniques suggested by the resources consisted of grinding to 600 grit, but using kerosene or light oil as coolant instead of water, rough polishing on a nylon wheel with 1 µm diamond paste and final polishing with 0.06 µm alumina slurry on a napped cloth. The resulting surface was not tarnished, but scratches and pits were still present using this technique. Repeated efforts, even with new media yielded similar results.The next technique attempted consisted of grinding to 1200 grit using lapping oil as a coolant and final polishing with colloidal silica on a napped cloth. The resulting microstructures were not perfect, but were at least usable. The base material, fin material and bonding material could be seen and boundaries could be determined. Also, intermetallics and/or secondary phases could be seen in the bonding material. There was no apparent metal loss due to corrosion.The intermetallics in the bonding material were mostly Mg-Si particles. Some of these particles were broken and could be seen at high magnifications. It was assumed that broken Mg-Si particles were pulled out of the microstructure during rough polishing causing the scratches and pits on the resulting metallographic surface.It should be noted that practical experience has proven some aluminum alloys may be ground and polished without any special techniques. However, aluminum alloys with a very high percent Al content may have to be specially prepared for microstructural assessment.

A 1010 steel elbow used in an automotive application had been formed from seam welded (ERW) tubing. Because a longitudinal mark was observed on the surface of the finished elbow, it was subjected to metallographic examination in order to determine if the surface mark was associated with the longitudinal seam weld. A metallographic cross section prepared through the mark revealed a shallow rounded groove approximately 0.001" (0.025 mm) deep and 0.003" (0.075 mm) wide when examined in the as-polished condition. In order to identify the position of the longitudinal seam weld, the polished cross section was etched with 2% nital.Examination of the etched section revealed a curious microstructure. Dark etching layers were observed at the inside and outside circumference with a very light etching band below the dark layer at the outside circumference. The remainder of the thickness of the elbow displayed a mixture of light and dark etching grains. These grains were found to be comprised of ferrite (light) with martensite and/or bainite at the grain boundaries. Because the cold drawing operations result in work hardening of the product, several cycles of annealing may have been performed in order to soften the steel and ease deformation to the final wall thickness.The annealing operations performed on this tubing often results in decarburization at the outside surface. Because of the length of the tubes, very little decarburization occurs on the inside surface. In addition, the cold working can promote grain growth of the decarburized layer during annealing. This would account for the light etching band below the outside circumference in the examined cross section.The dark bands at the inside and outside surface of the cross section were approximately 0.003" (0.75 mm) deep. This carburized layer was comprised predominantly of martensite with some indications of bainite. Carburizing can be performed at temperatures between 1550º F (840º C) and 1700º F (930º C). Because the carburized layer was relatively shallow on these parts, a lower temperature would be expected to have been used. At the lower temperature of the range, 1010 steel is in a two phase region (ferrite + austenite) on the iron-carbon phase diagram. Generally, the higher carbon content of the pearlitic areas of the as-manufactured tubing transform to austenite while the lower carbon areas of ferrite grains would be minimally affected. Again, using the phase diagram, a 1010 steel will not transform to 100% austenite until a temperature above 1600º F (870º C). This is further verification that the carburizing temperature was in the lower range. After carburizing the part is quenched to promote formation of martensite. Typically, a tempering treatment is performed to reduce the brittleness of the case.Microhardness tests performed on the carburized case at the inside and outside surfaces indicated converted values of 36 and 41 on the Rockwell C scale. In the decarburized layer near the outside surface, hardness was converted to be 64 on the Rockwell B scale. Te...