Analysis of 19th century boat anchor using field metallography techniques

Figure 4 – Light optical micrograph of as-polished slag inclusion – image was taken by carefully balancing anchor on microscope stage. Note presence of dendrites within slag inclusion. 25x Results: After completion of final polishing, it was evident that the anchor contained a high concentration of slag inclusions (Figures 2 and 3), aligned with the long dimensions in the anchor, indicating that the anchor was wrought. Note also the region near the shank-arm joint that is relatively free of inclusions. Preparation of thin film replicas of these inclusions (Figure 3) did not reproduce their fine substructure accurately. Consequently, the entire anchor was placed on the microscope stage and images of the slag inclusions were taken. These were found to have a dendritic substructure (Figure 4). While most of the anchor’s shank that was analyzed exhibited only ferrite, the region between the shank and arms that was free of inclusions (red arrows, Figure 2) was found to contain pearlite (Figure 5). Whether or not the presence of pearlite in this area was intentional is not known. However, pearlite was also found during analysis of the joint between the arm and palm (not shown), indicating that carbon was added in the regions where two pieces were to be joined. Additionally, mechanical twins were found in the replica prepared from the anchor’s shank (Figure 6). These twins may have been created during the manufacture of the anchor, or by overstressing the anchor during use.