What Really Sank the Titanic by Hooper McCarty Jennifer; Foecke Tim

Author:Hooper McCarty, Jennifer; Foecke, Tim
Language: eng
Format: epub
Publisher: Kensington
Published: 2012-01-25T16:00:00+00:00

ROUND THREE

Fractography of Charpy Results

Fractography is the detailed study of the broken end of a failed part and provides another critical technique in metallurgical forensics. The patterns created on fracture surfaces provide a means to qualify, and sometimes quantify, the type of failure. Fracture surfaces cut from the Charpy test specimens from the 1996 plate were examined in the scanning electron microscope in late 1997. In the case of Titanic hull steel, fracture was entirely transgranular (through the grains) (fig. 11, bottom left—see p. 126) with no indication that the grain boundaries had broken. This means that fracture did not occur in a manner consistent with problematic sulfur and phosphorus. One more time: Regardless of the suggestions that too much sulfur was causing the steel to be brittle, the images of fracture surfaces do not show any proof to support this suggestion. This observation is very significant. If the cause of the brittleness of the steel had actually been due to sulfur, we would expect to see sulfur sitting on the grain boundaries and some evidence of fracture in between the grains. Some cleaved grains were found, and some were seen to start at broken MnS particles. This was determined by tracing the crack lines on the broken grains back to where they converge (fig. 11, bottom right). This indicates that in some cases the MnS particles broke and started cracks, which is another way that sulfur can cause brittleness, but the number of these nucleated patches amounted to less than 10 percent of the surface area of the Charpy bar. So while the MnS particles were guilty of causing some cracking (as it often does when mild steels fail), it was not nearly as much as previously thought and was not a major factor.

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