The Titanic's Steel test

In 1996, several samples of steel from the Titanic—a hull plate from the bow area and a plate from a major transverse bulkhead—were recovered from the wreck site and subjected to metallurgical testing by Prof. H.P. Leighly at the University of Missouri-Rolla, as well as at the laboratories of Bethlehem Steel and the National Institute of Standards and Technology. Chemical testing revealed a low residual nitrogen and manganese content, and higher levels of sulfur, phosphorus, and oxygen than would be permitted today in mild steel plates or stiffeners. This indicates that the steel was produced by the open-hearth rather than the Bessemer process, most likely in an acid-lined furnace; the steel is of a type known as semi-killed, that is, partially deoxidized before casting into ingots. (Other fragments of the Titanic's hull have yielded slightly different results, suggesting a degree of variability in the chemical and, hence, the mechanical properties of the steel used in the ship.)
Excess oxygen can form precipitates that can embrittle the steel, and will also raise transition temperatures. In the absence of sufficient manganese, sulfur reacts with the iron to form iron sulfide at the grain boundaries; it can also react with manganese, in either case creating paths of weakness for fractures. Sulfide particles under stress can nucleate microcracks, which further loading will cause to coalesce into larger cracks; in fact, this was found to have been the mode of failure in the shell plating of the Titanic. Phosphorus, even in small amounts, has been found to foster the initiation of fractures. Of course, much of this metallurgical information has only been learned in the years since the Titanic went down.
To determine the steel's mechanical properties, it was subjected to tensile testing, as well as the Charpy V-Notch Test, used to simulate rapid loading phenomena; the test used samples oriented both parallel and perpendicular to the original direction of the hull plate. The ductile-brittle transition temperature (using 20 lbs.-ft. for the test) was found to be 20°C in one direction and 30°C in the other, compared with —15°C for a reference sample of modern A 36 steel—and a water temperature of —2°C on the night the ship collided with the iceberg. The Titanic steel was also shown to have approximately one-third the impact strength of modern steel.
When the Titanic samples were also examined with a scanning electron microscope, the grain structure of the steel was found to be very large; this coarse structure made it easier for cracks to propagate. Rivet holes were cold-punched, a method no longer allowed (they must now be drilled), nor were they reamed to remove microcracks.
The steel grain size; the oxygen, sulfur, and phosphorus content of the steel; and the cold-punched, unreamed rivet holes were found to have contributed to the breakup of theTitanic, along with the steel's relatively low ductility at the freezing point of water. The shell plates showed signs of brittle fracture, though some plates demonstrated significant plasticity.
Of course, the science of metallurgy has advanced considerably since the Titanic's day, and William Garzke of Gibbs and Cox and his collaborators emphasized in their report that "the steel used in the Titanic was the best available in 1909-1914" when the ship was built. In fact, they add that when 39,000 tons of water entered the bow, "no modern ship, not even a welded one, could have withstood the forces that the Titanic experienced during her breakup.
By Henry Baumgartner