METALLURGY: Stronger Steel from a Sunken Ship
Another aspect of science that advanced from a disaster was the field of metallurgy. Due to the sinking of the "unsinkable" Titanic, science made a giant leap forward by learning from its mistakes regarding the perceived strength of steel. On April 14, 1912, the seemingly unsinkable ship, the Titanic, struck an iceberg and sunk to its watery grave in under three hours. Upon recovery of a section of a steel plate from the Titanic's hull, scientists conducted several experiments to determine the cause of this impossible event.
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The first of these tests
evaluated the composition of the steel plates used in the hull. The steel was
found to contain a low manganese to sulfur of 6.8:1. Steel produced today (ASTM
A36) contains a 14.9:1 ratio. The low Mn:S ratio would render the steel very
brittle at temperatures below 59° C. Today's steel would have the same brittle
properties at much lower temperatures due to the other elements in its
composition. In addition, ASTM A36 steel has a
substantially lower phosphorus content, which will also lower the
ductile-brittle transition temperature. The water temperature at the time of the
collision with the iceberg was -2° C. Included in Table I is the composition of
one other steel: steel used to construct lock gates at the Chittenden Ship Lock
between Lake Washington and Puget Sound at Seattle, Washington. The ship lock
was built around 1912. Therefore, the steel used in the ship lock is about the same age as the steel from the
Titanic, although the steel could have been produced by a different method in a
different location.
|
Table
I. The Composition of Steels from the Titanic, a Lock Gate, and
ASTM A36 Steel |
|||||||||
|
|
C |
Mn |
P |
S |
Si |
Cu |
O |
N |
MnS:
Ratio |
|
Titanic
Hull Plate |
0.21 |
0.47 |
0.045 |
0.069 |
0.017 |
0.024 |
0.013 |
0.0035 |
6.8:1 |
|
Lock
Gate* |
0.25 |
0.52 |
0.01 |
0.03 |
0.02 |
— |
0.018 |
0.0035 |
17.3:1 |
|
ASTM
A36 |
0.20 |
0.55 |
0.012 |
0.037 |
0.007 |
0.01 |
0.079 |
0.0032 |
14.9:1 |
|
*Steel
from a lock gate at the Chittenden ship lock between Lake Washington and
Puget Sound, Seattle, Washington. |
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The second test evaluated the tensile
strength of the steel. Approximately 2/3 of the steel produced in the world in
the early 1900s was produced in Glasgow, Scotland using the acid-lined
open-hearth method. Therefore, it is assumed that this process was the method
used in the construction of the Titanic. However, the acid-lined
open-hearth method produces steel containing very large grains.
The tensile-test results are given in Table II. These data are compared with
tensile-test data for SAE 1020 steel, which is similar in composition. The steel
from the Titanic has the lower yield strength, probably due to the larger grain
size. The elongation increases as well, again due to the larger grain size.
|
Table
II. A Comparison of Tensile Testing of TitanicSteel and SAE 1020 |
||
|
|
Titanic |
SAE
1020 |
|
Yield
Strength |
193.1
MPa |
206.9
MPa |
|
Tensile
Strength |
417.1
MPa |
379.2
MPa |
|
Elongation |
29% |
26% |
|
Reduction
in Area |
57.1% |
50% |
Reprinted with Permissions from The
Minerals, Metals, and Materials Society
Considering the technology available in constructing the Titanic, it was probably not built with the strongest steel produced during that time. The steel used in the gate lock would indeed be stronger than that used in construction of the Titanic's hull. Unfortunately, it is highly probably that both types of steel in 1912 would have been brittle at -2°C. Fortunately, science has developed steel with different components that, under the same impact conditions, would require a water temperature of -59°C to create the same fate for the Titanic.