Metallurgy of the RMS Titanic

Introduction:

• The Titanic sank on April 12, 1912, after hitting an iceberg, resulting in over 1500 deaths.
• The study aims to determine the physical properties, microstructure, and chemistry of the steel and rivets used in Titanic’s construction.

Recovery of Material:

• Hull material and rivets were recovered from the wreck site in 1991 and 1996.
• Initial tests showed the steel was brittle at ice-water temperatures, leading to speculation about its role in the sinking.

Sample Preparation and Experimental Procedure:

• Samples were prepared and analyzed using various techniques, including optical and scanning electron microscopy (SEM), transmission electron microscopy (TEM), and mechanical testing.

Experimental Results:

• Metallography: The steel showed a ferrite-pearlite microstructure with large ferrite grains and coarse pearlite colonies, indicating low-speed rolling and air-cooling.
• Mechanical Testing: Tensile tests showed the steel met the design requirements, but Charpy impact tests revealed a high ductile-to-brittle transition temperature, making the steel brittle at ice-water temperatures.
• Fractography: SEM analysis of fracture surfaces showed transgranular fracture with cleavage patches nucleated by MnS particles.
• Chemical Analysis: The steel had elevated sulfur and low manganese levels, contributing to its brittleness.

Discussion:

• Fracture Behavior of Hull Steel: The steel’s low fracture toughness was due to a combination of high sulfur content, low manganese, large grain size, and coarse pearlite.
• Fabrication Techniques and Architectural Design: Stress concentrations, cracks at rivet holes, and variability in plate quality may have contributed to the steel’s brittleness.
• Loading Rate: The steel’s fracture behavior was strain-rate sensitive, with higher strain rates (e.g., iceberg impact) causing more brittle behavior.

Analysis of Rivets:

• The wrought iron rivets contained high levels of slag, making them anisotropic and prone to failure under impact.
• Residual stresses in the rivets increased their tendency to “pop” during collisions.

Conclusions:

• The steel used in Titanic’s hull had low fracture toughness at ice-water temperatures, likely contributing to the damage during the iceberg collision.
• The rivets’ microstructure and residual stresses may have played a role in the hull’s failure.
• The materials and construction techniques used were appropriate for the time, and no apparent metallurgical mistakes were made.