NIST-IR 6118

Metallurgy of the RMS Titanic

Tim Foecke

Metallurgy Division

National Institute of Standards and Technology

U.S. DEPARTMENT OF COMMERCE

Technology Administration

National Institute of Standards and Technology

Materials Science and Engineering Laboratory

Gaithersburg, MD 20899-0001
Abstract

Metallurgical and mechanical analyses were performed on steel and rivet samples recovered from

the wreck of the RMS Titanic. It was found that the steel possessed a ductile-to-brittle transition

temperature that was very high with respect to the service temperature, making the material brittle at

ice-water temperatures. This has been attributed to both chemical and microstructural factors. It

has also been found that the wrought iron rivets used in the construction of Titanic contained an

elevated amount of incorporated slag, and that the orientation of the slag within the rivets may hold

an explanation for how the ship accumulated damage during its encounter with the iceberg.

Keywords: Titanic, forensics, fracture, mild steels, ships, manganese sulfide, rivets, wrought

iron, historical metallurgy
Introduction

On April 12, 1912, on her maiden voyage, the liner RMS Titanic struck an iceberg in the Atlantic

and sank 400 miles southeast of Newfoundland, with a loss of over 1500 people. This loss was

particularly tragic when considered in the context of what Titanic represented. At the time of her

construction, she was the largest moving man-made object. She was designed with the latest

safety features and was thought to be man’s triumph over nature. The popular press dubbed her

“unsinkable”.

This most famous of all shipwrecks has been the subject of books, film, and forensic speculation

for over 85 years. Many questions were raised from the time of the Mersey Inquiry [1] (the

official British hearing into the sinking) to the present day about what happened that night:

• Why did Titanic sink so quickly (in less than three hours)?

• What was the nature of the damage to the hull from the impact with the

iceberg?

• In what sequence did the compartments flood?

• Did she break in half at the surface, or did she sink intact?

• Were there any design flaws that could have been avoided?

Robert Ballard of the Woods Hole Oceanographic Institute found Titanic under 12,000 feet of

water in 1985. Surprisingly, Titanic was found to be broken into two pieces oriented in opposite

directions. This confirmed the scattered testimony of some passengers that she broke at the

surface, but ran contrary to every account of the disaster given by surviving officers. This new

data fueled even more speculation as to how and why Titanic sank as she did.

Recovery of Material

The first piece of hull material recovered from the wreck site of the Titanic was brought back by the

French oceanographic institute submersible Nautile in 1991, during the filming of an IMAX

production on the sinking. This material came into the possession of Maritime Museum of the

Atlantic, who asked researchers at the Defence Research Establishment - Atlantic (DREA) in

Halifax, Nova Scotia, and CANMET in Ottawa to test the steel’s mechanical properties [2].

Charpy impact tests were performed by Ken KarisAllen and Jim Matthews of DREA, and they

found that the steel fractured in a 100% brittle fashion at ice brine temperatures. An observation of

these tests and subsequent limited analysis can be found in an article published in Popular

Mechanics [3]. This caused wide-spread speculation that the brittle character of the hull steel in ice

water might have been a major factor in the sinking of the ship. It was considered conceivable that

the impact with the iceberg, though minor, would have been sufficient to shatter the brittle hull

plates in the bow, allowing the rapid flooding of the ship.

The Marine Forensics Panel (SD-7) of the Society of Naval Architects and Marine Engineers

(SNAME), of which the author is a member, in cooperation with The Discovery Channel formed a

team that was charged with a scientific investigation of the causes of the sinking of the Titanic.

RMS Titanic Inc., headed by George Tulloch and salvor-in-possession of the wreck, provided

access to the wreck and facilitated the investigation during a salvage trip in August of 1996.

During this time, investigations of the biology of the “rusticles” hanging on the hull, the damage to

the bow now buried under fifty feet of mud by sub-surface sonar imaging, and the damage to the

ship on breakup were performed. Of particular importance to this report, a section of the Titanic’s

hull plating, along with several hull and bulkhead rivets, was recovered and turned over for

analysis. 

The purpose of this study was twofold. First, a determination of the physical properties,
microstructure and chemistry of the steel from the hull of RMS Titanic was made. These results

were compared to prior studies of another sample of the steel, and to modern and contemporary

standards to determine if it could be considered inferior material for the application. Secondly,

since a great deal of the other forensic evidence [4] points to the likelihood of seam opening and

rivet failure in the sinking, a detailed analysis of the microstructure of the wrought iron rivets was

performed. 

Sample Preparation and Experimental Procedure

Specimens of hull steel were cut from the larger pieces using a low speed diamond saw immersed

in cooling oil. Metallographic specimens were mounted in epoxy, mechanically polished, and

etched with 10% nital solution. Optical metallographs were obtained in all three orientations with

respect to the rolling direction. In addition, scanning electron microscopic (SEM) images of the

polished and etched surfaces were obtained to show the microstructure in more detail, particularly

to better determine the pearlite lamellar spacing. In addition, fracture surfaces cut from Charpy

bars tested at ice water temperatures were imaged in the SEM to determine percent ductile fracture

and to observe the effect of precipitates on fracture nucleation.

Transmission electron microscope samples were prepared from the plate material. Slices

approximately 1 mm in thickness were cut using a low speed diamond saw. These were

mechanically thinned using 600 grit SiC paper and 5 μm Al2O3 slurry on cloth. 3 mm disc

samples were mechanically punched from the thinned slices, and given a final thinning to

approximately 100 μm. These samples were then dimpled to a residual thickness of approximately

20 μm using cubic boron nitride slurry on a brass wheel. Finally, the samples were thinned to

electron transparency using a liquid nitrogen cold stage ion mill. The samples were imaged using

both a Philips 430 and JOEL 3010 transmission electron microscopes (TEM)1, operating at 300

kV. Parallel electron energy loss spectroscopy (PEELS) and energy-dispersive xray analysis

(EDS) were used in the 3010 to try to determine contaminant concentrations on grain boundaries.

In addition, imaging secondary ion mass spectroscopy (I-SIMS) was used to determine the

chemical composition of particles and the distribution of contamination elements in the matrix.

Mechanical characterization of the hull steel, in the form of room-temperature tensile tests and

Charpy tests run at various temperatures spanning the transition regime, were performed at the

University of Missouri - Rolla, under the supervision of Prof. H.P. Leighly [5]. Chemical

analyses were performed by Prof. Leighly [5] and also by Dr. Harold Reemsnyder of the Homer

Laboratories of Bethlehem Steel in Bethlehem, Pennsylvania [6].

Experimental Results

Metallography

Steel samples of all three orientations orthogonal with respect to the rolling plane were polished

and etched to reveal the microstructure. A ferrite-pearlite microstructure was seen, with large

ferrite grains (ASTM number = 4-5, 100 μm to 130 μm equivalent diameter) and large, coarse

pearlite colonies (roughly 0.2 μm lamella thickness, but quite variable). The microstructure shows

a large amount of banding in the rolling direction. MnS and oxide particles are evident throughout

the material, and were quite large, occasionally exceeding 100 μm in length. The MnS particles

were deformed into lenticular shapes instead of being melted into stringers. Given the lack of rareearth additions to increase the sulfide melting point (see table 2), this indicates a low rolling

temperature. The large grain size and coarse pearlite are consistent with air-cooling of the rolled

1 Identification of specific brand-names of experimental equipment does not imply

endorsement by either NIST or the U.S. Government.
plate, with no evidence of quenching or normalization treatments evident. All of this evidence is

consistent with the production of this plate in a low speed rolling mill, as was the norm in turn-ofthe-century Ireland. 

A comparable modern steel grade is AISI 1018, which has a similar chemistry and does not

possess a specialized microstructure. Micrographs of a modern 1018 steel show a finer grain size,

much finer pearlite, and smaller and less numerous rare-earth doped MnS particles. This

microstructure is typical of that produced in a modern high-speed mill, followed by a quench and

normalization treatment.

Figure 1: Scanning electron microscope image of the polished and etched longitudinal sections of

steel from the hull of the Titanic, and for comparison a modern hot-rolled 25 mm (1”) AISI 1018

plate. Note the differences in grain size, pearlite lamella spacing, and MnS particle sizes.
Mechanical Testing

The data produced from tensile tests performed on steel recovered in 1996 [5] and 1991 [2] is

shown in Table 1. The uncertainty in this data is unknown. These values are consistent with the

design requirements of “15-20 tonnes per inch squared” as specified by Harland and Wolff (the

shipbuilder who constructed Titanic in Belfast in 1911 [4]). Two groups of Charpy specimens

were prepared such that in one group the long direction of the specimens were parallel to the

longitudinal direction of the hull plate (LS) and in the second group the long axis of the specimen

was parallel to the transverse direction (TL). The adjoining figure compares the experimental

results from the Charpy impact test of the Titanic hull steel for the longitudinal and transverse

rolling directions with a modern ASTM A36 mild steel [7]. Unfortunately for the purposes of a

direct correlation of properties and microstructure, the comparison of mechanical behavior was

made versus A36 steel, which is chemically nearly identical to AISI 1018 used in the

microstructural comparison, but has a more specialized microstructure. Using 20 ft-pounds (27 J.)

for the determination of the ductile-brittle transition temperature, the author [5]obtains a transition

temperature of -15oC for the modern A36 steel, while the Titanic specimens yielded transition

temperatures of +40oC for specimens in the longitudinal direction and +70oC for the transverse

direction. The transition temperatures for the Titanic steel are much above the water temperature of

-2oC at the time of the ship-iceberg collision [1]. 

Figure 2: A plot of the impact

energy measured by the Charpy

test versus temperature for two

different orientations for the

Titanic hull steel, as well as

modern A36 (which is

c h e m i c a l l y a n d

microstructurally very similar to

AISI 1018). The transition

temperature is marked for each

series of samples, and is

defined as that temperature

where the sample exhibited 20

ft-lbs (27 J.) of energy. Data

from reference [5]. The

uncertainty in the data is

unknown.
Table 1

Tensile Tests Results

Plate recovered in: 1996 [7] 1991 [2]

Yield Stress 38 ksi (262 MPa) 41 ksi (280 MPa)

Ultimate Tensile Stress 62.5 ksi (430 MPa) 62.6 ksi (432 MPa)

% Elongation (50 mm gage length) 29% 30.9%

Fractography

Fracture surfaces cut from the Charpy test specimens tested from the 1996 plate were examined in

the scanning electron microscope. Fracture was entirely transgranular (figure 3), with no evidence

of fractured grain boundaries. This is significant, in that if the cause of limited fracture ductility of

the steel (as evidenced by the absence of microvoids) had been sulfur embrittlement, we would

expect sulfur segregation to the grain boundaries and intergranular fracture facets. At ice-brine

temperatures, the fracture was nearly entirely brittle, with the ductile portion of the fracture surface

estimated to be less than 5 percent (figure 4). Cleavage patches on the surface, made up of 4 to 15

cleaved grains, were seen to originate at fractured MnS particles, as evidenced by tracing river lines

on the facets. This indicates that in some cases the MnS particles acted as initiators, but the

incidence of these nucleated patches amounted to less than 10% of the surface area of the Charpy

bar fracture surface.

Figure 3: SEM fractograph of Charpy bar fracture surface (LT) from a sample fractured at 0o C. 

Note the presence of cleavage facets and absence of fracture grain boundaries. One or two

cleavage patches nucleated by MnS particles can be identified in this image.
Figure 4: SEM fractograph of

Charpy bar fracture surface from

a sample fractured at 0o C. Note

presence of ductility along ridges.

This micrograph contains the

largest amount of plasticity

observable on the surface in one

area of the fracture surface of this

sample.

Figure 5: SEM fractograph

showing the MnS particle that

fractured and nucleated a

patch of 15 cleaved grains.

This was determined by

tracing river lines within the

patch. Note the lenticular

shape of the particle, the

cleavage river lines eminating

from the particle, and the

fractured course pearlite

colony in the upper right

corner.

Chemical Analysis

The steel from the hull was analyzed for chemical composition. Two determinations were made on

material recovered in the 1996 expedition [5,6], and one of the 1991 material [2]. These are

summarized in table 2. It is seen that the hull is made up of a steel that is roughly equivalent to a

modern AISI 1018 mild steel, with somewhat elevated levels of sulfur and low manganese. The

oxygen content implies that this is a semi-killed steel, and the low nitrogen levels indicate that the

steel was produced in an open-hearth furnace and not by a Bessemer process [8]. Imaging of the

chemical distribution within the steel using secondary ion mass spectroscopy (SIMS) and by

parallel electron energy loss spectroscopy (PEELS) in the TEM showed that the sulfur in the steel

to be almost entirely tied up in the MnS particles and not distributed in the matrix nor on the grain

boundaries.
Table 2

Chemical Composition of the Hull Steel from the RMS Titanic

Element 1991 [2] 1996 [5] 1996 [6] AISI 1018 [8]

 (CANMET) (U.Mo, Rolla) (Beth. Steel) (ASM)

Carbon 0.20% 0.21 % 0.21% 0.18-0.23%

Sulfur 0.065% 0.069% 0.061% 0.05% max

Manganese 0.52% 0.47 % - 0.60-1.0%

Phosphorous 0.01% 0.045% - 0.04% max

Silicon 0.025% 0.017% -

Copper 0.026% 0.024% -

Nitrogen 0.004% 0.0035% 0.0026%

Oxygen - 0.013% -

Rare Earths - -

Mn/S Ratio 8.0:1 6.8:1 - 12:1 - 20:1

Mn/C Ratio 2.5:1 2:1 - 3:1 - 7:1

All measurements in volume percent, with unknown uncertainties.

Discussion

Analysis of the Fracture Behavior of the Hull Steel

The measured fracture toughness of the steel from the hull of Titanic is unacceptably low for use as

a structural material at ice water temperatures. This is likely not due to any one single material

characteristic, but a combination of several. These can be broken down into four general

categories: effects of chemistry, microstructure, architecture, and loading rate.

Effect of the Chemistry of the Steel

Several elemental constituents can increase or decrease toughness at various concentrations. The

sulfur level measured in the Titanic hull steel is higher than that acceptable in modern steels, as is

the phosphorus concentration. Both of these elements can decrease the measured upper shelf

toughness, but have been seen to have little effect on the transition temperature [9]. The steel was

also found to be low in Mn. This can lead to sulfur embrittlement if there is insufficient Mn to tie

up all the sulfur in MnS particles. However, SIMS and PEELS data indicate this is not the case,

but rather that the sulfur is mainly occupied in sulfide particles. Mn is also a powerful solidsolution toughening agent, which can shift the transition temperature several tens of degrees celsius

with small additions [10]. Thus the low Mn level may have had an impact on the toughness of the

ferrite matrix. Also found to be important in low-carbon steel is the ratio of manganese-to-carbon

[11], which has a desired value of 5 for a 1018 steel [12], but which measured 1.5 to 2 in the

Titanic hull steel.

It has been argued that the sulfur content of the hull steel was significantly higher than the standard

of the time, and that should have implied to the engineers that the ship was being made of material

that would have been substandard from a fracture viewpoint, given sulfur’s deleterious effect on

fracture toughness. However, it is important that one look at the sulfur content standard from a
historical viewpoint. The sulfur content standard for structural mild steel is 0.05% maximum

today. In 1906, the standard, which would have been in place at the time of the ship’s

construction, was placed at 0.04% [13]. This would indicate that the steel from the hull was even

more sub-standard at the time. However, a further investigation of the literature reveals that the

standard had been revised to 0.055% (1933, [14]) and 0.05% (1946, [15]) at various times

between 1906 and the present day. There is no evidence that the concentration level was set in

reaction to any data linking sulfur concentrations to fracture or tensile behavior, but rather seem to

be a series of estimates at an upper bound. Metallurgists of the era had an empirical knowledge

that elevated levels of certain tramp elements, most notably sulfur and phosphorus, increased the

likelihood of cracking in steel under certain service conditions. The effect had been known in

general terms for nearly a century, but a quantitative analysis was not performed until the analysis

of Liberty Ship failures during and after WW II [16]. Any assertion that the engineers constructing

the ship should have been able to link a chemical analysis showing high sulfur in any given plate to

a obvious risk of brittle fracture is unfounded. Also, it is far too simplistic to state that, simply

because there exist somewhat elevated sulfur concentrations, the steel was brittle, as will be

discussed in subsequent sections.

Effect of the Steel Microstructure

Trends have been found relating microstructural characteristics of mild steel with ferrite/pearlite

microstructures to fracture toughness. In general, larger ferrite grain sizes and pearlite colonies

give lower toughnesses [17]. There is a body of work in the literature, for example the analysis of

Ritchie, Knott and Rice [18] that the size, shape and distribution of carbides in mild steel is a

dominant factor in determining the shape and location of the brittle-to-ductile transition temperature

(BDTT). Since the steel from the hull appears to have been air-cooled and unannealed, most of the

carbon not in matrix solid solution is tied up in carbide lamella in the pearlite. It was not possible

in either the SEM or TEM to find precipitated particle carbides in the steel. So the carbide size that

would be controlling fracture behavior would be that in the pearlite, and thus a coarser pearlite

lamella spacing would cause a higher transition temperature.

The presence and large size of the MnS particles are considered deleterious to fracture resistance,

as they act as crack initiators within the steel at temperatures near the lower shelf [19]. It was seen

that the plate recovered in 1996 exhibited 5% ductile fracture during Charpy tests at ice-brine

temperatures, and that MnS particles, upon examination of the fracture surface, nucleated a few

patches of cleavage. However, the plate recovered in 1991 was 100% brittle even at room

temperature [20], placing it firmly in, not near the lower shelf regime. Thus MnS particles would

have little to no effect on toughness in this plate. The presence of MnS particles and their effect on

crack growth have been found to be much more important at high temperatures than lower

temperatures. Their effect on the fracture behavior of both the material in this study as well as the

1991 study [2] are considered negligible. Although cleavage patches have been identified on the

fracture surface as having come from the fracture of a MnS particle, and thus the formation of a

process-zone would have begun, the occurrence of this was relatively rare. It is believed that the

fracture mechanism that controlled at -2oC would have been weakest-link [18], where the first

fractured microstructural feature would have precipitated failure. And as the population of large

carbides, in the form of thick pearlite lamella, is many times that of large sulfides, it is more likely

that a fractured carbide would precipitate failure.

A finer microstructure, both in terms of grain size and in pearlite lamella spacing, would have

exhibited a significantly higher transition temperature at this composition. This could have been

obtained by rolling the steel at a higher speed and temperature, then subjecting the plate to a quench

and normalization anneal. However, the concept of notch sensitivity of iron-based alloys was little

understood, and the first quantitative ways to begin to evaluate the fracture toughness of a material,

among them the Charpy V-notch test [21], was only devised in the five or so years before the
construction of the ship. It was suggested in a rather off-hand manner in the Mersey Inquiry [1]

that Charpy-like testing should have been performed on the steel of the hull. However, in 1911,

the only materials being routinely tested for fracture toughness were ordinance steels [22], where

failures by fracture were thought to be much more likely than in structural steel under normal use.

Therefore, it would have been not intuitive for the designers and builders of Titanic to have tested

the hull steel for notch sensitivity, and even if they had, they had no information about what makes

steel notch sensitive in the first place, and how to fix it. Specifications of the time for steels at the

time called for only a range of tensile strengths and tensile ductility, which are a poor indicator of

fracture toughness. 

Effect of Fabrication Techniques and Architectural Design

Several practices common in turn-of-the-century shipbuilding may have contributed to making

brittle steel a factor in the sinking. All of these are noted here as possibilities only, and the exact

effect each may or may not have had on the sinking may never be known for certain.

• Stress Concentrations: Because of a lack of understanding of notch sensitivity in ironbased alloys, there was no attempt to remove stress concentrations from the architecture of

the ship. These are commonly found at hatch corners, strake junctions, and the like.

These were found to be sources of brittle cracks in Liberty Ships during and after WW II

[23]. 

• Cracks at Rivet Holes: The rivet holes in the hull plates of the Titanic, and of all

contemporary ships, were cold-punched using a steam-driven ram [24]. Upon close

examination, these rivet holes were found to contain a small number of cracks. However,

the shipbuilders generally did not worry about them because they were so small, and they

thought that a well-driven rivet would exert a clamping stress that would negate any risk

[24]. However, the residual stresses from the punching process would have been

significant, and was such that they exerted a driving force on the cracks. Furthermore,

upon impact of the plate at low temperatures, these cracks could have grown in a brittle

manner and linked up, resulting in failure of the plate. 

• Plate Variability: The two plate fragments recovered from the wreck and analyzed to date

(1991 [2] and this study) have exhibited significant differences in microstructure and

fracture properties. They appear to have been rolled at different temperatures, as evidenced

by the more severe banding and MnS particle melting in the 1991 plate. This variability

would have meant that some plates were at risk of brittle fracture at ice-brine temperatures,

while others would have been fine. This effect of plate variability in the hull was also seen

in the detailed analysis of Liberty Ship failures, where the initiation, propagation, and arrest

hull plates were found to have increasingly higher toughnesses at a given temperature [22].

This variability is not unexpected, as the Titanic and her two sister ships were twice as

large as any previously built, and iron feedstock was being assembled from all over the

United Kingdom [25]. Also, the plates were being produced in 40 ton batches, versus the

500 ton batches typical for today [25].

Effect of Loading Rate

Iron-based alloys are well-known to exhibit strain-rate sensitive fracture behavior. That is, the

faster the crack is loaded, the more brittle the fracture character. There is both direct and indirect

evidence that the steel used in the hull of the Titanic and her sister ships exhibited this behavior.

Imaging of the hull of the Titanic by Nautile showed considerable buckling resulting from the

impact with the seafloor [26]. Computer simulations of the sinking showed that this impact was

fairly gradual and that these plates deformed at low strain rates [7]. However, the impact of the
ship with the iceberg at 20+ knots would have occurred at strain rates more in line with a Charpy

impact test. At this rate, the steel would exhibit more brittle behavior. Additional evidence comes

from photographs of damage to the Titanic’s sister ship, RMS Olympic, after collision in Belfast

harbor with a Royal Navy cruiser, HMS Hawke [25] (figure 5). A close examination of the

photos show considerable bending of the plates around the hole, while reports of the physical

damage include a mention of a triangular piece of hull that fractured into the ship. This would be

consistent with a high strain rate impact causing fracture, and then progressively slower

deformation as the two ships pressed together, causing bending instead of cracking. 

Figure 6: A close-up of the damage to the RMS Olympic due to collision with the HMS

Hawke in the Solient in 1911. Note the man for scale. A considerable amount of plasticity in

the hull plates is indicated by the bending and twisting seen in the picture. Note missing rivets.

Photo from [25].

Analysis of the Fracture Behavior of the Rivets

The findings of the Marine Forensics Panel report [7] detail that parting of seams, and not a

mythical 90 m (300 ft) gash in the bottom of the hull, made up the damage to Titanic. This would

imply that failure of the rivets may have had a role in the sinking. A detailed analysis of two hull

rivets was undertaken to determine if any metallurgical factors may have given the rivets a tendency

to fail.
Effect of Microstructure

The Titanic was assembled using some 3,000,000 hydraulically-driven rivets [7]. These were

drawn from wrought iron, a mass of iron and iron silicate that extruded into a layered structure.

These were driven through the hull plate and the stringer, and flattened on the inside. Rivets were

considered to be acceptably driven if when tapped with a hammer, one heard a clean ‘ring’. If the

sound was a dull ‘thud’, the rivet was drilled out and another driven in. 

These rivets were made of wrought iron, which consists of a relatively pure iron matrix containing

2-3% (by volume) iron silicate slag. A micrograph of the structure can be seen in figure 7.

Quantitative metallography was performed on a cross-section of a hull rivet that had been cut and

polished. This showed that this rivet contained 9.3% +/- 0.3% slag on average, which is more

than 3 times the amount normally expected in wrought iron [27]. This slag had an almost bimodal-type distribution of sizes, ranging from a large amount in very long stringers (>200 μm

long) to a large number of small oblate spheroid particles (1 μm to 5 μm diameter).

The mechanical behavior of wrought iron, and especially the fracture behavior, is known to be

highly anisotropic [8]. Parallel to the direction of the silicate stringers, the tensile strength is on the

order of a strong mild steel, while perpendicular to this the measured strength is considerably

decreased. More strikingly, the tensile strain to failure, which is one of two parameters generally

specified in 1911 for the quality of wrought iron [27], is an order of magnitude lower in the

transverse direction than in the longitudinal direction. This behavior can be simply understood by

considering the microstructure. It is important to note that there is virtually no interfacial strength

between the ferrite and slag components of the microstructure. The slag merely takes up space in

the ferrite, from a mechanical point of view, in the transverse orientation. Worse, at low

temperatures, the silicate slag can fracture and nucleate cracks in the iron, a similar effect to MnS

particles in mild steel in the transition temperature regime. And in the transverse orientation, the

slag sheets present a very large area that can nucleate a crack.

Upon impact, these rivets might have a tendency to pop out of their holes after losing the interior

head. This is evidenced by both the rivets in possession, which are missing interior heads, and by

the higher magnification of the damage to RMS Olympic after collision with the Hawke (figure 8).

If you look at the photograph, dozens of rivets around the hole are missing. Loss of rivets, and

the resultant parting of seams and water leakage, is believed to be the main occurrence that caused

the sinking of the Titanic [7]. 

The two hull rivets in possession have been sectioned and examined. Both exhibit the abovementioned orientation distribution of slag stringers within the rivet, an increased amount of

incorporated slag, and are both missing the inner head. These metallurgical factors would have

degraded the mechanical performance of the rivet. If additional samples are obtained during an

expedition planned for August of 1998, further work will be performed to determine if this was a

major factor in the sinking of the ship. Rivets from an intact section of a lap joint will be sectioned

to see if rivets that did not fail contain elevated slag levels and transversely-oriented slag stringers.

It is important to reiterate that only two rivets have been sectioned to date, out of 3,000,000, some

minority percentage of which held the hull together. 

But it is also important to observe that not all rivets need exhibit these undesirable characteristics

for the rivets to have played a role in the sinking. If a load from the iceberg impact is borne by the

rivets of a lap joint on the edge of a plate, failure of a small fraction of the rivets (for whatever

reason) would transfer this load onto the remaining intact rivets. This load transfer would occur

disproportionately onto the rivets immediately adjacent to the failed ones. This could bring the

stress level in these neighboring rivets to the failure level and propagate the failure of the joint,

even if the neighboring rivets are of standard quality. The microstructure of the rivets is the most

likely candidate for becoming a quantifiable metallurgical factor in the loss of Titanic.
Figure 7: Montage of micrographs showing the orientation of silicate slag at various locations

within a cross-section of a Titanic hull rivet. Note that in the upper pre-formed head (formed onto

a hot rod of wrought iron prior to cutting the rivet to length), the slag spreads out evenly into the

head like the branches of a tree. At the bottom, where the inner head popped off, very near the

fracture surface the stringers are oriented perpendicular to the tensile axis. This occurred

presumably when the inner head was formed.
Figure 8: Blowup of damage to

Olympic after collision with HMS

Hawke. This image has undergone a

considerable amount of digital image

processing to bring out the empty rivet

holes. On the entire image after

processing, one can identify in excess

of 50 rivets missing from the immediate

area of the impact. Image from [25].

Effect of Residual Stresses

A properly driven rivet possesses a considerable amount of residual tensile stress. This develops

as the rivet cools and shrinks, clamping the two plates together, and is only partially relieved by

plastic deformation in the rivet. This stress could have an effect on the behavior of the rivets

during an impact of the hull plate. The residual stress does not have an effect on the tensile

strength of the material. However, it does have an effect on the amount of plate deflection would

be required to fail the rivet during an impact. For a given rivet, the presence of a residual tensile

stress decreases the amount of additional stress needed to exceed the ultimate tensile strength of the
material. This represents a smaller amount of deflection of the hull plate applying the stress though

leverage against the supporting rib inside the ship. High residual stresses would increase the

tendency of rivets to “pop” during collisions. The presence of high residual stresses in Titanic

rivets can be seen in a badly-corroded bulkhead rivet, seen in figure 9. The head of the rivet has

exfoliated and the slag stringers have spread, driven by residual stress during stress corrosion

cracking and dissolution of the ferrite.

Figure 9: Bulkhead rivet from RMS Titanic. Note the

portion of the head that exfoliated during corrosion of

the ferrite matrix of the wrought iron, under the

influence of the residual stress in the rivet.

Conclusions

• The steel used to construct the RMS Titanic’s hull, though adequate in strength, possessed

a very low fracture toughness at ice water temperatures

• The low toughness was likely due to a complex combination of factors, including low Mn

content, a low Mn/C ratio, a large ferrite grain size and large and coarse pearlite colonies.

• There is evidently a large variation in properties among the 2000 plates that made up the

hull of Titanic. This conclusion is based on the very different microstructures and fracture

behavior observed in the two plate samples recovered to date. This is a normal result of the

variability of feedstock and rolling conditions in turn-of-the-century ironworks.

• This variability makes it difficult to determine the effect of MnS particles and microcracks

in the sinking of the ship. An analysis of the actual plates involved in the collision would

be required for a more firm determination.

• It is possible that brittle steel contributed to the damage at the bow due to the impact with

the iceberg, but much more likely that the brittle steel was a factor in the breakup of the ship

at the surface. This is discussed in much more detail in the full Forensics Panel report [7].

• Steps could have been taken to heat-treat the steel to improve its fracture properties, but this

knowledge was simply not available in 1911.

• The microstructure of the rivets that evolved during their being driven into place, with the

slag stringers oriented perpendicular to the tensile axis, may have been a direct contributor

to the type and distribution of damage to the hull. This aspect is under further

investigation.

• Given the knowledge base available to engineers at the time of the ship’s construction, it is

the author’s opinion that no apparent metallurgical mistakes were made in the construction

of the RMS Titanic.
Acknowledgements

The author wishes to thank the following colleagues for material, data, advice,

consultation, and comments: 

Phil Leighly (Univ. of Missouri, Rolla, MO), Harold Reemsnyder (Homer Labs,

Bethlehem Steel, Bethlehem, PA), George Tulloch (RMS Titanic, Inc., New York, NY),

Bill Garzke (Gibbs and Cox and SNAME, Arlington, VA), Jim Matthews (Defence

Research Establishment - Atlantic, Halifax, Nova Scotia), Bob Brigham (CANMET,

Ottawa, Quebec), Ed McCutcheon (USCG (Retired), Bethesda, MD), Bill Gerberich

(Univ. of Minnesota, Minneapolis, MN), and John Bonevich (Metallurgy Division,

NIST).

References

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CANMET Metals Technology Laboratories, Ottawa, Canada.

3. “Titanic Steel: A Shattering Tale”, Popular Mechanics, February 1995.

4. Moss, M. and Hume, J.R. Shipbuilders to the World, 125 years of Harland and Wolff,

Belfast, Blackstaff Press, Belfast (1986).

5. K. Felkins, H.P. Leighly, and A. Jankovic, “The Royal Mail Ship Titanic: Did a

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