"Capt.Mooron" wrote:

Heh Joe... an estate has a 55 ft high carbon steel

Why high carbon? So it will hold an edge better? Seems I'd rather have
the ductility.

Cheers
Marty

carbon steel
Iron alloy phases
Austenite (γ-iron; hard)
Bainite
Martensite
Cementite (iron carbide; Fe3C)
Ferrite (α-iron; soft)
Pearlite (88% ferrite, 12% cementite)


Types of Steel
Carbon steel (up to 2.1% carbon)
Stainless steel (alloy with chromium)
Surgical stainless steel
Chrome moly
Tool steel (very hard; heat-treated)


Other Iron-based materials
Cast iron (2.1% carbon)
Wrought iron (almost no carbon)
Ductile iron


Carbon steel is a metal alloy, a combination of two elements, iron and
carbon, where other elements are present in quantities too small to
affect the properties. Steel with a low carbon content has the same
properties as iron, soft but easily formed. As carbon content rises the
metal becomes harder and stronger but less ductile. Typical
compositions of carbon a

Mild steel 0.10% to 0.25% (e.g., AISI 1018 steel)
Medium carbon steel 0.25% to 0.45% (e.g., AISI 1040 steel)
High carbon steel 0.45% to 0.95%
Very high carbon steel 0.95% to 2.1%
Steel with sufficient carbon compositions can be heat-treated, allowing
parts to be fabricated in an easily-formable soft state then made
harder for structural applications. Steels are often wrought by
cold-working methods, which is the shaping of metal through deformation
at a low equilibrium or metastable temperature.


Metallurgy
Heat-treatment is an important aspect of carbon steel processing and
involves the hypoeutectoid reaction between almost pure iron
(α-ferrite), cementite (Fe3C), and austenite, which is a reorganized
FCC iron structure that exists only at high temperatures. Carbon has a
higher degree of solubility in the austenite phase. The rate at which
the steel is cooled through this eutectoid reaction affects the rate at
which carbon diffuses out of austenite. Cooling through a hypoeutectoid
reaction in carbon steels results in a mostly pearlitic arrangement of
alternating layers of ferrite and cementite.

Mild steel is the most common form of steel as its price is relatively
low while it provides material properties that are acceptable for many
applications. Mild steel has medium carbon contents (up to 0.3%) and is
therefore neither extremely brittle nor ductile. It is also often used
where large amounts of steel need to be formed, for example as
structural steel.

Carbon steels which can successfully undergo heat-treatment have a
carbon content in the range of 0.30% to 1.70% by weight. Trace
impurities of various other elements can have a significant effect on
the quality of the resulting steel. Trace amounts of sulfur in
particular make the steel red-short. Low alloy carbon steel, such as
A36 grade, contains about 0.08% sulfur and melts around 2600-2800 F
[1].


Heat Treatment

Iron-carbon phase diagram, showing the temperature and carbon ranges
for certain types of heat treatments.Full Annealing: Heating to a high
temperature then cooling slowly. Results in a soft and ductile steel
with no internal stresses, often necessary for cost-effective forming.
Normalizing: Heating to a high temperature then cooling at a medium
rate in a furnace. Results in steel that exhibits a good balance of
mechanical properties, by offering high strength and a good degree of
toughness
Hardening: Heating to high temperature then cooling rapidly in water or
brine. Also called quenching. Results in steel that is extremely strong
but brittle containing a high degree of internal stresses. Results in
formation of Martensite, a form of steel that possesses a
super-saturated carbon content in a deformed crystalline structure (BCT
- Body-Centered Tetragonal) with a high resistance to deformation but
with extremely high internal stresses. The technique requires steel
with a carbon content high enough to be hardenable.
Case hardening, flame hardening and induction hardening: Only the
exterior of the steel part is heated and quenched, creating a hard,
wear resistant skin, but preserving a tough interior. The surface of
the steel is heated to high temperature then cooling rapidly through
the use of localized heating mechanisms and water cooling. Typical uses
are for the shackle of a lock, where the outer layer is hardened to be
file resistant, and mechanical gears where hard gear mesh surfaces are
needed to maintain a long service life while toughness is required to
maintain durability and resistance to catastrophic failure. Case
hardening requires a steel with a certain level of carbon to be
effective. Low carbon steels may be case hardened only if additional
carbon is introduced:
Packing low carbon steel parts with a carbonaceous material and heating
for some time diffuses carbon into the outer layers. The parts then
respond to heat treatments as above. A heating period of a few hours
might form a high-carbon layer about one millimeter thick.
Carboration may also be accomplished with an acetylene torch set with a
fuel rich flame and heating and quenching repeatedly in a carbon rich
fluid (oil).
Spheroidizing: Heating to a high temperature (austenitic) then cooling
at an extremely slow rate through active temperature control. Results
in spherically diffused carbon areas with mostly iron rich
compositions, also known as spheroidite, as opposed to elongated bands
of pearlite. Results in extreme softness and ductility, often only
necessary when a high degree of forming is necessary.
Tempering: Reheating hardened steel to a lower temperature then
cooling. Reforms crystal structure for a combination of strength and
toughness depending on temperature. Necessary when a high degree of
internal stresses are present or after quenching when the material is
too brittle to be viable for structural applications. Actual
temperatures and times are carefully chosen for each composition.
A limitation of plain carbon steel is the very rapid rate of cooling
needed to produce hardening. In large pieces it is not possible to cool
the inside rapidly enough and so only the surfaces can be hardened.
This can be improved with the addition of other elements resulting in
alloy steel.

Joe wrote:

carbon steel blah blah...

I hope you read and understood it all, now back to the point: Why high
carbon steel for a hull?

Cheers
Marty

Stronger, harder, stronger.. Steel with sufficient carbon compositions
can be heat-treated, allowing
parts to be fabricated in an easily-formable soft state then made
harder for structural applications.
High Carbon steel rolls and holds it's shape nicely, and I suppose high
carbon slows rust too!
I've never seen a carbon anything rust.

Joe

There is no good reason for using high carbon steel in a yacht hull.

It's harder to weld.

The weld heat affected zone has different characteristics to the parent
material, usually worse, nearly always different corrosion
susceptibility.

High carbon steel has somewhat greater tensile strength, but so what.
Steel yacht hulls are massively overstrength anyway, the plate
thickness is set by the need for min thickness for corrosion allowance
over the life of the hull.

High carbon steels with heat treatment become brittle and can fail from
shock loads. Not that anyone in their right mind would do this WRT
boats.

High carbon steels do *not* roll and hold their shape nicely, WRT low
carbon steels, because they WORK HARDEN and if not annealed, become
brittle and develop stress cracks and fail.

High carbon steel does *not* slow rust appreciably. Some steel alloys
have greater corrosion resistance but this is due to the alloying
elements, not the carbon. In fact, very *low* carbon steel resists
corrosion better than high carbon steel.

Feel free to argue about it all you like. I'll just quote more bits
from 'The Procedure Handbook of Arc Welding' by the Lincoln Electric
Company.

You might own a steel boat, Joe, but so do I. Just that mine's bigger
than yours :-)

PDW

In article .com, Joe
wrote:

Stronger, harder, stronger.. Steel with sufficient carbon compositions
can be heat-treated, allowing
parts to be fabricated in an easily-formable soft state then made
harder for structural applications.
High Carbon steel rolls and holds it's shape nicely, and I suppose high
carbon slows rust too!
I've never seen a carbon anything rust.

Joe

Joe wrote:

Stronger, harder, stronger.. Steel with sufficient carbon compositions
can be heat-treated, allowing
parts to be fabricated in an easily-formable soft state then made
harder for structural applications.
High Carbon steel rolls and holds it's shape nicely, and I suppose high
carbon slows rust too!
I've never seen a carbon anything rust.

Joe

It is unfortunatley very dificult to heat treat large pieces, such as
boat hulls. As for forming, untreated high carbon steels and low carbon
steels, as 1005 behave simalarly at the onset, but with repeated forming
the high carbon will likely work harden and become brittle.

Rust? Just leave a file out in the rain for a day or two, it'll rust
like hell and I assure you that files are made from very high carbon
steels.

Cheers
Marty