Krupp armour was a type of steel

naval armour Naval armour refers to the various protections schemes employed by warships, and is distinguished from other kinds of armour. Naval sailing ships have had protection from weaponry since at least ancient times, when Greek and Roman warships used s ...

used in the construction of

capital ship The capital ships of a navy are its most important warships; they are generally the larger ships when compared to other warships in their respective fleet. A capital ship is generally a leading or a primary ship in a naval fleet. Strategic im ...

s starting shortly before the end of the nineteenth century. It was developed by Germany's Krupp Arms Works in 1893 and quickly replaced Harvey armour as the primary method of protecting naval ships, before itself being supplanted by the improved Krupp cemented armour.

Original Krupp armour

The initial manufacturing of Krupp armour was very similar to Harveyized armour; however, while the Harvey process generally used nickel-steel, the Krupp process added as much as 1%

chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hard ...

to the

alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductili ...

for additional

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...

. Also, while Harveyized armour was carburized by heating the steel and placing charcoal on its surface for long periods (often several weeks), Krupp armour went a step further. Instead of inefficiently introducing carbon at the surface with coal, Krupp armour achieved greater depth of carbon cementation by applying carbon-bearing gases (

coal gas Coal gas is a flammable gaseous fuel made from coal and supplied to the user via a piped distribution system. It is produced when coal is heated strongly in the absence of air. Town gas is a more general term referring to manufactured gaseous ...

acetylene Acetylene ( systematic name: ethyne) is the chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure ...

) to the heated steel. Once the carburization process was complete, the metal was then transformed into face hardened steel by rapidly heating the cemented face, allowing the high heat to penetrate 30% to 40% of the steel's depth, then quickly

quench In materials science, quenching is the rapid cooling of a workpiece in water, oil, polymer, air, or other fluids to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, such as p ...

ing first the superheated side then both sides of the steel with powerful jets of either water or oil. Krupp armour was swiftly adopted by the world's major navies; ballistic tests showed that 10.2 inches (25.9 cm) of Krupp armour offered the same protection as 12 inches (30.4 cm) of Harvey armour.

Krupp cemented armour

By the early twentieth century, Krupp armour was rendered obsolete by the development of Krupp cemented armour (also "Krupp cemented steel", "K.C. armor" or "KCA"), an evolved variant of Krupp armour. The manufacturing process remained largely the same, with slight changes in the alloy composition: in % of total – carbon 0.35, nickel 3.90, chromium 2.00, manganese 0.35, silicon 0.07, phosphorus 0.025, sulfur 0.020. KCA retained the hardened face of Krupp armour via the application of carbonized gases but also retained a much greater fibrous elasticity on the rear of the plate. This increased elasticity greatly reduced the incidence of

spalling Spall are fragments of a material that are broken off a larger solid body. It can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ba ...

and cracking under incoming fire, a valuable quality during long engagements. Ballistic testing shows that KCA and Krupp armour were roughly equal in other respects.

Homogeneous Krupp-type armour

Developments in face-hardened armour in the late nineteenth and early to mid-twentieth centuries revealed that such armour was less effective against glancing oblique impacts. The hardened face layer's brittleness was counterproductive against such impacts. Consequently, alongside face hardened armour such as KCA, homogeneous armour types that combined ductility and tensile strength were developed to protect against glancing impacts. Homogeneous armour was typically used for deck armour, which is subject to more high-obliquity impacts and, on some warships such as and battleships, for lower belt armour below the waterline to protect against shells that land short and dive underwater. Examples of such armour include German ''Wotan weich'' (Ww) and US

special treatment steel Special treatment steel (STS), also known as protective deck plate, was a type of warship armor developed by Carnegie Steel around 1910. History STS is a homogeneous Krupp-type steel developed around 1910. The development of such homogeneous st ...

(STS) and Class B homogeneous armour.TABLE OF METALLURGICAL PROPERTIES OF NAVAL ARMOR AND CONSTRUCTION MATERIALS
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References

Bibliography

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