Laminated steel blade
Encyclopedia
A laminated steel blade or piled steel is a knife
, sword
, or other tool
blade made out of layers of differing types of steel
, rather than a single homogeneous alloy
. The earliest steel blades were laminated out of necessity, due to the early bloomery
method of smelt
ing iron
, which made production of steel expensive and inconsistent. Laminated steel offered both a way to average out the properties of the steel, as well as a way to restrict high carbon steel to the areas that needed it most. Laminated steel blades are still produced today for specialized applications, where different requirements at different points in the blade are met by use of different alloys, forge
d together into a single blade.
. The bloomery does not generate temperatures high enough to melt iron and steel, but instead reduces
the iron oxide
ore
into particles of pure iron
, which then weld into a mass of sponge iron, consisting of lumps of impurities in a matrix of relatively pure iron, with a carbon content of around 0.06%. The bloom must then be heated and hammered to work out the impurities, resulting in the relatively soft wrought iron
.
Iron is too soft to make a good cutting edge; a good edge requires the addition of carbon
to make steel. By heating thin iron rods in a carbon-rich forge, carbon could be added to the surface, making a thin layer of steel on the surface through a process called carburization
(see also case hardening
). From the beginning of the iron age, around 1200 BC, piled steel was the only way to get good steel. Obtaining the right level of carbon was an art, and was very important to the finished product. Too much carbon, or too many of the wrong trace elements, and the resulting steel becomes too hard and brittle, which can result in a catastrophic failure of a sword; too little carbon and the sword will not hold an edge. The ideal sword is one with a hard, sharp edge, and tough enough to bend, but not to shatter.
Blending a number of different pieces of iron and steel together averaged out the properties, ensuring that one bad piece would not produce a total failure of the finished product. This laminating different alloys together produces patterns that, with proper treatment, can be seen in the surface of the finished blade, and this forms the basis for pattern welding.
Since producing high carbon steel from wrought iron was very difficult, careful lamination of different alloys also served to conserve this difficult-to-make steel by using it only for the parts of the blades where it was needed. Many swords were made with the minimum possible amount of high carbon steel along the cutting edge, with the rest of the blade being made of low carbon steel or wrought iron. A thin strip of high carbon steel could be laminate
d between two layers of softer steel, or a core of soft steel could be wrapped in high carbon steel. The Japanese katana
was often found with complex patterns of soft and hard steels; having 5 sections of differing hardness welded together to form the final blade was not uncommon. The end result would be a blade with a very high carbon edge (as much as 1.0%, equal to the highest carbon content found in low alloy steels in use today) and a softer spine. The very hard, but brittle, edge made the swords extremely sharp, while the spine gave the blade flexibility, so that it would bend rather than break.
Many laminated steel blades, particularly those of the Viking
s, also used complex structures of steel to produce patterns
in the surface of the steel. These patterns were made by manipulating the piles, by twisting or otherwise distorting the piles, before they were forged into the blade.
Knife
A knife is a cutting tool with an exposed cutting edge or blade, hand-held or otherwise, with or without a handle. Knives were used at least two-and-a-half million years ago, as evidenced by the Oldowan tools...
, sword
Sword
A sword is a bladed weapon used primarily for cutting or thrusting. The precise definition of the term varies with the historical epoch or the geographical region under consideration...
, or other tool
Tool
A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tools that are used in particular fields or activities may have different designations such...
blade made out of layers of differing types of steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
, rather than a single homogeneous alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
. The earliest steel blades were laminated out of necessity, due to the early bloomery
Bloomery
A bloomery is a type of furnace once widely used for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. A bloomery's product is a porous mass of iron and slag called a bloom. This mix of slag and iron in the bloom is termed sponge iron, which...
method of smelt
Smelting
Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores...
ing iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
, which made production of steel expensive and inconsistent. Laminated steel offered both a way to average out the properties of the steel, as well as a way to restrict high carbon steel to the areas that needed it most. Laminated steel blades are still produced today for specialized applications, where different requirements at different points in the blade are met by use of different alloys, forge
Forge
A forge is a hearth used for forging. The term "forge" can also refer to the workplace of a smith or a blacksmith, although the term smithy is then more commonly used.The basic smithy contains a forge, also known as a hearth, for heating metals...
d together into a single blade.
Technique
Piled steel developed out of the necessarily complex process of making blades that were both hard and tough from the erratic and unsuitable output from early iron smelting in bloomeriesBloomery
A bloomery is a type of furnace once widely used for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. A bloomery's product is a porous mass of iron and slag called a bloom. This mix of slag and iron in the bloom is termed sponge iron, which...
. The bloomery does not generate temperatures high enough to melt iron and steel, but instead reduces
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
the iron oxide
Iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...
ore
Ore
An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....
into particles of pure iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
, which then weld into a mass of sponge iron, consisting of lumps of impurities in a matrix of relatively pure iron, with a carbon content of around 0.06%. The bloom must then be heated and hammered to work out the impurities, resulting in the relatively soft wrought iron
Wrought iron
thumb|The [[Eiffel tower]] is constructed from [[puddle iron]], a form of wrought ironWrought iron is an iron alloy with a very low carbon...
.
Iron is too soft to make a good cutting edge; a good edge requires the addition of carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
to make steel. By heating thin iron rods in a carbon-rich forge, carbon could be added to the surface, making a thin layer of steel on the surface through a process called carburization
Carburization
Carburizing, spelled carburising in the UK, is a heat treatment process in which iron or steel is heated in the presence of another material which liberates carbon as it decomposes. Depending on the amount of time and temperature, the affected area can vary in carbon content...
(see also case hardening
Case hardening
Case hardening or surface hardening is the process of hardening the surface of a metal, often a low carbon steel, by infusing elements into the material's surface, forming a thin layer of a harder alloy...
). From the beginning of the iron age, around 1200 BC, piled steel was the only way to get good steel. Obtaining the right level of carbon was an art, and was very important to the finished product. Too much carbon, or too many of the wrong trace elements, and the resulting steel becomes too hard and brittle, which can result in a catastrophic failure of a sword; too little carbon and the sword will not hold an edge. The ideal sword is one with a hard, sharp edge, and tough enough to bend, but not to shatter.
Blending a number of different pieces of iron and steel together averaged out the properties, ensuring that one bad piece would not produce a total failure of the finished product. This laminating different alloys together produces patterns that, with proper treatment, can be seen in the surface of the finished blade, and this forms the basis for pattern welding.
Other uses of laminated steel
Laminate
A laminate is a material that can be constructed by uniting two or more layers of material together. The process of creating a laminate is lamination, which in common parlance refers to the placing of something between layers of plastic and gluing them with heat and/or pressure, usually with an...
d between two layers of softer steel, or a core of soft steel could be wrapped in high carbon steel. The Japanese katana
Katana
A Japanese sword, or , is one of the traditional bladed weapons of Japan. There are several types of Japanese swords, according to size, field of application and method of manufacture.-Description:...
was often found with complex patterns of soft and hard steels; having 5 sections of differing hardness welded together to form the final blade was not uncommon. The end result would be a blade with a very high carbon edge (as much as 1.0%, equal to the highest carbon content found in low alloy steels in use today) and a softer spine. The very hard, but brittle, edge made the swords extremely sharp, while the spine gave the blade flexibility, so that it would bend rather than break.
Many laminated steel blades, particularly those of the Viking
Viking
The term Viking is customarily used to refer to the Norse explorers, warriors, merchants, and pirates who raided, traded, explored and settled in wide areas of Europe, Asia and the North Atlantic islands from the late 8th to the mid-11th century.These Norsemen used their famed longships to...
s, also used complex structures of steel to produce patterns
Pattern welding
Pattern welding is the practice in sword and knife making of forming a blade of several metal pieces of differing composition that are forge-welded together and twisted and manipulated to form a pattern. Often called Damascus steel, blades forged in this manner often display bands of slightly...
in the surface of the steel. These patterns were made by manipulating the piles, by twisting or otherwise distorting the piles, before they were forged into the blade.