News and Announcements

--News & Announcements--

Over the next 6 months, I won't be getting much time in the shop, or anywhere else for that matter due to a change in work schedule. However, there are a number of posts I have already worked out. In the coming weeks, I will hopefully have enough time to get them out there.

Watch for--
Excursion into Onesquethaw Cave
Ascent of Mount Washington
Iron Age bellows build

Saturday, December 20, 2014

on Iron [Part II]

A Prelude to Heat Treatment


It was originally my intention to cover heat treatment here, but I quickly realized that the level of detail I wished to achieve made combining the prerequisite information with those processes nothing short of cumbersome. So, the ultimate purpose of this exploration of knowledge must once again wait for a future post. Until then, below is a brief summary of those topics.


Molecular Geometry
Steel, or more specifically Iron, has the ability to take on various arrangements in its metallic lattice structure (as a solid), which are called allotropes. When pure iron is alloyed with other elements (namely carbon, amongst others), the amount of those elements changes the material properties of the alloy, and as a result, the temperature at which the allotropes exist. Those temperatures will be specific to each alloy (which includes the percentage of alloyed elements).
There are seven atomic crystal systems, although iron exists only in the Cubic system. Each of the seven systems have multiple variations depending on the non-corner nuclei, which define the geometry. This principle is important for the phases of steel. The seven systems are, for only the point of distinction, summarized below.

            -Triclinic- Each length of the sides is exclusively different, and the angles between lengths are also exclusively unequal.

            -Monoclinic- A prism where the ends are two parallelograms, where the angles of the non-parallelogram faces are 90 (perfect rectangles).

            -Orthorhombic- A rectangular prism where the faces have side-pairs of exclusively unequal lengths, resulting in three orthogonal pairs of parallel sides. (None of the faces are squares, but are all rectangles). The Cementite phase of steel exists in this form.

            -Tetragonal- The two end faces are square and parallel, resulting in the four side faces being equal rectangles. The martensitic phase of steel forms a body centred tetragonal lattice.

            -Hexagonal- A hexagonal prism with the ends being regular hexagons. An additional nucleus rests in the centre of each hexagonal face.

            -Trigonal- A system which is composed of a rhombus superimposed with an extruded regular hexagon, called a rhombohedron.

                                                  
                                    

Body Centred Tetragonal                                                  Orthorhombic
      (Martensite)                                                                 (Cementite)



Cubic Crystal System- This is the important system for the context of steel. The unit cell is an isometric lattice, meaning each side is of equal length and adjoining angle (perfect cube). There are three variations of the cubic system, of which the later two are found in steel.

            Primitive- Only the eight corner nuclei exist in the structure. It is the simplest of the cubic crystals.

            Body Centred Cubic- (cB, or bcc) A ninth nucleus rests in the centre of the eight corners. This is the predominant stable form of iron at room temperature (more will be discussed later). Due to the packing of the nuclei in this fashion, the cB unit cell has a relatively small packing factor of .68 (a measure of how tightly spheres are packed in a space, with 1 (impossible) being 100% of the space). In steel, different phases may transition to body centred tetragonal (as martensite), which is similar to cB excepting that one dimension is stretched to form a rectangle, while the angles and remaining two dimensions are unchanged.

                               
                         
  Body Centred Cubic                                                                     Face Centred Cubic
     (Ferrite)                                                                                       (Austenite)


            Face Centred Cubic- (cF, or fcc) In addition to the eight corner nuclei, there is an additional one in each of the centre of each face (but not centre of the entire cube), for a total of fourteen nuclei. Because the atom volume is constant between cells, the atoms in a cF cell are more tightly packed. This arrangement yields a packing factor of .74048 (which is the theoretical maximum for any sphere packing orientation). Because the atoms are so tightly packed, the cF cell is the most dense, which means it also occupies a smaller volume than the same number of atoms in a cB lattice cell. Iron in this form is called Austenite.




Phases of Steel

Along with molecular geometry, steel exists in various phases depending on its temperature. These allotropes are significant when it comes to heat treatment and the forging of steel. Temperatures at which these transitions occur (assuming no change in pressure) is dependent on the alloy of the particular grade of steel.

Delta Iron- (δ-Fe) When pure (elemental) liquid iron solidifies, which is approximately 1,540 °C (2,800 °F), this is the first form it takes. The molecular geometry is a cB lattice, and it remains in this form until cooing an additional 144 °C.

Gamma Iron- (γ-Fe) After reaching 1,394 °C, the iron becomes austenitic, meaning it transitions to a face centred cubic lattice, which is more closely packed than the body centred lattice and thus reduces in volume slightly (~8%). γ-Fe is capable of dissolving over 2% more carbon than other, lower temperature phases of iron.

Alpha Iron- (α-Fe) Below  912 °C (1,674 °F), pure iron transitions back to a cB lattice structure. If pure α-Fe exists in this form, it is also called Ferrite. α-Fe saturation for carbon is only .021% by weight, which is significantly lower than the previously mentioned γ-Fe. Depending on the temperature, Alpha Iron can exist in two forms, depending on its magnetic properties. Below the Curie Temperature (Tc), the temperature at which the metal transitions between being paramagnetic and ferromagnetic, the iron is considered only to be α-Fe. For pure iron, this temperature is 770 °C (1,418 °F), and below which the Ferrite is ferromagnetic, meaning it will respond to a magnetic field.

            Beta Iron- (β-Fe ) Above Tc but below the phase transition to Ferrite, the lattice (still body centred cubic), becomes paramagnetic. Beta Iron is identical to Alpha Iron excepting this difference. Due to the loss of magnetic response above the Curie Temperature, it is often used as a reference for simple high carbon steels during heat treatment. However, the difference (in pure iron, which decreases in eutectic steels) is still 142 °C (256 °F), which is fairly significant given the impossibility of hardening below the cB/cF transition.




Alloying Iron and the Crystal Structure

To alloy steel, additional elements must be introduced to the lattice. Because the distance between lattice points (centres spheres that represent the entirety of the atom which occupies that space) is dependent on the atoms that form the lattice, introduction of other atoms will change the crystal structure around that flaw. Several types of point defects exist within the crystal lattice, where two general types of involve the introduction of non-lattice elements. How the lattice is effected by the defects will determine many of the material properties in addition to what the particular atom is that causes that defect. Defects by definition do not change the classification of the parent crystal lattice system. It is also worth mentioning that a metallic alloy, rather than a specific repeated molecule like SiO2 in quartz which has a tetragonal base crystal lattice, there no base lattices that uniformly include all of the elements found within it. However, in certain situations, such as in steel, there can be centralized lattices between some of the alloyed elements (namely in the iron-carbon system, while the additional alloyed elements remain substitutional or interstitial defects).

            Vacancies- A type of lattice defect that exists in all lattices, whether or not there is a non-base atom introduced. This is a hole in the lattice where a lattice point would regularly have an atom reside. Because these defects always exist, all ductile metallic lattices can be work hardened, meaning the mechanical deformation of the lattice which results in the pinning of these defects in positions which require high amounts of energy to move.

            Substitutional- Point defects where a single lattice point of a uniform lattice is replaced with another element. In the case of steel, this will not replace iron with carbon, instead being additional alloyed elements such as vanadium or chromium. Depending on the relative size of the substituted element, the lattice will undertake compressive and tensile stress to accommodate the difference. The immediate neighbours of the substitutional point defect will experience the largest stress, while those farther out will experience little change.

            Interstitial- Point defects where additional lattice points are introduced between the normal points. In steel formed with ferrite, carbon is an interstitial defect, and occupies a space approximately twice the equivalent spherical volume of the interstitial holes present in the carbon, which introduces a large amount of stress to the structure and why the maximum dissolved carbon content is .021%.

Pinning of dislocations, whether vacancies, substitutions, or interstitial defects, will cause the material to become harder and more brittle, as the dislocations will require more energy to shift to an unpinned position. As a result, all metals which are capable of undertaking plastic deformation without failure are capable of work hardening. This also means that work hardening of a hardenable alloy of steel is distinctly different from the phase transformation which can harden it via quenching. Additionally, it should be noted that defects in steel will undergo diffusion, so alloy gradients will slowly equalize over time. At higher temperatures, this occurs more rapidly, as the defect atom (interstitial or substitutional) is given more energy to move out of the lattice position it occupies. Similarly, pinned defects will migrate to equilibrium within the material over time, again more rapidly at higher temperature, which may re-locate them from their pinned, dislocated position.




Eutectoid and Eutectic principles

A eutectic system is one in which two components at a given state (i.e. solid) can coexist at a certain temperature with their combined liquid form.

For the purposes of explanation, [A] and [B] will be two constituent materials which, when both melted, form a homogeneous material [C]. If the ratio of [A] to [B] is too low, [A] will begin to precipitate out of the liquid solution before [B], meaning [A] and [C] will exist at the same time. However, if there is too much of material [B], then it too will solidify first, leaving [B] and [C] to coexist. Now, if the ratio of [A] and [B] is at the eutectic composition, then [A], [B], and [C] will all exist at the same critical, eutectic temperature. At that ratio, the material is said to be in a eutectic system. It should be noted that not all systems have a eutectic ratio, most notable a mixture of silver and gold (Electrum).

When the phase of [C] is a solid instead of a liquid, but at some temperature a solid phase transition still occurs (of a crystal lattice), the material has a eutectoid temperature (as opposed to eutectic). This sort of system, which is illustrated above, exists for the forms of an iron/carbon mixture. At the eutectoid temperature 727 °C (1,341 °F) for the iron-carbon (Fe-C) system, Austenite, Ferrite, and Cementite all coexist simultaneously. For the Fe-C system, the eutectoid composition ratio is .76% Carbon by weight. Above the eutectoid temperature, Austenite (γ-Fe) exists, while below, a mixture of Ferrite (α-Fe) and Cementite forms. Should there be an excess of Ferrite, and thus iron, the steel will be a hypoeutectoid (below the eutectoid ratio); and if there is an excess of Cementite, and thus carbon, it will be a hypereutectoid.

Importantly, if a system has both a eutectoid and eutectic temperature, which the Fe-C system does, those two temperatures are not necessarily the same (and are quite different for steel).
A final note on eutectoids as they pertain to steel is that the presence of additional alloying elements changes the eutectoid ratio and temperature for that particular alloy. For example, Nickel and Chromium both lower the eutectoid ratio for carbon in steel.



Phases and Microstructures of Steel

Before understanding the heat treatment process, it is important to examine the forms of steel as it exists within the crystal structure. There is a distinct difference between phases and microstructures, although the terminology common between them is often confused. Phases are a product of the intermolecular kinetic energy distribution, whereas microstructures are, as mentioned in the discussion of native and meteoric iron, a relative arrangement of macro-lattices (as opposed to the crystal system micro-lattices). Both the phase and microstructure can have dramatic effects on the working properties of the steel, whether ductility, hardness, brittleness, strength, reaction to strain, conductivity, magnetic reaction, amongst many others. The following list is not meant to be all inclusive, but rather comprised of those relevant to bladesmithing.

-Phases-

            Ferrite- As aforementioned, ferrite is the cB crystal structure of pure iron. Ferrite does not exist as an alloy, although it can and often does exist in localized concentrations of iron based metals. When combined with other phase concentrations, ferrite can form certain microstructures. Maximum carbon content of .021% by weight.

            Austenite- Also mentioned above, γ-Fe is the cF, paramagnetic allotrope of iron that exists above 1,394 °C. This phase transition begins in pure iron at 912 °C where the first cB lattices change to cF, which, due to the change in atomic density, is able to dissolve approximately 2% more carbon. This is important when concerning heat treatment of steel and will be later discussed.

            Cementite- Iron Carbide (Fe3C), which is an orthorhombic base crystal lattice form. When combined with Ferrite, it commonly forms the Pearlite microstructure. In the orthorhombic system in which the lengths of the sides are stretched from their cubic form (three side sets are all inequal length but intersect at right angles), carbon is more easily accommodated in the interstitial holes. As a result, the interstitial stress is less significant and the lattice can hold more carbon before becoming unstable. Cementite is, in its pure form, 6.67% carbon. As Austenite cools, carbon diffuses into pockets that form cementite to take in what the Ferrite cannot hold. Cementite is extremely hard and brittle (a ceramic if pure Fe3C).

            Martensite- When Austenite is cooled with sufficient speed (varies with the alloy of steel), instead of being converted back to ferrite and cementite, the carbon is trapped in the lattice and forms a body cantered tetragonal structure that is, in effect, a super saturated form of ferrite. Due to the excess carbon held here instead of in localized pockets as cementite, there is a comparatively high amount of internal stress due to these interstitial carbon atoms being pinned in the tetragonal lattice. This is where Martensite gains its hardness, as the pinned shear dislocations do not permit the movement of defects across the lattice. Martensite is approximately 1.75x harder than pearlite on the Brinell scale. Different alloys of steel have different hardenability depending on the carbon concentration, as that is the determining factor of how much of the lattice is held in the martensitic form rather than lesser concentrations of carbon which return instead to ferrite or cementite. Past the eutectoid point, larger amounts of cementite will precipitate due to the larger stable ratio of carbon to iron (Fe3C).  Since Martensite is in a state unattainable in thermodynamic equilibrium, the introduction of thermal energy allows the Martensite lattice to convert back to cementite and ferrite due to the increased diffusion rate of dislocations. Of a lower density per lattice cell than Austenite, Martensitic conversion results in a volumetric expansion when formed. This mostly accounts for the curvature achieved through differential hardening of single edged blades and the warps and bends of thin cross sectional areas.

-Microstructures-

            Grains- All metals have grains. When cooled from a liquid state, imperfections in the metal called nucleation sites (non-alloying elements, foreign molecules, alloys of a higher melting temperature, etc.) are where crystalline lattices begin to grow. Since there is nothing that forces them to align in any particular fashion, the spatial orientation is random. The more energy that is transferred from the cooling metal to the growth of solid via metallic bonds, the larger the crystals grow outwards or, if the conditions are right, the growth at new nucleation sites. When the randomly oriented crystals meet, they form grain boundaries and stop growing. Since the crystal faces are not aligned, the bonds there will be weaker than inside the newly formed grains and of a higher stress. Because of this, the fewer the total number of grains and thus larger in size, the more ductile the material (as it will be more accepting of dislocation diffusion). Due to the stress concentrations of grain boundaries, materials tend to fail along those boundaries rather than through the grains themselves. Grain size and growth can be determined during many formative and heat treating processes, which will later be discussed in detail, whereas the shape of the grain boundaries is determined by other material properties (lamella, lenticular, spheroidic, acicular, etc.).

            Pearlite- Perhaps the most common microstructure of steel, a quasi-homogeneous combination of 88% Ferrite and 22% Cementite by weight. As shown in the above eutectic phase diagram, pearlite is formed by the cooling of Austenite below the critical temperature. In a given alloy, pearlite can exist along with cementite and ferrite, depending on the carbon concentration relative to the percent utilization by the pearlite (~1.5906% Carbon by weight). Within the pearlite complex, alternating layers of the carbon rich cementite and carbon deficient ferrite form a lamellar type microstructure (discussed previously with native iron).

            Bainite- Very similar to pearlite in that it is composed of ferrite and cementite. Bainite is formed from a more rapid cooling of austenite than when pearlite is formed, yet not so quickly that it instead converts to Martensite. However, instead of the lamella that pearlite grows, Bainite produces a radiating needle like patterns of ferrite clustered at a central nucleation point, called acicular crystals. Between the sheaves, cementite fills the voids, or in other phase transformations, Martensite or retained Austenite. Due to this structure, it is not as ductile as pearlite, although it is measurably harder. For this reason, and the fact that the tremendous internal stress of Martensite is not present, there is no need to temper or otherwise heat treat Bainite after its formation to retain its hardness.

            Widmanstätten Patterns- First introduced during the discussion of native and meteoric iron, Widmanstätten patterns are the product of iron-nickel crystal growth from the alternating layers of Taenite and Kamacite. The lamella meet at 60 degree angles and, due to the difference in diffusive properties between the iron and nickel, become easily visible on the surface. Beyond native and meteoric iron, these are relatively uncommon to metalworking.


            Tempered Martensite- In the formation of Martensite, the steel is subjected to a high internal stress. To relive that stress yet retain some of the hardness of the martensitic crystals, the material is tempered, allowing the decomposition of the body cantered tetragonal structure into a more stable form (cementite, ferrite, or together to become pearlite). While this process occurs, layers of Martensite form beside the other two phases of steel or beside pearlite. This forms, along with the intermediate microstructures, a final layered composition of lower internal stress while retaining hardness proportional to the temperature at which the martensitic steel was tempered (how much thermal energy was given to the steel determines the threshold for the energy required for a dislocation to be unpinned) and the time at which that temperature was held (unpinning of dislocations is a measure of probability, meaning longer times at that energy increases the chance for dislocations being freed at or below that energy also increases). In this sense, the degradation of Martensite is the result of the martensitic lattice, reaching thermodynamic equilibrium through the collapse of its structure into new, lower stress crystals. 

Sunday, November 23, 2014

on Iron [Part I]

Aspects of Metallurgical Chemistry

Over the course of my endeavours in bladesmithing, I have come across a vast amount of knowledge as it pertains to the chemistry behind steel, its origins, refinement, heat treatment, and formative processes which turn rocks into swords. In the interest of paying it forward, I decided to begin constructing a document which outlines the basic differences, processes, and general information to help eliminate the misnomers and misinformation that I often hear. Part II will follow in the next few weeks after I consolidate information as it pertains to heat treatment and the micro-chemistry of steel. Until then, below is an introduction to iron, steel, and the varying methods of processing ore and its subsequent refinement.

Because I myself am far from an expert on this information, the information here may be periodically updated or expand upon to ensure everything is as accurate as possible.

Naturally Occurring Iron


Ore- Any mineral aggregate that contains extractable metals that are bound in the mineral's crystalline structure.

            Magnetite- Naturally occurring ore with the highest average carbon content of 72.4% in the form of Iron (II,III) Oxide, Fe3O4. In its natural state, it can be either non-magnetic, or magnetic (called lodestone). In its pure state, Magnetite acts as a passive rust layer which inhibits further oxidation when exposed to a corrosive environment. Chemical bluing involves the formation of a thin Iron (II,III) Oxide layer on the surface of iron or steel.

                        Taconite- A silicate crystal (usually in the form of quartz and chert) laced with iron. Although typically trapped as magnetite, the 25~30% iron content can also be composed of hematite.
                        Iron Sand- A variety of sand which contains fine magnetite along with trace amounts of other alloying elements. 

            Hematite- (Ferrous ferric oxide) Second highest carbon containing, naturally occurring ore with C~69.9% in the form of Iron (II) Oxide, Fe2O3. Red rust is Iron (II) Oxide, which readily forms when exposed to water or corrosive environments. When exposed to oxygen and sufficient thermal energy, it can be converted to Magnetite.

                        Specular Hematite- Hematite is naturally found in a variety of forms and colours, the most metallic of which is called specular hematite. It is an area differential form with skewed co-linear/planar isometric lattices of Iron (II) Oxide. It derives its name and silvery reflective colour from the specular diffraction of light off the random variant angled layers, which each reflect light in parallel rays (as opposed to diffuse which scatters and has a matte reflective surface).

            Wüstite- FeO. Found in this state most commonly in native iron and genesis in non-atmospheric space (meteorites). Wüstite strongly interacts with silicates, oxidizes to form goethite-limonite, and in reduction/oxidation reactions with various minerals. Some of the related forms stem from Magnesium (periclase, brucite, diopside, magnesite, olivine, etc.), Calcium (wollastonite, enstatite, diopside), Silicon (pyroxene, olivine, etc.), and Carbonites amongst others.

            Iron Hydroxides- There are two major sources of iron that come from iron hydroxides (OH group), each of which yielding a significant percentage of iron when reduced. Of Goethite (FeO(OH), approximately 63% iron content and commonly used as pigments) and Limonite (FeO(OH).n(H2O)), Limonite is more commonly associated with iron ore. Limonite has historically been one of the major sources for iron, and is the primary constituent of bog ore.

            Ironstone- An iron based sedimentary rock that once provided a source of iron until more accessible and higher yield (magnetite and hematite) were made available. The yield is relatively low compared to other ores.

            Native Iron- Telluric Iron. A non-ore based concentration (metallic form) of iron. Rarely occurs naturally except in the region of Disco, Greenland. Although it shares a strong resemblance with meteoric iron, the nickel content is significantly lower. The nickel-iron crystals form a distinctive Widmanstätten pattern of lamella (small sheets, in this case varying between Taenite [high ratio of nickel] and Kamacite [high ratio of iron]) at 60 degree angles.

                        Type I- A natural form of cast iron with Carbon between 1.7~4% and Nickel content between .05~4%. Found in large metamorphosed igneous rocks varying from tonnes to tens of tonnes in weight.
                        Type II- Comparable nickel content to Type I native iron, but with far less carbon, usually less than .7%. Type II is much easier to work due to the lower concentration of carbon, worked easily into iron based tools (knives). Rather than being entwined in the metamorphic rock, Type II native iron formed in small granules trapped inside volcanic basalt, although it is not uncommon for the grains to be sintered (fused without being first melted- forge welding is a form of sintering) into larger masses.

            Meteoric Iron- A form of native iron that originates outside of earth. It has a lower carbon content and higher nickel content than terrestrial native iron. Meteoric iron exhibits the same Widmanstätten patterns of lamella. There are four forms of meteoric iron which are distinguished by their relative nickel content and crystalline structure with iron, most notably as the iron carbide Cementite.

Lesser Iron Containing Ores and Minerals- Many other non-precious ores contain iron in the lattice due to its natural abundance and ability to form 8 different oxidation states, and exist as an amphoteric (acidic or basic) oxide. As a result, traces of iron usually cohabit other common metals in that metal's primary ore source, although the yield of iron from extraction is uneconomical due to sacrificial losses of the other alloying element after which the ore was likely harvested to obtain.

            Pyrite/Iron Pyrite- FeS2. Also called Fool's Gold. Because of its ability to spark when struck, it was revered for use in early firearms.
            Ilmenite- FeTiO3, Iron and Titanium ore, the largest source for elemental Titanium (Ti)
            Chromite- (Fe, Mg)Cr2O4, the most common ore for extraction of elemental chromium (Cr)
            Cobaltite- (Co, Fe)AsS, source of elemental Cobalt (Co)
            Wolframite- (Fe,Mn)WO4, common source of elemental Tungsten (W)



Processed Forms of Iron


Over the centuries, iron has been processed in a multitude of ways, each of which yielding a distinct form of iron or steel. Modern steel is produced largely by precise, crucible processes that result in a relatively homogeneous, high tolerance alloy. Such alloys and the effects of the alloying elements will be discussed later. Below is an examination of the processed forms of iron and their distinction from one another.

Iron- A ductile transition metal that, in its most stable form exists as Fe-56 (26 protons), and is one of the most stable nuclei of any element. Iron has two molecular structures, body centred and face centred cubic (which are important for the hardenability of steel). Second only to oil, iron is the most driving extraction-economy in the world. Annually, the world's processing of iron ore exceeds 1,856 million tonnes.

Steel- Steel itself is, in its simplest form, an alloy of carbon and iron. Various other alloying elements can be introduced to change the properties of the steel, such as corrosion resistance, strength, impact resistance, and high temperature applications. A continuation of the discussion of Modern Steels can be found in its own heading below.

            Carbon Steel- I find this to be one of the most poorly named 'types' of steel, given that all steel has carbon in it. However, specifically Carbon Steel is any ally of steel with .12~2.0% C content. The American Iron and Steel Institute more specifically defines Carbon Steel by its constituent alloys (no specified range for carbon content). There is a maximum percentage for Manganese (1.65%), Silicon (.60%), and Copper (.60%). However, there is no minimum value for chromium, cobalt, niobium, molybdenum, nickel, titanium, tungsten, vanadium or zirconium.

Pig Iron- The resultant reduction of iron containing ore through a blast furnace, usually 3.4~4.5% C, brittle by nature, and mixed with dross (solid mass of impurities; equivalent solid of slag, which is by definition liquid), strongly consisting of silicates. Intermediate form of steel as a result of smelting in a carbon rich environment. Historically refined into wrought iron. Pig iron derives its name by how it is cast into ingots, resembling piglets suckling a sow. A row of the molten pig iron is poured into a sand mould, to which triangular ingots branch off to either side where they are broken off after cooling.
Puddle Iron- To refine pig iron, ingots were layered in a puddling furnace, similar to the ore/charcoal layers of a bloomery furnace. After the ingots melted, the liquid metal would form a puddle at the bottom. A combination of stirring and the passage of air over the surface allowed diatomic oxygen to react with the liquefied slag (silicon, manganese, phosphorous, and sulphur), which would react to form gaseous byproducts and purify the liquid steel. The carbon content is also reduced from the cast iron range into wrought iron (less than .1%) by forming gaseous carbon dioxide.

Blister Steel- 1.2~1.8% Carbon steel carburized from wrought iron through cementation. Because of carbon migration and diffusion, the carburized bars have a gradient of carbon from the edge to the centre. Although the process originated in Prague, cementation is most notably remembered in Sheffield, England.

Shear Steel- To further refine and homogenize blister steel, the carburized members are sintered (forge welded) together and forged to a smaller cross section which will have a more uniform carbon distribution. The resultant is shear steel.

Wrought Iron- A low carbon iron alloy, ranging between .04~.08% C, which contains comparably large amounts of slag. The grain of the wrought iron has a distinct direction and composes up to 2% of total mass.

Cast Iron- 2.1~4% Carbon containing steel, usually alloyed with silicon in the range of 1~3%. Excepting malleable cast iron (either Blackheart, Whiteheart, or Pearlitic malleable iron depending on the pearlite/ferrite matrix produced in heat treatment), cast iron tends to be brittle and difficult to work. Originally cast iron was a resultant product of pig iron. Depending on the ration of carbon to alloying elements, and the respective banding of these elements, cast iron has two basic forms.

             Grey Cast Iron- Predominating structure is composed of carbon based allotropic graphite. This is the most common form of cast iron, and produces a grey granulated surface when broken. Due to the graphite concentration, which is stabilized by the presence of silicon, internal stress is distributed as a polyhedral array. Resulting cracks propagate in dendritic fractures across the graphite flakes. When broken, the exposed surface is grey in colour.

            White Cast Iron- Predominating structure is built by carbide strands, most predominantly iron carbides but with additional slag element based carbides. These carbides allow stress and cracking to pass straight through the material unopposed, which when broken yields a white granulated surface.

Bloomery Steel- (Sponge Iron) The product of reducing iron oxides (ore) into a bloom, a porous combination of metallic iron and slag. Iron is precipitated from the iron oxide and removed from the silicates encasing it. In its unrefined form, bloom is high in slag and unusable without consolidation. Layers of ore and charcoal or coal are fed into the chimney of a bloomery furnace where the melted iron collects at the bottom, allowing it the possibility to carburize (based on the burn rate, air flow, fuel, and a number of other factors). The position of the tuyere, a pipe through which air enters the furnace, in the furnace itself will also vary the carbon content of the bloom.

            Tamahagane- The equivalent of sponge iron, which translates to Jewel Steel. Tamahagane results from the bloomery process and in this form is no further refined.
            Oroshigane- In Japanese metallurgy, Oroshigane is sword quality steel that is the product of refining tamahagane. It is not uncommon for the bladesmith to refine the Tamahagane in order to produce more exacting specifications for the piece it will become.

Hearth Steel- Steel refined or altered from one pre-existing metallic state to another through melting. A variety of different constructions for open hearth furnaces, such as Aristotle or Evenstad furnace, which can both purify, consolidate, and carburize/decarburize the input steel or iron. Blooms are not made in hearths.

Crucible Steel- Original crucible steel involved the melting of iron in excess of carbon to carburize the resultant puck into steel. In modern context, crucible steel has become in some ways comparable to wootz when the dendrites form upon cooling of the liquid steel matrix. Carburization is still possible, however it is not necessary for the formation or consolidation of steel in a crucible. 

Brescian Steel- Carburized low carbon steel by exposure at high temperatures to liquid steel with a very high carbon content, usually of cast iron or higher. The Paal, or Brescian process, originally involved taking a solidified bloom and submerging it in liquid cast iron (which has a lower melting point than lower % carbon steels) for a length of time until the carbon of the cast iron migrated into the lower carbon bloom. This was performed in a hearth, but has in modern times come to involve the carburization of homogeneous steels in cast iron melted in gas or induction furnaces where temperature control is more precise.

Wootz- Of Indian origin, possibly specifically to Persia before the spread of the ancient steel making process, wootz is a high carbon steel ranging between 1~2% carbon. Archaeological evidence suggests that wootz was made as a crucible steel in large, mound shaped furnaces as described by the late 17th century archaeologist Francis Buchanan. Although the precise mechanism for modern reproduction of the ancient wootz steel is unknown, the distinctive dendritic carbide grain pattern has been achieved in small scale crucible steel. For its time, wootz was far superior to the other refinement methods of steel and vastly out performed its peers in both strength and hardness. The word wootz itself is an adaption of the Persian name for steel.

Damascus- Much like wootz, modern knowledge of the original Damascus steel has been lost. It is theorized that Damascus steel was the product of the Persian knowledge being brought to Damascus, Syria where smiths could process the wootz into tools and blades. The distinctive damascene pattern that resulted in such pieces were a result of the texturing (a metallurgical term for the partial alignment of crystal grain boundaries due to mechanical deformation) represent rippling or waves. These patterns were made visible through polishing or etching. In modern times, Damascus is often used in reference to Pattern Welded steel, where similar patterns are a result of multiple, alternating layers of different alloys (such as 1080/15n20) where one metal is has different hardenability or chemical resistance from the other.

Pattern Welded Steel- A generic term used to describe the forge welding (or fire welding) of alternating layers of different steels or likewise weldable materials into a billet in order to produce a visual pattern in the finished piece. Perhaps the most common is 'random pattern' in which nothing is done to the layers beyond welding and folding or stacking to increase the layer count. Ranges in the tens of thousands of layers is not unreasonable, as each time a billet is folded in half, the count is doubled (or tripled if cut in thirds, quadrupled in fourths, etc.), and thus increases rapidly. With certain processes done to the billet at certain ranges of layers, other effects can be produced when brought back to flat. Historically, twisting was used in the edge and core of pattern welded swords and knives. Other patterns include, amongst others, 'raindrop' in which holes are partially drilled through the billet to produce concentric rings; 'ladder' in which lines are cut down the width; 'feather' in which a hot cut is used to bisect a billet which is then welded back together to produce what appears as the quill of the feather; and many others. Straight laminates are considered low layer pattern welded billets in which the layers remain relatively parallel, running the length of a piece.

            Mosaic- A type of pattern welded steel, usually called Mosaic Damascus, in which a pattern is produced through can welding (the placement of metal bits in a 'can' and surrounded by metal powder and sealed, which is fused solid by internal pressure at high temperatures). Mosaic Damascus can result in the formation of complex shapes and is generally limited to what can be cut into the bits placed in the can. Such decorative patterns are often contemporary in appearance and used in art knives.

            Lamination- The welding of an edge piece of steel inside two contrasting metals. When ground, the edge steel is revealed midway between the spine and edge of the blade, and when etched, the two layers are revealed for their distinction. Commonly wrought iron is used for its slag grain pattern as the outer two layers, but anything that can produce contrast when etched may be used. The outer layers may be non-hardenable or hardenable, stainless or carbon steel, or even non-ferrous materials such as nickel. San Mai is a Japanese term similar to laminated billets.
Other variations of pattern welding include fused cable, termed Cable Damascus, welded chain (motorcycle, bicycle, chain saw, etc.), an assortment of scraps, or anything that can be welded together and refined into a solid billet. When using bloomery steel, meteoric iron, hearth steel, or crucible steel, pattern welding may involve refined billets from different batches of production or different methods altogether.

Wednesday, October 15, 2014

Painted in Light

Rarely does the reach of man extend out into the untapped vastness of the universe, to the soundless depths of the ocean, or there beneath the land that we call home. Light fails and where the sight would guide us, only the lure of mystery and the call of the unknown serve as our guide. To many, the weight of the world pressing down upon them and the closing walls are the seed of nightmare. Yet for thousands of years, countless passages have wormed their ways in the hidden depths of the earth. In the early years of time they were created, sculpted, pushed and pulled just so, until what we can remember was left behind. So little travelled, delving into the cavernous depths of the mountains, beneath the labyrinth of roots that hold life to the forests, abandoned paths of rivers worn in their course, in a word, relics of that which we can no longer fathom beckons us to them like a siren's chilling call.


In this generation, there are precious few places that one can travel which have never been travelled before. Places that have never been explored, whose secrets remain hidden even after the passage of ten thousand generations. To many, the thrill of adventure is curiously- or perhaps depressingly- absent. However, to those who have been taken by a singularly unique and powerful sensation, the possibilities abound. There are more opportunities around every corner of the world than could be taken in a lifetime. In a dozen lifetimes. All that separates us from them is the willingness to venture into a place where the comforts of familiarity are behind us and only the unknown wilds remain.


Buried beneath the mountains lie countless tunnels and passages hewn by the Hand of time and the breath of nature. Earlier this year, in absence of my ability to pursue my love of the mountains to the north, we turned to another muse.  How often it is that we fail to see what is around us, the beauty of the world as it rests in its so fragile state, and even rarer still to what lies below.Or rather, between.


Incredible worlds exist beneath our feet that no eye can ever see, unimaginable in character and unfathomable in beauty. But beside the countless lands we cannot visit there are precious few which, to man, will still remain invisible. Twisting sculptures of rock, claddings of minerals deposited by the steady drip of water, shreds of subterranean life which cling to the surfaces like glittering veins of gold. Of these, there are many recounts, of which I have added one of my own in the previous excursion into the underworld.


This trip, however, brought about a different reflection of the humble caverns. Never in their lifetimes will they see the light of the natural world, for it is defining of their nature. Only by the whims of humanity can these shadowed walls be seen, through the flickering light of candles cradled in the hands of our forebears, the ethereal, pale light of the modern Age, or in this instance, something quite different altogether.

Only in the deep places of the world when all lights have been put out does the weight of our size and the frailty of our age press down. To some, such a revelation might come on the shifting tides that separate life from death. Here, only life could bring it about.


Painted in light, frozen in time, our coming was but a blink in the life of the world. Never again would our footprints be crisp or our breath held in a silver white nimbus. Never again would light pierce that absolute darkness in such a way as to form a living beast all its own.


Upon a canvass of black, the only to which such a creature can survive, something mesmerizing happened. That which was hidden became known, and that which was known faded away in the wake of infinite undiscovery.


Purple, blue, green, yellow, colour in its purest form untainted by the radiance of the sun each woven together to form phantasmagorical illusion.




As quickly as our time in the passage of the earthen splendour had come, it too was at an end. Countless generations of our kin have come and gone without our presence, and as many more will pass without a trace, as it was ever meant to be. And there in the darkness lie the spirits of the dark, presiding over the darkness of a world unseen.