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Thread: A Metallurgical Rosetta Stone

  1. #1
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    A Metallurgical Rosetta Stone

    The following is an ever-growing list of terms that could be used in this forum. If at any time you encounter a term that you are unfamiliar with you may find it, along with its definition, here. If you do not find it, please feel free to request a moderator to include it in this list.

    Ac1: The temperature, upon heating, that corresponds with the boundary between the ferrite-cementite field and the fields containing ferrite and austenite or cementite and austenite. See iron-carbon equilibrium diagram.

    Acm: The temperature that corresponds with the boundary between the cementite-austenite field and complete austenite. See iron-carbon equilibrium diagram.

    AISI/SAE steel designations: The American Iron and Steel Institute and the Society of Automotive Engineers classification systems for steel alloys based upon a numbering system according to the chemistry of the metal. Relevant Threads: AISI/SAE steel designations


    Alpha iron: Iron that has a body centered cubic (BCC) atomic configuration an a much lower ability to dissolve carbon into solution. This is the state of iron at room temperature.

    Austempering: A heat-treating process in which steel is quenched fast enough to avoid the formation of pearlite but the cooling is halted above the Ms point so that martensite cannot form. If held in this range (800 Fahr-450 Fahr), long enough the metastable austenite will begin to transform into Bainite. Shorter periods at 600Fahr to 800Fahr will result in upper bainite. In the lower range, 600Fahr-450Fahr lower bainite will be formed; with the hold time required increasing drastically the lower one goes. Due to the cooling variations required, salt baths are often utilized for this procedure, and shallow hardening steels can be more problematic than deep hardening alloys. Relevant Threads: bantie

    Austenize: To heat steel to the point at which one achieves austenite as an internal structure. Complete austenization would involve heating to a temperature in excess of Acm or A3.

    Bainite: Named for Edgar Bain, this is the microstructure that is formed by holding quenched steel at temperatures above the Ms ( Martensite start) point. There are two morphologies feathery (upper bainite) and acicular (lower bainite). Upper bainite will form at higher temperatures and will have lower hardness but greater impact toughness. Lower bainite will require much longer hold times at lower temperatures and will have greater hardness.Relevant Threads: bantie

    Cementite: Iron carbide (Fe3C), for the purposes of this forum this will mostly be used in reference to the form carbon takes in steel. Cementite is hard and brittle. In alloys greater than .83% (hypereutectoid) there will be pearlite and varying degrees of proeutectoid cementite leftover when the steel is slow cooled.

    CCT diagram: A diagram that shows the transformation products of austenite when cooled continuously, as opposed to the I-T (Isothermal Transformation) Diagram which shows transformation products at one temperature at equilibrium. Relevant Threads: metallurgical diagrams, TTT vs CCT chart usage?

    Curie temperature: The temperature at which a metal loses it magnetic properties. For iron this is 1414F. Relevant Threads: quick question on quenching T for 5160


    Deep hardening steel: See "Shallow hardening steel"

    Edge to edge damage: Damage inflicted upon the edge of a blade that has impacted another metal object of similar shape and hardness.Relevant Threads: Another one, conserning differential HT


    Eutectoid steel: A steel that having the carbon percentage described on the iron-carbon phase diagram as the eutectoid point (often represented as .83% carbon). This is the point at which the Ac1, A3 and Acm converge, making it the carbon/ferrite level that enters the pure austenite phase at the lowest temperature.

    Gamma iron: Iron that has a face centered cubic (FCC) atomic configuration.

    Hypereutectoid steel: A steel containing carbon levels in excess of the eutectoid in the iron-carbon phase diagram. Slow cooled Hypereutectoid steels will form pearlite with leftover (proeutectoid) cementite.

    Hypoeutectoid Steel: A steel having carbon levels less than the eutectoid in the iron-carbon phase diagram. Slow cooled Hypoeutectoid steels will form pearlite with leftover (proeutectoid) ferrite.

    Iron-Carbon equilibrium diagram: (iron-iron carbide equilibrium diagram, iron-carbon phase diagram). A diagram that indicates the phases present in alloys of iron and carbon. It can be used to predict the microstructure produced in carbon steels at various temperatures and different carbon levels. Relevant Threads: the iron/ iron carbide equalibrium diagram.


    Interstitial alloying: Alloying elements with atoms that are smaller than the solvent atoms in the metallic solid solution, and because of their size occupy spaces between the larger atoms. Carbon is the most obvious example of an insterstitial alloy element. Relevant Threads: Interstitial -vs- Substitutional

    Ms: "martensite start". The point on cooling austenite when a sufficient low temperature has been reached for the initiation of the diffusionless shear type transformation that results in martensite. The martensite start point for many of the simpler steels used in bladesmithing often falls within a range from 400F. to 500F. The martensite start point is designated Ms on charts such as I-T or TTT curves.

    Mf: "martensite finish". The point on cooling when the diffusionless shear type transformation that results in martensite is complete, and maximum martensite conversion is achieved. Certain alloys and circumstances can stabilize austenite causing Mf to actually fall below room temperature, resulting in retained austenite. The martensite start point is designated Mf on charts such as I-T or TTT curves.


    Pearlite: Lamellar microstructure made up of alternating bands of ferrite and cementite, that forms when simple steels are cooled slowly through the range from 1100 Fahr to 900 Fahr. Under the microscope it has an interesting mother of pearl appearance, giving it its name. Eutectoid steels will form total pearlite, while hypoeutectoid alloys will form pearlite with degrees of ferrite. Hypereutectoid steel will form pearlite with increasing amounts of cementite.

    Quenchant: The medium that steel is supercooled in to harden it. For bladesmiths this is most often liquid in form, with an oild based medium being the most common. Relevant Threads: Name you poison- Quenchants



    Reverse Curvature in Oil: The much encountered and frustrating phenomenon of blades of particular cross-sections taking a reverse curvature than what should be expected when quenched in oil. A blade edge-quenched in water has the tendancy to curve into a saber shape, yet the same blade quenched in oil will have the tip drop into a sickle shape.
    Relevant Threads: reasons for sori.

    Shallow Hardening Steel: This term most likely has its origin in the Jominy end quench test. In this procedure a round steel specimen is austenitized and then suspended vertically over a jet of water that super cools the end. Then areas down the sides of the specimen are prepared and hardness (HRC) readings are taken at regular intervals to determine the depth and degree of hardening. From this a hardenability curve is created to determine the hardenability of the tested steel. The same affect can be seen by cross sectioning any hardened piece of steel and testing the hardness from its outer surface to the center of the piece. Steels having low hardenability, and requiring faster quench speeds are thus said to be “shallow hardening”. Steels that easily reach higher HRC values farther from the quenched surface are said to be “deep hardening”. Many simple carbon steels (1060, 1084, 1095 and the “W” tool steels”) lack alloying elements that promote deeper hardening, in larger cross sections they require the quench speed of water and thus can be categorized as “water hardening”.

    Spark Test: A quick precursory test that can be performed in almost any shop that relies on the concept that various chemistry makeups of different steels will display a spark stream of different color, shape or intensity, when ground. An excellent resource for was provided by David Castro in this Relevant Thread: Spark Test

    Substitutional alloying: Alloying elements with atoms that are larger than the solvent atoms in the metallic solid solution, and because of their size can only replace an atom while occupying its space in the atomic arangement. Chromium would be an example of a substitutional alloying element.
    Relevant Threads: Interstitial -vs- Substitutional

    Tempering: The heat treatment operation which consists of heating a quench hardened piece of steel to a given temperature in order to reduce brittleness or increase toughness and relieve stress. Most blade steels will be tempered in a range from 350F., which will yield no appreciable loss of hardness, to 550F. which will result in extensive loss of hardness with a corresponding increase in “toughness”. Relevant Threads: types of tempering

    Wootz: An ultra-high carbon steel created in a unique ancient process orginating probaly in India, that involved sealing iron and carbonaceous materials in a clay vessal and heating to extremely high temperatures in order to achieve a true liquidus in an era when the direct process, which produced spongy blooms, was the most familiar in the west. The excess of carbides in the material produced two characteristics in the steel, upon segregation the carbide would produce a visible pattern in the steel somewhat resembling pattern welding, the same carbides also produced a highly abrasion resistant, toothy cutting edge.

    Youngs Modulus: (modulus of elasticity) The values obtained when a load or stress is applied to a metal, within its elastic range, to stretch it to a given length. For steel this is aproximately 30,000 PSI for .001". This will be the case regradless of the heat treatment. Relevant Threads: Breaking vs. Bending Swords

  2. #2
    Join Date
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    In order to keep the Metallurgical Rosetta Stone up to speed with demand for knowledge here, I am opening it to the participant s of this forum to add definitions. In order for this tool not to become a cluttered mess of off topic conversation there will need to be guidelines.

    If you have a definition you feel should be added here please feel free to post it here using the following format:

    Subject
    Definition
    Any relevant threads you would like to link to
    Submitted By: (your name)

    Example:
    Unobtanium: The metallic substance that all bladesmiths know exist, but are never able to find, that will give the heat treating characteristics, edge holding, strength, toughness, stain resistance, and ease of forging virtually everybody has been looking for.
    Relevent threads: none yet
    Submitted by Kevin R. Cashen


    Please only post these things here and then post commentary and requests for the same in the “definition discussion thread.” There the definition will have an opportunity for peer review before it gets added to the permanent Rosetta Stone section. Any commentary or off topic discussion here will either be moved or deleted.
    Last edited by Kevin R. Cashen; 02-18-2007 at 07:50 AM.

  3. #3
    Join Date
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    N.W. Indiana
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    Don't know why anyone has commented this yet - thanks for the thread, very cool info!

  4. #4
    This is pretty interesting, many of these I've never heard of before so it's cool to learn about it. Thanks
    Katana Reviews - Quality in our weapons leads to quality in our art.

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