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Japanese Sword: History Art Science

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  • Japanese Sword:




  • Imperial Regalia of Japan: Three Sacred Treasures

    Sword Ama-no-Murakumo-no-Tsurugi or Kusanagi-no-Tsurugi Sword of the Gathering Clouds of Heaven Grasscutter Sword Valor Atsuta Shrine in Nagoya

    Necklace Yasakani no Magatama Benevolence Kokyo (the Imperial Palace) in Tokyo

    Mirror Yata no Kagami Wisdom Grand Shrine of Ise in Mie prefecture "The Eight Hand Mirror"

    Initially belong to Sun Goddess Amaterasu lured out of the cave with the mirror sword: from Susanoo as a reconciliation gift sword was in the tail of fire spitting serpent

    She gave the regalia to her grandson Ninigi-no-Mikoto sent to pacify Japan and plant rice ancestor of the Japanese imperial line

    Sword in Japanese History and Mythology

    Jade magatama necklace from Japanese burial

    Amaterasu(that which) illuminates Heaven"


    Withering Wind of Summer

    God of the sea and storms

    Since 690 A.D. central part of the imperial enthronement no public viewing, location is unconfirmed no known photographs or drawings exist may be not originals

    After the WWII Potsdam Declaration on July 26, 1945 fate of the regalia was uncertain Emperor Showa ordered to secure regalia undisclosed location, protect "at all cost"

  • Nara period (710 794)Technology imported from China Oldest swords ~ 400 A.D.Straight blade, single cutting edgeFaulty tempering

    Heian period (794 1185)Improved technologyHorseback fighting Curved blade, up to 4 ft. Hung from the waist Edge down: tachi

    Muromachi period (1392 1573)Warring States period (Sengoku Jidai)Large demand, decline in qualityDark age of the Japanese sword200,000 nihont imported to China Development of the uchigatana

    about 24 inches, worn edge up one hand close quarters fighting curve is similar to tachi

    Kamakura period (1185 1333)Golden age of the Japanese swordRetired emperor Gotoba (1180 1239) patron of the finest smiths forged blades himselfMongol invasion attempts, 1274 & 1281 footlong tanto, hand-to-hand combat wider, heavier two-hand tachi

    Koto: Old sword

    Nanbokucho period (1336 1392)Gokaden (Five Traditions) Bizen Soshu (Sagami) Yamashiro Yamato Mino

    Chokuto (Ken): Ancient sword

    The History of Nihonto

    Tachi by Ichimonji.National Treasure. TNM

  • Imperial Japan (1912 1945)Mass production for imperial armyGunt swords: stamped, oil temperedSwords making prohibited after WWIILost generation of swordsmiths

    Momoyama period (1568 1603)Evolution of the uchigatana katana (24-30) and wakizashi (18)Symbol of power and status Shogunate decree for all samurai to wear daishoSchools are mixed: brighter steel, flashy blades

    Meiji Restoration (1867 1912)Abolishing samurai class 1971 edict forcing samurai to cut top-knots1873 creation of the Imperial Japanese Army1873 hereditary samurai stipends terminated 1876 wearing swords is prohibited

    Gendaito: Modern sword

    Shinto: New sword

    1953prohibition is lifted

    The History of Nihonto


    Edo period (1603 1867 )Tokugawa shogunateStrict class hierarchy samurai (shi) farmers (no) artisans (ko) merchants (sho)

    Appointed Chief Swordsmith grant competency certificates 910 licensed smiths

    Shinshinto swords

  • Evolution of the Nihonto

    Time Line

  • Time Line

  • Nippon Bijutsu Tken Hozon Kykai (NBTHK)

    Society for the Preservation of the Japanese Art SwordsFounded in 1960Strict regulations are enforced:

    To register the sword with NBTHK: produced by licensed swordsmith blade over 6, hamon, rivet hole in the tang less than 6: knifes ( kogatana ), no regulation

    Getting a license: apprenticeship under licensed swordsmith for a minimum of 5 years

    Number of swords: 2 long swords (>2ft.) and 3 short swords (

  • Anatomy of the sword

    Cut well Not bent Not breakConflicting properties of steel:

    hardness: maintain sharp edge, brittle ductility: withstand hard blow, soft

    Solution core of the soft steel, shingane jacket of the hard steel, kawagane harden only the edge, hamon


    kawagane shingane


    blade cross section

  • Properties of the Steel: Fe-F3C Phase Diagram

    Pearlite: -Fe (88%) and Fe3C (12%) composite Two-phase lamellar structure

    Austenite: exist above critical (eutectoid) temp. : 727 C -Fe : solid solution of carbon and iron Max. [C] solubility = 2.1% , ductile Face Centered Cubic (FCC) structure

    Martensite: Rapid quenching of austenite Traps carbon atoms, no time to diffuse out Body Centered Tetragonal (BCT) lattice

    Phase diagram:Equilibrium between the distinct material phases

    Steel [C] < 2.1% , Cast Iron [C] > 2.1%

    Ferrite: -Fe, fairly ductile Max. [C] solubility = 0.022% [C] atom ~ 2x interstitial Body Centered Cubic (BCC) structure

    Cementite: Fe3C, carbide, hard and brittle, ceramic Orthorhombic crystalline structure


  • Microstructure of the Iron Iron Carbide Phases

    Eutectic transitions: -Fe --> -Fe + Fe3C

    Pearlite: -Fe / Fe3C lamellar composite -Fe matrix Fe3C stripes

    Austenite: start above critical temperature: 723 C carbon content: 0.83%

  • Martensite: metastable, kinetic phase not on phase diagram needle-shaped grains

    Austenite: start above critical temperature: 727 C carbon content: 0.83%

    Microstructure of the Iron Iron Carbide Phases

  • Pearlite: 88/12 -Fe/Fe3C

    Pearlite + Ferrite:88/12 -Fe/Fe3C + -Fe

    Pearlite + Cementite:88/12 -Fe/Fe3C + Fe3C

    Microstructure of the Iron Iron Carbide Phases

  • Tradeoff : Ductility and Hardness

    Austenite:T > 727 C

    [C] < 0.83% [C] > 0.83%Pearlite + Ferrite:

    [C] = 0.83%Pearlite Pearlite + Cementite:






    Properties and appearance of the steel:- Location on the phase diagram - Subsequent processing & heat treatment

  • Tatara and Tamahagane: The Nittoho Tatara operated by NBTHK since 1977Three operating cycles during the winter - 7 days / 5 peopleClay vessel: 1.2m (H) x 4.5m (L) x 1.5m (W)10T of satetsu and 12T of charcoal ~ 2.5T of tamahaganeTypical carbon content: 0.6 -1.2 % ( optimum: 1.0-1.2% )

    Smelting : Iron ore (Fe2O3) comes as a fine black sand, satetsuThe furnace for smelting, tataraPrimitive and efficient method:

    combine ore and charcoal pump the air trough bellows temperature: 1200-1500 0C

    Low temperature reduction, no melting Alloys with impurities are not formed, removed with the slag Iron combines with carbon to form tamahaganeTamahagane mother of metal in kanji

    The Steel







    dense, heavy silvery color fine crystallites


  • Refining the Steel: Oroshigane

    Tamahagane - nonuniform, mixture of low and high [C] piecesOutside jacket kawagane, [C] ~ 0.7-0.8%Inside core shingane, [C] < 0.5%

    Continuous loss of carbon during the processStart forging with high carbon content, [C] ~ 1.0-1.5%

    adding [C]


    kawagane shingane


    removing [C]

    3FeCC3Fe + CO6 Fe2O3 2FeC 23 ++


  • Assembling Steel for Forging: TsumiwakashiT (C) T(F)700 1292

    1200 21921300 23721500 2732

    oroshigane, [C] ~ 1.0-1.5%

    heated to 1200-15000C and flattened into plates

    broken into pieces and sorted bright and clear high [C], kawaganedark and muddy low [C], shingane

    plate with similar to tamahaganecomposition is formed

    4-5 lb. of selected pieces stacked and wrapped in rice paper

    wafers are fused at 13000C and bar twice the length of the original tamahagane is prepared

  • Forging: Kitae Foundation forging: Shita-gitae

    Total of 6 folds: cleft, fold, hammer Each fold: 30 min. / 3 heat upsEach fold: 3 min. of hammering Remove impurities, homogenize, air bubbles Consumes of the original tamahagane

    make a cleft with a chiseldivide bar into two equal parts

    fold the bisected bar, fuse the halves and flatten the bar sorted

    repeat the folding, remove impurities and bubbles, homogenize

    The way metal is folded will affect jihada and jitetsu - depends on smiths style and school

    the final block is 10 x x 1 , divided with chisel into three equal parts

  • Initial tamahagane [C] ~ 1.4%0.3% lost in shita-gitae , 0.4% in age-gitaeTypically another of the steel lost

    Forging: Kitae Finish forging: Age-gitae

    for katana four steel pieces are stacked an fused

    another 6-7 foldsprevent oxidation with clay and straw

    Kawagane is ready, [C] ~ 0.7%

  • Hon-sanmai-gitaeKobuse-gitae

    Forming the Steel Stock: Tsukurikomi

    Shingane: prepare and shape long and narrow barFolded about 10 times, drive impurities out Typical shingane [C] ~ 0.2-0.5%



    Piercing tip (kissaki) is always made from the best kawagane

    Forging temperature: 1300 0C Extremely delicate and vital process

    perfect weld, no voids or gaps shingane completely covered by kawagane

  • Forming the Blank, Shaping and Rough Grinding the Blade

    Shiage: Preparation to harden the sword edge

    rough grinding and filing use sen to shave off irregularities

    Use carborundum stone to rough grind the blade Shape is well defined, edge is ~ 1/10

    Hizukuri: Drawing the cutting edge: ha-saki

    hummer 6 at a time yellow (~1100 0C) and cherry red (~700 0C)

    Require fast work and precision hammering overheated: separation of kawagane and shingane to cold: damage or fracture the sunobe kissaki , shinogi and mune are formed blade is growing in a straight line deceptively simple process

    A fully formed kissaki, shinogi,and mune from a sunobe

    Sunobe: Sword blank with no curve or edge 10% smaller, uniform thickness Define nakago and kissaki

  • Creating the Cutting Edge: Tsuchioki

    Yakiba hard cutting edge The hardest but brittle form of steel is martensiteHow to simultaneously:

    convert the edge to martensite keep the rest of the sword as ferrite + pearlite


    kawagane shingane


    Heat treatment process: kawagane [C] ~ 0.6-0.7% (optimum, see HRC) heat the blade above eutectic temperature: 723 C fast cooling: austenite -> martensite slow cooling: austenite -> ferrite + pearlite

    Hamon:- martensitic blade pattern Habuchi:- transitional zone

    Hardness vs. carbon steel carbon content:

    No gain, brittleSharp decrease in hardness

  • Controlling Cooling Rate with Insulating Clay

    Tsuchi-dori clay mixtureStick well to roughened during shiage stage surface

    clay for insulation charcoal powder for heating control sandstone (omura) to prevent cracking school specific ingredients

    Thin layer on the edge, thicker towards the backControl cooling rate via: thermal insulation increase surface area

    Prevent formation of the water bubbles on the surfaceFaster cool down with thin clay layer

    Distribution and thickness of tsuchi-dori will determine hamon pattern hardness is the objective of the process

    Making ashi literally means foot or leg thin tsuchi-dori strips perpendicular to the yakiba create pearlitic veins on hard martensitic edge stop crack propagation originated at the edge

  • Hardening the Edge: Yaki-ire

    Yaki-ire quenching in the cold water metal is transformed and the sword is born performed at night to accurately judge the temperature color of the steel is like the moon in February or August skill and experience each sword is unique

    Draw the sword through the hot coals slow and steady first edge up: 10-15 times then edge down: 2-5 times

    Achieve even and uniform color edge: bright red or orange back: red or cherry red

    Plunge the blade into the waterTale of the severed hand

    Yaki-modoshi tempering at 160 0C reheating and quenching again relieve the stress, break down martensite crystals

    of the swords do not survive yaki-ire

    Strict attentiveness followed by swift and uncompromised action(zen calligrapher, strike in kendo)

  • The Science: Yaki-ire

    Heat treatment heating to a high temperature holding at temperature cooling down at a specific rate

    Steel cracking is the problems during quenching high rate of cooling: surface cooler than interior surface forms martensite before the interior constrains from outer martensitic layer leading to residual stresses

    Continuous cooling transform. (CCT) diagram follow cooling curves from the top left to bottom right steel and sample specific

    a austenite

    f ferrite

    p pearlite

    b bainite

    m martensite

    CCT diagram for hypoeutectoid steel [C] < 0.8%

    Circles DPH ( diamond-pyramid hardness )

    Fast (~10sec): austenite > martensite Medium (~1min): austenite > mixtureSlow (~3min): austenite > ferrite:pearalite

  • Heat Transfer Modeling: Yaki-ire

    Prifile of yakiba-tsuchi

    Measured heat transfer coefficient

    800 - 400 0C:heat transfer coefficient with thin clayis higher than that of without any clay

    Thin clay nucleation boilingThick clay film boilingBare metal film boiling

    Inoue Tatsuo, Mat. Sci. Res. Int. Vol.3, No.4 pp. 193-203 1997

    Temperature distribution during yaki-ire

    Temperature, 0C








    gyaku-sori: reverse bending ~ 1s sori : normal bending ~ 10s


    Nucleation boiling: rapid, explosive, formation of bubbles strong local velocity within the liquid film increases heat transfer surface dependant

    Film boiling: continuous layer of vapor covers the surface insulating effect of the vapor reduced the rate of heat transfer Leidenfrost effect

  • Longitudinal stress distribution and residual stresses

    Stress , MPa





    Significant stress in yakibaFracture stress 1600-1700



    Heat Transfer Modeling: Yaki-ire

    Inoue Tatsuo, Mat. Sci. Res. Int. Vol.3, No.4 pp. 193-203 1997

    tsuchi: uniform 0.8 mm

    tsuchi: uniform 0.1 mm

    volume fractions of martensite %

    0.8 mm on the back0.1 mm on the edge

    Simulation of quenching with different tsuchi distribution





  • Martensitic transformation: No long range diffusion No compositional change Transformation occurs by shear Austenite to Martensite 4.3% volume increase


    CFCC Quench

    % 8.0)( '

    % 8.0)(

    Adjusting the Curvature: Sorinaoshi

    Sunobe is almost straight before quenching During yaki-ire curvature is increased by almost Volume change between austenite and martensiteAdjusting the curve

    straightening by hammering heating on copper block and quenching addjust sori locally

    (111) (011) [101] [111] [110] [100] [112] [011]

    Bain model structural transformation with a minimum of atomic motionOne-to-one correspondence between and atoms

    Two FCC unit cells: - contract by 20% in the z direction- expand by 12% along the x and y directions

  • Just a Beginning.

    Kajitogi : rough polishing Hi : decorative grooves ( add surface area! )Horimono : decorative carvings ( tatoo )Nakago : the tang, filed, never cleanedMekugiana : the rivet hole Mei : the signature, testing, owner etc.

    engraved in the very end often forged or destroyed legend of Kanemitsu

    Polishing: the art by itself put a sharp edge reveling the hamon, jihada, jitetsu bring the sword to life

    Habaki: blade is floating in the scabbard (saya)

    Shirasaya simple white scabbard ho tree (magnolia obovata) glued with sokui, paste from cooked rice carved with shallow lip for the edge

  • Saya kurigata kojiri sageo koiguchi

    Tsuba habaki seppa

    Tsuka fuchi / kashira

    makishitasame tsukaito menuki

    Fully Mounted Sword: Koshirae

    Shinto katana. 1600s. Signed Suruga no Kami Kunimasa. Yasusada School. Soshu style. Notarehamon. The mounts are original to the blade. Fuchi kashira done in shakudo and gold with a floral design. The tsuba is a large iron sukashi with a design of ginger leaves.

  • volume fractions ofmartensite %

    What Makes Katana a Superior Sword?

    Forging optimal [C] content folding process

    Heat treatment controlled quenching martensitic edge


    Design kawagane jacket shingane core hamon

  • Hagakure

    A certain swordsman in his declining years said the following:

    In one's life there are levels in the pursuit of study. In the lowest level, a person studies but nothing comes of it, and he feels that both he and others are unskillful. At this point he is worthless. In the middle level he is still useless but is aware of his own insufficiencies and can also see the insufficiencies of others. In a higher level he has pride concerning his own ability, rejoices in praise from others, and laments the lack of ability in his fellows. This man has worth. In the highest level a man has the look of knowing nothing.

    These are the levels in general. But there is one transcending level, and this is the most excellent of all. This person is aware of the endlessness of entering deeply into a certain Way arid never thinks of himself as having finished. He truly knows his own insufficiencies and never in his whole life thinks that he has succeeded. He has no thoughts of pride but with self-abasement knows the Way to the end.

    It is said that Master Yagyu once remarked:"I do not know the way to defeat others, but the way to defeat myself. ''

    Throughout your life advance daily, becoming more skillful than yesterday, more skillful than today. This is never-ending.

  • Extra

  • The Science: Yaki-modoshi

    Tempering heating below eutectoid temperature holding at temperature followed by cooling

    Tempered martensite: distribution of fine particles of Fe3C in matrix hardness more than pearlite, ductility more than martensite hardness and ductility controlled by tempering temperature and time


    CFeFe 3)( + CFeFeFe tempering 3)( )( + T

  • Fe-C diagram: austenite: FCC -Fe ductile ferrite: BCC -Fe fairly ductile FCC unit cell > BCC unit cell

    cementite: 2nd phase [Fe3C] brittle cementite: [C] is in excess of the solubility limit

    pearlite: two-phase lamellar structure pearlite: -Fe (88%) and Fe3C (12%) whiskers


    Eutectic transitions: Cementite: -Fe --> -Fe + Fe3C Ledeburite: L --> -Fe + Fe3C

    Martensite: tetragonal lattice rapid quenching of austenite. change in volume traps carbon atoms, no time to diffuse out

  • Heat Treatment









    Annealing Furnace cooling RC 15 Coarse pearlite

    Quenching Water cooling RC 65 Martensite

    Tempering Heating after quench RC 55 Tempered martensite

    Normalizing Air cooling RC 30 Fine pearlite

    Austempering Quench to an intermediate temperature and hold RC 45 Bainite

  • Continuous Cooling Transformation Diagram for Eutectoid Steel



    Coarse peralite

    Fine peralite

    Cooling curvesConstant rate

    t (s)









    0.1 1 10 102 103 104 105

    Water quench

    Oil quench


    Full anneal

    Coarse P

    P M M+ Fine P


    T( 0


  • Time Temperature Transformation Diagram for Eutectoid Steel



    Formation of bainite austemperingBainite: short needles of Fe3C in plates of ferriteLess strong but more ductile than martensite

    Upper bainite: Lower bainite:



  • References

    Front Picture: Blacksmith Munechika (end of the 10th century), helped by a fox spirit, forging the blade kogitsune-maru ("Little fox"). Engraving by Ogata Gekk (18591920), 1873.

    Materials Science and Engineering: An Introduction , 6th Edition William D. Callister, Jr., Univ. of UtahPhase Transformations in Metals and Alloys David Porter & Kenneth Esterling Van Nostrand Reinhold Co. Ltd., New York (1981)The Samurai Sword: A Handbook Yumoto, John M. Tuttle Publishing, 2002The Craft of the Japanese Sword by Leon and Hiroko Kapp and Yshindo Hoshihara; Kodansha America, Inc; 1987THE JAPANESE SWORD : The Material, Manufacturing and Computer Simulation of Quenching ProcessInoue Tatsuo, Material Science Research International Vol.3, No.4 pp. 193-203 1997The Forging of a Japanese Katana Michael Morimoto Colorado School of Mines June 14th, 2004Samurai: The weapons and spirit of the Japanese warrior by Clive Sinclaire; First Lyons Press; 2001The Japanese Sword: The Soul of the Samurai by Gregory Irvine; Weather Hill Inc; 2000The Arts of the Japanese Sword by Basil W. Robinson; Charles E. Tuttle Company; 1971The Japanese Sword by Kanzan Sato and Joe Earle; Kondansha International Ltd. And Shibundo; 1983