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Japanese Sword:




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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"

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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 nihontō 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

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Imperial Japan (1912 – 1945)Mass production for imperial armyGuntō swords: stamped, oil temperedSwords making prohibited after WWII“Lost 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

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Evolution of the Nihonto

Time Line

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Time Line

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Nippon Bijutsu Tōken Hozon Kyōkai (NBTHK)

“Society for the Preservation of the Japanese Art Swords”Founded 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 (<2ft.) per month– based on meticulous style of eminent smith Akihira Miyairi

All swords must be registered with the police

NBTHK Competition– one sword per swordsmith – 300-500 swords entered into competition– 15 judges: swordsmiths, appraisers etc.– 2 rounds with covered and open signature– swords ranked first to last– determine the value of the next year swords

– mukansa: above the competition– ningen kokuho: living national treasure

Contemporary Sword: Shinsakuto

NBTHK Tokubetsu Hozon Wakizashi from Mutsu no Kami Fujiwara Kanenobu, a Mino smith in 17th century

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Anatomy of the sword

“Cut well” “Not bent” “Not break”Conflicting 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

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Properties of the Steel: Fe-F3C Phase Diagram

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

Austenite:• exist above critical (eutectoid) temp. : 727 °C• γ-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:• α-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


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Microstructure of the Iron – Iron Carbide Phases

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

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

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

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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

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Pearlite: 88/12 α-Fe/Fe3C

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

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

Microstructure of the Iron – Iron Carbide Phases

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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

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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


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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 +→+


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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 ¼ “ 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

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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 ½ 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 smith’s style and school

the final block is 10” x ¾” x 1 ½ ”, divided with chisel into three equal parts

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Initial tamahagane [C] ~ 1.4%0.3% lost in shita-gitae , 0.4% in age-gitaeTypically another ½ 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%

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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

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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

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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

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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

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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 water“Tale of the severed hand”

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

½ of the swords do not survive yaki-ire

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

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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

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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

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Longitudinal stress distribution and residual stresses

Stress σ, 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





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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)( αγ

⎯⎯ →⎯

Adjusting the Curvature: Sorinaoshi

Sunobe is almost straight before quenching During yaki-ire curvature is increased by almost ½” Volume change between austenite and martensiteAdjusting the curve

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

(111)γ <=> (011)α’

[101]γ <=> [111]α’

[110]γ <=> [100]α’

[112]γ <=> [011]α’

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

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

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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

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Saya – kurigata – kojiri– sageo– koiguchi

Tsuba– habaki– seppa

Tsuka– fuchi / kashira

– makishitasame – tsukaito– menuki

Fully Mounted Sword: Koshirae

Shinto katana. 1600’s. 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.

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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

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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.

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The Science: Yaki-modoshi

Tempering – heating below eutectoid temperature– holding at temperature followed by cooling

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


CFeFe 3)( +≠ αCFeFeFe tempering3)( )( +⎯⎯⎯ →⎯′ αα




Tempered Martensite

Cold work: mechanical deformation of at relatively low temperatures– increase point defect and dislocations – stronger material

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Fe-C diagram:• austenite: FCC γ-Fe ductile• ferrite: BCC α-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: α-Fe (88%) and Fe3C (12%) whiskers


Eutectic transitions:• Cementite: γ-Fe --> α-Fe + Fe3C• Ledeburite: L --> γ-Fe + Fe3C

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

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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

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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 K

) →

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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:



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Front Picture: Blacksmith Munechika (end of the 10th century), helped by a fox spirit, forging the blade kogitsune-maru ("Little fox"). Engraving by Ogata Gekkō (1859–1920), 1873.

“Materials Science and Engineering: An Introduction” , 6th Edition William D. Callister, Jr., Univ. of Utah“Phase 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, 2002“The Craft of the Japanese Sword” by Leon and Hiroko Kapp and Yshindo Hoshihara; Kodansha America, Inc; 1987“THE JAPANESE SWORD : The Material, Manufacturing and Computer Simulation of Quenching Process”Inoue Tatsuo, Material Science Research International Vol.3, No.4 pp. 193-203 1997“The Forging of a Japanese Katana” Michael Morimoto Colorado School of Mines June 14th, 2004“Samurai: The weapons and spirit of the Japanese warrior” by Clive Sinclaire; First Lyons Press; 2001“The Japanese Sword: The Soul of the Samurai” by Gregory Irvine; Weather Hill Inc; 2000“The Arts of the Japanese Sword” by Basil W. Robinson; Charles E. Tuttle Company; 1971“The Japanese Sword” by Kanzan Sato and Joe Earle; Kondansha International Ltd. And Shibundo; 1983