VVELDING HANDBOOK...CHAPTER 15, 1NS 44444Ln666661566785 Requirements for Welding l lnspection...

43
Eighth Edition Volume VVELDING HANDBOOK Leonard P.Connor Editor AMERICAN VVELDING SOCIETY 550 N.W.LeJeune Road P.0.Box 351040 Miami,FL 33135 WELDING TECHNOLOGY

Transcript of VVELDING HANDBOOK...CHAPTER 15, 1NS 44444Ln666661566785 Requirements for Welding l lnspection...

  • Eighth Edition

    Volume l

     VVELDING

    HANDBOOK

    Leonard P.Connor

         Editor

    AMERICAN VVELDING SOCIETY

       550 N.W.LeJeune Road

         P.0.Box 351040

         Miami,FL 33135

    WELDING TECHNOLOGY

  • The Three Volumes of

    the VVeldin9 1`・・landbook.

       Eighth Edition

    1)WELDING TECHNOLOGY

    2)WELDING PROCESSES

    3)MATERIALS AND APPLICATIONS

  • L.M.Friedman,Chairman

    Westingbot4seEectγic

    C○γpoγatl0,7

    XVバV. Canary

    Teldyれe CAE

    P・J.Konko1

    USX Co巾oγatlon

    S. D. Reynolds Jr・

    Westingb014seEectγic

    Co巾07ati0,1

    一三~~~……・、。

    PREPARED BY A

    COMMITTEE CONSISTING

    OF:

    VVELDING

    METALLURGY禍IELDING HANDBOOKCOMMIITTEE IVIEMBERzL・ J. Privoznik

    WestingbouseElectγic

    Coゆor討jo,z

    103

    Weldability of Commercial AIloys

    ::||

    lntroduction

    General Metallurgy

    The Metallurgy of Welding

    jll

    112

    Supplementary Reading List 123

    Brazing and Soldering Metallurgy

    Weldability Testin9 119

    122

    - … … …

  • CONTENTS

    WELDING HANDB00K V

    VI

    CHAPTER I, SURVEY OF JOINING AND CUTTING PROCESSES …………………24678912356670

          111122222223

    rnd6747

    66688

    1243048niu

    33345556

    Resistance

    Flash

    Oxyfuel Gas

    Solid State

    Electron Beam W

    Laser Beam W

    Adhesive

    Thermal

    Thermal Cutting

    Supplementary

    CHAPTER 2, PHYSICS OF

    Energy Sources for

    Metal T

    Melting

    Physical Properties of Metals and Shielding

    Suppleme由ry R

    CHAPTER 3, HEAT FLOW IN

    Fundamentals of Heat

    Solidification

    Supplementary

    ㎜ ■ ■ ■ ■ ㎜ ㎜   ■

  • CONTENTS

    CHAPTER 4, WELDING MET,WWXWXWr  

               

    ll-fjfj

    111

    General

    The Metallurgy of

    Weldability of Commercial

    Weldability

    Brazing and Soldering

    Supplementary

    1;

    1;

    1:

    1!

    CHAPTER 5, DESIGN FOR WGeneral

    SIS N ~f l WWg

          

    Design

    Properties of

    Welded Design

    Sizing of Steel

    Aluminum

    Design of Welded

    Structural Tubular

    Supplementary

    CHAPTER 6, SYMBOLS FOR WELDING AND INSPECT10N ……………………… 1!WS~SS 9

      22

    Welding

    Brazing

    Nondestructive Examination

    2‘CHAPTER 7, RESIDUAL STRESSES AND DISTORT10N ……………………,‥‥‥ZZZZZZ22

    Weld

    Residual

    Causes of Residual

    Effects of Residual

    Measurement of Residual SIresses in

    Typical Residual Stresses in

    Reducing Residual Stresses and

    Supplementary

    CHAPTER 8, WELDING AND CUTI・ING COSTS: ESTIMATES AND CONTROLS ….2t6j 5j

    Estimating Weldin9

    Vi

  • 50356

    78888

    22222

    CONTENTS

    Capital

    Control of Welding

    Economics of Brazing and

    Economics of Thermal

    SupplementarY

    CHAPTER 9, FIXTURES AND POSIT10 7820

    8891

    2223

    Supplementary

    レに……::j CHAPTER 10,AUTOMAT10N AND 122365357

    31311323233343434

    Procurement

    Fundamentals of Welding

    Brazing

    Arc Welding

    Resistance Welding

    Problems of

    Supplementary

    CHAPTER 11, WELD 902249692

    45556677

    333333333

    Discontinuities in Fusion Weldin9

    Significance of Weld

    SupplementarY

    Causes and Remedies for Fusion Weld

    Discontinuities in Brazed and Soldered

    Discontinuities in Resistance and Solid State

    CHAPTER 12, TESTING FOR EVALUAT10N OF WE567825799

    383838394040404040

    Tensile Properties-Strength and

    Fracture T

    Corrosion Factors Affecting the Testing and Performance of Welded

    Fatigue Properties of Welded Structural

    Supplementary

    Elevated Temperature

    Tests of Thermal Spray

    Vii

  • CONTENTS

    411

    412

    413

    413

    415

    CHAPTER 13, CODES AND OTHER STAN

    78915234

    33355666

    44444444

    666788000455691222‐6no

    4141引414141む一″`’一`’″’む一む一む一む’n”`”り’り’り43

    American Welding

    American Bureau of

    American Association of State Highway and Transportation

    SAE

    Federal

    Compressed Gas

    American lnstit由of Steel

    American Petroleum l

    American National Standards l

    American Railway Engineering

    American Waterworks

    American SocietY for Testing and

    American SocietY for Mechanical Engi

    Association of American

    Canadian Standards

    National Fire Protection

    lntemational Organization for

    Underwriters

    Pipe Fabrication

    National Board of Boiler and Pressure Vessel

    Manufacturers’

    CHAPTER 14, QUALIFICAT10N AND CERTIFICA

    Procedure

    Qualification of Welding Procedure

    Performance

    〔luality Control and lnspection

    Standardization of〔lualification

    Supplementary

    566785

    666661

    44444Ln

    CHAPTER 15, 1NS

    Requirements for

    Welding l

    lnspection

    Nondestructive

    Destructive T

    Viii

  • CONTENTS

    516

    517

    Brazed

    Supplementary

    9076030

    122344Ln

    5555551jl

    CHAPTER 16, SAFEGeneral Weldin9

    Electrical

    Fumes and

    Handling of Compressed

    Supplementary

    一l一

    59

    iX

    ・   一 一 一 一 一

  • 90 Welding Meta川u「9y

    WELDINGMETALLURGY

    WELDING INVOLVESλ/IANY nletallurgical phenolnena.ing of welding metanurgy requires a broad knowledge of

    general metallurgy. For thisreason,general metallurgy

    is addressed first, and then the specific aspects of weld-

    ing metallurgy are discussed. The survey of general

    metallurgy is by no means eχhaustive, and those who

    wish to increase their knowledge of the discipline are

    directed to spedfic references in the Supplemcりtary

    Reading List.          ……,……………

    INTRODUCTION

    gical principles to the welding process.

     MZelding metallurgy differs from conventional metal-

    1urgy ill certain important respects, but an understand-

    transformations,thermal strains

    can cause nlany practical probk

    be avoided or solved by apply≒

    These phenonlenasuch as melting,

    GENERAL METALLURGY

    STRUCTURE OFMETALS           E2ch g13111 il1 3 p111e “le゛h1 311y p3111c山“elllpe13`

                                  ture has the same crystallme structure and the same

    SOLID METALS HAVE a crystalline structure in which the atomic spacing as an other grains. However,each grain

    atoms of each crystal arearranged in a specific geometric grows independently of every other grain, and the orien-

    pattem. This orderlyarrangement of the atoms, called a tation of the grain lattice differs from one grain to

    lattice,is responsible for many of the properties of met- another. The periodic and orderlyarrangement of the

    als.The most common lattice structures found in metals atoms is disruPted where the grains meet, and the grain

    are listed in Table 4.1,and their atomicarrangemellts bound21‘ies form a continuous network throughout the

    are nlustrated in Figure 4.1.                meta1. Becauseof this grain boundary disorder, there

     ln the liquid state, the atoms composing metals have  often aredifferences in the behavior of the metal at those

    no orderlyarrangement. As the liquid metal apProaches locations.

    the solidification temperature, solid partides called  Up to this point, only Pure metals have been consid-

    nuclei begin to form at Preferred sites, as shown in Fig- ered. However, most common engineering metalscon-

    ure 4.2(A).Solidification proceeds, Figure 4.2(B),as the tain residual or intentionally added metanic and

    individual nudei grow into larger solid partides called nonmetallic elements dissolved in the matrix. These

    grains. As the amount of solid metal increases, of ingrediellts,called alloying elements, affect the proper-

    course,the amount of liquid metal decreases propor- ties of the base metal. The atomicarrangement(crystal

    tionately, and the grains grow larger until there is no liq- structure),the chemical composition, and the thermal

    uid between them. The grains meet at irregular and mechanical history have aninfluence on the Proper-

    boundaries called grain boundaries, Figure 4.2(C).   ties of an anoy.

  • Welding Meta目u「9y 91

    B.Body Centered Cubic

      Chromium

      |「onb

      Molybdenum

      Columbium

    【Figure 4.1(B)】

      Titaniumc

      Tungsten

      Vanadium

      Zirconiumc

    SOLID GRAINS        Table 4.1

    Crystal Structures of Common Metals

      A.Face Centered Cubic[Figure 4.1(A)】

       Aluminum       lronb

       Cobalta        Lead

       Copper        Nickel

       Gold         Silver

    INITIAL CRYSTAL SITES

    SOLID GRAINS WITH

    GRAIN BOUNDARIES

    a.CobaFt is face・centered cubic at high temperalure and transforms to

    hexagonal c10se packed al lower temperatures.

    b.lron is body-centered cubic near the melting temperature and again at low

    temperatures,but at intermediate temperatures iron is face-centered cubic.

    c. Titanium and Zjrconium are body・centered cubic at high temperature and

    heχagonal c10se packed at lowertemperature&

    C.Hexa9onal Close Packed [Figure 4.1(C)]

     Cobalta       Titaniumc

     Magnesium      Zinc

     Tin          Zirconiumc

    (B)Continued

     Solidification

    (A)lnitial Crystal

      Formation

    (A)Face-Centered

      Cubic

    (B)Body Centered

         Cubic

    (C)Heχa9onal-Close

         Packed

      (C)Complete Solidification

    Figure4.2-Solidification of a Metal

     A110ying elements, caUed solz4。s,are located in the

    parent metal matrix inoneof two ways. The solute

    atoms mayoccuPy lattice sites replacing some atoms of

    the Parent metal atoms, called the so4zg耐.Alternatively,

    if the solute atoms are smallenough,they may fit into

    spacesbetween the solvent atoms.

    Substitutional AIloyin9. lf the solute atoms occupy

    sites at the lattice locations as shown in Figure 4.3(A),

    then the type of alloy is called a substitutional solid solu-

    tion. Examples of substitutional solid solutions are gold

    dissolved in silver, and copper dissolved in nickel.

    lnterstitial AIloyin9.Wyhen the alloying atoms are

    smalhn relation to the parent atoms, they can locate (or

    dissolve)in the spacesbetween the parent metal atoms

    without occupying lattice sites. This type of solid solu-

    tion is called 加たr兌丿庇z/,and is illustrated in Figure

    4,3(B).Small amounts of carbon, nitrogen, and hydro-

    gencanalloy interstitiany in iron and other metals.

    MUltiphaSe AI10yS

    FREQUENTLY,THE ALLOYING atoms cannot dissolve

    completely,either interstidaUyor substitutionally.The

    Figure4.1-The Three Most Common Crystal

          Structures in Metals

  • 92 Welding Meta川urgy

    (A)

    (A)

    (B)

    (B)

    result,in such cases, is the formation of miχed atomic

    groupings(different crystamne structures)within a sin-

    gle alloy. Each different crystalline structure is referred

    Figure4.3-Schematic lllustration of Substitutional

         and lnterstitial Solid Solutions

    ferrite and the darkareas arepearUte. The latter struc‘

    ture is comPosed of two Phases, ferrite and iroil carbide.

    Figure 4.4(B)shows multiple Phases within the grains of

    an aluminum-silicon alloy。

     Commercial metals consist of a primary or basic ele-

    ment and smaller amounts of one or more alloying ele-

    ments. The alloying elements lllay be intentionally

    to as a phase, and the alloy is called a multiphase alloy.

    The individual phases rnay be distinguished one from

                          -     ---another,under a microscope at magnificationsof50to

    2000 times, when the alloy is suitably polished and added,or they may be residual (tramp)elements.Com-

    etched. The process of Polishing, etching, and exalnin’ mercial metals may be single or multiphase alloys. Each

    ing metals at some magnification is called metallogra- phase will have its own characteristic crystalline

    phy.Metallographic eχamination isonexvay of studying structure.

    the mally characteristics of metals alld alloys.       The overall allrangelllent of the grains, grain bounda-

     Two examples of multiphase alloysareshown in Fig- ries, and phasespresent in a metal alloy is called the

    ure 4.4. The typical microstructure of low-carbon pearl- micTostn4ct14Teof the anoy. The microstructure is

    itic steehs shown in Figure 4.4(A).The light areas are largely responsible for the physical and mechanica1

    Figure 4.4-Typical Microstructure of Tvifo Phase

     Pearlitic Low Carbon Steel. (A)Light Areas are

    Ferrite,and Dark Areas are Pearlite. (B)Fine Grain

       SamDle with Small Pearlite Patches

    metal.Microstructule is affected by welding because of

    the thermal or mechanical effects, or both, but the

    changes are confined to the local region of the weld. The

    metaUurgical changes in the local region of the base

    meta1(called the heat4ffected zone)can have a

    properties of the metj. lt is affected by chemical coIIlpo’

    sition,thermal treatment, and mechanical history of the

    ||

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    w i t h   t h e   a U o y   c o n t e n t   p l o t t e d   o n   t h e   h o r i z o n t a l   a x i s   a n d

    t e m p e r a t u r e 0 n   t h e   v e r t i c a l   a x k   T h e   e x t r e m e   l e f t   h a n d

    e d g e 0 f   F i g u r e   4 j   r e p r e s e n t s   l ( ) ( ) p e r c e n C p u r e j   n i c k e L

    w h n e   t h e   e x t r e m e   r i g h t   h a n d   e d g e   r e p r e s e n t s   1 0 0   p e r  

    c e n t   l P u r e j   c o p p e r

     

      A t   t e m P e r a t u r e s   a b o v e ( 2 u l   v e   A   i n   F i g u r e   4 j R   c a l l e d

    t h   e   j i g M i j z 4   t h   e   o n l y   P h a s e   P r e s e n t   i s   l i q u i d   m e t a L   A t

    t e m p e r a t u r e s   b e l o w   C 1 1 a e   B   c a n e d   t h e   s o j i j 9 5

     t h e   o n l y

    p h a s e   p r e s e l l t   i s   s o l i d   m e t a l

     A 1 1   s o h d   a l l o y s   i n   t h i s   d i a  

    g r a m   a

     r e   h o m 0 g e n e o u s   s i n g l e   p h a s e   s o l i d   s o l u t i o n s

    c r a c k h l g   d u 1 q i l l g   t e l d i n g   o r   h e a t   t r e a t m e l l t

                   

    t e m   i n   w h i c h   b o t h   e l e m e n t s   a r e   c o m p l e t e l y   s o l u b l e   i n

        F i n e f r a i n e d   m e t a l s   g e n e r a l l y   h a v e   b e t t e r   m e c h a n i c a l   e a c h   o t h e r   i n   a n   P r o P o r t i o n s   a t   a l l   t e m P e r a t u r e s

     i n   b o t h  

    p r 0 p e r t i e s   f o r   s e r v i c e   a t   r o o m   a n d   l o w   t e m p e r a t u r e s o   t h   e   l i q u i d   a n d   t h e   s o l i d   s t a t e s o   P h a s e   d i a g r a m s   a r e   d r a w n

    で7

    、?

    Aで

    §§

     §

     §

    J ω ( ) O

    J M O O

    ニ ( ) O

    J O O O

    コJ み ( ) ○

    TE

    MP

    ER

    AT

    UR

    E,

    OC

          4 0       Q O

    { い ○ で l m F ’ } m 刀 ( い m Z 。 「

    1 0 00

      ○j O O Z 一

    S S

    r i g u 「 e 4 j   N 一 c k e l   C o p p e r   P h a s e   D i a 9 『 s ヨ

    - ド)

  • 94 welding Metallu,gy

     The silver-copper system exhibits a more compleχ

    phase diagram, Figure 4.6.This diagram is used eχten-

    sively in designing brazing alloys. All compositions in

    this system are entirely liquid at temPeratures above the

    liquidus.Similarly,all compositions aresolid at temper-

    atures below the solidus. However, the solid eχists as a

    single phase in two areas of the diagram and as two

    phases in anotherarea.The silver-rich phase is called

    alpha(α),and the copper-rich phase is called beta (β).

    Both phases are face-centered cubic, but the chemical

    compositions and the crystal dimensions aredifferent.ln

    the region between the solidus and liquidus lines, the liq-

    uid solution is in equilibrium with either αoΓβphase.

    Finally,thearealabeledα十βcontains grains of both

    alpha and beta。

     This phase diagram illustrates another feature-the

    どgなdj(;poj耐.A110ys of eutectic comPosition solidify at

    a constant temperature. The eutectic composition solidi-

    fies differently than pure metals in that small quantities

    of alpha and beta phases freezealtemately eχhibiting

    intermingled grains ofαandβin the microstructure. For

    thls reason, eutectlc composlt10n rnlcrostructureshave a

     ● ●  ●dlstmctlve appearance。

     The boundary between the βand the α十βΓegionsin

    Figure 4.6 represents the solubility limit of silver in

    coPper. The βsolubility increaseswith increasing tem-

    perature, which is tyPical for most liquid and solid

    solutions.

    載匹一.E1 一肌rk

    ’一

    .E一一一一一一一一

    一一一・=一一・・・・=一一・一一’」E=”‘

    一一一一t’・一一

    一 一一一E‘=-・・・・‘・f‘t・fJ‘’、ま.

    ’t’。’万.4.・.、.

    DefOrmatiOn and Annealin9 Of MelalS

    WHEN METALS ARE Plastically deformed at room tem-

    perature,a number of changes take place in the micro`

    structures. Each individual grain must change shape to

    achieve the overall deformation. As deformation pro-

    ceeds,each grain is deformed, and as a result becomes

    stronger, making it more difficult to deform it further,

    This behavior is called z4ノo飛haγdeni,lg.The effect of

    cold working on the strength and ductihty of a metahs

    illustrated in Figure 4.7(A).The original properties are

    Partially or completely lrestol°ed by heat treatlllellt as

    shown in Figure 4.7(B).The microstructures of mildly

    deformed,heavily deformed, and stress-relieved metals

    areshown in Figures 4.8(A),(B),and(C)respectively・

    When the metal is deformed below a critical tempera-

    ture,there is a gradual increase in the hardness and

    strength of the metal and a decrease in duφlity. This

    phenonlenonis knovvn asCOld UノOγkiれg。

     lf the same metal is worked moderately [Figure

    4.8(A)]or severely [Figure 4.8(B)]and then heated to

    progressively higher temperatures5several things hap-

    Pen. At temPeratures up to about 400°F (205°C)μhere

    is a steady dedine in the residual stress level but virtually ,

    no change in microstructure or properties. Atabout400 `

    to 450°F (205 to 230°C),the residual stress has

    decreased to a relatively low level, but the microstruc-

    ture has not changed [Figure 4.8(A)and(B)].The

    strength of the metal is still relatively high and the ductil-

    ity,while improved, iss磁l rather low. The reduction in

    stress level and the improvement in ductility are attrib-

    uted to the metanurgical phenomenon called γecotノどり,a

    term indicating a reduction in crystalline stresses with-

    out accomPanying microstructural changes。

     When the cold-worked metal is heated to a tempera-

    ture above 450°F(230°C),mechanical proPerty

    changes become apparent, as do changes in microstruc-

    ture.ln place of the deformed grains found in Figure

    4.8(A)or(B),a group of new grains for111 and grow [Fig-

    ure 4.8(C)1.These grains consume the old grains, and

    eventually all signs of the deformed grains disappear.

    The new microstructure resembles the microstructure

    prior to cold-working, and the metal is now softer 皿d

    more ductile than it was in the cold-worked condition.

    This Process is called rEじりぶなz//咄咄0,7,a necessary part

    of annealing procedures. (Annealing refers to a heating

    and cooling process usually aPPlied to induce softening.)

    When heated to higher temPeratures, the grains begin to

    grow and the hardness and strength of the metal are sig-

    nificantly reduced. Metalsareoften annealed prior to

    further cold working or machining・

    EFFECTS OF DEFORMAT10N AND HEAT

    TREATMENT

    00 00 00 00

    8 7 6 5

    μ2

    jo 3un1vu3d

    1300

    1200

    1100

    1000

    900uo]rDトく∝山Is』]ト

    400

    300

    200

       40   60

    COPPER,PERCENT

    0 80 10020

    Figure4.6-Silver-CopperPhase dia9『am

  • Welding Meta目urgy 95

      10 20 30 40 50 60

    AMOUNT OF COLD WORK, %

            (A)

    400

    AIU3dOUd

    トフご犬ANNEALづ[RECOVERYIRECRYSTALIZEI    GRAIN GROWTH   I

    1000

    (B)

    1200200 600    800

    TEMPERATURE °F

    Figure 4.7-(A)The Effect of Cold Work on Strength and Ductility of Metals. (B)The Effect of Post Cold Work

     Steehs an iron alloy containing less than two Percent

    carbon.The presence of carbon alters the temperatures

    at which freezing and Phase transformations take place・

    The addition of other alloying elements also affects the

           (A)             (B)             (C)

    Figure4.8-Grain Structureof(A)Lightly Cold Worked,(B)Serverely Cold Worked,and

                 (C)Cold Worked and Recrystallized

    PhaSe TranSfOrmaliOnS in lrOn and Steel

    STEEL AND oTHER iron alloys are the most common

    commercial alloys inuse. The properties of iron and

    metals.                          the various phases (austenite,ferrite,and cementite).

     Pure iron, as mentioned earlier, solidifies as a body- The iron-carbon Phase diagram is shown in Figure 4.9,

    centered cubic structure called delta iron or delta涙雨咆.

    0n further cooling, it transforms to a face-centered Delta Ferrite to Austenite (on coolin9).This transfor-

    cubic structure called gamma iron ot a14stentte、The aus- mation occurs at 2535°F (1390°C)in essentially pure

    tenite subsequently transforms back to a body-centered iron,but in steel, thc transformation temperature

    cubic structure known as alpha iron oralPha ferγite. increases with increasing carbon content to a maχimum

    steel are govemed by the phase transformations they transformation temperatures. Variations in carboncon-

    1111de啄o d111rillg processing. Understanding these trans- tent have a profound affect on both the transformation

    formations is essential to thesuccessful welding of these temperatures and the proportions and distributionsof

  • 96 Welding Meta川urgy

    Figure4.10-Typical LamellarAppearance of Pearlite

    400

        tenite at the expense of delta and alpha ferrite. The

        lower temperature of therange(AI)remains at 1333 °F

    200 (723°C)for all plain carbon steels, regardless of the car-

        bon leve1.

         Austenite can dissolve up to 2.0 percent of carbon in

    600

      ゜C

    1600゜F

    2800

    800

    Ausienit● to Ferrite Plus lion Carbide(on coolin9)・

    This isoneof the most imPortant transformations in

    steel.Control of it is the basis for most of the heat treat-

    ments used for hardening steel。

     This transformation occurs in essentially Pure iron at

    1670°F(910°C).ln steel with increasing carboncon-

     (1)Ferrite-A solid solution of carbon in alpha ilon

     (2)Pearlite-A miχture of cementite and ferrite that

    forms in plates or lamehe

     (3)Cementite-lron carbide, Fe3C,present in pearlite

    or as rnassive carbides in high carbon steels

    tent, however, it takes place over a range of tempera-

    tures between boundaries A3 and AI, Figure 4.9.The  When carbon steels are slowly cooled from the austen-

    upper limit of this temperature range (A3)varies from itic temperature range, the relative amounts of these

    1670°F(910°C)down to 1333°F (723°C).For eχam- three constituents at room temperature depend on the

    Ple, the A3 of a 0.10 percent carbon steehs 1600°F chemical composition. However, austenite decomposi-

    (870°C),while for a 0.50 Percent carbon steel it is tion is suPpressed when the cooling rate is accelerated。

    1430°F(775°C).Thus,both at high and low temPera- When transformation does begin, it Progresses more

    ture the presence of carbon promotes the stability of aus- rapidly, and larger volumes of pearlite are formed. As

       Figuie 4.9-Thelron-Carbon Phase Dia9「am    `‘「」`F・“゛゛`゛`゛゛゛“J“・・・`・・“・ ゜`・u゛“゛●Allしゝ・lala6・ゝよよa-                             tlc lamellar structure3 known as pearlite, is shown in

                                 Figure 4.10.

    0f2718°F(1492°C).Steels with more than 0.5 percent Most of the common anoying elements added to steel

    carbon freeze diredy to austenite at a temperature further alter the transformat19n temperatures. Room

    below 271 8 °F (1492°C)and therefore, delta ferrite tell11??tt111e 1111c??t°ctures of lron-carbonalloy? at the

    does not eχist in these ste

    :1s.              equUlbrlum condltlons coyered by 少ls dlag聊m mdude

                                 one or rnoreof the fonowmg constltuents:

    solid solution, but ferrite can dissolve only 0.025。-・p9-

    cent. At the Al temperature, austenite transforms to ferj

    rite and an intermetallic compound of iron and carbon

    (Fe3C),called cE謂ε耐丿&.Ferrite and cementite in adja-

    cent Platelets form a lamellar structure. The characteris-

    WEIGHT PERCENTAGE CARBON

  • place. A TTT

    steehs shown

    To Produce

    bon steel were austenitized at 1550°F (845°C).The

    samples were then quenched to a variety of temPeratures

    below 1300°F in molten salt baths. Each specimen was

    ’diagram for 0.80 percent plain carbon

    1n Figure 4.12.

    this diagram, samples of 0.80 percent car-

    1 1 1~~・U・

    1 ほI’

    Welding Meta目urgy 97

    The lSOthermal TranSfOrmatiOn OrTIIT Dia9「amS

    THE IRON-CARj30N PHASE diagram is very usefuI. How-

    ever,itdoesnot(1)provide information about the trans-

    formation of austenite to any structure other than

    equilibrium structuies, (2)furnish details on the sup-

    pression of the austenite transformation, nor(3)show

    the relationship between the transformation products

    and the transformation temperature. A more practical

    diagram is the isotbemlal t7a,lsfoTmation or zj削ど-teyyl-

    peγatuγe一飢z心かアフ心哨077 j必g77z777. lt is also knoxvn as a

    ΥΥΥd≒rΓα朋.This diagram graphically describes the

    time delay and the reaction rate of the austenite transfor-

    mation to Pearlite, bainite5 or martensite. lt also shows

    the temperature at which these transformations take

    cooling.

    COntinUOUS COOling TranSfOrmatiOn Dia9「amS

    TTT DIAGRAMs HELP to understand the isothermal

    transformation of austenite. ln most heat treating

    Processes,induding welding, austenite transforms dur-

    ing the cooling Process. A diagram, simnar to TTT

    curves,called a 6o耐加μ0μscoo/加g沁z心八)r777討j0,7 jiz-

    salt bath. The reaction start times and completion times

    were plotted as shown in Figure 4.13.

     As shown in Figure 4,12,austenite at 1300°F

    grams ol many ‘

    1000°F(540°C).

     At temperatures below the nose, the transformation

    products change from pearlite to bainite and martensite

    with their characteristic feathery and acicular structures。

     As carbon and aUoy content increases, the TTT

    curvesshift to the right. When the curves move to the

    right, the steels can transform to martensite at slower

    cooling rates. These steels are said to have higher

    hardenability.

    carbides in ferrite is formed instead of pearlite. This

    feathery arrangement of shear needles with fine carbides

    in a fe雨te matriχ is called baiれite、lt has significantly

    higher strength and hardness and lower ductility thanhigher strength and haldness and lower ductility than (700°C)begins to transform after about 480seconds(8

    fine pearlitic structures.                 minutes),and the reaction is complete after about 7200

     With very fast cooling�