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    SECTION 7.1

    WELDABILITY

    OF

    STAINJ,ESS STEEL

    Page

    7.1-1

    7.1-1

    7.1-9

    7.1-9

    SECTION

    7.2

    7.1-10

    7.1-12

    7.1-13

    7.1-13

    7.1-H

    7.1-14

    7.1-16

    1-1-16

    WELDIXG STAINLESS STEELS WITH

    TH.l ; SHIELDED METAL-ARC PltOCESS

    Selectiug

    Blectrodes.

    . 7.2-2

    Considerations in Welding . . . 7.2-4

    Welding ProROCESS

    Joint

    Design

    Welding 1'rocedures .

    Weld

    Rackup .

    Indination

    of

    Work .

    Welding Flux .

    Welding Eledrodes

    Welding Technique.

    7.3-1

    . 7.3-2

    . 7.3-2

    . 7.3-2

    . 7.3-2

    7.3-2

    . 7.3-3

    Section

    7

    WELDING ST INLESS STEEL

    SECTION 7.4

    WELDING

    STAINLESS

    STEELS

    WITH

    THE GAS

    METAL-ARC

    PROCESS

    Spray-Are

    Transfcr

    _ .

    Short-Circuiting

    Transfl r

    P u l ~ e d A r c Trausi cr

    \Velding Electrodes .

    Specia.l CunRiderations .

    SECTION 7.5

    .

    7.4-

    7.4

    . 7.4

    7.4

    . 7.4-

    W:ELDlNG

    STAINLESS STEELS WITH

    THE

    GAS TUNGSTEN-ARC PROCESS

    Electrodes

    and

    Gases .

    \ ~ e l d i n g Rods.

    W ~ l d i n g

    Prucedures

    .

    Automatc GTA Welding.

    Hot-Wire Welding

    Muttiple-Eh.cirode Welding

    . 7.5-

    7.5-

    . 7.5-

    -. 7.5

    7.5-

    -

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    7.1 1

    Weldability of tainless tee

    about 0.04 percent

    c a u s e ~

    .:hromium carhide pre

    cpitation

    when

    exposed

    to temperatures

    hetween

    800 and

    HlOO F.

    This rlepletea

    thD

    matri.x in

    ~ h r o m i u m and reduces the corrosion resistance in

    local area, leadin;:

    to

    inl.ergranular corn>5on

    Si icon, in larger amounu ihan used in othe

    alloys, increasca oxidution resistnce

    at

    high tenl

    p e r a t u r e ~

    Hulfur ami seienium impart free-machinin

    charactcristics. Niobium , . ] ~ o call ... I columbium

    tit.anium, and tant.alum additions stubilize carbide

    and reduce H u ~ c e p t i b i l i t y to intergranular couoHion

    ISI ST INLESS STEEL GR DES

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    7 1 2 Waldlng Stainless Steel

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    Weldability t Stainless Steel 7.1 3

    TABLE 71. Correiation

    ol

    Specificafions

    lor

    Stainless Sfeels Conlinued)

    Casi Alloys

    e

    1

    -

    1- -

    r=--

    50442

    CB

    30 A2g6

    _ _ _ l _ - - ' ' c = ' c - c ~ , O ~ . ~ -

    j_' _ _'

    ____:_ A : -

    A296,

    A35

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    71 4 Welding tainless teel

    Othert

    7_

    6

    P

    10.0 Mn

    6

    P

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    We/dability o Stain ess Steel 7.1-5

    Fig 71

    l

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    7.1 6

    elding

    Stainless Steel

    single

    alues dencte m a ~ i J r v m porcen agc unless QlherwLOC noled.

    Untes

    ctlwrwisa oo:oo. utl1er gloments of all alloys l1sled lncltJde maxlmum contsnts nf 0 SI.

    O

    040% P n 0.0300 S Balance

    is Fa

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    We/dability

    o

    Stainless Steel 7.1 7

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    7 1 8 Welding tainless teel

    T SLE 7-. Typicat

    C o m p o s i t i o ~ s

    ol Miirtensitic Slairlless Steels

    :composmon

    ( )

    1 ' '

    '

    j j _ = ; ~ ~ _ ~ 2 5 2 ~ -

    1

    12.0-14.0

    1 25 Mn. O 15 S min). 0.060 P. 0.60 Mo opt)

    ,

    ; ~ : ~

    =

    : : ~ i 1.25 Mn, O 060 P. O 15 Se rnin)

    Duplex nfcgs

    Steels

    The duplex stainless

    s\.eels typicully

    consist

    of a

    micro5tmcture

    of

    ahout

    50

    percent

    ferrite

    and 50 percent

    austenite

    but may

    range from 20

    t< >

    80 volume percent

    ferrite

    They

    were developed

    to pro

    vide a

    higher

    strengttiTurrosion-

    reHiatant- alternative to....the

    300

    series austenitic

    stainless steels.

    Compositinns

    are modified

    to

    favor

    the high

    ferrite levels

    by increasiug

    the

    chromium

    tu 22-26%, increaaing mulybdenum to 2-5%, decreas

    ing

    the

    nickel

    to

    4-8%

    aud adding copper up to

    2%.

    These compositions, .

    Table

    7-8, p r o v i d ~ exr.ellcnt

    resiatance to pitting, crevice corrosion and stress

    corrosion

    cracking.

    These compositiuns

    also provide

    oseful m ~ c h u n i c l properties,

    l able

    7-9, over a

    temperature

    range from as low as 50 F to 500

    with yield

    strength

    nearly twice thaL of wro1 1ght

    austenitic otail'lless steel and duetility and toughness

    approaching those of

    austenitic

    stainless steel. The

    pretrred 50 percent ferrite - 50

    percent austenite

    microstrudure uf ihe duplex ~ t a i n l e 8 s steels is

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    ; _

    Weldabifity o Stainless Steel 7. 1 9

    T BLE

    7-8. Composiliorl ol

    Duplex

    S t a i r ~ l e s s

    Steels

    experimental duplex ~ l a i n l e ~ s steels u deter1nine

    the effects of

    filler

    metal composilion and welding

    a

    type

    304L stainli'SS steel

    of

    FN 4.5 hut. l ~ s

    susceptible

    than

    a typc

    304L

    stainless steel of

    FN

    O. The two

    experimental

    duplex alloys identified s

    21-9 and 2il-7 in 'fable 7-R were le&R susceptible to

    weld metal hot cracking than the commercial duplex

    stainless. Bot.h of these experimental allnys

    are

    < ~ 8 t l l t i . . l l . y

    free

    of

    M

    u and

    Cu.

    This leads the

    belief

    that

    :Mo

    anrl

    Cu

    form low

    melting

    with

    iron which could

    cause

    Lhe hut.

    s u ~ c e p t i b i l j t y .

    pm.:edure

    on

    weld

    properties

    a:nd l1ot cracking WELDING THE ISI ST INLESS STEELS

    tendenc.y. Metallographic examinatio n, tensile

    tests,

    Charpy impact

    tests

    and Varestraint

    tests

    were used

    not

    to evalnate

    the welds

    by

    severa. investiga.tors.

    the

    Mechanical test results showed that when ferr.ite-

    eontent

    is

    below 60 EFN (approJrimately 60%) in

    nearly

    matching

    wt>ld deposits for alloys 255 and

    ~ 2 0 5 sufficient ductility and

    toughness

    would be

    attained t pass

    a

    side b< lld test and provide

    a

    Charpy "V" notch energy of

    20 ft-lhs

    at

    50"F.

    Weld

    deposits of

    nearly makhing

    compositions with

    ferrite

    conients ur OYt r ao EFN

    (appro:ximately

    30%)

    providcd tensile strength and

    yield

    strength

    equivalent

    to

    that

    of

    baae metal.

    While

    molybdenum

    is added

    to r o ~ i d e

    r ~ s i s t a n c e

    to

    pitting and

    crevice

    rorrosion, high

    l ~ v e l s

    (4.0%

    and over) cause embrittlcment

    of

    the deposit, even

    for

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    7.1 10 Wefding Stainless Stee/

    limitations

    thut

    require

    cureful a t t ~ n t i o n r l u r i n ~

    procesaing. Anst.enitic ~ t e e l s

    h v ~

    a h1gh coeIiciont

    of

    thermal

    expansion - over 50 highEr

    than

    that

    of

    carbon

    ~ t e e l or

    of

    the

    100-series alloys - which

    d e m n d ~ maximum ~ r e tfl minimize disWrtion and

    warping of wclded parts. Sorne of Lhcse alloys are

    sus(:eptible to the formatiun of sigma

    phase

    whcn

    expo&ed

    to certain high

    t e m p ~ r t u r e

    ranges, which

    can cause cracking und reduce corrosion r ~ a i ~ t a n c e

    unrler

    c ~ r t a i n

    conditions. Welding can

    als o

    cause

    carbde vrecipitatlon in sorne ~ t a i i l l : f f l s grades which

    decrcases the corrosion resistance in sorne chemical

    media.

    errite and Sigma Phase

    Austenitic stainless steels may be

    susceptible tu

    hot cracking (micro-fisSurin) if the

    ferrite

    t:ontent

    in the weld metal is. not

    properly

    controll_ed.

    This

    problem

    is

    corrected by

    u ~ i n g

    electrodes

    that

    deposit

    weld metal containing a small amount of ferrit..-.

    Thus, recommended- electrodes for many Htandard

    austenitic

    grades may deposit weld metal that

    contains 3

    to

    5% ferrit. llvt: n, tbough

    tbe

    same

    grade base metal c u n ~ i n s no-fe:rrite. Since e r r i t ~

    li magnetic, it s casily

    detected

    in :m otherw:ise

    IlDrunagnetic weldment

    Ferrite is best determiwd by measurernent

    with

    a magnetic instTument

    caltbrated to

    AWS A 1.2. It.

    can

    also be estnated from the c-omposition of the

    base material

    and

    filler material

    wilh

    the u ~ e of

    any of severa

    constitution

    diagrams.

    The oldest

    .of

    these

    is

    tbe

    19-tS Schaeffler

    Diagram.

    The

    Cr

    equivalent ( Cr +

    %

    Mo + 1.5 x

    %

    Si + 0.5

    x Cb)

    plotted

    on the

    horizontal

    axis

    and the

    nicke] equivalent { Ni + 30 X C 0.;) X

    Mn)

    on

    the vertical axis. Despite long u ~ e , the

    Schaeffler Diagram is now outdnted because it does

    not cunsider nitrogen

    effects

    and because it

    has o-f

    proVen possible

    to

    s t a b l i ~ h

    agreement

    among severa]

    measures

    as

    to

    the ferrite percent

    in a given weld

    metal.

    An

    i m p r o v ~ m e n t

    on the

    Schaeffler

    Diagrsm

    ia

    the 1973 WRC-DeL

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    1

    1

    _\

    eldabifity

    o

    tainfess teel

    7 1 ~ 1 1

    Fig.7-4.

    Oelo c o n e l l ~ o n

    dragram fe aJstenltic s t a ~ n . e s s steel weld

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    7.1 12 Welding Stainless Stee/

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    Weldabi ity o Stainless Steel 7.1 1:3

    Ferritic Grades

    These grades have what is me1allurgir.ally known

    a

    ferritk

    mirrostructure. 'l'hey

    are magnetic and

    nnnhardcnable

    hy heat treatment.. Typical applica-

    automobilc trim und

    rnufflcn, interiur

    lectrode Selection Without Heat Treating

    Ferritic or

    martenaitio;...steel weldments

    to

    he

    used in

    the as-welded

    condition

    shou d he welded

    with

    E308,

    E309,

    or

    E3HJ electrodes.

    The

    ductile

    chrominm-nickel welds r e s i ~ i cracking from

    ddor

    nt8lion

    nd impact

    bett.er

    than ifthe

    wcld

    and hcat

    Hlicctocd zone wcre [)()th

    brittle.

    However, d i T e r e n c e ~

    in thermal e pansion rates, weld

    and

    base metal

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    7.1 14 Weldng Stainless Steef

    propert.ies ffi>JY require

    chromium-typc clcctrode.

    Duplex Stainless Steels

    The

    duplex

    stainless attain

    their

    duplcx

    structure of roughly 50 and 50 austenite

    after an anncaling heat treatmenl or hul wurking.

    Weld deposits in these alloys with matching filler

    metals

    solidify

    and remain

    mmrly

    100%

    ferrite. This

    single plw.se deposit is mnch more su&eeptible

    hot cracking than a

    mixed

    d ~ p o s i t of ferrite

    auslenite.

    A

    post

    weld

    annealing

    l . n n m ~ n l

    o :auRe

    the

    ferrite to partly transform to austenite

    and improve

    the dnctility_ H o w e ~ e r

    hot

    cracking

    normlly would occur

    befare

    t he h o>ai

    l r e H L m ~ n i

    could

    be accomplished.

    In many

    cases,

    t

    would not

    be acceptable

    or

    feasible lo

    heat

    treat the

    entire

    welded assembly.

    Preheating and Postheating

    - Austenilic

    slululcss-steeh

    are best wetded without

    preheat except

    to

    reduce shrinkage stresses on thick

    ~ e c t i o n s

    or reslrainedjuints. No preheat,

    low

    interpaas

    t ~ m p e r a t u r e

    or a

    stringer-head tech:nique reduce

    the

    time the heat-affected

    wne

    in the s e n ~ i t i z i 1 1 J 5

    range

    {800-l60WF).

    thereby reducing the amount of

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    ~ L r c n g l . h e n P d

    by a low-tempenttun (900 tu 1150'F)

    heal. r . r e a l m ~ n t .

    Precipitation hardcning is mcthod

    of increasing hardness aod

    strength

    metal.

    Although sorne

    variatinns apply to

    grades,

    precipitation bardening

    H

    g e n ~ r a l l y accomplished

    by a three-step heat

    treatmcnt

    consisting of solution

    l.reatment, rapid cooling. and

    c o n t r o l l ~ d

    reheating

    (aging)

    The first step

    (solutinn

    heat treating) d h s o l v e ~

    ccrtain elcnwnts such as copper, titanium, niobium,

    and aluminum, t h a l _ a r ~ normally

    insoluable

    at

    room

    icmpemture.

    1'llis mechanism might be ~ : o m p a r e d

    with

    thc

    abilily

    o hot water

    tu dissolve more

    salt

    than can

    cold

    waler

    The ~ e c o n d stcp

    {quenching) eools

    the

    metal

    ra]Jidly

    to retain thc

    solution cffcct

    al room

    temperatme.

    'Fhia conditlun sumetimes called a

    s u p e r ~ u l u r a t e d solid solution.

    The

    third

    step involves

    reheating-

    of lhe super

    saturaWd metal to a relutively low aging

    temperature

    (about

    900"F

    for sorne

    grade>s 1p1ns

    Aus1enitic Grades

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    heat exchangen v a l > E . ~ and high t ~ m p e r t u r e steam

    lines

    Weldability o Stainless Steel 7 1-17

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    7.1-18 We ding Stain ess Steel

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    1.2 1

    Welding Stainless

    teels with

    the hielded Metal Are

    Process

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    72 2 Welding tainless teel

    SELE TING ELE TRODES

    Mechanical properties of

    stainless-steel v eld

    mdul

    usually are not as impmtant the chemical

    compositin (Table 7-14)

    and

    the heat treatment.

    l h e r ~

    lli

    little difference in mechanical propertieR

    or

    chemicRI

    composition

    hetween

    the

    DC

    EXXX-

    15) ~ n r l the AC-DC (EXXX-lG) weld deposits made

    Vith

    electrodes of the same

    dass.

    Typical mechanical

    ofstaiillCHH-Hted weld

    metal are

    giv en

    in

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    TABLE

    7-14. Typical Compositions

    ol SlainlessSieel Weld Metal

    AWS

    Compogl\ion ( )

    Type

    C 1 .

    c

    1

    Nb (Cb)

    ~

    ~ ~ : ;

    . .

    TABLE 7-15. Typical Mechanical Properties

    ot t a i r ~ l e s s t e e l

    Weld

    Melal

    AWS Type

    1 e n ~ ~ ~ ~ s ~ : ; g t h

    00

    Elongatlon

    n

    2in.( )

    ~

    -- --

    more care t-o

    avoicl slag inclt1sions.

    Thcso clectrodes

    ~ r e

    recommenderi

    for

    horizontal

    fillets

    and fnr

    al

    fiat-position

    welding.

    EXXX-16

    electrodos

    are

    also

    \lRed

    in

    all

    positions

    by skilled

    weldors.

    Selecting

    the

    proper

    electrode must bu done

    with

    care

    because of the lar;e

    nLJmlJ

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    7_2 4 Welding Stainless teel

    TABLE 7 7

    T y p i c < ~ l

    Filiar Metells f,r D h ~ s l ~ l l a r Metal Joints

    Austenitic Stainless

    ~ - ~

    304L 1 308 309

    J\l9S J10S 3 ; ~ ~ J16L

    317 2 ~ ~ =

    - - , = , ~ , _

    = , + - - - - + - - + - - - + - + - - - - - ~ - - - + - - - - + -

    1

    CONSIDE TIONS IN WELDING

    Cleaning

    .l< or

    high-quality

    welds, joints must be

    dean and d;... The choice of power b r u ~ h i n g

    degreasing,

    pickling, grinding, or msrely

    wiping

    depends 1.1pon the kind and amount of dirt. Sorne

    specific recommendations

    are;

    l Remove moisture by heating or by

    with

    dry

    air

    beware

    of

    mniHlure

    in

    lino). Moisturc caJJ collect

    overnight in high-humidity

    3. Flame-beveling and machining

    may

    leave

    n>ntaminants or

    oxide films 1

    hat

    must be

    removed.

    4.

    Avoid

    zinc

    COJltamination from b r u s h ~ ~ or

    tools

    that

    have

    heen

    uRed

    on galvani:r.ed steel.

    UHe nnly

    stainless-steel win< bruahliB

    that

    have been used

    only on

    s t a i n l ~ s s steel.

    Welding Procedure

    ,Joint Design Accurate

    fitup

    and good

    preparation are

    necessary for good wtdd

    minimum

    disiortiun. Joint desig:ns are to

    those dcscriUed for mild BteeL

    For

    butt

    welds on

    plate to

    l/2-in.

    thick,

    the

    beve

    shuuld

    b J a 60"

    induded

    angle for good

    penetration and easy

    slag

    removaL On plate

    owr

    1/2-in. thid1. and up tD

    1-1/2

    in.

    tlck,

    a double bev.,J ;

    r e ~ o m m e n d e d i f

    the

    welding

    can

    be

    done from

    both sidcs.

    Fot buU

    welds

    over 1-in.

    thick

    that

    m u ~ t be

    done from

    one

    side, a

    U-groove is used.

    For

    butt

    welds in plate over

    l-J/2

    in. thick

    that can

    be

    welded

    from bnth sides,

    a duuble U-gruuve is recommended.

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    Welding l . e c b n i q u ' ~

    can

    lwlp control

    distortion.

    \Veld

    witb

    low

    current consistent

    with

    sufficient

    penfltYaLion

    tu

    r e < : l u c ~

    the heat

    inpLJ\,

    to the work

    Table 7-lB). s t r i n g ~ r beads-11t a

    higher

    speed

    ratht r than

    wide heads

    at

    a slower speed.

    f

    weave

    bcads nust be

    made, limit the weave

    to

    2-112

    times

    the etectrode diameter.

    Ol.l1er

    means to

    contml distortion a.-e:

    IJse rigid fixt.ures

    to

    hold parts in < ~ l i g n m e n t .

    Shielded Metal Are Procass 7.2 5

    : : : ~ 7 5 . Bunenng' t&:hmque lor JOin c ; mtld steel

    ~ ' o r

    prelwating

    and postheating

    information

    HH J

    Mction7-l .

    Joining Stainless tmd Other Stecls:

    lLl ~ o m e

    applicativns,

    stainless-stcel

    weld-mcutl

    s applied tu

    mild steel: for example,

    lining

    mild-steel vessels

    ur

    t:ontainer

    with

    ijtainlcss steel.

    fo'or such

    applications,

    stainless

    electrodes

    with

    higher

    alloy

    content are

    \13ed so

    th

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    Shielded Metal Are Process 7.2 7

    SIIIELDED METAL-ARC MANUAL)

    A l S I 3 0 0 S e r i e < S t ~ l n l e . . Steels

    =:- :=ce==---- - - - - - - - - - - - - - - - - -

    SHIELDED M E T A L ~ R C MANUAL)

    Al SI Seris

    300

    Stainler s t ~ ~ l

    ~ ~ ~ ~ - - - -

    ~

    e

    l >ockng

    go

    1/4

    ~

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    7.2-8 We ding Stainless Sfeel

    \Vhen

    stainless-steel

    b

    joined to mild steel, t h ~

    mild steel is buttered with

    stainlesB steel. This

    technique consists oi dpositing a ]ayer of atainless

    on the surfacc o the mild steel. then

    complcting

    the

    joint wth

    stainleas eleclrude, as illuslrated in

    Flg. 7-5.

    The

    elec:trode

    commonly

    used for buttering

    is F.309. 'fhiH tedmique is ahm u ~ e d for

    joining

    hurd-toweld or high-carbon steels

    that

    cannot

    be

    preheated.

    J < ~ 3 8

    Blectrmle is

    used

    l'or juinln(

    > H J ~ 1 H n i t i ~

    mnngancse

    steel to

    carhon steel

    or

    to

    manganese

    stt'el. However, for

    cornpunents

    that ITI\JSt be rep aced

    periodically, such

    as

    dippcr

    teeih,

    a

    mangauese

    clectrode ia recommended because the stainless weld

    is

    more difficulLt torch

    cut.

    There

    are

    severa] methods for applying a stainless

    sllrface to

    mild

    steel.

    For

    a

    small area. overlapping

    wcld beads

    are used, Wl illustrated

    in Fig.

    76(a).

    For larger

    areas, staiuless

    sheets are plug-welded to

    the mild steel [log. 7-6(b}, or stainless

    strips

    are

    attach

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    Electrodes and Gases

    7.5 1

    Welding

    Stainless

    Steels with

    the as Tungsten rc Process

    Welding Rods

    \Velding

    rods

    (filler metal) J'or gas lungsten-ar,.

    welding are specified in AWS Af>.9-8l, and Lheir

    chemical compositions are shown in Table 4-20.

    TlwrB

    no

    specificatino

    forthe

    mechani.,al

    r o p e r t i e ~

    of

    the

    weld metal. According

    to

    AWI:i A5.9-81

    thc

    c l s ~ i f i c t i o n

    is on

    the basis of

    chPmical

    composition

    of

    th"'

    iillcr metal

    manufactur ed. Meehanical

    testl

    have not

    bE

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    7.5 2 Welding Stainless Stee/

    tu thE has"

    metal

    of

    corresponding

    chcmica.l

    I'Oropooit.ion

    Welding rocedures

    Typical procedures

    for gas

    tnngsten-arc

    weldinr;

    of

    sLa.inless stee] are givcn in 'l'ablc 7-23.

    Filler-metal

    selection

    is

    very

    important in

    GT

    welding and um mlly "pecifed

    by the

    design

    engineer. f

    no

    class of filler

    metal is

    speclficd,

    - Table

    716 can

    be 11sed

    as

    a general guide

    to

    filler

    metal ~ e l e c t i o n .

    When two dilferent

    t.ypes of t a i n l e s s

    steels

    are

    t o be

    joined, Table

    7-17

    can

    be

    used

    as

    a guide.

    However, the

    tables should be

    used

    with

    caution. Where

    corrosive

    conditions

    are severe,

    the

    filler-metal selection

    can

    be very r i t i c a ~ as indicated

    in the footnot.e to

    Table

    7-16

    The

    DC pQwer

    ~ o u r c e

    for

    gM

    Lunghtcn-rc

    welding must be a

    variablevultage

    typc,

    and l t

    is

    recommended that

    a highfrequen

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    1

    1

    AUTOMA TIC GTAW WELDING

    Stainless

    steels

    are

    readily welded

    with

    automatic

    GTAW Are voltage is

    propurtional

    to are

    lcngth

    -

    thna, a reliablc signa

    can

    be generated to

    operate

    automat.ic arc voltage control

    cquipment.

    Filler metal

    may be used, or light-gagc material

    ma.v

    be juined

    by Himple fusion of the

    joint

    e d g e ~ .

    Wheu c o l d ~

    filler

    meil

    is u ~ e d ,

    it

    is

    always

    added

    to

    the front

    -

    of

    the puddle.

    Hot Wire Welding

    The

    so-called

    hot.wire

    method ofwelding gives

    greatly

    increased deposition

    ratBs

    and

    wf'lding

    sp1 do..

    The wire - which tra1ls thc torch,

    S

    i lustrated in

    Fig. 7-13 -

    is resistsnce heated by

    a separat.e AC

    1

    1 power supp]y,

    lt

    ia fed through a contad tube and

    extcnds beyond

    ihe

    tubo.

    The

    extension is resistance-

    heated that t

    approaches

    ur read1e11 the melt.ing

    Gas

    Metal Are Process 7.5 3

    hase

    metal

    and the AC power oupJIIY furniHheo.

    a

    targe portion

    of the

    energy

    needed to

    resistance

    melt

    the filler wire. The hot-wirl'

    method

    iH, in

    cl feet,

    an adaptation of the

    long siidwut principie

    u ~ e d in anllmerged-arc

    and

    aelf-shie\ded flux-cored

    are welding. The wire u

    sed

    for hot-wire

    GT A W

    welding is usually 0.045-in. diametn Since the wire

    is mclled - or very nearly melted - by ita own

    power

    sources,

    the

    deposition rate can

    be contrvl Rd

    almost independPntly

    of

    the

    Using the GTAW

    hot-wiru

    rates up to

    18

    lb/hr

    can

    be

    at

    -100 to 500 amp DCI ;N {Table

    greater

    depositiun rates

    can

    be ubtained using an automatic

    oscillated welding technique. Voltage control ia

    e ~ ~ e n t i l

    to achieve

    control

    uf

    the

    large pudlile

    when

    welding at high depoAition ratt'S.

    For this

    reason,

    GTA hut-.oorire welding requires

    t h ~

    use

    of

    ~ - o l i l l g c

    cuntrol equipment.

    Multiple Eiectrode Welding

    i l ~ ~ ~ t ~ ~ f o ~ c i r ~ ~ ~ i ~ ~ ~ ; l i ~ ~ s w ~ ~

    ~ ~ ~ ~ ~ ~ ~

    By

    using cloHely ~ p c e d multiple

    tungsten

    electrodes,

    the

    welding speed

    can also

    be

    increased

    s u b s t . ~ n t i ~ l l y when

    GTA\V we ding: stainles8-Meel

    tuhing

    or sheet.

    Multiplc cleill_mhl prNctically

    climinate

    the problem

    ofundercutting

    l l t higl1 ~ p c P d s .

    TABLE

    7-25.

    Typtcat Speeds and Deposition Rafes

    with GT W HDI Wlre

    Oeposition

    lb/hr

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    7.5 4 Welding Stainless Steel

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    JOINT O SIGN

    7.3 1

    Welding

    Stainless

    Steels with

    he Submerged-Arc

    Process

    l:mtted since weld hHcking is not. u s ~ d - Thc advantagc

    of this

    joint

    design

    is

    that

    it

    requires

    a

    of ocdge preparativo,

    yet

    produces

    weJ,-JH

    qualily having- ~ d e q l l e pen.,lration

    Single-V

    groove

    welds with

    a root

    face, Figure

    7- Tb, are used with nonfusible backing for single

    pass butt welds of 5/16-in. thickness or greater. Fur

    most industrial applications, tho maximum thickness

    is of

    the

    onl.,r of 1-114

    Lo

    1-1/2 in. Ruot face

    dimensions

    are

    1/8

    to

    3/16 in.

    This

    joint design is

    also

    UsBd for

    lwn-pll m wcldb wit.hnut

    b a c k i n ~

    whcre

    plat.e

    thickness

    < Xceeds

    5/8

    in.

    The

    first

    p a ~ s is

    made in

    the

    V

    of the joint,

    Figt1re 7-Th- The work

    is thcn turned

    over

    and

    th

    first pass bcomes the

    backing

    pass. n this position, the

    finishing

    pass is

    made

    on thc llat ~ i d c of the

    joint

    penetrating into

    the rootofthe first pass. l herootface isapproximately

    3/8

    in.

    for

    l w n - p a ~ welds.

    The doub\e-V groove butt, Figure 7-7d,

    is the

    basic joint desi;;n for Kubmerged-an; welding. A \ar.;e

    root face is generally ued with this desig:n. Figure

    Fig

    lar submerged arc w ~ l d 1 n ~

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    7.3 2 Wefding Stainfess Steel

    7 8

    shows

    a

    typieal

    double-V groovc wcld in

    3 in.

    3[)4 plate and d e ~ c r i b e s

    the welding

    se

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    Submerged Arc Process 7.3 3

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    7.3 4 Weldmg Stainless Steel

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    7.4 1

    Welding Slainless Sleels with

    lhe as

    Metal Are Process

    SPRAY ARC TRANSFER

    l

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    7_4 2 Welding tainless teel

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    PULSED ARC TRANSFER

    as

    Metal Are Process 7.4 3

    Pulsed CMA welding < haracteristicR are excellcnt

    tranafer

    with lowcr currellts. Thcre are many

    advantageo

    with thia

    procesa

    induding

    low Rpatter,

    pcnctrirrilm without

    melt through and

    excellent

    operator appeal

    WELDING ELECTRODES

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    7A-4 Welding Starn ess Steef

    will he

    ul>ta.iue_d at

    a welding

    \:llrtent

    of

    amp

    llC:EP. F ~ u r e 7 12

    i l l m t r _ a t ~ s

    t.yPical

    ra_te c:urves

    f ~ r various stamless-

    steel

    Kas

    ~ z ~ ~ u ~

    : ; ~ ~ n ~ ~ ~ ~ i ~ l ~ i ' ~ ~ : t : l ~ ~ ;

    ~ ~ i ~ d ~ :

    minimum

    current

    minim11m

    are

    volt.agc must

    also

    be

    obtained.

    fhis 1s generully

    betwccn

    24 anct

    31)

    v

    It increases

    with

    an increase in

    current.

    and

    i8

    h i K h e ~

    for

    helium

    ~ h i e l d i n g t.han for

    argon or

    arKon CO,

    SPECI L CONSIDER TIONS

    _______

    .

    -------

    whcn wclding magnet

    :> For uniform fusiun.

    centered

    over- the

    joint.

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    Gas Metal Are Process 7.4 5

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    7.4 6 Welding Stainless Steel