Chapter 1 - Weldability of Metals.pdf

1. Weldability of Metals

1. Weldability of Metals

4

DIN 8580 and DIN 8595 classify welding into production technique main group 4 "Joining“, group 3.6 "Joining by welding“, Figure 1.1.

Production Techniques DIN8580

Maingroup 2 Deforming

Maingroup 1 Forming

Group 4.1  Assembling

Group 4.2 Filling

Group 4.3 Pressing

Maingroup 3 Separating

Group 4.4 Joiningby forming

Maingroup 4 Joining DIN8593

Group 4.5 Joiningby deforming

Maingroup 5 Plating

Group 4.6 Joiningby welding

Sub-group 4.6.1 Pressurewelding

Maingroup 6 Changingmaterial characteristics

Group 4.7 Joiningby soldering

Group 4.8 Bonding

Sub-group 4.6.2 Fusionwelding

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ClassificationofProduction Techniques toDIN8580

Figure 1.1

Material Weldingsuitability

Weldability of a component is determined

by three outer features according to DIN 8528, Part 1. This also indicates whether a given joining job can be done by welding, Figure 1.2.

W     e  l    M    d    i    a  n   n    g     p   u    f     a  c   o  s  s   t    i    b    u    r    l    e   i    i    t     y   

Weldability ofa component

   t  y    e    f   as   n   g    g    n    i    i   s    l  d    D  e   e W

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Influencing Factors on Weldability to DIN 8528 Part 1

Figure 1.2

1. Weldability of Metals

5

Material influence on weldability, i.e. welding suitability, can be detailed for a

better

understanding

in

three subdefinitions, Figure 1.3.

The chemical composition of a material and also its metallurgical

properties

are

mainly set during its production, Figure 1.4. They have a very strong influence on the physical

Figure 1.3

characteristics of the material .

Process steps on steel manufacturing, shown in Figure 1.4, are the essential steps on the way to a processible and usable material. During manufacture, the requested chemical composition (e.g. by alloying) and metallurgiBlastfurnace: Reductionoforeto rawiron IntakeofC,S,andP

Top-blow(BOF)-,bottom blow(OBM)-,stirrerconverter 

Converter: RemovalofCandP throughoxygenandCaO

cal properties (e.g. type of teeming) of the steel are obtained.

Another modification of the material behaviour takes place during subsequent treatment, where the raw material is rolled to t o processible

Injectionof  solidmaterial orfeeding coredwires

Ladletreatment:  Alloyingandvacuum  Alloyingandva cuum degassing(removal ofN2,H2,CO/CO2) Ladletreatment electricallyheated

semi-finished goods, e.g. like strips, plates, bars, profiles, etc.. With the rolling process, material-typical

transformation

processes,

hardening and precipitation processes are used to adjust an optimised material characContinuouscasting: castingofbillets, blooms,slabs br-er01-04-E.cdr 

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Important Process Steps During Steel Production

Figure 1.4

teristics (see chapter 2).

1. Weldability of Metals

6

A survey from quality point of view about the influence of the most important alloy elements to some mechanical and metallurgical properties is shown in Figure 1.5.

C

Si

Mn

P

S

O

Cr

Ni

Al

Tensilestrength

+

+

+

+

(-)

+

+

+

+

Hardness

+

+

+

+

+

+

+

Charpy-V-toughness

-

-

+

-

-

(-)

++

+

+

-

-

--

Hotcracking Creepresistance

+(-400°C)

(+)

Critical coolingrate

-

-

-

Formation ofseggregations

+

++

++

Formation ofinclusions

+Increaseofproperty ++Strongincreaseofproperty

++ (+)

+ + withMn withS

-

++

(-)

+ +

+ with Al

+

-Decreaseofproperty --Strongdecreaseofproperty ©ISF2002

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Influenceof AlloyElements onSomeSteelProperties

Figure 1.5

Figure 1.6 depicts the decisive importance of the carbon content to suitability of fusion welding of mild steels. A guide number of flawless fusion weldability is a carbon content of C < 0,22 %. with

C-content(%) (Meltanalysis)

Fusionweldability

S185(St33)[EN10025]

unlimited (upto0,30)

Notguaranteed,howevermostlyno problemwithlowC-content

S250GT (St34), (St34),S235JR(St S235JR(St37), 37), S275JR(St42)[EN10025] L235GT (St35),L275GT (St45) [SteelsfortubingEN10208] P235GH(HI),P265GH(HII),P285NH(HIII) [SteelsforpressurevesselconstructionEN10028] C10(C10),C15(C15),C22(C22) [CasehardeningandtemperingsteelsEN10083]

upto 0,21

upto0,22%C:goodweldable(exception: platethickness <0,5mm,specialorder  condtions),aslongascontentof  impurities(P,Setc.)nottoohigh

S355J0 (St 52)

up to 0,22 and higher   contentsofMnandSi

Weldable

E295(St E295 (St50) 50)Ste Steelfo elformec rmechanica hanicaleng lengineeri ineering ng

unlimited, unlimited, about0,30

Restrictedweldabilitywithelectricarc methods,nogasweldingofthinplates.

E 35 35 5 ( St 6 6 0) 0) ,, C3 C3 5 5 (C (C 35 35 )

a bo bo ut ut 0, 0,4 0

We ld ld ab ab le le w w itit h h sp spe ci ci al al e e le le ct ct ro ro de de s a nd nd mostlypre-andpost-weldingheat treatment.

E360(St70),C45(C45)

about0,50

Veryrestrictedweldabilityinspite ofspecialmeasures

Material

upto 0,17 upto 0,22 up to 0 ,1 ,1 8 (up to 0 ,2 ,2 4) 4)

higher C contents, there is a danger of hardening, and welding becomes only pos-

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sible by observing special

FusionWeldabilityof  UnalloyedQualitySteels

precautions (e.g. pre- and post-weld heat treatment).

Figure 1.6

1. Weldability of Metals

7

In addition to material behaviour, weldability is also essentially determined through the design of a component. The influence of the design is designated as welding safety, Figure 1.7.

WeldingSafety

(Weldingsafetyduetodesign)

Design

Stresscondition

e.g.Powerflowinworkpiece  Arrangementofjoints Materialthickness Notcheffect Stiffnessdifferences

e.g. Typean TypeandLevelofstrain dLevelofstrain inworkpiece Dimensionaldegreeofstrain Stressspeed Temperature Corrosion

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WeldingSafety

Figure 1.7

WeldingPossibility

The influence of the manufac(weldingpossibilityduetomanufacture)

turing process to weldability is called welding possibility, Figure 1.8. For example, a pre-

and

post-weld

heat

treatment is not always possible, or grinding the weld surface

before

welding

the

Welding preparation e.g.Weldingmethod Consumbletype andauxiliaries Jointtype Grooveshape Preheating  Actionsinthecase ofunfavourable weatherconditions

Executionof  welding e.g.Heatcontrol Heatinput Weldingsequence

WeldingPossibility

carried out (narrow gap welding).

Figure 1.8

e.g.Post-weldheattreatment Grinding Pickling

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subsequent pass cannot be

Post-treatment