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HOW TO WELDfully austenitic stainless steels


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How to weld fully

austenitic stainless steelsThanks to their excellent properties, high-alloy fully austenitic steels(also referred to as super austenites or super austenitic steels) areused for most applications where requirements are severe.

The prime dierence between fully austenitic steels andmore conventional stainless steels is corrosion resis-tance. However, mechanical properties can also dier

signicantly. This is primarily due to fully austeniticsteels having high chromium, nickel, molybdenumand, in certain cases, nitrogen and copper contents.

The extremely good corrosion properties give fullyaustenitic steels a wide eld of application in the mostdemanding environments.

These steels have good weldability and can be wel-ded using all common welding methods. However,compared with low-alloy austenitic steels, more careis needed when handling and welding fully austeniticsteels.

Chemical compositionsTable 1 gives the chemical compositions of parentmetals (plate, strip, pipe, etc.) and recommended llermetals.

The fully austenitic stainless steels 254 SMO, 4529and 4565 are alloyed with nitrogen. In addition to nitro-gen, 4565 also has around 6% manganese. Alloy 28 and

904L are alloyed with around 1 1.5% copper.Nickel base alloys are normally used for welding254 SMO, 4529, 4565 and 654 SMO. In some cases (e.g.where transpassive corrosion may arise), weldingshould be with an iron base alloy, e.g. Avesta P54.This can also be used when welding 4565.

Uses Process equipment in the chemical industry Equipment for bleaching paper pulp Flue gas cleaning Heat exchangers Desalination plants

Sea water systems Oshore (oil and gas) Applications in the pharmaceutical industry

1) Hot-rolled plate, cold-rolled plate, bars, pipes, pipe ings and anges.2)MIG, TIG and SAW wire.3) EN ISO 3581, EN ISO 14343, EN ISO 17633, EN ISO 14172, EN ISO 18274.4)AWS A5.4, AWS A5.9, AWS A5.22, AWS A5.11, AWS A5.14, AWS A5.34.

2

Table 1: Chemical compositions parent and ller metals, typical values

Parent metal EN ASTM C N Cr Ni Mo Other

Plate1) 725LN

Alloy 28

904L

254 SMO

4529

4565

654 SMO

1.4466

1.4563

1.4539

1.4547

1.4529

1.4565

1.4652

S31050

N08023

N08904

S31254

N08926/N08367

S34565

S32654

0.01

0.02

0.01

0.01

0.01

0.02

0.01

0.12

0.20

0.20

0.45

0.50

25

27

20

20

20

24

24

22.3

32

25

18

25

17

22

2.1

3.5

4.3

6.1

6.5

4.5

7.3

Cu 1.0

Cu 1.5

Cu

Cu

Mn 5.5

Mn 3, Cu

Filler metal EN3) AWS4) C N Cr Ni Mo Other

MMA 254 SFER

383

904L

P12-R bas

P625

P54

P16

25 22 2 N L R

27 31 4 LR

20 25 5 Cu L

Ni Cr 21 Mo Fe Nb

Ni Cr 22 Mo 9

Ni Cr 25 Mo 16

E383

E385

ENiCrMo-12

ENiCrMo-3

ENiCrMo-13

0.03

0.02

0.02

0.02

0.02

0.02

0.02

0.14

0.35

25.0

27.0

20.5

21.5

21.5

25.5

23.5

21.0

32.0

25.0

Bal.

Bal.

25.5

Bal.

2.5

3.7

4.5

9.5

9.5

5.0

15.5

Mn 2.5

Cu 1.0

Cu 1.5

Nb 2.2, Fe < 3

Nb 3.5, Fe < 1.5

Cu 0.8

Nb < 0.1

Wire2) 254 SFER

904L

P12

P12-0Nb

P54

P16

25 22 2 N L

20 25 5 Cu L

Ni Cr 22 Mo 9 Nb

Ni Cr 22 Mo 9

Ni Cr 25 Mo 16

ER385

ERNiCrMo-3

ERNiCrMo-20

ERNiCrMo-13

0.02

0.01

0.01

0.01

0.02

0.01

0.13

0.35

22.0

20.0

22.0

22.0

26.0

25.0

22.0

25.5

Bal.

Bal.

22.0

Bal.

2.2

4.5

9.0

9.0

5.5

16.0

Mn 4.5

Cu 1.5

Nb 3.6, Fe 1

Nb < 0.1, Fe 1, W 2.8

N 0.35

Nb < 0.1, Fe 1

FCW P12 ENiCrMo3 0.02 21.5 Bal. 9.0 Nb 3.3, Fe 1


3/20


4/204

Figure 1: Microstructure of, respectively, plate and weld metal with high content of secondary precipitates.

MicrostructureThe chemical composition of fully austenitic steelsgives a structure that is entirely austenitic in the solu-

tion heat-treated condition. Fully austenitic steels maycontain traces of secondary precipitates (sigma phase),

but the contents are, generally speaking, very low anddo not signicantly aect mechanical properties orcorrosion resistance.

When welding fully austenitic materials with highmolybdenum contents, there is a tendency towardsmolybdenum segregation and secondary precipitates.These have a negative eect on both corrosion resis-tance and mechanical properties. Consequently, nickel

base alloys with a high molybdenum content (e.g. P12,P625, P16, etc.) should be used for welding.

Secondary precipitates can also arise if the materialis exposed to temperatures between 600 and 1,000C.Hence, unnecessary exposure to these temperaturesmust be avoided. Consequently, to minimise the riskof precipitation, welding must be with low addedenergy (heat input). Welding methods associated withhigh heat input, e.g. submerged arc welding (SAW),require more care than do, for example, MMA, FCAW,MIG and TIG. Please also see under Heat input.

Additionally, there is an evident risk of secondaryprecipitates if the weldment has to undergo subse-quent heat treatment. Please also see Hot workingand Heat treatment (pages 7 and 14).

Provided that the welding, hot working and heattreatment recommendations are followed, the negativeeect is small.

Figure 1 shows the microstructure of a cold-rolledplate and a weld metal with a high content of secon-

dary precipitates.

Mechanical propertiesNitrogen alloyed fully austenitic steels are characterised

by high strength (yield and tensile). The mechanical

properties of fully austenitic steels that are not nitrogenalloyed (e.g. 904L) are equivalent to those of austeniticstandard steels. Table 2 shows typical mechanical pro-perties of parent and weld metals.

The high tensile strength means that the fatigue pro-perties are also very good. However, fatigue strengthis highly dependent on the components shape. Thefatigue properties of welded joints are also clearlyinferior. Welding method and joint type are of greatsignicance. A TIG welded joint generally has consi-derably beer properties than one made using asubmerged arc. Austenitic steels have very good

ductility and can be used at low temperatures (downto 196C).Avesta Weldings P12-0Nbller metals give a weld

metal that has very good impact strength. Nonethe-less, tensile and yield strength are on the limits ofwhat is required of the parent metal.

Avesta P54 gives a high strength weld metal, butelongation and impact strength are somewhat lowerthan they are for P16.

Corrosion propertiesThe high content of alloying elements gives fully

austenitic stainless steels outstandingly good resis-

tance to most types of corrosion.As shown by table 3 and diagrams 1 and 2, resis-

tance to general corrosionis very good.904L, which is alloyed with copper, has especially

good properties in phosphoric and sulphuric acid.This is one of the few stainless steels that can with-stand sulphuric acid up to 35C at concentrationsfrom 0 to 100%.

Steel grade Corrosion rate, mm per year

4404

904L

254 SMO

654 SMO

> 6

0.47

0.27

0.06

Table 3: General corrosion in pickling acid* at 25C

* 20% HNO3+ 4% HF.


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Steel grade/

fller metal

Min. values1)(EN) Typical values, pure weld metal

P H C MMA MIG TIG SAW FCW

725LN/254 SFER

Rp0.2

(MPa)

Rm(MPa)

Elongation A5(%)

Impact strength (J)+20C

196C

250

540

40

60

440

660

32

55

440

650

35

180

130

904L/904L

Rp0.2

(MPa)

Rm(MPa)

Elongation A5(%)

Impact strength (J)

+20C

196C

220

520

35

60

220

530

35

60

240

530

35

60

400

565

34

70

50

340

570

38

130

100

410

610

35

180

130

350

560

36

100

254 SMO/P12

Rp0.2

(MPa)

Rm(MPa)

Elongation A5(%)

Impact strength (J)

+20C

196C

300

650

40

60

300

650

35

60

320

650

35

60

480

730

37

90

70

480

750

42

170

150

490

740

37

130

110

460

730

41

80

460

750

40

75

45254 SMO/P12-0Nb

Rp0.2

(MPa)

Rm(MPa)

Elongation A5(%)

Impact strength (J)

+20C

70C

300

650

40

60

300

650

35

60

320

650

35

60

380

630

36

240

220

440

670

41

220

210

400

630

36

120

110

4565/P16

Rp0.2

(MPa)

Rm(MPa)

Elongation A5(%)

Impact strength (J)

+20C

40C

420

800

30

90

420

800

30

90

420

800

30

90

550

780

35

60

40

470

700

33

120

510

760

43

135

480

720

37

65

60

654 SMO/P16

Rp0.2(MPa)R

m(MPa)

Elongation A5(%)

Impact strength (J)

+20C

40C

430750

40

60

430750

40

60

430750

40

60

550780

35

60

40

470700

33

120

510760

43

135

480720

37

65

60

Table 2: Mechanical properties parent and ller metals

1) P = hot-rolled plate, H = hot-rolled coil, C = cold-rolled coil.

100

80

60

40

20

254 SMO

654 SMO

904L

4404

4404

0 10 20 30 40 50 60 70 80 90 100

H2SO4%

4565

00

80

60

40

20

0 2 4 6 8 10

HCI %

254 SMO

654 SMO

904L

4404

Temperature, C

Diagram 1: Isocorrosion curves, 0.1 mm per year, in pure sulphuric acid.

Temperature, C

Diagram 2: Isocorrosion curves, 0.1 mm per year, in pure hydrochloric acid.


6/206

Table 4: Pitting resistance equivalent

Steel

grade4404 4439 2205 904L 2507 254 SMO 4565 654 SMO

PRE 25 33 35 35 43 43 46 56

Critical pitting temperature (CPT), C

Diagram 3: Typical piing temperatures (CPTs) in 1M NaCl as perASTM G150, measured in the Avesta cell. Test surfaces were wetground to 320 mesh. CPT varies with type of product and surface.

CPT min./max.Parent metal

CPT min./max.Welded joint

0

20

40

60

80

100

4404

254SMO

2507

904L

2205

Resistance to piing and crevice corrosionis prima-rily determined by chromium, molybdenum and nitro-gen contents. A simple way of assessing the resistanceto piing is to calculate the piing resistance equivalent(PRE): PRE = %Cr + (3.3 x %Mo) + (16 x %N).

Table 4 gives the PRE values for some common

stainless steels.

In this connection, the critical piing temperature(CPT) is a beer way of ranking stainless steels. Dia-gram 3 shows the piing corrosion resistance in bothparent metal and a welded joint that has been brushedand pickled.

There are many ways of measuring CPT. Thediagram shows CPT measured in the Avesta cell(ASTM G150), an accelerated test that has no directcorrespondence with real operating conditions. How-ever, it is a good tool for ranking steels. Chloride content and temperature greatly aect

corrosion resistance. Diagram 4 shows the highestoperating temperatures at which various stainlesssteels can be used at dierent chloride contents.

The diagram is general and factors such as weldingdefects, oxide lms, contamination and pH value allhave a great impact on nal results.

The high strength of the nitrogen alloyed fully aus-tenitic steels also means that resistance to stress cor-rosionis very good. Thanks to the low carbon content,intergranular corrosionis rarely a problem.

For the most part, the corrosion resistance of awelded joint is slightly lower than that of the parentmetal. This is primarily due to: the temperature cycleundergone by the weld and the heat-aected zone(HAZ); the shape of the weld surface; and, the conta-minants and defects generated in welding. To achievethe best conceivable corrosion resistance, both the

weld reinforcement and the plate should have evenand clean surfaces. Weld metal and HAZ must bepickled aer welding. Please also see the Pre-weldcleaning and Post-weld cleaning sections (pages12 and 15).

Detailed information is given in Avesta FinishingChemicals brochures, at www.avestanishing.comand in Outokumpus corrosion handbook.

80

70

60

50

40

30

20

100 10,000 100,000

Cl-ppm

p = pitting corrosion (solid line) c = crevice corrosion (dashed line)

1,000

904L c 254 SMOc

4404 c

4404 p2205 c

2205 p

904L p

254 SMOp

Diagram 4: Diagram of the risk of piing corrosion and crevice corrosionaecting high-alloy stainless steels at dierent chloride contents andtemperatures.

Temperature, C


7/207

WorkingCold workingof fully austenitic steels is possibleusing conventional methods such as bending, pressingand stretch forming. Fully austenitic steels have verygood ductility and, in many respects, 904L is similar to1.4301/304 and 1.4401/316 while 254 SMO, 654 SMO,

4529 and, in particular, 4565, harden considerablymore and faster under deformation. This, in combina-tion with inherent high strength, means that high pressforces are required. Springback is also considerablygreater than with, for example, 1.4401.

Spinning of, for instance, end plates requires highdeformation forces to give full plastic deformation.The weld metal is subject to stringent requirementsand, as the parent metal is very strong, there is a riskthat the weld metal will crack during spinning. Con-sequently, the weld metal must be as free from secon-dary precipitates as possible and it is extra important

that welding is carried out correctly. This appliesespecially to SAW. A process in which spinning andheat treatment are executed in steps may oen benecessary.

Hot working, if required, must be performed at thetemperatures given in table 8 (page 14). To reduce thequantity of precipitates, the workpiece should under-go solution heat treatment aer hot forming. Providedthat hot working is carried out at a temperature ofat least 1,100C and the component is cooled rapidlythereaer, subsequent heat treatment is not necessaryfor 904L.

Machining(e.g. drilling, turning and milling) ofaustenitic steels is generally considered to be moredicult than it is for low-alloy steels. This very muchalso applies to fully austenitic materials. Nonetheless,provided that the right tools and right parameters areused, all sorts of machining can be carried out withgood results.

Filler metalAs already stated, ller metals of the nickel base typeshould be used for welding fully austenitic materials.Allooy 28 and 904L are exceptions. They are to be wel-ded with a ller metal of a matching composition. Incertain cases, 254 SMO and 4565 can be welded using

an iron base alloy, Avesta P54. Filler metal recommen-

dations are given in table 5.MMA welding of 254 SMO and 4529 can be car-

ried out with two alternative ller metals, P12-R (Ni22 Cr 9 Mo Nb Fe / ENiCrMo-12) and P625 (Ni 22 Cr9 Mo Nb / ENiCrMo-3). The dierence is that P12-Rhas a lower niobium content than does P625. Niobiumincreases the tendency towards secondary precipitates.In its turn, this can lead to hot cracking in the weldmetal. Thus, P12-R is slightly less sensitive than P625.

However, in environments with high working tem-peratures (over 400C), P625 is a beer option because

the higher niobium content gives superior structurestability here.Welding of, in particular, thick workpieces in 254

SMO and 4529 can be carried out using P16. Generallyspeaking, this gives a less crack prone weld metal thanP12/P12-R and P625.

MIG, TIG and submerged arc welding of 254 SMOand 4529 is normally carried out with P12 (Ni 22 Cr 9Mo Nb / ENiCrMo-3). P12-0Nb, which is niobium free,is an alternative ller metal. It gives a weld metal that,in principle, is completely free from secondary preci-pitates. The ductility of MIG and TIG weld metals isextremely high.

P16 (Ni 25 Cr 16 Mo / NiCrMo-13) is normally usedfor welding 4565, but the iron base alloy P54 can also

be used. However, impact strength and elongation aresomewhat lower than they are with P16.

654 SMO must be welded with P16 ller metal(Ni 25 Cr 16 Mo / NiCrMo-13).

Autogenous welding (i.e. without a ller metal) isnot to be recommended because the microsegregationin the weld metal during cooling leads to lower ducti-lity and greatly reduced corrosion resistance. The soleexception is where a complete solution heat treatmentcan be carried out aer welding.

Table 5: Filler metals

Steel grade MMA MIG TIG SAW FCW

725LN 254 SFER 254 SFER

Alloy 28 383

904L 904L 904L 904L 904L (P12-PW)

254 SMO P12-R Bas, P625, P16, P54 P12, P12-0Nb, P16, P54 P12, P12-0Nb, P16, P54 P12, P12-0Nb, P16 P12-PW

4529 P12-R Bas, P625, P16, P54 P12, P12-0Nb, P16, P54 P12, P12-0Nb, P16, P54 P12, P12-0Nb, P16 P12-PW

4565 P16, P54 P16, P54 P16, P54 P16

654 SMO P16 P16 P16 P16


8/208

Welding methodsAll conventional welding methods such as MMA,MIG/MAG, TIG, SAW, FCAW, plasma and laser can beused to weld fully austenitic steels.

Property requirements, positional weldability andproductivity usually determine the choice of welding

method.

MMA weldingis an excellent method, particularlyfor position welding, single-sided welding and whereaccess is limited. Avesta Welding has a wide range ofcovered electrodes for fully austenitic steels:

Avesta AWS EN Position254 SFER (-17) R All positions383 AC/DC -17 R All positions904L-3D -17 R All positions904L-PW -17 R Position weldingP12-R -15 B All positions

P625 -15 B All positions

P54 -15 B FlatP16 -15 B All positions

Welding with rutile-acid electrodes (-17/R) is pos-sible using both alternating and direct (DC+) current.However, direct current always gives beer weldingresults. To give a weld metal with as low an oxygencontent as possible (and thereby minimum oxidesand inclusions), all nickel base alloy electrodes have a

basic coating (-15/B). The weldability of basic electro-des is, generally speaking, somewhat poorer than that

of rutile-acid electrodes. Direct current (DC-) mustalways be used when welding with basic electrodes.

A short arc is to be used for welding. This gives thebest stability and reduces the risk of nitrogen pick-up.

The laer can lead to pore formation and increasesurface oxidation.

MIG welding(which, as it is oen carried out with anactive component in the shielding gas, is really MAGwelding) is a particularly good method for weldingsheet metal up to around 6 mm thick. Welding is usu-ally from two sides, but sheet metal (< 4 mm) can bewelded single-sided with a root backing.

A pulsed current is best for welding, but a spray arccan be used in some cases. Drop transfer is conside-rably more sedate and more controlled with a pulsedarc. The opportunity for position welding, especiallyvertical-down, is thus very great. The advantage of

spray-arc welding is the higher deposition rate. Howe-

ver, arc stability is lower and, because the weld poolis relatively large, position welding possibilities arelimited.

The MIG method is especially suited to robot orautomated welding in all positions.

Welding is normally with a pulsed arc and wires of1.00 or 1.20 mm in diameter.

Arc stability varies greatly between not only dierentarc types and steel grades, but also between dierentwelding machines.

Figure 2: TIG welding with Avesta P12.


9/209

TIG weldingis normally used for thin materials (upto around 4 mm), especially when joining pipes in all

welding positions. The method is also highly suitablefor welding single-sided root beads (both with andwithout root backing). Subsequent beads can then bewelded using a method with a higher deposition rate.

Welding is normally with wires of 1.60 or 2.40 mm indiameter.

Submerged arc weldingof fully austenitic steels isassociated with certain diculties, but can certainly

be carried out if the conditions are right. The problemwith fully austenitic steels and SAW is the relativelyhigh heat input, which increases the tendency to formsecondary precipitates. If present in suciently largequantities, these can cause hot cracking or solidica

-

tion cracking during welding. The risk increases withheat input and the materials thickness (the degree ofrestraint). To minimise the risk, welding should bewith as lile restraint as possible and the minimumconceivable heat input (max. 1.5 kJ/mm). Please alsosee the Defects section (page 16).

Regardless of this, productivity is high and the endresult is a weld with a very ne nish. Furthermore,the work environment with SAW is considerably bet-ter because both fume generation and radiation areminimal.

SAW must be with a basic agglomerate ux such asAvesta Flux 805 and a wire diameter of no more than2.40 mm (max. 3.2 mm with 904L).

Flux cored arc welding(FCAW) is suitable for mate-rial thicknesses above approximately 2.5 mm. Thanks

to the slag that is formed, positional weldability isvery good. When FCW is used, the arc and weldpool are protected by both the slag and the shieldinggas. Drop transfer is even and nishes are extremelysmooth and ne. For welding 254 SMO and 4529,there is Avesta FCW P12-PW ux cored wire. This isan all-round wire for all welding positions. It is alsoused for overlay welding and welding 904L.

Laser, laser hybrid and plasma weldingare highproductivity methods that are very suitable for fullyaustenitic steels. However, as previously stated, if aller metal is not used, the workpiece must be heattreated aer welding.

Laser hybrid is a particularly interesting method. Itcombines keyhole welding (laser) with arc welding(MIG/MAG, TIG or plasma). The method ensures ahigh productivity process that, thanks to the llermetal and the low heat input, preserves metallurgicalproperties.

Table 6 gives typical welding parameters for severaldierent types of joints.

Figure 3: Welding with ux cored wire (FCW).


10/2010

Method Steel grade Shielding gases

MIG 904L, P12, P12-0Nb,

P54, P16

Ar + 30% He + 1 3% CO2

Ar + 30% He + 1 2% O2

TIG 904L, P12, P12-0Nb,

P54, P16

Ar, Ar + 1 5% H2+ 10 30% He or

Ar + 2N2+ 10 30% He

FCAW P12 Ar + 16 25% CO2or100% CO

2

Plasma 904L, P12, P12-0Nb,

P54, P16

Plasma: Ar + 5% H2or

Ar + 20 30% He + 1 2%N2

Shielding gas: Ar orAr + 5% H2or

Ar + 20 30% He

Root pro-tection

904L, P12, P12-0Nb,P54, P16

90% N2+ 10% H2orAr

Table 7: Shielding gases for MIG, TIG, FCW and plasmaShielding gasesMIG weldingis best with a three-component gas Ar + 30% He + 1 2% O

2or 2 3% CO

2. The oxygen

and carbon dioxide here serve as arc stabilisers. An ad-dition of 30 50% helium is advantageous. It increasesarc energy which, in turn, increases weld pool uidityand enables higher welding speeds. Pure argon canalso be used. The gas ow is typically 15 l/min.

An addition of 0.03% NO (nitrogen monoxide) is goodnot only from the environmental viewpoint (reducedozone emissions), but also because it has a positive ef-fect on arc stability.

TIG weldingis usually performed with pure argon asthe shielding gas. A typical gas ow is 8 12 l/min.The addition of around 30% helium markedly in-creases arc energy and thus enables a 20 30% in-crease in welding speed. An addition of 1 3% hydro-gen gives a similar eect and is used particularly forautomated welding in tube/pipe manufacture.

Single-sided root beads must be welded with a back-ing gas. This is normally the same as the shieldinggas. However, Formier gas (90% N

2+ 10% H

2) is an

alternative. This also provides good root protection.A backing gas should also be used as early as tack wel-ding and all the way up until weld thickness is at least8 mm. Backing gas ow is typically 8 12 l/min.

FCAWis most suitably performed using argon withan addition of 16 25% carbon dioxide as the shiel-ding gas. A typical gas ow is 20 25 l/min.

Plasma weldingis normally carried out with argonor argon with an addition of hydrogen. Mixtures ofargon, CO

2and N

2are oen used as the shielding gas.

Typical gas ows are 3 7 l/min for plasma and10 15 l/min for backing gases.

Laser weldingcan be carried out with pure argon,nitrogen, helium or mixtures of these gases.

Edge preparationWhen welding stainless steels, meticulous edgepreparation and the correct choice of joint type areimportant for good results. This applies even moreparticularly to fully austenitic steels.

Because of the weld pools slightly poorer fusionpenetration and uidity (compared with standardaustenites), the joint must be correctly designed togive full penetration without risking burn-through.

The groove angle must be suciently wide to allowthe welder full control of the arc, weld pool and slag.A groove angle of around 35 (i.e. somewhat largerthan for austenitic standard steels) is to be recommen-ded for manual welding.

General recommendations:

An X-joint can advantageously be used for platethicknesses above approximately 15 mm.

For plate thicknesses above approximately 30 mm,a double U-joint is advantageous.

In single-sided welding, a root gap of 2 3 mm and

a straight edge of about 0 1 mm are recommen-

ded. For double-sided welding, the straight edgecan be increased to 1.5 2 mm.

Table 6: Welding parameters for several different types of joint

MethodThickness

mmFiller

Diameter

mm

Position

EN/ASTMBead

Current

A

Wire feed

cm/min

Voltage

V

Speed

cm/min

MMA 12 904L 3.25

4.00

PA (1G) Root

Cap

100 110

140 150

25 26

26 27

15 25

20 30

MMA 5 P12-R 3,25 PA (1G) Root/cap 105 115 25 27 20 30

MMA 20 P12-R 2.50

3.25

PF (3F) Root

Cap

55 60

70 75

23 24

23 24

6 8

6 8

MMA 10 P16 3.25

4.00

PA (1G) Root

Cap

95 100

120 125

25 27

26 27

15 25

20 30

FCAW 10 P12 1,20 PA (1G) Root

Cap

185 195

220 230

6.5 8.5

9.5 11.5

24 25

26 27

30 40

35 45

MIG 10 904L 1,20 PA (1G) Root/cap 200 220 6.0 7.0 28 30 30 40

MIG 5 P12 1,20 PA (1G) Root/cap 180 200 6.0 7.0 26 28 25 35

TIG 3 P12 1,60 H-L 056 (6G) Root/cap 45 55 10 11 2 6

TIG

SAW

16 P12

P12

1.60

2.40

PA (1G) Root

Cap

140 150

300 350

10 12

30 33

4 10

40 45

SAW 20 P12-0Nb 2,40 PA (1G) Root

Cap

300 350

300 400

29 31

31 33

40 45

40 45


11/20


12/2012

Pre-weld cleaningTo ensure good weldability and reduce the need forpost-weld cleaning, all joint surfaces, and the surfacesadjoining these, must be thoroughly cleaned beforewelding. Dirt, oil and grease must be removed using,for example, a cleaning agent such as Avesta Cleaner.

All rough edges, etc. must be carefully removed bygentle grinding.

Oxides, paints and primers must be meticulouslyremoved, not only in the joint, but also in the 50 mmfrom the joint edges.

Tack weldingSo that shrinkage during welding does not preventfull burn-through, precise tack welding is extremelyimportant. For metal thicknesses up to 6 mm, tacklength should be 10 15 mm. This should be increasedto 20 25 mm for thicker workpieces. A suitable dis-

tance between tacks is 150 200 mm.In single-sided welding, the entire tack must be

ground away before welding. In double-sided wel-ding, it is sucient to grind away the beginning andthe end of the tack. A common alternative in single-sided welding is the use of bridges or distance pieces.These must be made of, and tacked using, matchingmaterial. Note that gap width must be constantthroughout the joint.

Figure 5: Tack welding using distance pieces.

Starting and stopping Striking and extinguishing the arcIt is very important to use the right technique whenstriking and extinguishing the arc. As regards metal-lurgical, mechanical and corrosion properties, eachstart and stop is a critical area.

To avoid striking scars, the arc must always bestruck down in the joint. If, despite this, striking scarsoccur, they must be meticulously repaired by grin-ding, polishing and pickling or, in the worst cases,repair welding.

In MMA welding, the arc must be extinguishedcarefully by rst making several circular movementsin the centre of the weld pool. The electrode is thento be moved slowly backwards 10 mm through theweld pool before being gently lied. If this is done tooquickly, crater cracks and slag inclusions may result.

Modern power sources for MIG and TIG welding

oen have a so-called crater lling facility. This givessmooth and controlled stops.

To remove any crater cracks and slag inclusions,each start and stop must be carefully ground using asuitable grinding disc.

Figure 6: Penetrant testing (PT) is a simple and highly visual way ofinvestigating weld metal quality as regards surface-breaking defects. At the

top, an approved joint where there are no indications of surface-breakingdefects. Below, a rejected joint where there are problems with both hotcracks and end crater pipes.


13/2013

Planning the welding sequenceBecause it makes burn-through unnecessary, double-sided welding is always to be preferred over single-sided welding. To ensure full burn-through on thelast bead, the root side must be ground to clean metal.A grinding disc not exceeding 2 mm in width is a

suitable tool.If it is dicult to decide whether grinding has reached

the rst bead, penetrant testing (PT) can be used.In double-sided MMA welding, electrodes with a

diameter of 3.25 mm (in some cases, even 4.00 mm)can be used from the very start. Single-sided welding ismost easily carried out with root backing, but can also

be performed without. A 2.50 mm diameter electrodemust be used for the root bead and 3.25, 4.00 or 5.00mm for lling the joint. Choice of electrode diameter isdetermined by welding position. In certain cases (e.g.pipe joints) single-sided welding without root backing

is required. TIG welding (diameter 1.60 2.40 mm) iseasiest for this.As already stated, a backing gas must be used in TIG

welding. Single-sided welding without root backingplaces high demands on even and thorough edgepreparation.

Root beads must satisfy three important requirements:

Correct metallurgy and structure (right root gap toensure sucient quantity of ller metal).

Correct geometry (no root concavity, undercuingor lack of fusion).

Best possible productivity (always in relation to

weldability).

Figure 8: Root bead correctly executed using TIG welding.

Figure 7: Root, ller and cap beads welded using Avesta P12-R basiccovered electrodes.

Figure 9: Grinding scars.

Filler beadsmust be deposited with the highest pos-sible productivity. At the same time, structure andmechanical properties have to be maintained. In mostcases, ll passes use the same ller metal as that usedin root passes. High productivity welding methodsmay be economical for joint lling. Several common

choices are: TIG root pass + MMA, MIG or SAW ll passes.

TIG root pass + SAW or FCAW ll passes.

Generally speaking, welding is carried out with thehighest possible heat input (max. 1.5 kJ/mm) thatis still consistent with maintained properties andweldability. Visual inspection between the passes isimportant.

Slag residues and severe welding oxide are to beremoved before depositing the next layer. Otherwise,there is always the risk of slag inclusions being le

behind. A suitable grinding disc must be used. Toavoid damaging adjacent surfaces (please see gure 9),grinding should be carried out with some care.

The cap beadis primarily intended to give the weldgood corrosion protection. Besides structure, surfacegeometry can also play a critical role here. Undercut-ting, unevenness, high reinforcements, gaps, etc. canall have a negative impact on corrosion resistance.Aesthetic considerations are oen also important.

When using slag forming welding methods, weldreinforcements must be cleaned of all slag residues.


14/2014

Welding techniquesIn the at position, there should be no signicantweaving. In the vertical-up position, weaving of upto 20 mm is advantageous. For the best control of arcand weld pool, welding is normally carried out with atorch or electrode angle of around 10 away from the

welding direction, i.e. backhand.In submerged arc welding, the nozzle is not nor-

mally angled.

DistortionFully austenitic steels have a greater coecient ofexpansion than do low-alloy steels and duplex stain-less steels. This means that distortion during weldingis also greater. Consequently, to reduce distortion,tack welding has to be carried out precisely and thewelding sequence meticulously planned.

PreheatingGenerally speaking, stainless steels (fully austeniticsteels included therein) must not be preheated beforewelding. Welding is normally carried out at roomtemperature. At lower temperatures, preheating toa maximum of 50C is advisable. This drives o anymoisture that may otherwise lead to pore formation.When welding castings, or where the workpiece is thickor where restraint is high, preheating to a maximum of100C may, in certain cases, be advantageous. In thesecases, a suitable preheating method is the use of electric

blankets or similar. The use of soot-depositing ames

can result in local carburisation. This reduces resistanceto intergranular corrosion.

Interpass temperatureBecause fully austenitic materials are prone to inter-metallic precipitates, the interpass temperature mustnot be above 150C for 904L and 100C for other fullyaustenitic materials.

Thermal conductivity is of the same order as foraustenitic stainless steels, i.e. considerably lower thanit is for low-alloy and carbon steels. This means that,compared to carbon steels, it takes longer to reach the

correct interpass temperature. The cooling rate can beincreased by using compressed air. This is most suitably

directed at the back of the plate or the inside of the pipe.Compressed air directed straight into the welded jointpresents the risk of contamination. Cooling can also beaccelerated by intermient welding or using a correctlyplanned welding sequence.

The interpass temperature must be measured. Some

form of thermometer or thermoelement is appropriatefor this. Temperature crayons seldom give good resultsand must be avoided.

Heat inputTo avoid intermetallic precipitates, the heat inputwhen welding fully austenitic materials must be keptas low as possible without thereby giving rise to anyrisk of lack of fusion, etc. One general recommenda-tion is a maximum of 1.5 kJ/mm. However, the criticalupper limit depends very much on welding methodand the thickness of the workpiece. For example, MIG

is not as sensitive as SAW and a 5 mm joint is lesssensitive than a 20 mm joint.

Especially in automated welding, heat input is easyto control.

{ }Heat input = U x Ik x V x 1,000U x I

mm/s x 1000

= kJ/mm

U = voltageI = currentV = speed

Welding method Factor, kMMA, FCW, MIG/MAG 0.8TIG 0.6SAW 1.0

Although it is always desirable to optimise producti-vity by increasing the welding parameters, this must

never happen if it would result in a too high heatinput.

Post-weld heat treatmentFully austenitic stainless steels do not normally needpost-weld heat treatment. However, in certain situa-tions, solution heat treatment may be necessary. Table 8gives the recommended temperatures.

Heat treatment requires very precise control of bothtime and temperature. It must only be carried out by

qualied personnel using suitable equipment.

Type of treatment 904L 254 SMO 4529 4565 654 SMO

Hot forming** 1150 850 1200 1000 1150 850 1200 950 1200 1000

Solution heat treatment** 1060 1140 1150 1200* 1120 1180 1120 1170 1150 1200

Stress-relieving annealing 400 500 300 400 300 400 300 400 300 400

Pressure vessel approval 196 +400 196 +400 196 +400 (196) +400 RT +427***

Table 8: Recommended heat treatment

* So that material properties are not too seriously impaired, workpieces over 2 mm thick require quenching in water.Thinner workpieces can be cooled quickly in air.

** As per EN 10088-2.*** ASME Code Case 2195-1.


15/2015

How to weld fully austenitic materials toother materialsWelding fully austenitic steels to carbon or low-alloysteels is best carried out using the same ller metals asthose for welding stainless steel to stainless steel.

However, in certain cases, Avesta P5 (309MoL) can bea more economical alternative. This applies particular-ly to thin workpieces (t < 10 mm) where the degree ofrestraint and dilution are low.

Welding to other stainless steels such as EN 1.4301/ASTM 304 or EN 1.4401/ASTM 316 is also entirely pos-sible. It can be carried out with a fully austenitic llermetal or, in certain cases, Avesta P5.

Welding to duplex stainless steels must be with asuitable duplex or nickel base alloy. Please see table 9.

Because it gives rise to a risk of brile secondaryphases, it is important to minimise dilution when wel-ding high-alloy materials to each other. Consequently,this must be taken into account in the choice of jointdesign and welding techniques.

Figure 10: Stainless steel pressure vessel for the petrochemical industry partly pickled.

Post-weld cleaningPost-weld cleaning is critical in achieving fully satis-factory corrosion resistance. Clearly enough, it is thusan integral part of the entire stainless steel weldingprocedure. Despite this, post-weld cleaning is not

always standard.The method and extent of cleaning is determined

by the requirements imposed in respect of corrosionresistance, hygiene and appearance.

Generally speaking, one basic requirement is thatdefects, welding oxide, organic contaminants andcarbon steel contamination must be removed fromweld and parent metal surfaces. This can be done me-chanically (grinding, brushing, polishing, blasting) orchemically (pickling). An important rule of thumb forgrinding is to always nish with polishing. The risk ofharmful grinding scars is otherwise very great.

The demonstrably most reliable method is a com-

bination of mechanical and chemical cleaning, i.e.brushing with a stainless steel brush followed by

degreasing, pickling and passivation.Avesta Finishing Chemicals has a complete product

programme for the pickling of stainless steel welds. Itcomprises cleaning products, pickling pastes, picklingsprays, pickling uids and various items of equip-ment. Fully austenitic steels are generally slightly moredicult to pickle than are austenitic steels such as1.4301 (304) and 1.4404 (316L). Thus, Avesta BlueOneand Avesta RedOne, which are comparatively strongpickling products, should be used.

Further details are available at www.avestanishing.com or can be obtained directly from Avesta FinishingChemicals.

Table 9: Suitable ller metals for welding fully

austenitic steels to other materials

Parent

metal

Recommended fller metal

254 SMO 2205 2507 316/304 Carbon

steel

904L P12 P12 2507/P100 904L/P5 P5/904L

254 SMO P12 P12 P16/P12-0Nb P12 P12

654 SMO P16 P16 P16 P16 P16


16/2016

DefectsApart from the risk of hot cracking, fully austeniticsteels are generally no more prone to defects than areother stainless steels. However, certain factors requirespecial aention.

The high nitrogen content gives poorer penetration.

Arc stability, uidity and arc control are somewhatpoorer than they are for austenitic stainless steels.This applies particularly to 4565/EN 1.4565/ASTMS34565, which has a high manganese content.

To avoid problems with poor penetration, slaginclusions or pores, recommendations for jointdesign and welding parameters must be followedprecisely.

Hot cracking (a classic problem for fully austeniticmaterials).

During solidication, secondary precipitates form in

the weld metal. If the cooling rate is too low and theheat input too high, these precipitates may collect andform lms of late-solidifying phases at grain bounda-ries. Under the inuence of the residual stresses al-ways present in weld metal, the lms can crack. Thesehot or solidication cracks form particularly at thecentre of the weld metal, where the stress is greatest.

Figure 11: Width to depth ratio.

Width

Depth

In workpieces of around 10 mm thick and upwards,cracking can also arise when, in multilayer welding,subsequent passes heat the underlying weld to a tem-perature where precipitation can occur. Here too, lmsthat may crack are formed.

The risk of hot cracking generally reduces with: Reduced heat input (max. 1.5 kJ/mm).

Reduced restraint.

The use of ller metals that do not contain niobium(e.g. Avesta P12-0Nband Avesta P16).

A good width to depth ratio, i.e. the width of theweld must be around 1 to 1.5 times its depth (pleasesee gure 11).

Using covered electrodes or TIG for root beads(beads 1 3) when welding thick workpieces whereSAW is to be preferred.

Figure 12:Hot cracks in a weld surface (le) and enclosed (right).

Figure 14: Weld surface, P12 MIG with poor arc stability.Figure 13: Root defect caused by incomplete penetration.


17/2017

Repair weldingSo that corrosion resistance is not impaired, all defectsmust be repaired. Minor surface defects such as spat-ter, slag and oxide islands can easily be remedied bygrinding followed by polishing using an at least 320mesh disc. Note that a grinding disc intended for

stainless steel must be used. Aer polishing, conven-

tional pickling is to be carried out. Pickling paste ismost oen the simplest alternative.

Defects must never be repaired by TIG dressing(remelting using a TIG electrode). This has the sameeect as welding without a ller metal, i.e. there isa risk of a high content of secondary precipitates inthe weld metal. If this occurs, ductility and corrosionresistance will be lower.

Large defects and subsurface defects require heaviergrinding with a coarser grinding disc. Once the entiredefect has been removed (which can be checked by, forexample, penetrant testing), the ground area is to be l-led using a suitable method, most oen MMA welding.

In-built defects in thick workpieces can be removed

by gouging with a plasma arc. Because of the resul-tant carbonisation, carbon arcs should not be used.

The problem with both plasma and carbon arcs is thepowerful spaer. If care is not taken, this can damageadjacent surfaces. The laer should be protected using,for example, Masonite boards or chalk paint.

Aer gouging, the area must be ground before wel-ding can start. Plasma gouging can be carried out at leastve times with no negative impact on the parent metal.

3. The ground out area is repaired using a suita-ble welding method (oen covered electrodes).

Figure 15: Typical welding sequence in repair welding

1. Using a suitable grinding/cuing disc, thedefect is ground from the surface. To avoid un-necessary grinding scars, be careful with thesurrounding areas.

2. Using a suitable grinding/cuing disc, thedefect is ground to a depth and width (width, min.3 mm and depth, min. 10 mm) that is sucient forrepair welding. To ensure that the entire defect has

been ground away, PT can be carried out.

4. The weld is ground ush with the plate. 5. Using a suitable polishing disc (at least 320

mesh), the surface is polished.

Measuring ferrite contentAs can be judged from the name, fully austenitic steelscontain no ferrite. There is thus no reason to measureor calculate the ferrite content.

Overlay weldingOverlay welding of carbon steel can be carried outusing all types of ller metals. Directly from the rstlayer, welding can be with a nickel base alloy (e.g.P12) or 904L. Filler metals of the 309L or P5 type canalso be used as a rst layer. This is considerably more

cost-ecient.Correctly executed, the overlay metal is extremely

resistant to corrosion.

All welding methods can be used. However, coveredelectrodes, MIG and FCAW, where dilution is rela-tively easy to control, most oen give the best results.SAW gives high productivity, but also high dilution.Thus, it is extra important to use the correct parameterseings.

Welding should be with as lile dilution of theparent metal as possible. Welding parameters andtechnique are of great importance. Dilution can beminimised by building on the preceding bead andavoiding directing the arc at the parent metal.

Table 10 gives examples of the chemical composi-tion of the overlay weld metals resulting from various

methods and ller metals.

6. End with pickling.


18/2018

How to weld fully austenitic steels ofsimilar compositionsIn addition to the already described stainless steels,there are many steel grades of a similar composition.Table 11 gives some general recommendations

Table 11: How to weld similar fully austenitic steels

Method Filler Layer Chemical composition, % by weight

C Si Mn Cr Ni Mo Other

MMA 904L 1 0,022 0,89 1,38 20,1 23,7 4,0 Cu 1.2

904L 2 0,022 0,87 1,30 20,6 25,9 4,2 Cu 1.5

MMA P12-R 1 0,018 0,35 0,39 20,2 59,2 8,6 Fe 8.5

P12-R 2 0,016 0,36 0,35 21,8 63,0 9,1 Fe 2.8

FCW P12 1 0,017 0,6 1,4 22,0 12,0 8,4 Fe 3.8

P12 2 0,015 0,5 0,4 21,5 58,0 9,0 Fe 0.4

Table 10: Example chemical compositionsof overlay weld metals

Inspection and quality assuranceThe rules that apply to structural steels apply also tostainless steels. The following are some of the relevantinternational standards:

EN ISO 5817, which gives guidelines on acceptancelevels for various defects in welded joints. EN ISO 1560715614 and ASME IX, which describeapproval of welding procedures.

However, fully austenitic steels are used in applica-tions where strength and corrosion requirements areoen very severe. There is thus every reason to beextra careful from beginning to end. Welding oxide,spaer, striking scars and grinding scars must be re-moved to achieve the correct corrosion resistance. Forthe best fatigue resistance, the weld surface must beeven with no sharp edges.

Nondestructive testing is an integral part of the exa-mination of welded joints. Suitable methods are visualinspection, penetrant testing (PT), radiographic testing(RT) and ultrasound testing (UT). In ultrasoundtesting, it is important that surfaces are ground at so

that defects such as pores and cracks can be reliablydetected.

Steel grade

EN ASTM

Recommended fller metal

Avesta Welding

1.4466 S31050 254 SFER

1.4563 N08023 383

1.4539 N08904 904L

1.4547 S31254 P12, P12-R

1.4529 N08926/N08367 P12, P12-R

1.4565 S34565 P16

1.4652 S32654 P16

Handling of ller metalsStainless steel covered electrodes, ux cored wires(FCWs) and uxes can be prone to moisture pick-up.Avesta Weldings consumables are supplied in packa-ges that have been designed to resist moisture.

However, for the best possible results, the followingstorage and handling precautions are still recommended.Storage of unbroken packages: Covered electrodes,FCWs and uxes must be stored in their unbroken,original packaging. Storage in opened packaging canconsiderably shorten the products service life. Fol-lowing the rst in, rst out principle, storage timemust be kept as short as possible. Covered electrodes

and uxes should not be stored longer than 5 years.The corresponding time for FCWs is 2 years.Products that are over 5 (2) years old should beredried before use.

Covered electrodes, FCWs and uxes should not bestored in direct contact with oors or outer walls.

Storeroom temperature must be kept as even aspossible ( 5C) and should not fall below 15C. Therelative air humidity should not exceed 50%.

Handling of opened packages: Electrodes that remainunused at the end of a shi should be replaced in theirpackaging and resealed. Alternatively, they can be put

in a warm heating cabinet at 60 70C. The relative airhumidity should not exceed 50%.

Flux that has not been used should be stored in aheating cabinet at 60 70C.

If the relative air humidity is above 55%, FCWs shouldnever be le unprotected for more than 24 hours.

Handling during welding: It is an advantage if

welding can be carried out at room temperature andlow relative air humidity. Covered electrodes, FCWsand uxes should be used at the same rate as theyare unpacked preferably within 24 hours. Duringshis, electrodes must be kept as dry as possible. Ifthe climate so demands, they should be kept warmin a portable heat-retaining container or similar. Onealternative is to use smaller packs, e.g. half or quartercapsules.

Redrying: Electrodes that have sustained slightmoisture damage can be redried for around 3 hoursat 250 280C. Heating and cooling must both be

gradual. Items should not be redried any more than 3times.Fluxes that have sustained slight moisture damage

can be redried for 2 hours at 250 300C.FCWs that have sustained slight moisture damage

can be redried for 24 hours at 150C.Procedures that have been approved for carbon steel

electrodes are also completely satisfactory for stainlesssteel electrodes. This is because the laer are not asprone to moisture pick-up.

Recycling: Because they can be reused, leover pro-ducts and scrap are valuable. Wherever possible, pro-

ducts and packaging must be recycled in accordancewith local regulations.


19/2019

Health and safetyThe fumes and radiation given o during weldingcan be hazardous to health. Spaer, molten metal andarcs can cause burns and res. Furthermore, electricalequipment is used. If it is not handled correctly, thereis the risk of electric shock. Thus, it is of the greatestimportance that welders and supervisors are aware ofall the potential dangers.

Ensure that ventilation is adequate and that thewelding site has an extractor system that removesfumes and gases from the welders breathing zone.

When welding in conned spaces, use respiratory

protective equipment or a compressed air linebreathing apparatus.

The right to make changes without warning or notication is reserved. Great care has been taken to ensure that the contents of this publication are correct.However, Bhler Welding Group Nordic AB cannot accept responsibility for errors or for information that is found to be misleading. Suggestions for, ordescriptions of, working methods or of the use, treatment or machining of products are for information only and Bhler Welding Group Nordic AB can acceptno liability in respect thereof. Before using products supplied or manufactured by the company, customers should satisfy themselves of product suitability.

Figure 16: Thanks to their excellent properties, high-alloy fully austenitic steels are used for most applications where requirements are severe.

Use safety equipment for hands, eyes and body, e.g.:gloves; helmet or face mask with lter glass; safety

boots; apron; and arm and shoulder guards.

Keep the workplace and equipment clean and dry.

Regularly check that safety clothing and equipmentare in good condition.

As far as possible, insulate all conducting elements

Further information on each product group is con-tained in Avesta Weldings material safety data sheets.These can be downloaded from Avesta Weldingswebsite, www.avestawelding.com , or ordered from

Avesta Weldings distributors and retailers.


20/20

Avesta WeldingP O Box 501, Modellvgen 2

SE-774 27 Avesta, Sweden

Tel: +46 (0)226 857 00

Fax: +46 (0)226 857 16

[email protected]

www.avestawelding.com

10

1101EN-GB,

Centrumtryck,

Avesta,

2012

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