Avesta Welding: How to weld fully austenitic stainless steels

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HOW TO WELDfully austenitic stainless steels

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) are used for most applications where requirements are severe.

The prime difference between fully austenitic steels and more conventional stainless steels is corrosion resis-tance. However, mechanical properties can also differ significantly. This is primarily due to fully austenitic steels having high chromium, nickel, molybdenum and, in certain cases, nitrogen and copper contents.

The extremely good corrosion properties give fully austenitic steels a wide field of application in the most demanding environments. These steels have good weldability and can be wel-ded using all common welding methods. However, compared with low-alloy austenitic steels, more care is needed when handling and welding fully austenitic steels.

Chemical compositions Table 1 gives the chemical compositions of parent metals (plate, strip, pipe, etc.) and recommended filler metals.

The fully austenitic stainless steels 254 SMO, 4529 and 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 welding 254 SMO, 4529, 4565 and 654 SMO. In some cases (e.g. where transpassive corrosion may arise), welding should 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• Offshore (oil and gas)• Applications in the pharmaceutical industry

1) Hot-rolled plate, cold-rolled plate, bars, pipes, pipe fittings and flanges. 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 filler metals, typical values

Parent metal EN ASTM C N Cr Ni Mo Other

Plate1) 725LNAlloy 28904L254 SMO®

45294565654 SMO®

1.44661.45631.45391.45471.45291.45651.4652

S31050N08023N08904S31254N08926/N08367S34565S32654

0.010.020.010.010.010.020.01

0.12– –0.200.200.450.50

25272020202424

22.3322518251722

2.1 3.5 4.3 6.1 6.5 4.5 7.3

–Cu 1.0Cu 1.5CuCuMn 5.5Mn 3, Cu

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

MMA 254 SFER383904LP12-R basP625P54P16

25 22 2 N L R27 31 4 LR20 25 5 Cu LNi Cr 21 Mo Fe NbNi Cr 22 Mo 9–Ni Cr 25 Mo 16

–E383E385ENiCrMo-12ENiCrMo-3–ENiCrMo-13

0.030.020.020.020.020.020.02

0.14––––0.35–

25.027.020.521.521.525.523.5

21.032.025.0Bal.Bal.25.5 Bal.

2.5 3.7 4.5 9.5 9.5 5.015.5

Mn 2.5Cu 1.0Cu 1.5Nb 2.2, Fe < 3Nb 3.5, Fe < 1.5Cu 0.8Nb < 0.1

Wire2) 254 SFER904LP12P12-0Nb

P54P16

25 22 2 N L20 25 5 Cu LNi Cr 22 Mo 9 NbNi Cr 22 Mo 9–Ni Cr 25 Mo 16

–ER385ERNiCrMo-3ERNiCrMo-20–ERNiCrMo-13

0.020.010.010.010.020.01

0.13––––0.35

22.020.022.022.026.025.0

22.025.5Bal.Bal.22.0Bal.

2.2 4.5 9.0 9.0 5.516.0

Mn 4.5Cu 1.5Nb 3.6, Fe 1Nb < 0.1, Fe 1, W 2.8N 0.35Nb < 0.1, Fe 1

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

4 5

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

MicrostructureThe chemical composition of fully austenitic steels gives a structure that is entirely austenitic in the solu-tion heat-treated condition. Fully austenitic steels may contain traces of secondary precipitates (sigma phase), but the contents are, generally speaking, very low and do not significantly affect mechanical properties or corrosion resistance.

When welding fully austenitic materials with high molybdenum contents, there is a tendency towards molybdenum segregation and secondary precipitates. These have a negative effect 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 material is exposed to temperatures between 600 and 1,000°C. Hence, unnecessary exposure to these temperatures must be avoided. Consequently, to minimise the risk of precipitation, welding must be with low added energy (heat input). Welding methods associated with high 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 secondary precipitates if the weldment has to undergo subse-quent heat treatment. Please also see “Hot working” and “Heat treatment” (pages 7 and 14).

Provided that the welding, hot working and heat treatment recommendations are followed, the negative effect is small.

Figure 1 shows the microstructure of a cold-rolled plate and a weld metal with a high content of secon-dary precipitates.

Mechanical properties Nitrogen alloyed fully austenitic steels are characterised by high strength (yield and tensile). The mechanical properties of fully austenitic steels that are not nitrogen alloyed (e.g. 904L) are equivalent to those of austenitic standard 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 strength is highly dependent on the component’s shape. The fatigue properties of welded joints are also clearly inferior. Welding method and joint type are of great significance. A TIG welded joint generally has considerably better properties than one made using a submerged arc. Austenitic steels have very good ductility and can be used at low temperatures (down to –196°C). Avesta Welding’s P12-0Nb filler metals give a weld metal that has very good impact strength. Nonethe-less, tensile and yield strength are on the limits of what is required of the parent metal.

Avesta P54 gives a high strength weld metal, but elongation and impact strength are somewhat lower than they are for P16.

Corrosion properties The 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 corrosion is 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 35°C at concentrations from 0 to 100%.

Steel grade Corrosion rate, mm per year

4404904L254 SMO654 SMO

> 60.470.270.06

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

* 20% HNO3 + 4% HF.

4 5

Steel grade/filler metal

Min. values1) (EN) Typical values, pure weld metalP H C MMA MIG TIG SAW FCW

725LN/254 SFERRp0.2 (MPa)Rm (MPa)Elongation A5 (%)Impact strength (J) +20°C–196°C

250540 40

60–

–––

––

–––

––

44066032

55–

–––

––

44065035

180130

–––

––

–––

––

904L/904LRp0.2 (MPa)Rm (MPa)Elongation A5 (%)Impact strength (J)+20°C–196°C

22052035

60–

22053035

60–

24053035

60–

40056534

7050

34057038

130100

41061035

180130

35056036

100–

–––

––

254 SMO/P12Rp0.2 (MPa)Rm (MPa)Elongation A5 (%)Impact strength (J)+20°C–196°C

30065040

60–

30065035

60–

32065035

60–

48073037

9070

48075042

170150

49074037

130110

46073041

80–

46075040

7545

254 SMO/P12-0Nb

Rp0.2 (MPa)Rm (MPa)Elongation A5 (%)Impact strength (J)+20°C–70°C

30065040

60–

30065035

60–

32065035

60–

–––

––

38063036

240220

44067041

220210

40063036

120110

–––

––

4565/P16Rp0.2 (MPa)Rm (MPa)Elongation A5 (%)Impact strength (J)+20°C–40°C

42080030

90–

42080030

90–

42080030

90–

55078035

6040

47070033

120–

51076043

135–

48072037

6560

–––

––

654 SMO/P16Rp0.2 (MPa)Rm (MPa)Elongation A5 (%)Impact strength (J)+20°C–40°C

43075040

60–

43075040

60–

43075040

60–

55078035

6040

47070033

120–

51076043

135–

48072037

6560

–––

––

Table 2: Mechanical properties – parent and filler metals

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

100

80

60

40

20254 SMO®

654 SMO®

904L

4404

4404

0 10 20 30 40 50 60 70 80 90 100

H2SO4 %

4565

100

80

60

40

20 0 2 4 6 8 10

HCI %

254 SMO®

654 SMO®

904L4404

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 7

Table 4: Pitting resistance equivalentSteel grade

4404 4439 2205 904L 2507 254 SMO 4565 654 SMO

PRE 25 33 35 35 43 43 46 56

Critical pitting temperature (CPT), ºC

Diagram 3: Typical pitting temperatures (CPTs) in 1M NaCl as per ASTM G150, measured in the “Avesta cell”. Test surfaces were wet ground 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

254

SMO

2507

904L

2205

Resistance to pitting and crevice corrosion is prima-rily determined by chromium, molybdenum and nitro-gen contents. A simple way of assessing the resistance to pitting is to calculate the pitting 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 pitting temperature (CPT) is a better way of ranking stainless steels. Dia-gram 3 shows the pitting corrosion resistance in both parent metal and a welded joint that has been brushed and pickled.

There are many ways of measuring CPT. The diagram shows CPT measured in the “Avesta cell” (ASTM G150), an accelerated test that has no direct correspondence with real operating conditions. How-ever, it is a good tool for ranking steels. Chloride content and temperature greatly affect corrosion resistance. Diagram 4 shows the highest operating temperatures at which various stainless steels can be used at different chloride contents. The diagram is general and factors such as welding defects, oxide films, contamination and pH value all have a great impact on final results.

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

For the most part, the corrosion resistance of a welded joint is slightly lower than that of the parent metal. This is primarily due to: the temperature cycle undergone by the weld and the heat-affected zone (HAZ); the shape of the weld surface; and, the conta-minants and defects generated in welding. To achieve the best conceivable corrosion resistance, both the weld reinforcement and the plate should have even and clean surfaces. Weld metal and HAZ must be pickled after welding. Please also see the “Pre-weld cleaning” and “Post-weld cleaning” sections (pages 12 and 15).

Detailed information is given in Avesta Finishing Chemicals’ brochures, at www.avestafinishing.com and in Outokumpu’s corrosion handbook.

80

70

60

50

40

30

20

100 10,000 100,000Cl- ppm

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

1,000

904L c 254 SMO® c

4404 c

4404 p2205 c

2205 p

904L p

254 SMO® p

Diagram 4: Diagram of the risk of pitting corrosion and crevice corrosion affecting high-alloy stainless steels at different chloride contents and temperatures.

Temperature, ºC

6 7

WorkingCold working of fully austenitic steels is possible using conventional methods such as bending, pressing and stretch forming. Fully austenitic steels have very good ductility and, in many respects, 904L is similar to 1.4301/304 and 1.4401/316 while 254 SMO, 654 SMO, 4529 and, in particular, 4565, harden considerably more and faster under deformation. This, in combina-tion with inherent high strength, means that high press forces are required. Springback is also considerably greater than with, for example, 1.4401.

Spinning of, for instance, end plates requires high deformation forces to give full plastic deformation. The weld metal is subject to stringent requirements and, as the parent metal is very strong, there is a risk that 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 applies especially to SAW. A process in which spinning and heat treatment are executed in steps may often be necessary.

Hot working, if required, must be performed at the temperatures given in table 8 (page 14). To reduce the quantity of precipitates, the workpiece should under-go solution heat treatment after hot forming. Provided that hot working is carried out at a temperature of at least 1,100°C and the component is cooled rapidly thereafter, subsequent heat treatment is not necessary for 904L.

Machining (e.g. drilling, turning and milling) of austenitic steels is generally considered to be more difficult than it is for low-alloy steels. This very much also applies to fully austenitic materials. Nonetheless, provided that the right tools and right parameters are used, all sorts of machining can be carried out with good results.

Filler metalAs already stated, filler metals of the nickel base type should be used for welding fully austenitic materials. Allooy 28 and 904L are exceptions. They are to be wel-ded with a filler metal of a matching composition. In certain 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 filler metals, P12-R (Ni 22 Cr 9 Mo Nb Fe / ENiCrMo-12) and P625 (Ni 22 Cr 9 Mo Nb / ENiCrMo-3). The difference is that P12-R has a lower niobium content than does P625. Niobium increases the tendency towards secondary precipitates. In its turn, this can lead to hot cracking in the weld metal. Thus, P12-R is slightly less sensitive than P625. However, in environments with high working tem-peratures (over 400°C), P625 is a better option because the higher niobium content gives superior structure stability here.

Welding of, in particular, thick workpieces in 254 SMO and 4529 can be carried out using P16. Generally speaking, this gives a less crack prone weld metal than P12/P12-R and P625.

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

P16 (Ni 25 Cr 16 Mo / NiCrMo-13) is normally used for welding 4565, but the iron base alloy P54 can also be used. However, impact strength and elongation are somewhat lower than they are with P16. 654 SMO must be welded with P16 filler metal (Ni 25 Cr 16 Mo / NiCrMo-13).

Autogenous welding (i.e. without a filler metal) is not to be recommended because the microsegregation in the weld metal during cooling leads to lower ducti-lity and greatly reduced corrosion resistance. The sole exception is where a complete solution heat treatment can be carried out after 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 9

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

Property requirements, positional weldability and productivity usually determine the choice of welding method.

MMA welding is an excellent method, particularly for position welding, single-sided welding and where access is limited. Avesta Welding has a wide range of covered electrodes for fully austenitic steels:

Avesta AWS EN Position 254 SFER (-17) R All positions 383 AC/DC -17 R All positions904L-3D -17 R All positions 904L-PW -17 R Position welding P12-R -15 B All positions P625 -15 B All positions P54 -15 B Flat P16 -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 better welding results. To give a weld metal with as low an oxygen content as possible (and thereby minimum oxides and 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-) must always be used when welding with basic electrodes.

A short arc is to be used for welding. This gives the best stability and reduces the risk of nitrogen pick-up. The latter can lead to pore formation and increase surface oxidation. MIG welding (which, as it is often carried out with an active component in the shielding gas, is really MAG welding) is a particularly good method for welding sheet metal up to around 6 mm thick. Welding is usu-ally from two sides, but sheet metal (< 4 mm) can be welded single-sided with a root backing.

A pulsed current is best for welding, but a spray arc can be used in some cases. Drop transfer is conside-rably more sedate and more controlled with a pulsed arc. The opportunity for position welding, especially vertical-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 pool is relatively large, position welding possibilities are limited.

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

Welding is normally with a pulsed arc and wires of 1.00 or 1.20 mm in diameter.

Arc stability varies greatly between not only different arc types and steel grades, but also between different welding machines.

Figure 2: TIG welding with Avesta P12.

8 9

TIG welding is normally used for thin materials (up to around 4 mm), especially when joining pipes in all welding positions. The method is also highly suitable for welding single-sided root beads (both with and without root backing). Subsequent beads can then be welded using a method with a higher deposition rate.

Welding is normally with wires of 1.60 or 2.40 mm in diameter.

Submerged arc welding of fully austenitic steels is associated with certain difficulties, but can certainly be carried out if the conditions are right. The problem with fully austenitic steels and SAW is the relatively high heat input, which increases the tendency to form secondary precipitates. If present in sufficiently large quantities, these can cause hot cracking or solidifica-tion cracking during welding. The risk increases with heat input and the material’s thickness (the degree of restraint). To minimise the risk, welding should be with as little restraint as possible and the minimum conceivable heat input (max. 1.5 kJ/mm). Please also see the “Defects” section (page 16).

Regardless of this, productivity is high and the end result is a weld with a very fine finish. Furthermore, the work environment with SAW is considerably bet-ter because both fume generation and radiation are minimal.

SAW must be with a basic agglomerate flux such as Avesta Flux 805 and a wire diameter of no more than 2.40 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 is very good. When FCW is used, the arc and weld pool are protected by both the slag and the shielding gas. Drop transfer is even and finishes are extremely smooth and fine. For welding 254 SMO and 4529, there is Avesta FCW P12-PW flux cored wire. This is an all-round wire for all welding positions. It is also used for overlay welding and welding 904L. Laser, laser hybrid and plasma welding are high productivity methods that are very suitable for fully austenitic steels. However, as previously stated, if a filler metal is not used, the workpiece must be heat treated after welding.

Laser hybrid is a particularly interesting method. It combines keyhole welding (laser) with arc welding (MIG/MAG, TIG or plasma). The method ensures a high productivity process that, thanks to the filler metal and the low heat input, preserves metallurgical properties.

Table 6 gives typical welding parameters for several different types of joints.

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

10 11

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% CO2 or 100% CO2

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

Plasma: Ar + 5% H2 or Ar + 20 – 30% He + 1 – 2%N2

Shielding gas: Ar or Ar + 5% H2 or Ar + 20 – 30% He

Root pro-tection

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

90% N2 + 10% H2 or Ar

Table 7: Shielding gases for MIG, TIG, FCW and plasmaShielding gasesMIG welding is best with a three-component gas – Ar + 30% He + 1 – 2% O2 or 2 – 3% CO2. The oxygen and carbon dioxide here serve as arc stabilisers. An ad-dition of 30 – 50% helium is advantageous. It increases arc energy which, in turn, increases weld pool fluidity and enables higher welding speeds. Pure argon can also be used. The gas flow is typically 15 l/min.

An addition of 0.03% NO (nitrogen monoxide) is good not only from the environmental viewpoint (reduced ozone emissions), but also because it has a positive ef-fect on arc stability.

TIG welding is usually performed with pure argon as the shielding gas. A typical gas flow 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 effect and is used particularly for automated welding in tube/pipe manufacture.

Single-sided root beads must be welded with a back-ing gas. This is normally the same as the shielding gas. However, Formier gas (90% N2 + 10% H2) 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 least 8 mm. Backing gas flow is typically 8 – 12 l/min.

FCAW is most suitably performed using argon with an addition of 16 – 25% carbon dioxide as the shiel-ding gas. A typical gas flow is 20 – 25 l/min.

Plasma welding is normally carried out with argon or argon with an addition of hydrogen. Mixtures of argon, CO2 and N2 are often used as the shielding gas.Typical gas flows are 3 – 7 l/min for plasma and 10 – 15 l/min for backing gases.

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

Edge preparationWhen welding stainless steels, meticulous edge preparation and the correct choice of joint type are important for good results. This applies even more particularly to fully austenitic steels.

Because of the weld pool’s slightly poorer fusion penetration and fluidity (compared with standard austenites), the joint must be correctly designed to give full penetration without risking burn-through. The groove angle must be sufficiently wide to allow the welder full control of the arc, weld pool and slag. A groove angle of around 35° (i.e. somewhat larger than for austenitic standard steels) is to be recommen-ded for manual welding. General recommendations:• An X-joint can advantageously be used for plate

thicknesses 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 edge can be increased to 1.5 – 2 mm.

Table 6: Welding parameters for several different types of joint

MethodThickness mm

FillerDiametermm

Position EN/ASTM

BeadCurrent A

Wire feedcm/min

Voltage V

Speed cm/min

MMA 12 904L 3.254.00

PA (1G) RootCap

100 – 110140 – 150

– 25 – 2626 – 27

15 – 2520 – 30

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

MMA 20 P12-R 2.503.25

PF (3F) RootCap

55 – 60 70 – 75

– 23 – 2423 – 24

6 – 8 6 – 8

MMA 10 P16 3.254.00

PA (1G) RootCap

95 – 100120 – 125

– 25 – 2726 – 27

15 – 2520 – 30

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

185 – 195220 – 230

6.5 – 8.59.5 – 11.5

24 – 2526 – 27

30 – 4035 – 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 P12P12

1.602.40

PA (1G) RootCap

140 – 150300 – 350

– 10 – 1230 – 33

4 – 1040 – 45

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

300 – 350300 – 400

– 29 – 3131 – 33

40 – 4540 – 45

10 11

84

Edge preparation

Joint preparations Table 7.1

No. and joint type Sides Method Thickness

1. I-joint One side TIG < 2.5 mmNo root gap1)

2. I-joint Two sides SAW 6 – 9 mmNo root gap2)

3. I-joint One side PAW 1 – 8 mm

4. I-joint One side MMA < 2.5 mmD = 1.0 – 2.0 mm MIG

TIG

5. I-joint Two sides MMA < 4 mmD = 2.0 – 2.5 mm MIG

TIGFCW

6. V-joint One side MMA 4 – 16 mmα = 60°3) MIGC = 0.5 – 1.5 mm TIGD = 2.0 – 4.0 mm FCW

7. V-joint Two sides MMA 4 – 16 mmα = 60°3) MIGC = 2.0 – 2.5 mm TIGD = 2.5 – 3.5 mm FCW

8. V-joint One side FCW 4 – 20 mmα = 60°3) againstC = 1.5 – 2.5 mm backingD = 4.0 – 6.0 mm

9. V-joint Two sides TIG+ 3 – 16 mmα = 80 – 90° SAWC = 1.5 mmNo root gap1)

10. V-joint Two sides SAW 8 – 16 mmα = 80 – 90°C = 3.0 – 6.0 mm4)

No root gap

11. V-joint Two sides PAW+ 6 – 16 mmα = 80 – 90° SAWC = 3.0 – 4.0 mmNo root gap

1) There must be a root gap when welding special grades.2) A ground groove, 1 – 2 mm deep and wide.3) The joint angle for special grades is 60 – 70°.4) A root land of 5 mm and above may require the torch to be angled towards the direction of travel, 4) see ”Width and depth” in chapter 4.

D

α

DC

α

DC

α

C

C

M

Y

CM

MY

CY

CMY

K

Fig 2-4.pdf 06-10-30 14.24.40

85

Edge preparation



12. V-joint One side MMA 4 – 16 mmβ1 = 45° FCWβ2 = 15°C = 1.0 – 2.0 mmD = 2.0 – 3.0 mm

13. V-joint Two sides MMA 4 – 16 mmβ1 = 45° FCWβ2 = 15°C = 2.0 – 2.5 mmD = 2.0 – 2.5 mm

14. V-joint One side FCW 4 – 20 mmβ1 = 45° againstβ2 = 15° backingC = 1.5 – 2.5 mmD = 4.0 – 6.0 mm

15. X-joint Two sides MMA 14 – 30 mm8)

α = 60°3) MIGC = 2.0 – 3.0 mm TIG6)

D = 2.0 – 2.5 mm FCW

16. X-joint Two sides SAW 14 – 30 mmα = 80°C = 3.0 – 8.0 mm4)

No root gap

3) The joint angle for special grades is 60 – 70°.4) A root land of 5 mm and above may require the torch to be angled towards the direction of travel, 4) see ”Width and depth” in chapter 4.6) Normally only for the first 1 – 3 runs. Followed by MIG, FCW, MMA or SAW.8) A thickness above 20 mm can be prepared as an asymmetrical X-joint.

D

C

β1

β2

D

C

β1

β2

α

D

C

α

C

C

M

Y

CM

MY

CY

CMY

K

Fig 4 ny.pdf 06-10-30 14.31.25

Figure 4: Examples of common joint types

84

Edge preparation







TIG


TIGFCW






No root gap



D

α

DC

α

DC

α

C

C

M

Y

CM

MY

CY

CMY

K

Fig 2-4.pdf 06-10-30 14.24.40

1. I-joint for single-sided MMA, MIG, TIG and plasma arc welding. Suitable root protection must be used for single-sided TIG welding.

2. V-joint (t > 4 mm) for single and double-sided MMA and TIG welding as well as double-sided MIG and FCAW.

3. V-joint for SAW. So that full penetra-tion is possible, the root bead must be ground precisely.

4. In SAW, an X-joint is to be recommen-ded where plate thickness exceeds 16 mm. Straight edge, 3 – 4 mm.

5. Edge preparation for pipe joints. TIG or MMA welding is the most appropriate.

6. Half V-joint with full burn-through. Single-sided welding requires TIG or electrode for the root bead. In this type of joint, the distance between tacks should not exceed 150 mm. This is so that shrinkage does not prevent full burn-through.

7. Single-sided or double-sided U-joint for welding thick sections, t > 30 mm. The joint can advantageously be made as a symmetrical or asymmetrical double U-joint. Root welding is most suitably carried out as a TIG or MMA weld fol-lowed by SAW.

84

Edge preparation







TIG


TIGFCW






No root gap



D

α

DC

α

DC

α

C

Joint type 1I-joint, t < 2.5 mmD = 1.0 – 2.0 mmSingle-sided without root backing

I-joint, t < 4.0 mmD = 2.0 – 2.5 mmDouble-sided with root grinding

Joint type 2V-joint, t = 4 – 16 mmα = 60° – 70°C = 0.5 – 1.5 mmD = 2.0 – 4.0 mmSingle-sided without root backing

V-joint, t = 4 – 16 mmα = 60° – 70°C = 2.0 – 2.5 mmD = 2.5 – 3.5 mmDouble-sided with root grinding

Joint type 3V-joint, t = 8 – 16 mmα = 80° – 90°C = 3 – 6 mmNo root gap

Joint type 4X-joint, t = 14 – 30 mmα = 80° – 90°C = 3 – 4 mm No root gap



28. Half V-joint One side MMA 4 – 12 mmα = 50° MIGC = 1.5 – 2.5 mm TIG6)

D = 2.0 – 4.0 mm FCW5)

29. Half V-joint Two sides MMA 4 – 16 mmα = 50° MIGC = 1.5 – 2.5 mm TIG6)

D = 1.5 – 2.5 mm FCW

30. K-joint Two sides MMA 14 – 30 mm8)

β = 50° MIGC = 2.0 – 2.5 mm TIG6)

D = 2.0 – 4.0 mm FCW

31. Half V-joint 7) Two sides MMA 4 – 16 mmα = 50° MIGC = 1.0 – 2.0 mm TIG6)

D = 2.0 – 3.0 mm FCW

32. Half pipe One side MMA 4 – 16 mmα = 45° MIGC = 1.5 – 2.0 mm TIGD = 1.0 – 2.0 mm FCW

88

Edge preparation

5) Welding performed against ceramic backing (round type).6) Normally only for the first 1 – 3 runs. Followed by MIG, FCW, MMA or SAW.7) For openings such as manways, viewports and nozzles.8) A thickness above 20 mm can be prepared as an asymmetrical X-joint.

α

D

C

C

D

β

α

CD

α

CD

C

M

Y

CM

MY

CY

CMY

K

Fig 5 ny.pdf 06-10-30 14.40.27

Joint type 5V-joint, t = 4 – 16 mmα = 50°C = 1.0 – 2.0 mmD = 2.0 – 3.0 mmSingle-sided without root backing

Joint type 6Half V-joint, t = 14 – 30 mmα = 50° C = 1.5 – 2.5 mmD = 2.0 – 3.0 mm Double-sided

Joint type 7U-joint, t > 30 mmα = 10° R = 8 mmC = 2.0 – 2.5 mmD = 2.0 – 2.5 mmSingle-sided without root backing or double-sided with root grinding



21. Fillet weld One or MMA > 2 mmNo root gap two sides MIGA ≈ 0.7 x t TIG

FCW

22. Half V-joint One side MMA 4 – 16 mmα = 50° MIGC = 1.0 – 2.0 mm TIG6)

D = 2.0 – 4.0 mm FCW

23. Half V-joint Two sides MMA 4 – 16 mmα = 50° MIGC = 1.5 – 2.5 mm TIG6)

D = 2.0 – 3.0 mm FCW

24. Half X-joint One side MMA 14 – 30 mmα = 50° MIGC = 1.0 – 1.5 mm TIG6)

D = 2.0 – 4.0 mm FCW5)

25. Half X-joint Two sides MMA 14 – 30 mmα = 50° MIGC = 1.5 – 2.5 mm TIG6)

D = 2.0 – 3.0 mm FCW

26. Fillet weld Two sides MMA < 2 mmNo root gap MIG

TIGFCW

27. Fillet weld Two sides MMA 2 – 4 mmD = 2.0 – 2.5 mm MIG

TIGFCW

87

Edge preparation

α

t2

C

Dt1

5) Welding performed against ceramic backing (round type).6) Normally only for the first 1 – 3 runs. Followed by MIG, FCW, MMA or SAW.

A

t1

t2

αD

t2

t1

C

D

C

M

Y

CM

MY

CY

CMY

K

Fig 6 ny.pdf 06-10-30 14.38.48

86

Edge preparation



17. X-joint Two sides MMA 14 – 30 mm8)

β1 = 45° MIGβ2 = 15° TIG6)

C = 1.5 – 2.5 mm FCWD = 2.5 – 3.0 mm

18. X-joint Two sides SAW9) 14 – 30 mmβ1 = 45°β2 = 15°C = 3.0 – 8.0 mm4)

No root gap

19. U-joint Two sides MMA < 50 mmβ = 10° MIGR = 8.0 mm TIG6)

C = 2.0 – 2.5 mm FCWD = 2.0 – 2.5 mm SAW10)

20. Double U-joint Two sides SAW9) > 20 mmβ = 15°R = 8.0 mmC = 4.0 – 8.0 mm4)

4) A root land of 5 mm and above may require the torch to be angled towards the direction of travel, 4) see ”Width and depth” in chapter 4.6) Normally only for the first 1 – 3 runs. Followed by MIG, FCW, MMA or SAW.8) A thickness above 20 mm can be prepared as an asymmetrical X-joint.

09) TIG or MMA can be used for root runs. Grinding from the back. C = 3.0 mm.10) SAW can be used for fill and cap passes.

β2

C

D

β1

DC

Rt

β

C

R

β2

C

β1

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Fig 7_Fog NYTT.pdf 06-11-01 15.03.40

12 13

Pre-weld cleaningTo ensure good weldability and reduce the need for post-weld cleaning, all joint surfaces, and the surfaces adjoining these, must be thoroughly cleaned before welding. 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 by gentle grinding.

Oxides, paints and primers must be meticulously removed, not only in the joint, but also in the 50 mm from the joint edges. Tack welding So that shrinkage during welding does not prevent full burn-through, precise tack welding is extremely important. For metal thicknesses up to 6 mm, tack length should be 10 – 15 mm. This should be increased to 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 sufficient to grind away the beginning and the 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, matching material. Note that gap width must be constant throughout the joint.

Figure 5: Tack welding using distance pieces.

Starting and stopping – Striking and extinguishing the arc It is very important to use the right technique when striking and extinguishing the arc. As regards metal-lurgical, mechanical and corrosion properties, each start and stop is a “critical” area.

To avoid striking scars, the arc must always be struck down in the joint. If, despite this, striking scars occur, 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 extinguished carefully by first making several circular movements in the centre of the weld pool. The electrode is then to be moved slowly backwards 10 mm through the weld pool before being gently lifted. If this is done too quickly, crater cracks and slag inclusions may result.

Modern power sources for MIG and TIG welding often have a so-called crater filling facility. This gives smooth and controlled stops.

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

Figure 6: Penetrant testing (PT) is a simple and highly visual way of investigating weld metal quality as regards surface-breaking defects. At the top, an approved joint where there are no indications of surface-breaking defects. Below, a rejected joint where there are problems with both hot cracks and end crater pipes.

12 13

Planning the welding sequence Because it makes burn-through unnecessary, double-sided welding is always to be preferred over single-sided welding. To ensure full burn-through on the last 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 difficult to decide whether grinding has reached the first 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 is most easily carried out with root backing, but can also be performed without. A 2.50 mm diameter electrode must be used for the root bead and 3.25, 4.00 or 5.00 mm for filling the joint. Choice of electrode diameter is determined 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) is easiest for this.

As already stated, a backing gas must be used in TIG welding. Single-sided welding without root backing places high demands on even and thorough edge preparation. Root beads must satisfy three important requirements:• Correct metallurgy and structure (right root gap to

ensure sufficient quantity of filler metal).• Correct geometry (no root concavity, undercutting

or lack of fusion).• Best possible productivity (always in relation to

weldability).

Figure 8: Root bead correctly executed using TIG welding.

Figure 7: Root, filler and cap beads welded using Avesta P12-R basic covered electrodes.

Figure 9: Grinding scars.

Filler beads must be deposited with the highest pos-sible productivity. At the same time, structure and mechanical properties have to be maintained. In most cases, fill passes use the same filler metal as that used in root passes. High productivity welding methods may be economical for joint filling. Several common choices are:• TIG root pass + MMA, MIG or SAW fill passes.• TIG root pass + SAW or FCAW fill passes.Generally speaking, welding is carried out with the highest possible heat input (max. 1.5 kJ/mm) that is still consistent with maintained properties and weldability. Visual inspection between the passes is important.

Slag residues and severe welding oxide are to be removed before depositing the next layer. Otherwise, there is always the risk of slag inclusions being left behind. A suitable grinding disc must be used. To avoid damaging adjacent surfaces (please see figure 9), grinding should be carried out with some care.

The cap bead is primarily intended to give the weld good corrosion protection. Besides structure, surface geometry can also play a critical role here. Undercut-ting, unevenness, high reinforcements, gaps, etc. can all have a negative impact on corrosion resistance. Aesthetic considerations are often also important.

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

14 15

Welding techniquesIn the flat position, there should be no significant weaving. In the vertical-up position, weaving of up to 20 mm is advantageous. For the best control of arc and weld pool, welding is normally carried out with a torch 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 coefficient of expansion than do low-alloy steels and duplex stain-less steels. This means that distortion during welding is also greater. Consequently, to reduce distortion, tack welding has to be carried out precisely and the welding sequence meticulously planned.

Preheating Generally speaking, stainless steels (fully austenitic steels included therein) must not be preheated before welding. Welding is normally carried out at room temperature. At lower temperatures, preheating to a maximum of 50°C is advisable. This drives off any moisture that may otherwise lead to pore formation. When welding castings, or where the workpiece is thick or where restraint is high, preheating to a maximum of 100°C may, in certain cases, be advantageous. In these cases, a suitable preheating method is the use of electric blankets or similar. The use of soot-depositing flames can result in local carburisation. This reduces resistance to intergranular corrosion.

Interpass temperature Because fully austenitic materials are prone to inter-metallic precipitates, the interpass temperature must not be above 150°C for 904L and 100°C for other fully austenitic materials.

Thermal conductivity is of the same order as for austenitic stainless steels, i.e. considerably lower than it 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 be increased 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 joint presents the risk of contamination. Cooling can also be accelerated by intermittent welding or using a correctly planned welding sequence.

The interpass temperature must be measured. Some form of thermometer or thermoelement is appropriate for this. Temperature crayons seldom give good results and must be avoided.

Heat input To avoid intermetallic precipitates, the heat input when welding fully austenitic materials must be kept as low as possible without thereby giving rise to any risk of lack of fusion, etc. One general recommenda-tion is a maximum of 1.5 kJ/mm. However, the critical upper limit depends very much on welding method and the thickness of the workpiece. For example, MIG is not as sensitive as SAW and a 5 mm joint is less sensitive than a 20 mm joint.

Especially in automated welding, heat input is easy to control.

Heat input = U x I

k x –––––––––– V x 1,000

U 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 heat input.

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

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

14 15

How to weld fully austenitic materials to other materialsWelding fully austenitic steels to carbon or low-alloy steels is best carried out using the same filler metals as those for welding stainless steel to stainless steel. However, in certain cases, Avesta P5 (309MoL) can be a more economical alternative. This applies particular-ly to thin workpieces (t < 10 mm) where the degree of restraint 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 filler metal or, in certain cases, Avesta P5.

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

Because it gives rise to a risk of brittle secondary phases, 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 joint design and welding techniques.

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

Post-weld cleaning Post-weld cleaning is critical in achieving fully satis-factory corrosion resistance. Clearly enough, it is thus an integral part of the entire stainless steel welding procedure. Despite this, post-weld cleaning is not always standard.

The method and extent of cleaning is determined by the requirements imposed in respect of corrosion resistance, hygiene and appearance.

Generally speaking, one basic requirement is that defects, welding oxide, organic contaminants and carbon steel contamination must be removed from weld and parent metal surfaces. This can be done me-chanically (grinding, brushing, polishing, blasting) or chemically (pickling). An important rule of thumb for grinding is to always finish with polishing. The risk of harmful 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. It comprises cleaning products, pickling pastes, pickling sprays, pickling fluids and various items of equip-ment. Fully austenitic steels are generally slightly more difficult to pickle than are austenitic steels such as 1.4301 (304) and 1.4404 (316L). Thus, Avesta BlueOne™ and Avesta RedOne™, which are comparatively strong pickling products, should be used.

Further details are available at www.avestafinishing.com or can be obtained directly from Avesta Finishing Chemicals.

Table 9: Suitable filler metals for welding fully austenitic steels to other materials

Parent metal

Recommended filler 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 17

DefectsApart from the risk of hot cracking, fully austenitic steels are generally no more prone to defects than are other stainless steels. However, certain factors require special attention.• The high nitrogen content gives poorer penetration.• Arc stability, fluidity and arc control are somewhat

poorer than they are for austenitic stainless steels. This applies particularly to 4565/EN 1.4565/ASTM S34565, which has a high manganese content.

• To avoid problems with poor penetration, slag inclusions or pores, recommendations for joint design and welding parameters must be followed precisely.

• Hot cracking (a classic problem for fully austenitic materials).

During solidification, secondary precipitates form in the weld metal. If the cooling rate is too low and the heat input too high, these precipitates may collect and form films of late-solidifying phases at grain bounda-ries. Under the influence of the residual stresses al-ways present in weld metal, the films can crack. These hot or solidification cracks form particularly at the centre 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, films that 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 filler metals that do not contain niobium

(e.g. Avesta P12-0Nb and Avesta P16).• A good width to depth ratio, i.e. the width of the

weld must be around 1 to 1.5 times its depth (please see figure 11).

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

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

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

16 17

Repair weldingSo that corrosion resistance is not impaired, all defects must be repaired. Minor surface defects such as spat-ter, slag and oxide islands can easily be remedied by grinding followed by polishing using an at least 320 mesh disc. Note that a grinding disc intended for stainless steel must be used. After polishing, conven-tional pickling is to be carried out. Pickling paste is most often the simplest alternative.

Defects must never be repaired by TIG dressing (remelting using a TIG electrode). This has the same effect as welding without a filler metal, i.e. there is a risk of a high content of secondary precipitates in the weld metal. If this occurs, ductility and corrosion resistance will be lower.

Large defects and subsurface defects require heavier grinding with a coarser grinding disc. Once the entire defect has been removed (which can be checked by, for example, penetrant testing), the ground area is to be fil-led using a suitable method, most often 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 the powerful spatter. If care is not taken, this can damage adjacent surfaces. The latter should be protected using, for example, Masonite boards or chalk paint.

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

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

Figure 15: Typical welding sequence in repair welding

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

2. Using a suitable grinding/cutting disc, the defect is ground to a depth and width (width, min. 3 mm and depth, min. 10 mm) that is sufficient for repair welding. To ensure that the entire defect has been ground away, PT can be carried out.

4. The weld is ground flush 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 steels contain no ferrite. There is thus no reason to measure or calculate the ferrite content.

Overlay weldingOverlay welding of carbon steel can be carried out using all types of filler metals. Directly from the first layer, welding can be with a nickel base alloy (e.g. P12) or 904L. Filler metals of the 309L or P5 type can also be used as a first layer. This is considerably more cost-efficient.

Correctly executed, the overlay metal is extremely resistant to corrosion.

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

Welding should be with as little dilution of the parent metal as possible. Welding parameters and technique are of great importance. Dilution can be minimised by building on the preceding bead and avoiding 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 filler metals.

6. End with pickling.

18 19

How to weld fully austenitic steels of similar compositions In 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 compositions of overlay weld metals

Inspection and quality assuranceThe rules that apply to structural steels apply also to stainless steels. The following are some of the relevant international standards:• EN ISO 5817, which gives guidelines on acceptance levels for various defects in welded joints.• EN ISO 15607–15614 and ASME IX, which describe approval of welding procedures.

However, fully austenitic steels are used in applica-tions where strength and corrosion requirements are often very severe. There is thus every reason to be extra careful from beginning to end. Welding oxide, spatter, striking scars and grinding scars must be re-moved to achieve the correct corrosion resistance. For the best fatigue resistance, the weld surface must be even with no sharp edges. Nondestructive testing is an integral part of the exa-mination of welded joints. Suitable methods are visual inspection, penetrant testing (PT), radiographic testing (RT) and ultrasound testing (UT). In ultrasound testing, it is important that surfaces are ground flat so that defects such as pores and cracks can be reliably detected.

Steel gradeEN ASTM

Recommended filler 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 filler metals Stainless steel covered electrodes, flux cored wires (FCWs) and fluxes can be prone to moisture pick-up. Avesta Welding’s consumables are supplied in packa-ges that have been designed to resist moisture. However, for the best possible results, the following storage and handling precautions are still recommended.Storage of unbroken packages: Covered electrodes, FCWs and fluxes must be stored in their unbroken, original packaging. Storage in opened packaging can considerably shorten the product’s service life. Fol-lowing the “first in, first out” principle, storage time must be kept as short as possible. Covered electrodes and fluxes 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 be redried before use.

Covered electrodes, FCWs and fluxes should not be stored in direct contact with floors or outer walls.

Storeroom temperature must be kept as even as possible (± 5°C) and should not fall below 15°C. The relative air humidity should not exceed 50%.

Handling of opened packages: Electrodes that remain unused at the end of a shift should be replaced in their packaging and resealed. Alternatively, they can be put in a warm heating cabinet at 60 – 70°C. The relative air humidity should not exceed 50%.

Flux that has not been used should be stored in a heating cabinet at 60 – 70°C.

If the relative air humidity is above 55%, FCWs should never be left unprotected for more than 24 hours.

Handling during welding: It is an advantage if welding can be carried out at room temperature and low relative air humidity. Covered electrodes, FCWs and fluxes should be used at the same rate as they are unpacked – preferably within 24 hours. During shifts, electrodes must be kept as dry as possible. If the climate so demands, they should be kept warm in a portable heat-retaining container or similar. One alternative is to use smaller packs, e.g. half or quarter capsules.

Redrying: Electrodes that have sustained slight moisture damage can be redried for around 3 hours at 250 – 280°C. Heating and cooling must both be gradual. Items should not be redried any more than 3 times.

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

FCWs that have sustained slight moisture damage can be redried for 24 hours at 150°C.

Procedures that have been approved for carbon steel electrodes are also completely satisfactory for stainless steel electrodes. This is because the latter are not as prone to moisture pick-up.

Recycling: Because they can be reused, leftover pro-ducts and scrap are valuable. Wherever possible, pro-ducts and packaging must be recycled in accordance with local regulations.

18 19

Health and safety The fumes and radiation given off during welding can be hazardous to health. Spatter, molten metal and arcs can cause burns and fires. Furthermore, electrical equipment is used. If it is not handled correctly, there is the risk of electric shock. Thus, it is of the greatest importance that welders and supervisors are aware of all the potential dangers.• Ensure that ventilation is adequate and that the

welding site has an extractor system that removes fumes and gases from the welder’s “breathing zone”.

• When welding in confined spaces, use respiratory protective equipment or a compressed air line breathing apparatus.

The right to make changes without warning or notification is reserved. Great care has been taken to ensure that the contents of this publication are correct. However, Böhler Welding Group Nordic AB cannot accept responsibility for errors or for information that is found to be misleading. Suggestions for, or descriptions of, working methods or of the use, treatment or machining of products are for information only and Böhler Welding Group Nordic AB can accept no 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 filter glass; safety boots; apron; and arm and shoulder guards.

• Keep the workplace and equipment clean and dry. • Regularly check that safety clothing and equipment

are in good condition. • As far as possible, insulate all conducting elements

Further information on each product group is con-tained in Avesta Welding’s material safety data sheets. These can be downloaded from Avesta Welding’s website, www.avestawelding.com , or ordered from Avesta Welding’s distributors and retailers.

Avesta Welding P O Box 501, Modellvägen 2

SE-774 27 Avesta, SwedenTel: +46 (0)226 857 00Fax: +46 (0)226 857 16

[email protected]

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Avesta Welding: How to weld fully austenitic stainless steels

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