Sudura Inox

CODE OF PRACTICE

Classement prvu : 90 - 00 - 151 / - - - Sce N Tl

Responsable du document P. SCHWARTZ 65810 53130

Pilote(s) technique(s) B. NICOL 65520

Date de mise jour :

Normalisation Renault Automobiles

90 - 00 - 151 / - - -

WELDING OF STAINLESS STEEL

EXHAUST LINES

Service 65810Section Normes et Cahiers des Charges

VISA RESPONSABLE(S)

SIGNATURE :

NOM :SERVICE :DATE :

04/09/2001

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RENAULT 2001 Page 2/42

This document is to be considered as a whole, the parts of which must not be separated.

RENAULT 2001.No duplication permitted without the consent of the issuing department.No circulation permitted without the consent of RENAULT.

FIRST ISSUE

September 2001 - - - This issue originates from draft NC 2001 0631 / - - -.

REVISION

REFERENCED DOCUMENT

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CONTENTS

Page

1. GENERAL INFORMATION ON STAINLESS STEELS 5

1.1. NOTE ON BASIC CONCEPTS RELATIVE TO STAINLESS STEELS 5

1.1.1. Definitions 5

1.1.2. Classification 5

1.2. FERRITIC STAINLESS STEELS 6

1.2.1. Chemical composition, additions, mechanical characteristics 6

1.2.2. Diagrams: Roles of alloy elements (Extract from UGINE documentation) 8

1.3. AUSTENITIC STAINLESS STEELS 10

1.3.1. Chemical composition, additions, mechanical characteristics 10

1.3.2. Diagrams: Roles of alloy elements (Extract from UGINE documentation) 11

2. CHARACTERISTICS OF MATERIALS FOR EXHAUST LINES (BY DANIEL GOURDET - DEPT64140 - DIMAT - ISSUE OF 08/2000) 12

2.1. INTRODUCTION 12

2.2. SYMBOLS AND UNITS OF CHARACTERISTICS INDICATED 13

2.3. CHEMICAL COMPOSITION OF GRADES (% IN WEIGHT) 14

2.4. PHYSICAL PROPERTIES OF SHEETS AND TUBES (AVERAGE VALUES) 14

2.5. MECHANICAL CHARACTERISTICS OF PRODUCTS AT AMBIENT TEMPERATURE 15

2.6. STATIC MECHANICAL CHARACTERISTICS OF PRODUCTS WHEN HOT 15

2.6.1. Tensile test 15

2.6.2. Sag Test 18

2.7. ENDURANCE CHARACTERISTICS WHEN HOT 19

2.7.1. 4 point fatigue under alternating bending test (R = -1) 19

2.7.2. Torsion fatigue test on tubes when hot (As per ME-60152-A-009) 19

2.8. TUBE IMPLEMENTATION CHARACTERISTICS 20

2.9. RESISTANCE TO CORROSION 20

2.9.1. Aluminated mild sheets 20

2.9.2. Stainless steels 21

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CONTENTS (continued)

3. WELDING STAINLESS STEELS 23

3.1. REMINDER 23

3.1.1. Schaeffler diagram 23

3.2. WELDING OF FERRITIC STAINLESS STEELS 25

3.2.1. Metallurgical consequences of thermal welding cycles 25

3.2.2. Choice of welding conditions 25

3.3. WELDING AUSTENITIC STAINLESS STEELS 28

3.3.1. Metallurgical consequences of thermal welding cycles 28

3.3.2. Sigma phase 28

3.3.3. Choice of welding conditions 29

3.4. HETEROGENEOUS WELDING OF STAINLESS STEELS 30

3.4.1. General 30

3.4.2. Bystram diagrams 30

4. STAINLESS STEEL WELDING TECHNIQUES 33

4.1. MIG WELDING 33

4.1.1. Description of process 33

4.1.2. Metal transfer modes inj the arc. (Pulsed, Lincoln STT, axial spray) 34

4.1.3. Gases and gas mixtures 36

4.1.4. Solid and flux-cored electrode wire 38

4.2. TIG WELDING 41

4.2.1. Description of process 41

5. BIBLIOGRAPHY 42

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1. GENERAL INFORMATION ON STAINLESS STEELS

1.1. NOTE ON BASIC CONCEPTS RELATIVE TO STAINLESS STEELS

1.1.1. Definitions

Stainless steels are iron - chromium alloys with a minimum chromium content of 12 % and which maycontain:

- additive elements necessary for their manufacture (Mn, Si),- impurities (S, P and in certain cases, C and N),- alloys such as Ni, Mo, Ti, Nb, Cu , W, Al and for certain Mn, Si, C and N. These alloy elements

are added in different quantities in order to modify and improve certain properties of the stainlesssteels.

The most important elements are carbon and nickel which directly influence the micrographicstructure of the steel.

Carbon: It acts by its character - gene (austenitic) and by its competition with the chromium,element - gene. The carbon, in the presence of a carburigen element such as chromium, may formcarbons and thereby promote intergranular corrosion.

Nickel: In low quantities, maximum 1 %, there is no incidence on the structure of the steels. Beyond 6to 8 %, there is an effect - gene, which results in the stainless steels remaining austenitic at ambienttemperature T.

1.1.2. Classification

Insofar as they are essentially iron-based alloys, stainless steels like other steels, are liable to displaydifferent structural conditions: There are three main categories:

- Martensitic stainless steels (magnetic)Martensitic steels have higher Carbon contents and may also contain small quantities of alloyelements (Ni, Cr, Mo). Their mechanical resistance may be considerably increased by heattreatment.

They are represented by 23 % grades of chromium (example X20Cr13) with a sufficient carboncontent (> 0,08 %). These steels have a behaviour comparable to that of conventional heattreated steels.

In general:

C > 0,08; 0,20 Si 0,35; Mn = 0,35; 12 Cr 14.

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- Ferritic stainless steels (magnetic)Ferritic steels have low carbon contents and, as a result, do not undergo significant hardeningafter heat treatment; cold work-hardening endows them only with a hardening level less than thatencountered on austenitic steels; they are mostly used in the annealed condition, a state whentheir main characteristic, i.e. their resistance to corrosion, is most prominent. They are sensitiveto grain expansion by heating at high temperature and in general, are not very suitable forwelding; on the other hand, they are amenable to machining and are well suited to sheet-metalwork and stamping. In addition, their resistance to corrosion is greater than that of martensiticsteels.

Even if certain grades have a chromium content of up to 30 %, grade X6Cr17 (1,4016) and itsmolybdenum variant X6Cr17-1 (1,4113) are representative of this class.In general:

C 0,05; Si 0,5; Mn 0,5;12 Cr 20 and Ni 1.

- Austenitic stainless steels (amagnetic)Austenitic steels have greater mechanical strength and better resistance to corrosion than ferriticand martensitic steels; furthermore, austenitic steels do not harden after heat treatment; on theother hand, their resistance may be considerably improved by cold rolling or work hardening. Inthe annealed condition, austenitic steels display ductility and tenacity properties making thenamenable to cold forming; they are very weldable.

Many basic grades have been modified into grades with less carbon or into stabilized gradesmainly in order to improve resistance to corrosion.

In general:

0,03 C 0,08; 0,5 Si 1; 1 Mn 2; Cr 16 and Ni 7.

1.2. FERRITIC STAINLESS STEELS

1.2.1. Chemical composition, additions, mechanical characteristics

The basic composition consists of carbon and chromium, a composition that has been balanced toensure that the steel is entirely ferritic at high temperature.

These types of steels do not have any transformation point and are practically ferritic at alltemperatures. It follows that they are very sensitive to grain expansion and are therefore brittle whenheated for the purposes of forming, welding and thermal treatment, such effects being cumulative.

In addition, they have the specific characteristic of containing very little austentite at hightemperature; this austentite will therefore be very rich in carbon; if cooling is very slow, it transformsitself into ferrite; on the other hand, if it occurs too rapidly, it will transform into hard and fragilemartensite at the joints of the ferrite grains.It is very important to take this characteristic into account when studying welding problems.

The most frequent addition is molybdenum (0,8 to 1,5 %) in order to improve resistance to corrosion;sometimes, copper is associated with the molybdenum; however be careful, if the quantity of copperexceeds 0,5 to 1 %, there is a risk of the steel becoming martensitic.

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The other added elements encountered are:

- Titanium, the role of which is to fix the carbon in order to prevent the austentite from beingoverloaded in carbon and from transforming into martensite after the welding operation or toprevent the carbon from combining with Cr, which would promote intergranular corrosion.

Titanium does not prevent grain expansion, however it should be added in a significant quantity.

Ti 10 at 12 *C for stabilization of C.

Ti 4,2 (C + 2N2) for resistance to corrosion without heat treatment after welding.

- Niobium (Nb); the role of which is similar to titanium, however which should be added in a higherquantity.

Impurity

- Nitrogen (N2) remains present as an impurity, however if its quantity is too high, it causes fragilityafter welding.

In general:

C + N2 0,04.

If this condition is effectively observed, the brittleness after welding is noticeably reduced; in addition,an improvement in the intergranular corrosion after welding is observed.

The values of the mechanical characteristics are average:

Rm mini = 440 to 490 N/mm2

R0,02 = 245 to 275 N/mm2.

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1.2.2. Diagrams: Roles of alloy elements (Extract from UGINE documentation)

EUROPEAN DESIGNATIONAs per NF EN 10088-2

(Nov. 95)

Previousdesignation of

NF A 35573(Cancellation

Nov. 95)

ASTM Chemical composition for reference

Variants

Annealed state forreference

(Average values)

NAME N (CancellationNov. 95) AISI UNS C Si Mn Cr Mo Ni Other Rm Rp0,2 A%

FERRITIC STAINLESS STEELS

X6Cr13 1,4000 Z8C12 410S S41008 0,05 0,35 0,30 12,70 480 330 26

X2CrTi12 1,4512 Z3CT12 409 S40900 0,02 0,50 0,30 11,50 Ti = 0,180 410 250 32

Z2CrNi12 1,4003 410S* S41008 0,02 0,50 0,60 11,00 0,40 1,4516 510 350 28

X6Cr17 1,4016 Z8C17 430 S43000 0,05 0,35 0,40 16,50 F 18 (Cr 17,5) 500 340 26X3CrTi17 1,4510 Z4CT17 430 Ti** 0,02 0,35 0,40 16,50 Ti = 0,400 AISI 439 (Cr 17,5) 450 300 30X6CrMo17-1 1,4113 Z8CD17-01 434 S43400 0,05 0,35 0,40 16,50 1,00 F 17 MS (Mo = 1,25) 540 370 27X6CrNi17-1 1,4017 Z8CN17 0,02 0,15 0,40 16,80 1,40 700 360 20

X2CrTiNb18 1,4509 Z3CTNb18 441 S44100 0,02 0,50 0,50 17,80 Ti + Nb = 0,700 490 300 30

X6CrMoNb17-1 1,4526 Z8CDNb17-01 436 S43600 0,04 0,40 0,50 17,50 1,25 Nb = 0,600 520 370 27

X2CrMoTi18-2 1,4521 Z3CDT18-02 S44400 0,02 0,40 0,40 17,70 2,00 Ti + Nb = 0,450 540 380 27

X2CrTi20 1,4604 Z3CT20 0,02 0,20 0,30 20,00 Ti = 0,500 480 320 28

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Improvedresistance

to corrosionwith pitting

Mo greater

1.4113Mo : 1,00

Mo : 1,25 Low C+ Mo, stabilized Nb 1.4526C < = 0,025

Mo : 1,00 + Nb

Low C+ Mo, stabilizedTi et NbImproved application (formability,weldability)Localized pitting corrosion, equivalent to316 L

Resistance to corrosion improved

1.4521C < = 0,025Mo : 2,00Ti and Nb

1.401617 Cr

C < = 0,10Low CStabilizedTi orNb

Cold formingimprovedweldability

Low CStabilizedZr or Tior Nb

Good resistanceto oxidationwhen hot

1.4509Zr or Tior Nb

Cr : 18Al : 2,00

+ Cr + Alstabilized TiImproved resistanceto corrosion

FERRITIC STAINLESS STEELSWITH 17 % CHROMIUM

1.4510C < = 0,030

Ti or Nb

+ Mo

1.4003C : < = 0,03

Mechanical characteristicsand weldability improvedMechanical strengthof welded joints (assembly).

12 CrC < = 0,15

Low C content

Improvedweldability

FERRITIC STAINILESS STEELSWITH 12 % DE CHROME

Reduced Ccontent+ Ni + Ti

1.4000C < = 0,030

1.4512C : < = 0,03

Improved resistance to oxidationwhen hotWeld ductility

Low C contentStabilized Ti

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1.3. AUSTENITIC STAINLESS STEELS

1.3.1. Chemical composition, additions, mechanical characteristics

The basic elements of the chemical composition are chromium and nickel:

- chromium greater than 16 % to ensure oxydability,

- nickel greater than 7 % to obtain an austenitic structure.

They all contain:

- carbon, whose content may be classified into three categories:

C 0,030 - steels with low carbon content,

0,03 < C 0,08 - steels with average carbon content,

C > 0,08 - high carbon content steels,

- manganese,

- silicon,

- sulphur and phosphorous as impurities.

They are characterized by:

- a totally austenitic structure in the delivery state: hyper-quenched treated condition bymaintenance between 1 025 C and 1 150 C according to the composition, followed by rapidcooling in air or water,

- absence of transformation point: if follows that there can be no recrystallization (thereforerefinement of the grain) by thermal treatment unless there has been sufficient workhardening (atleast 20 to 25 %),

- the possibility of the appearance of ferrite subsequent to thermal effects other than hyper-quenching, e.g. the thermal effects due to hot processing and welding. It is important to be ableto determine, beforehand, the ferrite rate liable to occur during a welding operation. Thiscomputation is possible using a Schaeffler diagram (see 3.),

- good behaviour at low and high temperatures.

They may contain various additive elements intended:

1) either stabilize the carbon content if such content is greater than 0,03, addition made in order toprotect the metal against the risk of intergranular corrosion:

. addition of titanium with a maximum of 0,6 %,

. addition of niobium with a maximum of 1,1 %,

2) or improve the resistance to corrosion with respect to certain fluids:. addition of molybdenum in the presence of halogenous products and reducing acids,

. addition of copper in the presence of sulphuric acid,

. addition of silicon in the presence of nitric acid,

3) or to improve the mechanical characteristics by addition of nitrogen4) or to improve the creep characteristics by addition of boron.

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The values of the mechanical characteristics are:

Rm min. = 500 N/mm2,

R0,02 = 240 to 340 N/mm2.

1.3.2. Diagrams: Roles of alloy elements (Extract from UGINE documentation)

EUROPEAN DESIGNATIONAs per NF EN 10088-2

(Nov. 95)

Previousdesignation of

NF A 35573(Cancellation

Nov. 95)

ASTM Chemical composition for reference

Variants

Annealed state forreference

(Average values)

NAME N (CancellationNov. 95) AISI UNS C Si Mn Cr Mo Ni Other Rm Rp0,2 A%

AUSTENITIC STAINLESS STEELS

X10CrNi18-8 1,4310 Z11CN17-08 301 S30100 0,10 0,60 1,00 17,20 7,40 800 300 48

X10CrNi18-8 1,4310 Z11CN18-08 301 S30100 0,10 1,00 1,20 16,80 0,70 6,80 740 320 50

X2CrNiN18-7 1,4318 Z3CN18-07Az 301 L 0,025 0,50 1,50 17,50 6,80 N = 0,15 780 360 48

X5CrNi18-10 1,4301 Z7CN18-9 304 S30400 0,05 0,50 1,10 18,20 8,30 670 320 50

X5CrNi18-10 1,4301 Z7CN18-9 304 S30400 0,04 0,50 1,50 18,20 8,70 630 300 52

X5CrNi18-10 1,4301 Z7CN18-9 304 S30400 0,04 0,50 1,50 18,00 9,20 610 270 55

X2CrNi18-9 1,4307 Z3CN18-10 304 L S30403 0,025 0,50 1,50 18,20 9,20 620 310 50

X2CrNi19-11 1,4306 Z3CN18-10 304 L S30403 5 (C + N) 610 280 48X4CrNi18-12 1,4303 Z6CN18-12 305 S30500 0,04 0,60 0,90 18,30 12,20 580 250 52

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C < = 0,03017 Cr 5 Ni

8 MnN = 0,20

18 Cr 9 NiC < = 0,08

AUSTENITIC STAINLESS STEELS

Low CImprovedweldability

Low CLow MnLow NiIncreased mechanicalcharacteristics,improved weldability

1.431818 Cr 7 Ni1,50 MnN = 0,15

Low CIntergranularcorrosion

1.4307C < = 0,030

+ Ni1.4306

1.440418-13 MSC < = 0,03

Low CImproved resistanceto intergranularcorrosion

Very low NiAdditionMn and N

Increasedmechanicalcharacteristics

16 Cr 4 Ni6 Mn

N = 0,15

Low C,low Ni

Mechanicalcharacteristics= workhardening

17 Cr 7 Ni

+ Nistabilized Tior NbIntergranularcorrosionmechanicalcharacteristics

1.4541 18 Cr 10 Ni Ti 18 Cr 10 Ni Nb

+ Mostabilized TiLocalizedand intergranularresistance tocorrosion

17 Cr 11 Ni2,00 Mo

Ti

Increased generalizedand localizedresistance to corrosion

17 Cr 12 Ni2,00 Mo+ Mo

2. CHARACTERISTICS OF MATERIALS FOR EXHAUST LINES (BY DANIEL GOURDET -DEPT 64140 - DIMAT - ISSUE OF 08/2000)

2.1. INTRODUCTION

The purpose of this document is to synthesise the main utilization and implementation characteristicsof metallic materials usually used on exhaust lines.

This information is intended for designers and developers of these types of parts.

The materials mentioned are classified into two families:

- mild steels coated with aluminium-silicon alloy by immersion,

- stainless steels.

The products concerned are sheets and tubes.

The values indicated in the tables have been given to us by our main suppliers of rolled products ortubes (SOLLAC, UGINE, LA MEUSIENNE and VALLOUREC). Products of different origins shall bevalidated by the corresponding supplier.

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2.2. SYMBOLS AND UNITS OF CHARACTERISTICS INDICATED

Symbol Designation Unit Remarks

density kg/dm3

E longitudinal elasticitymodule

GPa E 1=

11 = main stress

1 = corresponding linear variation.

l average linearexpansion coefficient

10-6/C l = lo (l . T) l = variation in lengthlo = initial lengthT = temperature variation.

C mass thermal capacity J/kg C Quantity of heat (energy) to be applied to 1 kg of materialin order to raise its temperature to 1 C.

thermal conductivity W/m C Thermal flow transmitted by unit of time and unit ofsurface as a function of a temperature gradient anddistance.

Rm tensile resistance MPa Stress conducive to tensile rupture.

Rp0,2 conventional elasticitylimit at 0,2 % elongation

MPa Stress corresponding to the elasticity limit of the material.Beyond this stress, the material retains a permanent set.

A elongation after rupture % Residual elongation measured after rupture of the tensilespecimen.

r plastic strain ratio sans A high r indicates a strong resistance to thinning of thesheet and corresponds to a good capacity to shrinkagedeformation before appearance of striction.

n work-hardeningcoefficient

sans A high value n reflects a good tendency of the product todistribute (uniformise) local deformations over a bigvolume (large surface) of the material and therefore todelay local thinning during expansion.

Sag-Test mm Sage sustained by a specimen resting on 2 supportsseparated by a distance of 254 mm, under its own weight,after 100 h at the same temperature.

Endurancecharacteristic

MPa Stress conducive to 50 % rupture of samples after Ncycles under a given force (type and ratio R).

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2.3. CHEMICAL COMPOSITION OF GRADES (% IN WEIGHT)

Grade C Si Mn S P Ni Cr Mo Al Other

ES - AS 18/18 0,08 0,04 0,40 0,025 0,025 0,0150,050 Ti + Nb 0,15

ES HT - AS 18/18 0,02 0,10 0,40 0,025 0,025 0,0150,050 Ti 9 x (C + N) - N 0,008

CS - AS 18/18 0,09to 0,12 0,05 0,30 0,025 0,025 - - -0,0200,060 -

E THT - AS 18/18 0,02 0,50 0,40 0,020 0,020 - 0,7 - 0,601,00 Ti 0,4 - Nb 0,3 - N 0,007

X 2 CrTi 12(1.4512) 0,030 1,0 1,0 0,015 0,040 -

10,512,5 - - Ti = 6 x (C + N) to 0,65

X 6 Cr 17(1.4016) 0,080 1,0 1,0 0,015 0,040 -

16,018,0 - -

X 3 CrTi 17(1.4510) 0,050 1,0 1,0 0,015 0,040 -

16,018,0

- 4 x (C + N) + 0,15 Ti 0,80X 2 CrTiNb 18

(1.4509) 0,030 1,0 1,0 0,015 0,040 -17,518,5 - -

Ti = 0,10 to 0,603 x C + 0,3 Nb 1,00

X 6 CrMo 17-1(1.4113) 0,080 1,0 1,0 0,015 0,040 -

16,018,0

0,901,40 -

X 6 CrMoNb 17-1(1.4526) 0,08 1,0 1,0 0,015 0,040 -

16,018,0

0,801,40 -

N 0,0407(C + N) + 0,10 Nb 1,00

X 5 CrNi 18-10(1.4301) 0,07 1,0 2,0 0,015 0,045

8,010,5

17,019,5 - - -

X 6 CrNiTi 18-10(1.4541) 0,08 1,0 2,0 0,015 0,045

9,012,0

17,019,0 - - Ti = 5 x C to 0,70

The chemical compositions of mild aluminated steels are in conformity with RENAULT SpecificationRENAULT 11-04-809/--B.The chemical compositions of the stainless steels are in conformity with European Standard 10088-1.

2.4. PHYSICAL PROPERTIES OF SHEETS AND TUBES (AVERAGE VALUES)

Grade

Density

Longitudinal elasticitymodule

E(GPa)

Mean expansion coefficient lbetween 20 C and ....

(10-6/C)

Massthermal

capacity at20 C

C

Thermal conductivity

(W/m.C)

(kg/dm3) 20 C 500 C 700 C 200 C 400 C 600 C 800 C (J/kg C) 20 C 500 C 700 CES - AS 18/18 7,9 210 170 150 11,5 13,6 14,7 15,3 472 62 40 32

ES HT - AS 18/18 7,9 210 170 150 11,5 13,6 14,7 15,3 472 62 40 32CS - AS 18/18 7,9 210 170 150 11,5 13,6 14,7 15,3 472 62 40 32

E THT - AS 18/18 7,9 215 175 155 11,5 12,8 13,7 14,2 472 62 40 32X 2 CrTi 12

(1.4512) 7,72 215 170 130 11,0 11,5 12,1 12,8 460 26 31 32X 6 Cr 17(1.4016) 7,7 205 180 150 10,5 11,5 11,7 12,5 460 26 31 32

X 3 CrTi 17(1.4510) 7,7 205 180 150 10,5 11,0 12,0 12,8 460 26 31 32

X 2 CrTiNb 18(1.4509) 7,72 220 190 170 11,0 11,5 12,1 12,8 460 26 31 32

X 6 CrMo 17-1(1.4113) 7,7 215 190 160 11,7 12,1 12,7 14,2 460 26 31 32

X 6 CrMoNb 17-1(1.4526) 7,7 215 170 130 11,7 12,1 12,7 14,2 460 30 31 33

X 5 CrNi 18-10(1.4301) 7,9 200 170 150 17,5 18 19 19,6 500 15 21,5 24

X 6 CrNiTi 18-10(1.4541) 7,9 200 175 145 17 18 19 19,6 500 14 22,2 23

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2.5. MECHANICAL CHARACTERISTICS OF PRODUCTS AT AMBIENT TEMPERATURE

Grade Mechanical characteristics of sheetsMechanical characteristics of tubes

(valid for 35 to 55 mm - th. 1,2 to 2 mm) 4)Rm

(MPa)Rp 0,2(MPa)

Rp / Rmmax.

A 1)( % )

n 2)(10% Ag)

r 3)(Ag)

Rm(MPa)

Rp 0,2(MPa)

Rp / Rmmax.

A( % )

ES - AS 18/18 280 / 350 160 / 200 0,66 37 0,16 1,4 300 / 370 250 / 310 0,85 44ES HT - AS 18/18 300 / 370 180 / 210 0,68 31 0,15 1,3 330 / 380 290 / 340 0,85 42

CS - AS 18/18 380 / 470 270 / 360 0,80 24 - - 400 / 460 300 / 410 0,90 36E THT - AS 18/18 350 / 450 210 / 270 0,75 28 0,14 1,2 380 / 480 300 / 400 0,90 30

X 2 CrTi 12(untreated) (1.4512) This state does not exist for rolled products 420 / 480 300 - 30

X2CrTi 12(annealed) (1.4512) 380 / 450 220 / 300 0,66 30 360 / 450 200 - 40

X 6 Cr 17(1.4016) 450 / 550 280 / 390 0,70 24 this grade does not exist in the form of a tube

X 3 CrTi 17(1.4510) 420 / 480 250 / 350 0,70 27 420 / 620 300 - 30

X 2 CrTiNb 18(1.4509) 450 / 530 260 / 330 0,66 28 420 / 620 300 - 30

X 6 CrMo 17-1(1.4113) 490 / 570 330 / 420 0,70 24 this grade does not exist in the form of a tube

X 6 CrMoNb 17-1(1.4526) 490 / 560 330 / 400 0,70 27 450 / 580 350 - 30

X 5 CrNi 18-10(1.4301) untreated This state does not exist for rolled products 600 / 800 500 - 45

X 5 CrNi 18-10(1.4301) hyper-

quenched600 / 720 250 / 370 0,60 48 500 / 700 205 - 45

X 6 CrNiTi 18-10(1.4541) 540 / 650 240 / 340 0,60 48 (600 / 800) ( 500) - ( 45 )

1 ) specimen ISO 20 x 80 mm - Lo = 80 mm as per Standard EN 10002 - Sample in crosswisedirection.2 ) n = work-hardening coefficient measured according to Standard ISO 10275 between 10 %

and Ag.3 ) r = plastic strain ratio measured according to ISO standard ISO 10113 at Ag.4 ) as per Product Specifications 11-05-217/C for aluminated mild steel tubes (AS 18/18) and

11-05-228/A for stainless steel tubes.(-) = average values as per Supplier technical sheets (not validated for our applications).

2.6. STATIC MECHANICAL CHARACTERISTICS OF PRODUCTS WHEN HOT

2.6.1. Tensile test

2.6.1.1. Aluminated mild steels

GradeTensile characteristics according to temperature T C

(average values for rolled products of 1,5 mm of thickness)(limit T of utilization

recommendation) Prop. 20 200 300 400 500 600 700 750 800 850ES - AS 18/18 Rm 330 232 212 192 175 135 (95) (63)

(650 C) Rp0,2 185 141 135 118 112 103 (79) (56)ES HT - AS 18/18 Rm 335 269 236 219 209 150 88 68

(800 C) Rp0,2 200 180 165 150 146 110 75 58CS - AS 18/18 Rm 425 418 392 307 193 144 (86)

(650 C) Rp0,2 315 254 235 199 159 119 (77)E THT - AS 18/18 Rm 395 320 299 290 254 218 120 80 61 42

(900 C) Rp0,2 245 236 228 220 181 163 107 71 57 35

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2.6.1.2. Stainless steels

Grade Tensile characteristics as a function of TC(mean values for rolled products of thickness 1,5 mm)

(T operating limit)Prop. 20 200 300 400 450 500 550 600 650 700 750 800 850 900 950Rm 413 380 348 315 290 254 218 175 131 92 53 39 27

Rp0,2 239 219 192 170 186 143 113 109 103 75 47 30 181.4512 (annealed) Ag 18,8 12,9 10,9 11,8 5,8 3,1 3

X 2 CrTi 12 A 36,3 19,8 18,8 23,4 26,4 53 66,4(820 C) Z 66 68 73 71 75 87 93

K 772 617 464 327 169 63 33,5n 0,21 0,21 0,16 0,13 0,07 0,04 0,06E 224 219 143 106 80

Rm 520 412 366 323 290 254 210 160 105 70 43 31 22Rp0,2 363 254 225 198 186 165 113 116 89 67 41 30 21

1.4510 Ag 21 17,8 8 2 1X 3 CrTi 17 A 25 28 68 113 149

(830 C) ZK 763 622 139 47 25n 0,22 0,20 0,08 0,02 0,01E

Rm 460 422 405 383 360 342 322 288 222 121 75 43 35 26Rp0,2 260 228 208 189 172 161 150 132 122 99 65 36 29 23

1.4509 Ag 19,5 18,1 13,4 8,3 3,6 3,5 2,8X 2 CrTiNb 18 A 33 25,6 20,5 16,1 27 60,2 131,4

(920 C) Z 62 65 54 50 83 94 94K 803 695 660 623 612 229 54 28n 0,2 0,21 0,22 0,23 0,27 0,21 0,07 0,03E 210 181 168 147 134 108 93 78

Rm 500 436 417 392 360 330 300 241 162 101 70 41 31 20Rp0,2 354 262 244 232 218 203 182 155 122 92 60 39 29 19

1.4526 Ag 19,9 14,4 11,8 9 3,3 1,8 1,8X 6 CrMoNb 17-1 A 30 21,3 18,1 15,4 61,5 88,5 105,4

(920 C) * Z 63 48 47 54 85 91 91K 848 731 659 550 392 120 47 31n 0,22 0,22 0,20 0,18 0,17 0,04 0,03 0,11E 210 181 168 147 134 108 93 78

Rm 610 480 450 430 410 390 345 285 240 186 140 111 88 65Rp0,2 270 200 178 163 152 149 140 132 124 108 95 82 69 56

1.4301 Ag 56,9 31,4 28,7 22,7 17,2 10,1 16X 5 CrNi 18-10 A 60 37,4 38,6 44,3 59,3 65,2 110,7

(830 C) Z 75 49 48 56 78 81 69K 1759 999 853 526 302 162 98n 0,57 0,40 0,39 0,25 0,18 0,13 0,14E 202 168 153 147 138 113 98

Rm 600 480 448 438 425 417 400 345 295 239 200 159 123 88Rp0,2 290 290 287 272 258 251 244 234 220 207 180 153 120 88

1.4541 Ag 50 23,1 21,9 16,4 7,7 1,8 0,5X 6 CrNiTi 18-10 A 53 30,8 28,3 36,1 53,9 44 52,1

(900 C) Z 65 54 64 58 73 73 85K 1379 884 867 842 595 321 184 104n 0,44 0,31 0,31 0,31 0,21 0,09 0,03 0,03E 202 168 162 153 147 138 113 98

In bold: test results submitted by UGINE "Exhaust database - Mechanical resistance when hot".

In italics: values obtained by interpolation on the basis of test temperatures.

* = utilisation temperatures not validated.

RENAULT 90 - 00 - 151 / - - -


Tensile test when hot

0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800 900 1000Test temperature

Rm

(M

Pa)

1.45121.45101.45091.45261.43011.4541

0

100

200

300

400

0 100 200 300 400 500 600 700 800 900 1000Test temperature

Re

( M

Pa)

1.45121.45101.45091.45261.43011.4541

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2.6.2. Sag Test

The Sage Test is an empirical and comparative test consisting in sagging a specimen under its ownweight (flat 25 x 205 mm specimen).The sag is weighed after 100 h at the same temperature.

2.6.2.1. Aluminated mild steels

Test results submitted by SOLLAC

Grade Sag (mm) after 100 h at same temperature (C)700 750 800 850 900 950 1 000

ES - AS 18/18 5

ES HT - AS 18/18 2 11

CS - AS 18/18

E THT - AS 18/18 1 4 12

2.6.2.2. Stainless steels

Test results submitted by UGINE.

Grade Sag (mm) after 100 h at same temperature(C)700 750 800 850 900 950 1 000

X2CrTi 12(1.4512)

0,7 3 to 6

X 3 CrTi 17(1.4510)

15

X 2 CrTiNb 18(1.4509)

0,2 to 1 4 to 10

X 6 CrMoNb 17-1(1.4526)

2,1

X 5 CrNi 18-10(1.4301) brut

1 to 3 10 to15

X 5 CrNi 18-10(1.4301) hypertr.

0,6 2,7

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2.7. ENDURANCE CHARACTERISTICS WHEN HOT

2.7.1. 4 point fatigue under alternating bending test (R = -1)

- Tubular specimen - longitudinal weld positioned at 45 with respect to neutral axis.

- Stress (MPa) conducive to 50 % rupture of samples after N cycles.

Test temperature

Grades Tube dimensions Number ofcycles

450 C 550 C 650 C 750 C 850 C 950 C

ES - AS 18/18ES HT - AS 18/18 D 45 x 1,5 2 . 10 6 115 60

CS - AS 18/18D 45 x 1,5 (key 6) 2 . 10 5 133

E THT - AS 18/18 D 45 x 1,5 (key 6) 2 . 10 6 81D 45 x 1,5 (key 5) 2 . 10 6 105 80D 48 x 1,5 (key 5) 2 . 10 6 133

1.4512 (X 2 CrTi 12) D 45 x 1,5 2 . 10 6 65 (40)1.4510 (X 3 CrTi 17)

1.4509 (X 2 CrTiNb 18) D 45 x 2 2 . 10 6 (170) 1001.4526 (X 6 CrMoNb 17-1) D 48 x 1,5 2 . 10 5 160

D 48 x 1,5 2 . 10 6 165 102 481.4301 (X 5 CrNi 18-10)

1.4541 (X 6 CrNiTi 18-10) D 48 x 1,5 2 . 10 6 145 70

2.7.2. Torsion fatigue test on tubes when hot (As per ME-60152-A-009)

Dimensions Test temperature

Grades of tube 400 C 600 C

Diam. Thick. 10 5 10 6 10 7 gradient 10 5 10 6 10 7 gradient

ES - AS 18/18 45 mm 1,5 mm 72 67 62 - 30,28ES HT - AS 18/18

CS - AS 18/18 45 mm 1,5 mm 62 52 44 - 14,41E THT - AS 18/18

1.4512 45 mm 1,5 mm 115 106 97 - 25,9 77 68 59 - 18,2X 2 CrTi 12 50 mm 1,5 mm 116 103 92 - 19,45 81 73 68 - 25,63

50 mm 0,7 mm 115 108 92 - 14,51.4510 50 mm 1,2 mm 128 110 95 - 15,54 122 100 82 - 11,76

X 3 CrTi 17 50 mm 1,5 mm 123 106 91 - 15,08 88 79 71 - 21,971.4509

X 2 CrTiNb 18 50 mm 1,2 mm 130 104 84 - 10,51 124 102 84 - 12,03

1.4526X 6 CrMoNb 17-1 50 mm 1,2 mm 160 128 102 - 10,34 119 107 96 - 21,05

50 mm 0,7 mm 115 108 101 - 35,7 99 89 79 - 20,031.4301 50 mm 1,2 mm

X 5 CrNi 18-10 50 mm 1,5 mm

Original tube Tubificio di Terni

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2.8. TUBE IMPLEMENTATION CHARACTERISTICS

Deformation mode Weldability / filler metal PriceGrade Bending R / D maxi. 1)

(angle = 90)Flangedcone 60

(1 to 5) index

Tube 40 x 1,5

Tube 55 x 1,5 % ES ESHT CS E THT 1.4512 1.4509 1.4526 1.4301 1.4541

2)(au

19/5/98ES - AS 18/18 1,2 1,2 50 61

ES HT - AS 18/18 1,2 1,2 50 3 3 3 3 64CS - AS 18/18 1,3 1,3 45 60

E THT - AS 18/18 1,5 1,5 45 3 3 3 3 87X 2 CrTi 12 (brut)

(1.4512) 1,4 1,4 45 4 4 4 4 to 5 4 to 5 100X 2 CrTi 12(annealed)(1.4512)

1,3 1,3 45 4 4 4 4 to 5 4 to 5

X 6 Cr 17(1.4016) does not exist in form of tube - - - - -

X 3 CrTi 17(1.4510) 4 4 to 5 4 to 5 4 to 5 4 to 5 116

X 2 CrTiNb 18(1.4509) 1,3 1,3 45 4 to 5 4 to 5 4 to 5 4 to 5 119

X 6 CrMo 17-1(1.4113) does not exist in form of tube - - - - -

X 6 CrMoNb 17-1(1.4526) 1,3 1,3 45 4 to 5 4 to 5 4 to 5 4 to 5 144

X 5 CrNi 18-10(1.4301) 1,1 1,1 50 5 5 151

X 6 CrNiTi 18-10(1.4541) 1,1 1,1 50 5 5 157

1) Bending on mandrel, with lubrication, without thrust.2) Price index indicated on base 100 for tube TSR X2 CrTi 12 (1.4512) 50 x 1,5 mm, length1 500

mm (extra-alloys included).

2.9. RESISTANCE TO CORROSION

2.9.1. Aluminated mild sheets

Appearance as per T C(B.E target service life)

Corrosionwhen cold Corrosion when hot

GradeBrilliant

Oxidation oralliation with

greyappearance

Red rust

ES - AS 18/18 < 450 C 450 C< 1 % of red

rust

ES HT - AS 18/18 < 450 C 800 C6 years

without R.R.on specimen

surface To be indicated by SOLLAC

CS - AS 18/18 < 450 C 450 C(of 30 Lardy

cycles)after 9 cycles

of test

E THT - AS 18/18 < 450 C 900 C of corrosion

3C 1)

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2.9.2. Stainless steels

Corrosion when hot

GradeAppearance as per T C

(B.E target service life)Corrosionwhen cold

Isothermal oxidation2)

Cyclic oxidation at950 C

3)

BrilliantOxidation oralliation with

greyappearance

Red rust 800 C 850 C 900 C 100 h 400 h

X 2 CrTi 12 (brut)(1.4512) Delivered mat 5 20 200

outsiderange

outsiderange

X 2 CrTi 12(annealed)(1.4512)

Delivered mat 5 20 200 outsiderange

outsiderange

X 6 Cr 17(1.4016)

Colouring

X 3 CrTi 17(1.4510)

as 6 yearswithout R.R.

X 2 CrTiNb 18(1.4509) Delivered mat

of (or 30 Lardycycles)

none- 4 5,5 15 32

X 6 CrMo 17-1(1.4113)

X 6 CrMoNb 17-1(1.4526) Annealedbrilliant

200 C 2,5 3,25 6 15

X 5 CrNi 18-10(1.4301) j 200 C underway > 200

outsiderange

X 6 CrNiTi 18-10(1.4541) j 200 C underway 180 >> 350

1) On flat specimen having being subjected to an equi-biaxial deformation of 20 % (as per 3.1.6.of Product Specifications 11-04-809).

2) Weight gain (g/m2) after 50 h of hold.3) Weight gain (g/m2).

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Annex A

Correlation between mild steel grades

RENAULTdesignation

RENAULTspecifications

Approximatecorrespondence

Commercial names

of grade (P) = Rolled products(T) = Tubes

as per European StandardEN 10154 SOLLAC GALVALANGE E.C.I.A

ES - AS 18/18 11 - 04 - 809 (P)11 - 05 - 217 (T) DX53D + AS 120 Alusi BSR AL5 AS 120-05

ES HT - AS 18/18 11 - 04 - 809 (P)11 - 05 - 217 (T) DX55D + AS 120 Alusi BHT ALT AS 120-06

CS - AS 18/18 11 - 04 - 809 (P)11 - 05 - 217 (T) none Alusi BV - AS 120-07

E THT - AS 18/18 11 - 04 - 809 (P)11 - 05 - 217 (T) none EXTRATHERM A - AS 120-11

Annex B

Correlation between stainless steel grades

Designation of grade RENAULT Commercial names

As per EN 10088-1 as per previous Typespecification

Name NAFNOR A.I.S.I (P) = Rolled products

(T) = TubesUGINE A.S.T. THYSSEN

X 2 CrTi 12 1.4512 Z 3 CT 12 409 * (P)11 - 05 - 228 (T) F 12 T 409 4512

X 6 Cr 17 1.4016 Z 8 C 17 430 none (*) F 17 -

X 3 CrTi 17 1.4510 Z 4 CT 17 430 TIor 439

* (P)11 - 05 - 228 (T) F 17 T 439M

X 2 CrTiNb 18 1.4509 Z 3 CTNb 18 441 * (P)11 - 05 - 228 (T) F 17 TNb 441 -

X 6 CrMo 17-1 1.4113 Z 8 CD 17-01 434 none(*) F 17 M -

X 6 CrMoNb 17-1 1.4526 Z 8 CDNb 17-01 436 * (P)11 - 05 - 228 (T) F 17 MNb 436 4526

X 5 CrNi 18-10 1.4301 Z 6 CN 18-09 304 * (P)11 - 05 - 228 (T) 18 - 9 E 304 4301

X 6 CrNiTi 18-10 1.4541 Z 6 CNT 18-10 321 none(*) 18-10 T 321 4541

(*) References based on European Standards EN 10088-1 and 2.

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3. WELDING STAINLESS STEELS

3.1. REMINDER

Various methods are proposed to evaluate the structure of the molten metal after return to ambienttemperature according to its chemical composition:

3.1.1. Schaeffler diagram

This diagram, by means of a chromium equivalent (alphagene) and a nickel equivalent(gammagene), is used to describe the structure of the molten metal after complete cooling. Inaddition, it facilitates handling the heterogeneous welding problem by indicating conditions thatenable:

- the formation of martensite to be avoided,

- to keep the ferritic tendency to an appropriate level.

Schaeffler diagram

3028262422201816141210

86420

0 4 8 12 16 20 24 28 32 36 40

Zone A :Austenite

Zones B and C : A + FZone D :A + M

Zone E : Martensite

Zone G : FerriteZone F : M + F

Ni E

quiva

lent

Cr Equivalent

M + F

0 % 5 %

10 %

20 %

40 %

80 %

100 %

For this diagram:

Crq= % Cr + % Mo + 1,5 * % Si,

Niq= % Ni + 30 * % ( C + N ) + 0,5 * % Mn.

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Calculating the dilution rate

Lug

s1

s2

S

Tube

Dilution % = s1 s2S+

x 100

The method of utilization of this diagram may be illustrated using the following examples:

- welding of two parts made from same steel without filler product: the figurative point of thejoint shall be that determined on the basis of the basic metal composition,

- welding of two parts made from different steels without filler product: the figurative point ofthe joint shall be located on the right hand segment defined by the two points determined on thebasis of the compositions of the base metals, the composition of the point will depend on therelative contribution of each metal to the composition of the molten metal,

- welding of two parts made from the same steel with a filler product: the figurative point ofthe joint will shall be located on the right hand segment defined by two points determined on thebasis of the base metal composition and filler metal composition; the position of the point willdepend on the dilution,

- welding by one operation on two different steel parts with a filler product: the figurativepoint is determined in two stages:

1. determine relative mean point relative to base metals (by applying the procedure describedfor welding various steels without filler metal),

2. determine figurative point of molten metal (by applying the procedure described for weldingtwo identical steels with filler metal on the basis of the mean point of base metals and therelative point of filler metal by incorporating dilution).

All these points fall within the various zones of the diagram, which provides a view of the joint of basemetal and of the risks associated with welding.

- Zone A ( austenite):sensitivity to cracking when hot, good resistance to corrosion and heat.- Zone B (austenite up to 5 % of ferrite): good resistance to corrosion and no sensitivity to

cracking when hot.

- Zone C (austenite from 5 to 100 of ferrite): no sensitivity to cracking, mean resistance tocorrosion, structure sensitive to sigma phase formation (brittle phase in all temperature ranges.The time necessary for this phase to elapse is very long (several hundred hours); it maytherefore not come about during hot work operations, but only when steels are used between 650and 930 C).

- Zone D (austenite + martensite): brittleness under cooling - quench cracking - imperativepreheating with slow cooling - heat treatment necessary after welding.

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- Zone E ( martensite ) : cracking at temperature < 400 C imperative preheating before welding.- Zone G (ferrite): no sensitivity to quenching - grain expansion beyond 950 C, regeneration

impossible by heat treatment.

3.2. WELDING OF FERRITIC STAINLESS STEELS

3.2.1. Metallurgical consequences of thermal welding cycles

During thermal welding cycles, these steels do not sustain any structural transformation andaccordingly the main result of the heating of the metal to a high temperature will be a significant grainexpansion.

It is important to note that the brittleness after welding of the steels that do not contain a stabilizingadditive element (Ti or Nb) is more a result of the presence of martensite at the joints that of grainexpansion; unless such grains have reached significant dimensions, e.g. 3 mm. Steels containing anaddition of Ti or Nb, owing to the presence of TI or Nb precipitates, are slightly less sensitive to thiscondition. This also applies to steels with a very low content of carbon and nitrogen.

In short, the sensitivity of these steels to the thermal effects of hot working and welding may havefour origins:

- expansion of grains that cannot be refined except by significant work hardening when coldfollowed by heat treatment, which would prompt recrystallization,

- precipitation, during rapid cooling, of a martensitic phase consisting of a surface film on the grainjoints,

- precipitation prompting structural hardening and affecting all chromium steels containing morethan 13 to 14 % of chromium. The temperature hold time necessary to conduct precipitation isshorter as the chromium content increases. The temperature zone liable to cause precipitation isbetween 350 and 550 C. It should be noted that this phenomenon is reversible and it ispossible to recover these precipitations, and thereby eliminate this brittleness, by heat treatmentat 800 C,

- formation of the sigma phase (see 3.3.2.).In addition, heating of the metal in the ZAT above 950 C, causes the chromium carbides to dissolve.These will reprecipitate during cooling. Such intergranular precipitation of the chromium carbidescauses intergranular sensitivity to corrosion unless the carbon content of the steel is very low or if thesteel contains a sufficient quantity of Ti or Nb.

3.2.2. Choice of welding conditions

3.2.2.1. General

Because of grain expansion and the presence of martensite, resilience at ambient temperature isgenerally low. The assembly becomes sensitive to brittle rupture, however for this to occur, the metalwill have to be subjected to tri-axial stress (which excludes constructions made from thin productsfrom this risk) and to rather brutal loading conditions. Accordingly, we are only interested here in thewelding of products that do not exceed 6 mm.

Furthermore, and more for other stainless steels, welding procedures by fusion that may be employedwhen processing ferritic stainless steels shall ensure perfect protection against molten metal. Thisrequirement significantly reduces the possibilities of welding with a coated electrode, which does notensure perfectly satisfactory protection.

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Accordingly, procedures used for welding ferritic stainless steels will preferably be those usingprotective gas flow, i.e. TIG, MIG and plasma welding.

For these procedures, the following requirements shall be ensured:

- good continuity without any surface defects that may constitute incipient corrosion,

- a good conservation of resistance to corrosion of the assembly. This result will be obtained if theprocedure prevents the departure of useful alloy elements (in particular, chromium) and theaddition of any noxious element such as carbon (which would create the risk of porosityformation),

- good mechanical strength which is usually achieved if the geometry of the assembly and themolten metal are satisfactory, in particular with respect to the latter, if the problems caused thepresence, if any, of martensite and intergranular chromium carbides have been resolved.

To do so, the following measures will be taken:

- limit the quantity of energy applied (< 7 KJ/cm) during welding in order to reduce, insofar aspossible, grain expansion,

- use steels containing titanium or niobium to avoid intergranular precipitations of chromiumcarbide which will reduce the resistance to corrosion,

- during welding of totally ferritic steels, avoid any addition of carbon and nitrogen liable to causethe formation of martensite and thereby reduce the ductility of the molten metal,

- in all cases, avoid adding hydrogen and to do so:

. choose welding products that do not add hydrogen (pure argon, if necessary basicelectrodes appropriately cured),

. carefully prepare the parts to be assembled (elimination of lubricant traces, rust, humidity,dirt),

. weld in the absence of excessive humidity.

For molten metal, high ductility may confer it with an austeno-ferritic structure by using an austeniticfiller metal. It should be noted however that this procedure does not resolve the metallurgicalproblems caused by the zone affected by the heat and that furthermore no post-welding treatmentshould be performed as there is a risk of thermal treatment on the austenitic steel.

3.2.2.2. TIG welding

In this procedure, the protection of the molten metal and of the hot metal is ensured by neutral gas.

It may consist of:

- pure argon,

- pure helium or helium mixed with argon,

- pure argon mixed with hydrogen.

These gases shall be perfectly exempt of humidity.

Once the thickness exceeds 2 to 3 mm, it is necessary to add a filler metal in the form of strips orwires.

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The filler metals used for welding the ferritic stainless steels are not defined in a specific standard.

In general, a filler metal with a similar composition (use of Schaeffler diagram) as that of the basemetal is chosen. For the welding of totally ferritic steels, the filler metals containing titanium orniobium, have a higher chromium content and a lower carbon content in order to avert the risk ofmartensite appearing in the molten metal.

3.2.2.3. MIG welding

This procedure uses a fusible electrode in the form of a renewable wire, the protection of the moltenmetal and of the hot metal being ensured by a current of inert gas.

The filler wire contains the filler elements necessary to form the molten metal.

The protection gas may consist of:

- pure argon or argon to which small quantities of other gases (CO2 or O2) have been added. Theaddition of the gas increases the stability of the arc, improves wetting of the base metal andincreases penetration; however, it creates a risk of metal impoverishment in terms of oxidablealloy elements (Cr and Ti),

- argon or helium mixed with argon.

The useable filler metals for MIG welding may be of the same type as those employed during TIGwelding however their content in silicon shall be slightly higher (up to 1,1 %) in order to improve thedeoxidation of the of the bath and wetting of the base metal; however, more generally, they are madefrom austenitic steel.

3.2.2.4. Shielded metal arc welding

This procedure uses electrodes whose metallic core has a chemical composition which generallycorresponds to that of the metal to be welded.

The function of the coating is to ensure the protection of the molten metal by the diffusion of carbonicgas (due to the dissociation of carbonates incorporated in the coating) and the formation of aprotective slag. In certain cases, the necessary alloy elements may be added by this coating in ratherlarge proportions.

In general, it is considered that with the shielded metal arc welding of ferritic stainless steels, theprotection obtained is not totally satisfactory and there is a tendency not to recommend this process.

RENAULT 90 - 00 - 151 / - - -


3.3. WELDING AUSTENITIC STAINLESS STEELS

3.3.1. Metallurgical consequences of thermal welding cycles

In general, the chemical composition of these steels is established such that, upon equilibrium, theirstructure is austenitic at all temperatures of less than 1 100 C approx. At higher temperatures, thestructure may be either mixed austeno-ferritic, or even totally ferritic.

It should be noted here that the presence of carbon in austenitic stainless steels may be responsiblefor the deterioration in their resistance to corrosion when such steels are subjected to a long durationat temperatures of between 500 and 850 C. In effect, if the conditions permit (slow cooling, hold atappropriate temperature), the carbon will precipitate in the form of carbides, generally chromiumcarbides; this precipitation, which occurs primarily in the grain joints and elsewhere in the grainsthemselves, impoverishes the chromium content of the neighbouring austentite, thereby rendering itsensitive to corrosion in an intergranular fashion.

However, as already seen, there are two types of procedures to reduce or eliminate the risk ofprecipitation:

- reduce the carbon content,

- add titanium and niobium elements.

An austenitic steel weld may sustain cracking at high temperature (hot cracking) caused by shrinkagethat develops in the interdendritic spaces of the molten metal. The presence of certain elementsfacilitates such cracking: sulphur, silicon, niobium, phosphorous, boron. The most efficient remedy,apart from adding manganese, consists in ensuring that the metal contains a certain proportion offerrite (from 1 to 5 %). It is also recommended to weld while limiting the energy intake and check thatbetween the passes, the temperature of the joint drops sufficiently (< 100 C).Furthermore, there is a risk of a sigma phase occurring in austenitic steels (see 3.3.2.).

3.3.2. Sigma phase

Intermetallic compounds may be formed at high temperature in stainless steels, beyond a chromiumlevel of 18 to 20 %, and in the welds. These compounds may enclose notable quantities of otherelements than iron and chromium. Their occurrence in a large quantity has the effect of reducing theductility of the alloy, a very significant reduction in elongation, a reduction the resilience of the steel,with an increase in hardness and sensitivity to incision. In addition, under certain conditions, theresistance to corrosion of the steel is greatly affected by the sigma phase.

Conditions of formation:

- Temperatures: Hold the alloy between 550 and 900 C; beyond 900 C, stability limit andpossibility of return to solution. Extremely low formation between 550 and 600 C Very rapid formation in the region of 800 - 850 C.

- Chemical compositions: The increase in the chromium content of alphagenic elements isconducive to the appearance of the sigma phase. Case of molybdenum, titanium, niobium,silicon. Molybdenum and silicon expand upwards in the temperature range in which the sigmaphase appears.

Nickel and carbon reduce the tendency of steels to form the sigma phase.

RENAULT 90 - 00 - 151 / - - -


3.3.3. Choice of welding conditions

3.3.3.1. General

A number of fusion welding processes may be used in order to attach stainless steels. In this paper,we focus on the most commonly used.

For these processes, ensure:

- good geometrical surface continuity without any defects that may constitute incipient corrosion,

- satisfactory preservation of resistance to corrosion of the assembly. This result will be obtained ifit prevents the separation of useful alloy elements (in particular, chromium) and the addition ofnoxious elements such as carbon,

- good mechanical strength, which will generally be achieved if the geometry of the assembly andthe chemical composition of the molten metal are satisfactory, especially if the conditionsnecessary to prevent cracking under heat are satisfied.

3.3.3.2. Shielded metal arc welding

(See note 3.2.2.4.).A number of shielded electrodes are proposed for the manual arc welding of austenitic stainlesssteels. Upon examination of their chemical compositions, the main grades of austenitic stainlesssteels are found with the following specific features:

- the carbon limit contents are often lower,

- the manganese limit contents are higher,

- the chromium contents are higher.

The purpose of these modifications are to counteract any metal deficiency in Cr and Mn and anyenrichment in C so as to contribute to the attainment of good corrosion resistance. Furthermore, suchdifferences enable the acquisition of the quantity of ferrite necessary to eliminate the risk of crackingwhen hot.

It should be noted that amongst the chemical compositions of the deposited metals, there is notitanium metal; this condition is due to the fact that titanium oxidizes and its transfer is not optimum inthe electrical arc. For welding titanium steels, it is therefore necessary to use electrodes depositing ametal containing niobium.

3.3.3.3. TIG welding

(See note 3.2.2.2. and 3.3.3.2. for the filler metal).

3.3.3.4. MIG welding

(See note 3.2.2.3.).The filler metals used for MIG welding of austenitic stainless steels are the same type as those usedfor shielded metal arc welding, however, their silicon content is slightly higher in order to improvedeoxidation of the liquid metal and wetting of the base metal.

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3.4. HETEROGENEOUS WELDING OF STAINLESS STEELS

3.4.1. General

This type of assembly remains a special case that can only be processed by a specialist afterexamining all the specific aspects. In this document, therefore, we will only devote a brief overview tothis procedure.

When a non alloyed carbon steel or a ferritic steel is assembled with an austenitic steel, the fillermetal is chosen according to the Schaeffler diagram (see 3.1.1.). The objective is to obtain amolten area with a austeno-ferritic two-phase structure. In effect, a content greater than 2 % of ferriteis desirable in order to avoid the hot cracking phenomenon.

To ensure weldability in the molten zone, it is essential to avoid the "high risk" structures:

- risk of cracking when cold if the structure is martensitic,

- risk of cracking when hot if the structure is austenitic,

- risk of brittleness by expansion of the grains if the structure is ferritic,

- risk of brittleness during sigma phase if the chromium equivalent placed on the Schaefflerdiagram is very high.

In practice, the structure without any metallurgical problem is situated around an eqCr = 20 and aneqNi = 11 in the Schaeffler diagram. This is confirmed on the various Bystram diagrams, whichidentify the various high risk zones and the optimum weldability zone on the Schaeffler diagram.

3.4.2. Bystram diagrams

3.4.2.1. Cold cracking area

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 4 8 12 16 20 24 28 32 36 40

Martensite

Ferrite

A+M

M+F

A + F

M+F

0% 5%

10%

20%

40%

80%

100%

Austenite

Niq

Crq

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3.4.2.2. Hot cracking area

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 4 8 12 16 20 24 28 32 36 40

Martensite

Ferrite

A+M

M+F

A + F

M+F

0% 5%

10%

20%

40%

80%

100%

Austenite

3.4.2.3. Grain expansion brittleness area

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 4 8 12 16 20 24 28 32 36 40

Martensite

Ferrite

A+M

M+F

A + F

M+F

0% 5%

10%

20%

40%

80%

100%

Austenite

Niq

Crq

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3.4.2.4. Sigma phase brittleness area

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 4 8 12 16 20 24 28 32 36 40

Martensite

Ferrite

A+M

M+F

A + F

M+F

0% 5%

10%

20%

40%

80%

100%

Austenite

3.4.2.5. Optimum weldability area

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 4 8 12 16 20 24 28 32 36 40

Martensite

Ferrite

A+M

M+F

A + F

M+F

0% 5%

10%

20%

40%

80%

100%

Austenite

Niq

Niq

Crq

Crq

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4. STAINLESS STEEL WELDING TECHNIQUES

4.1. MIG WELDING

4.1.1. Description of process

Definition: The MIG/MAG welding process applies an arc under gas protection. The electrode isfusible and serves as a filler metal. The electrode, the metal transferred in the arc and the liquid weldmetal are protected from ambient air by a gas flux, which is inert in the case of MIG welding andactive in the case of MAG welding.

Hence the terms MIG Metal Inert Gas and MAG Metal Active Gas. During Manuel welding, theseprocesses are also called "semi-automatic" because the wire is unrolled automatically as soon asarcing commences. The MAG process, in an active atmosphere, is reserved for steels with a low orwithout any alloy content. The MIG process, in an inert atmosphere, is used for light alloys andcupreous alloys. In the case of stainless steels, when the atmosphere is slightly active, the term MIGis usually used to differentiate from the case of carbon steels.

GunFusibleelectrode wireMtaltransfr

Base metal

Deposited metal

Gas shield

Electrical supply: The MIG/MAG welding arc is supplied with a direct current in reverse polarity withthe fusible electrode at the positive pole. The wire is then subjected to an electron flux, whichfacilitates its fusion. Reverse polarity ensures better arc stability.

Direct polarity is not suitable because it causes less heating of the wire, the metal drops are bigger,fewer in number and they do not detach in a very clear manner. The seam obtained is dome shaped.In exceptional cases, e.g. on sheathed wires, this polarity is not employed.

_

e

+

+

_

e

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Field of application: Productivity is the main advantage of the MIG and MAG welding processes.Because the volume of metal deposited is very large, these processes are suitable for big thicknessesand for filling the chamfer by multiple runs. Easily implemented, the MIG and MAG welding processescan be applied manually, automatically or robotically. They enable welding in all positions.

4.1.2. Metal transfer modes inj the arc. (Pulsed, Lincoln STT, axial spray)

The fusion of the wire and the transfer of metal in the arc may be conducted in many ways dependingon the type of protective gas, voltage and current of the arc.

4.1.2.1. Basic transfer modes

Transfer by short circuit:

This setting is obtained for low arc energies (50 to 200 A - 15 to 20 V). A drop forms at the end of thewire and expands until it comes into contact with the liquid weld metal. The current then increasesrapidly causing a pinch to occur, which facilitates detachment of the drop, and the arc is formedagain. This phenomenon is repeated at frequencies of 50 to 200 Hz. In a so-called cold setting, with ashort arc, the transfer by short circuit is used to weld small thicknesses and to control the liquid weldmetal during an in-position weld.

V25

150

100

50

ATime

Arc time Short-circuittime

Axial spray transfer:

At high energies and beyond a certain current density (greater than 250 A/mm2 according to the typeof wire and protective gas), the tip of the wire is in the form of an elongated cone. Transfer takesplace in the form of very fine droplets, the diameter of which is less than that of the wire and whichare sprayed at a very high speed. The arc is 4 to 6 mm long. This metal transfer forms a stable arcwith little splashing. It allows for significant penetrations and high metal deposits. It is used forthicknesses greater than 5 mm. The volume and fluidity of the liquid metal makes it ideally suitablefor flat welding, except for aluminium and its allows, which may be welded in all positions.

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Globular transfer:

At welding energies between those providing short-circuit transfer and axial spray transfer, the dropsbuild up slowly. The current amperage is not high enough to create a pinching effect inducingseparation and the drop gets bigger exceeding the size of the wire diameter. Transfer occurs by short-circuit when the drop touches the liquid metal, or by separation of the drop under the effect of gravity.The drop then follows a random path, which is not always aligned with the axis of the arc. This is anunstable transfer mode inducing weak penetrations and numerous splashes. If possible, it should beavoided.

4.1.2.2. Derivative transfer modes

Pulsed setting:

Current peaks are superimposed onto a basic current which maintains the established arc. When thepulse is applied, the high current density causes a fine droplet to be transferred. This transfer iscomparable to axial spray (stability, absence of splash) however the average current is lower. If thethickness or the welding metallurgy requires an energy corresponding to a conventional globulartransfer, the use of a pulsed current eliminates the problems associated with globular transfer.

CurrentPeak current

Average current

Basic current

Time

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Controlled short-circuit transfer (Lincoln STT).This process has been designed to avail of the advantages of the short circuit transfer process whileavoiding the disadvantages (bonding, splash reduction, arc instability, etc.). To do so, the current isreduced by about 10 A when the wire comes into contact with the part in order to avoid splashing.After this period, a higher current is applied in order to accelerate the pinching effect and therebyreduce the cold period causing arc instability. The current level is then reduced a few millionths of asecond before separation of the drop to a value sufficiently low to ensure there are little or nosplashes. A very high current is then applied (in the order of 300 to 450 A) after the drop hasseparated in order to avoid any risk of bonding.

4.1.3. Gases and gas mixtures

Gas protects the liquid weld metal and the metal transferred in the arc from the ambient air. The gasshould also facilitate the formation and stability of the arc.

Inert gas:

Argon, owing to its characteristics, is the basic gas used for MIG welding. Helium can also be added.The greater the arc voltage, the hotter and more diffuse the arc, a condition that increases thepenetration or welding speed, improves wetting and makes for a flatter seam. Argon and mixtures ofargon and helium are used for aluminium and copper alloys.

Carbon dioxide:

MAG welding of steels is different from MIG welding in that it is conducted in an oxidizingatmosphere. Originally, the gas used was carbon dioxide. The dissociation of CO2 in the arc leads tothe formation of oxygen, which causes localized oxidation. Such oxides are emitted, the arc remainsattached and stable. However the CO2 atmosphere causes significant oxidation of the metal and theloss of alloy elements (except carbon). The type of wire used is therefore very important in order tolimit this phenomenon.

Under the current range conventionally used, the CO2 does not enable transfer by axial spraying.The pinching effect is minimal, the significant viscosity of the molten wire causes bit drops which aretransferred in an explosive manner inducing instabilities and splashes. Pure CO2 is therefore limitedto short circuit and big drop transfers, whereby the viscous liquid enables work in all positions. Thedisadvantages of CO2 are eliminated by argon-CO2 mixtures, which enable transfer by axial spraying.Standard mixtures have a CO2 content of between 2 and 25 %. Small additions are used for stainlesssteels, the bigger contents for carbon steels. In the case of stainless steels, an excessive percentageof CO2 may cause carburation liable to undermine the corrosion resistance.

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In the case of carbon steels, mixtures with a CO2 content less than 10 % improve surface appearanceand limit the formation of silicates. The amount of splash and fume emissions are also reduced. Agas limiting the amount of splash can be used to considerably reduce the soiling of the welding gun.

Oxygen:

Oxygen may be used instead of CO2 in order to stabilize the arc. By reducing the surface tension ofthe liquid metal, oxygen facilitates the formation of drops and improves wetting of the bath. Bymaking a more rigid and hotter arc than the one formed with CO2 , the addition of oxygen facilitatesthe transfer by axial spraying and subsequently induces more effective penetration than with argon-CO2 mixtures. Oxygen argon mixtures contain between 1 to 8 % of oxygen, smaller contents areused for stainless steels. Ternary mixtures may be used (Ar - CO2 - O2).

Hydrogen:

When welding stainless steels, low hydrogen contents (< 3 %) may be added. Like helium, hydrogenincreases the energy of the arc by applying a higher voltage level. Because of its reducing power, thehydrogen provides a very clean seam appearance. Hydrogen may be the cause of cold cracking ofquenched materials. Mixtures containing hydrogen are therefore mainly used for austenitic steels.Hydrogen may cause porosities in the weld seams. Mixtures containing hydrogen shall be mainlyused for one-run welding.

GAS Advantages DisadvantagesAr Inert Basic gas for Arc processes

He Inert "Hot" gas increased V welding

Limited to 20 % vertical and ceiling

CO2 Oxidizing(< O2)Softer MIG transfer

No splashesLimited oxidizing power

"Blank" seam

Limited to 20 % practical < 5 %Prohibited for TIG

O2 Oxidizing Regularizes MIG transfer(if < 5 %)Conventional gas 1 to 3 %

Highly oxidizing oxidized seamsProhibited for TIG

H2 Reducing "Hot" gas increased V welding

Reducing Blank seam

Not advisable for stainless steelsMartensitic, Ferritic and Duplex

N2 Neutral Nitrogen grades (> 0,1 %) Compensates for losses

Stabilizes austentite

Not advisable for stainless steelsFerritic

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4.1.4. Solid and flux-cored electrode wire

Electrodes used for manual electrical arc welding with a fusible electrode wire in the form of acontinuous thread reaching the arc at which point it melts. The wires used are solid bare wires, orbare flux-cored wires. The first make the use of a protective gas mandatory, the second may be usedwith or without a protective gas, in which case the liquid metal is shielded either by the action of thecore flux (formation of a slag and a gas) or by the combination of the action of the flux and that of theprotective gas.

Composition:

By its very composition, the wire incorporates the elements liable to modify the characteristics of theweld. The alloy elements shall be adjusted in order to obtain a weld, the properties of which are equalto or better than those of the base metal (mechanical properties, corrosion...).

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Position of various compositions on Schaeffler diagram

:

28

24

20

16

12

8

4

00 4 8 12 16 20 24 28 32 36 40

Austnite

F+ M

M + F

A + M + F

Ferrite

6

9

8

7

1

23

4 5 A + F

0 %

Ferrite

5 %

10 %

20 %

40 %

80 %

100 %

N

I

C

K

E

L

E

Q

U

I

V

A

L

E

N

T

=

%

N

i

+

3

0

x

%

C

+

0

,

5

x

%

M

n

CHROMIUM EQUIVALENT = % Cr + % Mo + 1,5 % Si + 0,5 % Nb

Example of filler metals

19-10 (308L)

19-12-3 (316L)ou 19-12-3 Nb

24-12 (309L)ou 22-15-3 (309MoL)

20-10-3

22-8-3

29-10 (312)

18-8 Mn (307)

19-12-3 (316LN)

25-20 (310)

SCHAEFFLER DIAGRAM

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However, low additions of certain elements may have consequences on:

- the stabilization of the arc and on the transfer of the metal due to active components,

- the reduction of splashes and fumes (elements such as titanium, silicon, manganese facilitatesuch a reduction),

- the reduction of oxygen in the welded metal: the use of oxidizing gases is compensated by theaddition of deoxidizing elements in the wire such as manganese and silicon. The silicates thusformed are deposited on the upper part of the weld.

Bare solid wires:

These are cold-drawn wires with an appropriate chemical composition for welding, often covered witha film of copper used as a cold drawing lubricant. This layer of copper shall be regular and very fine inorder to avoid too great an addition of copper in the metal forming the joint. Flux-cored wires:

A flux-cored wire consists of a sheath of steel filled with a powder core. The sheath consists either ofa soldered tube or is made from a folded strip. The principle of arc welding with a flux cored wire isthe same as that for MIG and MAG welding. The arc is established between the electrode wire andthe parts to be welded. The electrical supply is always a direct current, the polarity depends on thewire and is indicated by the supplier for each item.

1

2

The elements contained in the core may be either metallic or non-metallic, the functions of theseelements are:

- to stabilize the arc,

- act as a deoxidant,

- emit gases, in certain cases,

- add alloy elements.

There are two main families of flux-cored wires: those used without protective gas and those usedwith protective gas.

During welding with a flux-cored wire without gas protection, the core protects the molten metal bydiffusing gases into the arc and by producing a slag that covers the molten metal. The use of suchwires is advantageous on a job or at any location where it is difficult to bring in gas. However, theyare difficult to use meaning that the welders require good training.

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More commonplace, the flux-cored wires with gas may be divided into two families:

- 1 - Rutile flux-cored wires (transfer in fine droplets and average level of hydrogen, welding in allpositions), 2 - Basic flux-cored wires (globular type transfer and very low level of hydrogen, delicateposition work),

- slagless flux-cored wires ( metallic core),the components of the core are mainly metallic: iron, iron-silicon, iron-manganese. A smalladdition of non-metallic elements may be added in order to stabilize the arc. These wires makefor a high rate of deposit due to the abundance of metallic elements in the core. Positionwelding is possible with a small diameter wire. Because the metallic powders are nothydroscopic, only a small amount of hydrogen can be diffused into the weld. These wires arebeing used more and more.

4.2. TIG WELDING

4.2.1. Description of process

Definition: TIG welding, inert gas welding with non fusible electrode, is a procedure in which theenergy necessary for the fusion of the parts to be assembled is provided by an electric arcestablished between a refractory tungsten electrode and the joint to be welded. The electrode and theliquid metal are protected from ambient air, i.e. from nitrogen and oxygen by an inert gas flux. Hencethe term Tungsten Inert Gas.

Depending on the job at hand, the thickness, geometry of the joint, type of materials to be assembled,a filler metal in the form of a strip may be used. This wire is melted in the arc and protected by theinert atmosphere of the welding gas.

Gun

Inertgas

Arc

Fillermetal

Base metal Liquidweld metal

Moltenarea

Refractorytungstenelectrode

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Electrical supply: The type of current depends on the material to be welded and on the assembly tobe formed:

- Direct current: Direct polarity (negative pole on electrode) for welding of all metals.- Pulsed current: This technique, consisting in successively developing periods of high an low

current amperage, is used to reduce the volume of the molten metal. This facilitates the positionwork, the welding of thin assemblies and ensures optimum regularity of the penetration.

- Alternating current: Mainly used for the welding of aluminium alloys. Upon alternation to thereverse polarity, the gush of electrons from the sheet towards the electrode cracks therefractory alumina layer. At the subsequent alternation, the direct polarity ensures penetration.

Field of application: TIG welding is characterized by the high quality of welding achieved. The liquidmetal is calm, there are no splashes and only a small amount of fumes. To benefit from such ha levelof quality, it is necessary to work with special care ( Clean and stripped sheets, separated straightedges, constant arc length, regular welding advance ).TIG welding is used to weld most metals and alloys, whether on the flat or in position. It is conductedmanually, automatically or robotically.

The weldable edge-to-edge thicknesses for a single-pass weld with argon, are between 0,5 mm and3 mm for most materials. It is also possible to weld thicknesses greater than 3 mm, by preparing theedges to be assembled (chamfer) and by multiple-pass welding. However, because the welding speedand the volume of metal deposited are low, TIG welding is preferably used to ensure a regularpenetration and satisfactory quality at the first pass.

5. BIBLIOGRAPHY

Soudage a larc Tome 3 by Bertrand le Bourgeois, Publication de la soudure Autogne.

Les aciers inoxydables , Mise en uvre et soudage by J. Varriot.

Prcis de mtallurgie by J. Barralis and Grard Maeder.

Documents

Sudura Inox