Technical Report

Welding Duplex Stainless Steels M. Niset & R. Daemen, S.A. Soudometal 24, Blvd Maurice Herbette, Brussels, B-1070, Belgium

Abstract An account is given of some of the duplex steels now

available, their properties and in particular means of welding them.

Introduction Duplex stainless steels have microstructures which

contain about 35 to 75% ferrite, the rest being austenite. One of the first duplex type stainless steels was developed around 1935 as AISI 329 with a basic composition of C 0.08%, Cr 25%, Ni 4%. In 1963 a copper bearing AISI 329 steel appeared in the U.S.A. under the designation CD4MCu and since then a whole series of duplex steels have been developed- see Table 1.

The originally developed duplex steels suffered from poor ductility & weldability and were only available as castings. This was a great limitation since they had high yield strengths and excellent resistance to chloride and acid corrosion.

However, the modern low C, Mo and N bearing duplex steels are characterised by much better combinations of various properties - see Table 2. Corrosion resistance became even more prominent and the welding difficulties were overcome substantially. They are now available in the form of rolled plates and hence the necessity for satisfactory welding technology and consumables.

WeldabiUty Duplex steels are readily weldable with most of the

existing fusion welding processes. Table 3 for instance gives the description and properties of Soudocrom S 4462 covered electrode for manual metal arc welding.

In general it can be stated that: (a) except in particular cases, duplex steels are welded

without preheat. (b) during welding, the interpass temperature should

preferably not exceed 200°C. (c) postweld heat treatments are to be avoided. (d) Charpy V impact strength in both the weld metal

and the heat affected zone is essentially a function of the ferrite-austenite balance. This balance is is different for the base materials and for the weld deposited metals.

(e) The amount of ferrite that can be tolerated in the heat affected zones of the base materials is on average higher than the ferrite content which is to be considered as optimum in the case of a weld metal. This explains why the welding consumables

Stress corrosion cracking (38,0%)

causes (7,7%)

954 Cases

Intergranular corrosion (11,5%)

Pitting / General (25,0%) corrosion

07,8%)

Fig. 1 Summarys of the results, as they were published in the literature footnote of a survey on corrosion problems experienced with AIS1304 steel in the chemical process industry in Japan. It shows the relative importance of various forms of corrosion.

for duplex steels are systematically overalloyed with Ni. The Ni overalloying is on average 3 to 4% as compared with the Ni content of the base metal.

(f) cold or hot cracking are practically never a concern. (g) with the exception of the Ni overalloying, it is

recommended that the duplex steels be welded with consumables of similar composition, and

(h) welding with "dissimilar" weld metal may lead to erratic results.

Conclusion The modern ferritic-austenitic duplex steels are character-

ised by very interesting combinations of properties. Although they are not adapted for the use at service temperatures above 300°C, they offer an attractive alternative to the use

MATERIALS& DESIGN Vol. 5 No. 6 DECEMBER/JANUARY 1985 291

for example of 316(L) and 317(L) alloys, for equipment in the following industries: processing and pipelines for the transportat ion of wet sour gases & oil; desal inat ion;

phosphor ic acid, urea and pulp & paper plants as Well as pollution control (wet scrubbers), waste water treatment, food processing & brewing industry and the sugar refining industry. They can also be used for t ransportat ion and storage vessels for various chemicals.

Provided that the necessary precautions are taken, the steels are readily weldable. Suitable welding eonsumables

exist for the M M A - T I G - M I G and submerged arc processes. The consumables which exist for joint welding can be used also for surfacing purposes, i.e. the fabrication of tube plates.

S. Bernardsson and J. Oredsson - Stress corrosion cracking resistance of Duplex and high alloy austenitic stainless steels- SAND VIK- Reprint of paperpresented at the CORREX 82 Conference London, Nov. '82.

T A B L E 1

Chemical Compos i t ions of typical Dup lex stainless steels

No. Designation

1 AISI 329 - 1.4820 - XI 2 CrNi25.4

2 1.4417 (X2CrNiMoSi1853) 3 X3 CrNiMo 25-6-2 4 1.4462 (X2CrNiMoN22.5 .3)

5 X3CrNiMoCu 25.5.3.2 6 X4CrNiMoCuN 26.5.3.2.

C Mn Si Cr Ni Mo N Cu Ti/Nb

0.10 0.5 0.5 25-26 4-5 (15 ) - - - - - -

0.02 1.7 18.5 5 3 <0.10 0.030 25 6 15 <0.10 - - - - 0.03 2 m a x 1 max 22 5.5 3 0.15 - - - -

0.03 25 5 3 <0.10 1.5-3 - - 0.04 1 0.5 26 5.5 3 0.15- 1.75 - -

0.20

T A B L E 2

Physical & Mechanical Properties of some stainless steels

Type Condition

(1) AISI 316 Q-A

C F 8M Q-A AISI 329 Q-A 1.4417 Q-A

R E A KCV (J) Thermal Conduct

(MPa) (MPa) (%) + 2 0 ° C - 10°C W/(m°C)

500/700 210 45 250

6 1 1 ; 1 B * & ! 1 ~ | |1; . '~

[oloI~IOlOl l ~ ~ I O l m [ O l ',}

1.4462 Q-A 700/900 450 25 190 180 (27 /~

_ 5 0 o c )

C W 20% 965 895 C W 50% 1020

CD4MCu Q-A 770 550 15 40 F E R R A L I U M 255 Q-A 780 530 30 120

~ A + T 880 650 28 70 F E R R A L I U M 288 Q-A 800 500 25 65

Thermal Expansion (2 )

mm/°C (xl0 "6)

+ 20°C : 15 20 h IO0°C : 16 + lO0°C : 16 20 h 200°C : 17 + 300°C : 19 20 h 300°C : 17.5

+ 20°C : 20 20 ~ loo°C : 13.1 + lOO°C : 20 20 ~ 200°c : 13.7 + 300°c : 24 20 ~ 300°c : 14.1 + 20°c : 19 20 ~ lOO°C : 13.7 + lOO°C : 19 20 ~ 200°c : 14.2 + 300°c : 23 20 h 300°c : 14.7

HV

160

260

260

(1) Q-A = Quench-Annealed (1020-1100°C + H20 ) T ---- Tempered C W ---- Cold Worked

(2) For mild steel: 12,5 - 13 - 13,5

292 MATERIALS & DESIGN Vol. 5 No. 6 DECEMBER/JANUARY 1985

T A B L E 3

Description and properties of MMA Electrode Soudoerom S 4462

1. Coating 2. Weld. Positions 1,6 to 4 mm diam. 3. Nature of current 4. Classification DIN

5. Chemical composition

6. Ferrite content

7. Tensile Properties: (all weld. Met.)

8. Charpy V Impact Prop. (J)

.

ELECTRODE WELD METAL

Rutile All except vertical down

AC and DC 4- X2 CrNiMoN 22.9.3.

At room temperature

At280°C

C Mn Si Cr Ni Mo N Cr 6q. Ni 6q. PRE 131 PRE 2

FN

YS UTS A5d. YS UTS A5d.

+20 °C _20°C -30°C

Intergranular, pitting and stress corrosion resistance

0,025 0,95 0,8

22 9 2,75 0,12

26 13.8

33,9

25

650 MPA 795 MPa

25 % 478 MPa 640 MPa

23 %

55 46 43

satisfactory

MATERIALS &DESIGN Vol, 5 No. 6 DECEMBER/JANUARY 1985 293