How to Specify and Predict Ferrite Number in Stainless Steel Welds

ow to nd re errite in stainl el s

pe ify ict um er ss te l

A produ t of Enginee ing Pulse Li ited, UK Logos, nam s used within thi document are c pyrighted by En ineering Pulse © 2013 Any unauth rized use is illegal and strictly pro ibited.

Info: weld weldpulse.c om Sales: s les@engine ringpulse.c .uk

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How t specify and predict ferrite n mber

First Wor s

Ferrite content plays n important role in deter ining the p operties and in-service p rformance of stainless teels weld j int. When stainless steel are used for handling a certain process it is pertin nt to set the li itations of f errite content in order to ave the desired properti s and in-ser ice perform nce. Therefor , ferrite con ent is usuall specified for a stainless steel welding job, predict d using met ods available and then actual value is easured by instruments fter welding. Ferrite content is measured as a num er and the common ter inology to d al with this is Ferrite Nu ber (FN). This document would help you in s ecifying a f rrite numbe for the wel ing job you and to pr dict that nu ber using eldPulse® before you ac ually weld. easuring ac weld join s is out of scope of this d cument. Ha ing capabili y of specifyi g ferrite nu predictin that for a c rtain welding job using eldPulse® ould provide you a comp dealing ith welding f stainless steels.


re dealing with ual ferrite o the ber and titive edge in


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Ferrite Num er Ferrite number is the content f ferrite in stainless steel weld an it defines the mechani al (including toughn ss etc.), agnetic and corrosion resisting roperties along with its susceptibility to ho cracking.

Mechanical properties

Magnetic properties

FN

orrosion esistance

Hot cracking during welding

Fig. 1 Re resentation of properties linked with errite Number

Ferrite number needs to be specified considering the service requirem nts. Low an high values have t eir own adv ntages and isadvantag s however, i certain cas s, a low ferrite number is benefi ial and still i other cases a higher nu ber helps.



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What increases fer ite? Chro ium, Molyb enum, Niobium (known ollectively a Chromium quivalent) What ecreases fe rite? Nickel, Carbon, Nitrogen, Copp r – austenizing elements (known coll ctively as Ni kel Equiv lent)

Chromium Equivale t taking FN up

ickel Equivalent decreasi g FN

Fig. 2Effect on f rrite numbe with varyin Cr and Ni e uivalent While predicting f rrite using t e most commonly used equivalents are de ined as: Cr(eq) = Cr + Mo + .7 Nb Ni(eq) = Ni + 35 C + 0.25 Cu

RC 1992 diagram, Chromium & Nic el

Fig. 3 W C 1992 Diagram A produ t of Enginee ing Pulse Li ited, UK Logos, nam s used within thi document are c pyrighted by En ineering Pulse © 2013 Any unauth rized use is illegal and strictly pro ibited.


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Pre icting ferrite in weldin consu ables Take the mill test certificate o the weldin consumabl and note own the required chemi al comp sitions as re uired by WRC 1992 diag am to predict ferrite number. WeldPulse helps y u in doing this as illustrat ed below: 1. Select the welding calculations module 2. Clic “Ferrite Nu ber Check”



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3. Sele t “Welding onsumable” from the “C eck For:” combo box 4. Input the chemic l compositi n as listed in mill test cer ificate for the welding co sumable

Please note that a y minor change in chemical composition of the lements list d may have a major impact on the predicte ferrite nu ber. Please check your inputs bef re taking a y decision. Predicted ferrite num er is as per WRC 1992 iagram whi h allows ferrite predicti n from FN 1-100. We will now in ut the che ical composition of one stainless steel bare wire in WeldP lse Predict errite module to see the redicted ferrite number.



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This ferrite number is only the r presentatio of welding onsumable owever while welding with this consumable, a tual ferrite check is subjected to change based up n certain factors during the welding. Those fac ors are discussed next.



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Effect on ferrite nu ber due to dif erent

Nitrogen

Oxidation

hielded met l arc weldin (SMAW) - Nitrogen ingress from air reduces N - Oxidation reduces Chro ium and f errite number - High heat in ut results in low f errite level - Arc length allows more nitrogen i gress in the weld

Arc length linked with Nitrogen) High heat input

F

Flux ored arc welding (FCAW) - Reduction in wir speed increases Nitrogen and dec eases FN

Arc l ngth (linke with nitrogen) Nitrogen

F

Oxidation

Arc length

Nitrogen

High heat input

Oxid tion

elding

Loss of gas shielding

N


Re uction in wire speed (linked with nitrogen)

High heat input

GTAW /G AW - Loss of gas shielding r sult in nitrogen ingress from air - Carbon g in decreasing ferrite number if O2 is a shielding gas

arbon (if CO2 as shielding gas)


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Arc length

Loss of flux

Flux composition

Nitrogen

Oxidation

F

Submerged Ar Welding (S W) - Loss of flux re ult in nitrog n in ress from ai - Flux composition can change the fe rite number

Heat input

In addition to all th factors discussed above weld dilution obviously nd the weld cooling rates have an effect on f rrite numbe . Dilution is ifferent wit different w lding processes. Rapid coolin increases f rrite numbe .

Da ages a sociated with ferrite c ntent

Hig FN

Lo FN

Low creep rupture at high temperature

Sus eptibility to h ot cracking

Less resistance to corrosive media

Compromised mechanical pro erties in Dupl ex s ainless steels

Low toughness at low temperature



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Recommen ed ferrite ranges

.5

ax.

3.0 - 8.0

•Severe corr osion (like in Ure Plants) •Heat resisti ng weld metals li e SS310 •Cryogenic applications belo -105 C

•High temp rature applicatio s up to 700 C

.0 - 2.0

•High temp rature applicatio up to 350 C

.0 - 5.0

•High temp rature applicatio up to 400 C

30 - 70

•For duplex stainless steels

Fully auste itic typical che ical c mposition For corrosive servi es: C: 0.03; n: 4.5; Cr: 2 ; Ni: 22; Mo: 2; N: 0.15 For heat resisting eld metals: : 0.12; Mn: ; Cr: 25; Ni: 20.5 For cr ogenic applications: C: 0.03; Mn: 4.5; r: 17; Ni: 16; Mo: 2.5



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Pre icting errite n mber f a wel metal

Fin l words Ferrit number pl when service is c There ore, it is im joint. eldPulse® infor ation befor deeper when deali

ys an important role in he perform nce of a st inless steel eld especi lly rrosive, inv lves exposure to high emperature or very low temperatures. ortant to ta e into acco nt the factors defining the ferrite number of a w ld rovides a si ple and eas -to-use mo ule of Predi t Ferrite to et some useful taking a welding decision. The purpose is to enable engin ers dig a lit tle g with stainless steels, the most com only used aterial in pe rochemicals.



How to Specify and Predict Ferrite Number in Stainless Steel Welds

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