SS347 overlay but FN is too low

[bo gyi]

Dear all,

I have encountered that Ferrite No is too low for SS347 overlay to P1
(SAW).

I used ESAB ER309L & ER347 together with OK flux 10.93 and heat input
is about 0.9 - 1 kJ/mm.

My Ferrite no is as bellow . (check by Ferrite scope)

1st layer 309L (2mm thk from BM) , FN no. < 0.5

2nd layer 347 ( 4 mm thk from BM) , FN no < 2

3rd layer 347 ( 6 mm thk from BM) , FN no < 3.5

Required FN is 5 to 11 FN,

My welding parameters are as follow.

For 309L , 280 – 330 A, 30 – 32 V , travel speed 720 – 800 mm/min

For 347 , 330 – 350 A, 32 – 34 V , travel speed 720 – 800 mm/min


Please advice.

Regards,

Bogyi

[Roy Liu]

Lower the Amperage, Higher the velocity.


Roy
Bohler Welding Group


-----原始邮件-----
From: bo gyi
Sent: Thursday, May 31, 2012 8:40 AM
To: Materials & Welding
Subject: [MW:14422] SS347 overlay but FN is too low

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[pgoswami]

High Bogyi,

Please see the extract from the following IIW document below. The causes behind such low ferrite could be "Nitrogen pick up" due to high travel speed, which could cause insufficient flux coverage(thin flux coverage). If you see the attached Delong diagram, other than Nickel it's "C" and 'N" are most influencing alloying elements, which could cause a spike in the resultant "Nickel Equivalence" and very low ferrite in the weld metal.

If the travel speed is reduced to 400-500 mm/min at the existing weld parameters, then getting the desired "ferrite"(5-10FN) would not be a problem.

Also advise is to calculate the CR/Ni equivalence as per the consumable MTR. This suggested literature values:- if CR/Ni equivalence > 1.4-1.5, then the primary mode of solidification is "austenite, i.e low ferrite in the weld metal.

Hope this would help.

Thanks.


Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario, Canada.
Email-p...@sympatico.ca,
pgos...@quickclic.net

 

IIW-1166-92-IX-H-233-90:-Guidance on specifications of ferrite in stainless steel weld metal

1. In submerged arc welding, the flux provides the shield from the air. Loss of flux cover, usually easily noticed due to "flashing" of the arc, can produce nitrogen gain and ferrite loss.
2. Certain fluxes high 'in manganese silicate (or high in other oxides which are less stable thermodynamically than chromium oxide) can produce chromium oxidation and resultant reduction in ferrite.
3. On the other hand, some fluxes contain metallic chromium bonded within the flux particles which can add chromium to the weld metal and thereby increase the ferrite.
4. With either a flux that oxidizes chromium (and reduces ferrite) or a flux that adds chromium (and increases ferrite), the effect is magnified by choice of welding conditions favoring a high ratio of the amount of flux melted to the wire melted.