In schaeffler diagram, Ni equivalent is calculated on Ni, C, Mn & Cr equivalent is based up on Cr, Mo, Si, Cb. Delong diagram in addition to above takes note of nitrogen, a strong astenitiser.
Delta Ferrite: Depending on the relative proportions of ferrite and austenite forming elements present, the weld metal solidifies initially as grains of delta ferrite or grains of asutenite. As solidification proceeds, initial ferrite grains transform to austenite grains. If ferrite forming elements are more, delta ferrite forms in the micro structure. If the structure is austenite, it remains austenite till the end of solidification.
Ferrite % & Ferrite no: Schaeuffler used metallographic method for determining the ferrite percentage (%) in the weld metal, Delong has used a magnetic measuring instrument (Magne Gauge) in his work. Delong has adopted an arbitrary standard called Ferrite Number (FN) to indicate the ferrite content. Metallographic measurements are helpful but difficult to run accurately due to small size of ferrite particles.
Ferrite % and Ferrite Number are identical at low levels of ferrite, but they differ widely when Ferrite levels are high.
Variation of Ferrite in your measurement: Ferrite content as claimed by the manufacturer in his batch report can be reproduced on production welds, only when correct welding procedure is used i.e., with controlled heat in put, use of smaller size electrodes, stringer bead runs, faster cooling rates, low inter pass temperature etc. Use of high currents will also increase the ferrite level and reduce the resistance to corrosion.
At times use of long arc and in-adequate shielding may induce Nitrogen (a strong austenitiser) into the weld and may reduce the ferrite levels to some extent.
Trust above details will help you to overcome your problems.
sridhar.
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Delta Ferrite: Depending on the relative proportions of ferrite and austenite forming elements present, the weld metal solidifies initially as grains of delta ferrite or grains of asutenite. As solidification proceeds, initial ferrite grains transform to austenite grains. If ferrite forming elements are more, delta ferrite forms in the micro structure. If the structure is austenite, it remains austenite till the end of solidification.
Ferrite % & Ferrite no: Schaeuffler used metallographic method for determining the ferrite percentage (%) in the weld metal, Delong has used a magnetic measuring instrument (Magne Gauge) in his work. Delong has adopted an arbitrary standard called Ferrite Number (FN) to indicate the ferrite content. Metallographic measurements are helpful but difficult to run accurately due to small size of ferrite particles.
Ferrite % and Ferrite Number are identical at low levels of ferrite, but they differ widely when Ferrite levels are high.
Variation of Ferrite in your measurement: Ferrite content as claimed by the manufacturer in his batch report can be reproduced on production welds, only when correct welding procedure is used i.e., with controlled heat in put, use of smaller size electrodes, stringer bead runs, faster cooling rates, low inter pass temperature etc. Use of high currents will also increase the ferrite level and reduce the resistance to corrosion.
At times use of long arc and in-adequate shielding may induce Nitrogen (a strong austenitiser) into the weld and may reduce the ferrite levels to some extent.
Trust above details will help you to overcome your problems.
sridhar.
---------------------------------------------------------------------------------------------------
From: meisam shokri arfaei <meisamshokri@gmail.com>
To: materials-welding@googlegroups.com
Sent: Wednesday, 22 August 2012 4:25 PM
Subject: Re: [MW:15105] Ferrite Number
As I know 100FN is approximately shows 65% of ferrite volume, so this is the reason for the difference between FN and ferrite VOL%.
As you can see in below diagram the relation between FN and ferrite VOL% have been shown.
Also when you follow the standard procedure for evaluating FN the deviation of ±2 (approximately) is not prevented. So assume the deviation when you didn't follow standard procedure.
--
M. Shokri Arfaei
International Welding Engineer (IWE)
ASNT NDT Level III
ERI Metallurgy Lab. Manager
Tel: +98-21-66282127
Fax: +98-21-66282779
Please don't print this e-mail unless you really need to. BeGreen!
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