Ferrite No and percentage
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Manav Malhotra
Dec 8, 2010, 11:29:03 AM12/8/10
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Can anyone tell me whats the difference between ferrite no and percentage and its required for which materials?
Suresh Babu
Dec 8, 2010, 12:46:57 PM12/8/10
to Materials & Welding
Ferrite Number is an arbitrary standardized value designating the
ferrite content of an austenitic stainless steel weld metal. It should
be used in place of percent ferrite or volume percent ferrite on a
direct replacement basis.
FN has been adopted as a relative measure for quantifying ferritic
content using standardized magnetic techniques. The FN approach was
developed in order to reduce the large variation in ferrite levels
determined on a given specimen when measured using different
techniques in different laboratories. FN approximates the "volume
percent ferrite" at levels below 8 FN; above this level, deviation
occurs.
A number of instruments are commercially available for determining the
ferrite content of welds, including the Magne gage, Severn gage, and
ferrite scope.
For more clarity have glance to the following:
Ferrite number is a means of measuring the proportion of Delta-Ferrite
present
A magnetically determined unit for ferrite determination.
Delta-Ferrite is the Solid solution of Carbon in Delta -iron.
Found only in high temperature region (>1410ºC)
BCC structure
Max. solid solubility of carbon is 0.1% at 1495ºC
Minimum FN is required to decrease hot cracking tendency of the weld.
Higher values of FN reduces the Corrosion resistance property of the
weld
FN can be :
Predicted using Constitution Diagrams
Measured using instruments like Feritscope
An instrument which directly gives the value of Ferrite Number present
in a weld.
Works on Magnetic Induction principle
ferrite content of an austenitic stainless steel weld metal. It should
be used in place of percent ferrite or volume percent ferrite on a
direct replacement basis.
FN has been adopted as a relative measure for quantifying ferritic
content using standardized magnetic techniques. The FN approach was
developed in order to reduce the large variation in ferrite levels
determined on a given specimen when measured using different
techniques in different laboratories. FN approximates the "volume
percent ferrite" at levels below 8 FN; above this level, deviation
occurs.
A number of instruments are commercially available for determining the
ferrite content of welds, including the Magne gage, Severn gage, and
ferrite scope.
For more clarity have glance to the following:
Ferrite number is a means of measuring the proportion of Delta-Ferrite
present
A magnetically determined unit for ferrite determination.
Delta-Ferrite is the Solid solution of Carbon in Delta -iron.
Found only in high temperature region (>1410ºC)
BCC structure
Max. solid solubility of carbon is 0.1% at 1495ºC
Minimum FN is required to decrease hot cracking tendency of the weld.
Higher values of FN reduces the Corrosion resistance property of the
weld
FN can be :
Predicted using Constitution Diagrams
Measured using instruments like Feritscope
An instrument which directly gives the value of Ferrite Number present
in a weld.
Works on Magnetic Induction principle
Karthik
Dec 9, 2010, 2:27:25 AM12/9/10
to material...@googlegroups.com
| Hi, Please find below. 01. What is the difference between ferrite number and ferrite percentage? Ferrite percentage no longer used,it has been replaced by Ferrite Number |
|
Ferrite Number is an arbitrary standardized value
designating the ferrite content of an austenitic stainless steel weld metal. It
should be used in place of percent ferrite or volume percent ferrite on a
direct replacement basis. FN has been adopted as a relative measure for quantifying ferritic content using standardized magnetic techniques. The FN approach was developed in order to reduce the large variation in ferrite levels determined on a given specimen when measured using different techniques in different laboratories. FN approximates the "volume percent ferrite" at levels below 8 FN; above this level, deviation occurs. A number of instruments are commercially available for determining the ferrite content of welds, including the Magne gage, Severn gage, and ferrite scope. |
| 02. its required for which materials? Ferrite number is a measure of = Chromium & Nickel equivalent in an Austenitic stainless steel material. It should be between 3-7% max. Very low ferrite can lead to cracks. It is a measure of denoting the ferrite content in an stainless steel. Ferrite Number has been adopted as a relative measure for quantifying ferritic content using standardized magnetic techniques. The Ferrite Number approach was developed in order to reduce the large variation in ferrite levels determined on a given specimen when measured using different techniques in different labratories. The ferrite level is only important to assure minimum exposure to solidification cracking when depositing austenitic stainless steel weld metal. The lower ferrite number is better for corrosion resistance, while balancing higher ferrite content to avoid solidification cracking in the weld deposit. I would not worry about lower ferrite numbers for clad overlay welding, if no cracking is observed (Liquid Penetrant verification). Thanks & Regards, (Karthik) Karthikeyan.S QA/QC Manager Getabec Energy Co.,Ltd. 379,Moo6,Soi8,Nikhomphatana, Rayong-21180, Thailand. Phone: 0066 38 897035-8
(Off) Fax: 0066 38 897034 Hand Phone: 0066 892512282 --- On Thu, 12/9/10, Suresh Babu <suresh...@gmail.com> wrote: |
|
c sridhar
May 17, 2013, 4:18:45 AM5/17/13
to material...@googlegroups.com
To understand it, one has to know
reason for ferrite formation. Welding metals like 304L, 316L,
retain some
amount of delta ferrite formed at grain boundaries, due to composition of
weld metal
& welding conditions like high temperature (5500 -
9500 C). Both factors determine the percentage of
delta ferrite as well as its size,
morphology and distribution. Though delta ferrite reduces risk of micro
fissuring / cracks, if it exceeds 8-10%, corrosion resistance of SS decreases steeply.
Ferrite level
beyond 7% is unacceptable for high temperature service. Again,
Zero or very low ferrite may create
micro – fissures. Ferrite turns to brittle
sigma phase (rich in Cr) at high
temperature and affects ductility,
toughness and
also cause inter granular corrosion due
to Cr depletion from austenite matrix.
Hence it
has to be maintained depending up on service requirements.
These details were brought by
Schaeffler by metallographic i.e., Ferrite
Percentage which helps to
determine the structure of weldment, like ferrtic, austenitic, percentage of delta ferrite at normal conditions
etc. The limitation is the non-equilibrium cooling rate, selection of welding process,
shielding gas, Nitrogen
(a strong austenite former) pick up which has influence on the ferrite
morphology.
Delong has modified the Schaeffler
diagram (claimed to be ±4% accurate) improving the accuracy to ± 2%.
Delong diagram differs
with Schaeffler diagram in that the values
are based on magnetically
determined
ferrite content. i.e., the Ferrite No & Nitrogen
is included in the calculation of nickel equivalent with a
coefficient
equivalent of 30.
Hence it is generally believed that, Delong diagram gives
more accurate values compared to Schaeffler
diagram. AWS has switched over to
Ferrite No. (FN) instead of percentage ferrite since, FN is derived by a
standard measurement and calibration procedure as approved by Welding Research Council
.
b) In Schaeffler diagram, Nickel and Chromium
equivalents are calculated and Delta
Ferrite percentage is obtained by plotting the values.(Cr Equiv. % Cr +
% Mo + 1.5 % Si +0.5%Cb. & Ni Equiv. : % Ni + 30% C + 0.5% Mn) This
method involves actually counting the ferrite phase using point counter method
and estimating the percentage)
In Delong diagram the Delta Ferrite No. i.e., FN is calculated by adding additional 30% N in Ni
equiv.)
These method is based upon the
theory that, ferrite is a magnetic phase in a non magnetic austenitic matrix.
While nitrogen level in SMAW is 0.06%, it is 0.02% through GTAW &
0.04% in GMAW process.
Magnetic saturation method is a DT
to determine the absolute percentage of delta ferrite in the sample and
independent of size, shape, orientation of
the phase etc. Cannot be used to measure ferrite in an actual equipment.
Ferrite
scope, Magna gauge are
other methods, to measure the delta ferrite and their results are said to be
accurate and widely used due to its simplicity. They are NDT methods and could
be used any one. Both gauges are available easily in the market and can be done
by yourself if the no. of checking are frequent and on a long run.
Other special methods used in a research institute
are X-ray diffraction, electro chemical
etc.
Delong diagram provides a better
correlation between the calculated and measured ferrite content of the
weld
metal. Typically 8% volume fraction
ferrite would equal 8 FN. Beyond this value, Ferrite No would be more accurate.
However as per AWS and other WRC documents Delong diagrams upper limit is up to
18 FN or typically 15% Ferrite.
A number of instruments are
commercially available for determining the ferrite content of welds, including
the
Magne gage, Severn gage, and ferrite scope.
Ferrite No (FN) cannot be converted directly in to volume % Ferrite unless saturation ferrite Magnetization of the ferrite level is taken into the account of these alloys. With various calculations, an approximate relationship has
been developed using formula.
Volume F% of Ferrite = 0.7 (FN) +
0.54 , where ‘F’ is residual ferrite and FN is ferrite content.
This is an app. Equivalent Value
and varies to some extent from alloy to alloy .
Trust above information shall be of
help to you.
From: "az...@metalcaregroup.com" <az...@metalcaregroup.com>
To: material...@googlegroups.com
Cc: karth...@yahoo.com
Sent: Thursday, 16 May 2013 9:20 PM
Subject: Re: [MW:17693] Re: Ferrite No and percentage
Hi
Is there a way of converting the
Ferrite Number to Vol%?
regards
Azmi
On Dec 8, 7:29 pm, Manav Malhotra <manav6...@yahoo.com> wrote:
> Can anyone tell me whats the difference between ferrite no and percentage and
> its required for which materials?
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