Dear Friends,
Sincere thanks esp to Jeff, Manprit & Vaidehi for their "Valuable Suggestions"
Although some questions are still raising as following.
Although some questions are still raising as following.
1) Why BCC structure allows more rapid diffusion of impure elemetns??
I think the packing factor of FCC is 0.72 and that of BCC is 0.68
(Packing Factor= V of Sphere of atom / V of Unit Cell ). So, Austenite is already more denser than ferrite. So, diffusion i.e. movement of atoms will be towards the new site for our case it is ferrite having BCC structure.
2) Jeff, as you mentioned that Interfaces reduces /increases the wetting of the liquid films along the grain boundries. How it takes place?? & How Austenite/Ferrite interfaces reduces the wetting of the liquid films along the grain boundry.??
3) Why & How FN of the order of 15 FN reduces the low temperature tough ness in cryogenic applications. Also, How it can promote the Sigma-Phase Formation at elevated temp/prolonged heat treatments??
Dear Jeff,
Collegue working with me are from the Metallurgy background and they are really happy and are appreciating your reply.
Hope for your Valuable Suggestions.
Regards.
Jignesh
On Thu, Jul 22, 2010 at 12:39 PM, manpreet <manpreetsin88@rediffmail.com> wrote:
Hi
A minimum ferrite content is necessary to avoid hot cracking in stainless steel welds. The amount of ferrite in the weld
metal also controls the micro structural evolution during high temperature service. Moreover the amount of ferrite
controls the corrosion and stress corrosion resistance. The low temperature toughness of the weld metal is also related to
the weld metal ferrite content
The exact amount of it can't be specified, depends on different materials. for eg-
-When joining ASME P-8, Group 1 austenitic stainless steels, the filler metal must contain at least 1 FN or 1 percent ferrite. However, 347 electrodes shall contain at least 4 FN.
-When joining 310 or 330 stainless steels and for cryogenic and special corrosive service, 0 FN filler metal may be used.
-For service temperatures exceeding 430°C (800°F), the deposited weld metal shall not exceed 10 FN.
-For cryogenic service with temperatures of –100°C (–150°F) and lower, the ferrite content of all austenitic stainless steel welding material shall be in the range of 2 to 5 percent.
Hope Mr. Jeff has solved your quarry, this is just an example to demonstrate that ferrite content can't be specified.
Regards
Manpreet Singh
Welding Engineer
Spiecapag
On Wed, 21 Jul 2010 12:58:22 +0530 wroteAlso, what happens if Delta- Ferrite is very low of theorder of 0.5
>
Hi,
We have come across, with very low delta ferrite (
0.5- 1.5%) in the weld, leading to cracking & failure of components. With
high % of delta ferrite also (10%), cracking is observed (even during storage).
Minimum 3% is required to avoid fissuring. Low and high FN-both are not
advisable. I can explain afterwards, how it prevents.
Regards,
Vaidehi Ganesan.
-----------------------------------------------------------------------------------------------------------------------------
----- Original Message -----
From:
jignesh
makwana
To: materials-welding@googlegroups.com
Sent: Wed, Jul 21, 10 9:43
Subject: [MW:0] How Delta- Ferrite
prevents Solidifacation Cracking/ Hot Cracking in SS??
>
Dear All,
Good Morning
I have query regarding the solidification Cracking.
Generallly, FeS the compound responsible for solidification cracking.
Also Arsenic, Sulphur shows same phenomenon.
Now Delta- Ferrite in 3-8 FN proportion prevents hot cracking.
But how ?? In most of the books, it is written that, " Delta- Ferrite has
tendency to lock the impurities".
But how Delta- Ferrite can be helpful for the prevention of hot cracking
by locking the impurities??
FN or so or what happens if Delta-Ferrite is high of the order of 15 FN or
so.
Dear All,
Please help me to find the answers.
Thanks in advance.
Jignesh
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