I disagree,
the cracking occurs because a brittle phase is formed at around 800 deg C.
This is expressed by the FN number which has to be above 5.
We avoid the hot cracking by using electrodes with higher Cr and Ni content (309 type)
Dr. G. Dilintas - Authorized Inspector Supervisor
I&F Regional Technical Manager
Bureau Veritas Piraeus - Greece
Tel: +30 210 40 63 113/4
Fax: +30 210 40 63 118
Cell: +30 69 44 64 62 04
JASPAL SINGH <jaspaldhesi@gmail.com>
Sent by: materials-welding@googlegroups.com 09/07/2010 13:12
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Dear Ankur,
This is with reference to your clarification on cracking when welding
carbon steel on SS.
In metallurgy there is concept of solubility means all the components
having limited solubility with respect to each other. Like in SS 304.
Cr is ~ 18 to 21% and Ni 8-10%. Any composition below or above this
will not meet the required mechanical properties because of solubility
issue.
For example:
Welding of Carbon Steel on SS with SMAW(bead on plate):
CS chemistry: Fe + small other elements
SS 309: 21% Cr + 12% Ni
Composition of weld metal with 35% dilution : Cr= 6.4% , Ni = 3.1%
Fe=93%. Which is unknown chemistry even Cr and Ni do not want to mix
with each other at this level. So cracking occur during
solidification.
On the other side while welding on Carbon Steel with SS
The resultant chemistry will be : Cr will be 17 to 18 % Ni in the
range of 8 o 10 % which is chemistry of known composition (SS304)
having perfect solubility, so no cracking .
This is the basic phenomenon of cracking while we are welding CS on
SS. You can refer any metallurgy book for behavior of elements during
solidification.
Regards
Jaspal Singh, CWI-AWS, CSWIP-3.1
Assistant Manager – Quality Assurance
Process Equipment Division
ISGEC, Yamuna Nagar, Haryana -135001
Phone: 911732307251
Ext: 251 Mb: +91 9996624244
On 9 जुला, 12:07, "Welder's Helper" <vettaikkaran2...@gmail.com>
wrote:
> Welding of stainless steel with carbon steel electrodes results in formation
> of martensite structure which is prone to cracking under stress or it may
> crack immediately during welding depending upon the welding conditions,
> thickness of the part being welded, deposition of consumable etc. But in
> actual practice, cracks do not come up always. Many a times, welders weld
> the stainless steel piping with carbon steel in order to avoid the need of
> purging and they successfully make the weld without any defects that can be
> picked up in radiography. They weld the root pass with carbon steel
> consumables and the rest of the welding is made in SS consumable.
>
> However, welding of stainless steel with low alloy steel electrodes would
> definitely come up with cracking as it is more susceptible to cracking than
> carbon steel consumables. Same martensite structure formation would occur
> and LAS consumable being used without any preheating protocol would crack
> itself during welding mainly due to uncontrolled cooling.
>
> Both of the situations can be seen visually during inspection and one can
> say that carbon steel or LAS consumable has been used but if gone
> un-inspected then one may not get it picked with radiography especially in
> the case of carbon steel consumable, however, LAS consumable has pretty
> higher chances of getting cracked and picked up.
>
>
>
>
>
> On Thu, Jul 8, 2010 at 10:09 PM, Ankur Mande <prince.an...@gmail.com> wrote:
> > Hello friends,
>
> > I have just joined this wonderful & group with "active members". I
> > have one query. Please let me know as to why we observe cracking when
> > carbon / low alloy steel is accidently welded on stainless steel. If
> > any body has any backup or paper related to this, request you to post
> > it.
>
> > Regards,
>
> > Ankur Mande.
> > 09925027848
>
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