Cracks on Hard Facing Overlay
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sevak hiren
Jun 21, 2013, 12:19:43 AM6/21/13
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Dear Experts,
One of the manufacturer is using XL-CCH electrodes for Hard Facing Weld Overlay on c arbon steel material. (Chromium Carbide Alloy Deposit Hard Facing Electrode).
The weld overlay outer surface is showing parallel hair line cracks.
The manufacturer is arguing that these cracks are bound to develope due to inherrent properties of electrode & it is good to observe cracks on weld for ensuring the application of these type of electrode. The electrode catalogue also states that cracks can be developed on weld surface.
My question is which code/standard allow cracks on such hard facing overlay ?
cbe swamy
Jun 21, 2013, 1:30:16 AM6/21/13
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Dear All,
Where direct fusion welding is not appropriate, as in the case of an extremely hot-crack-sensitive casting, other
approaches might prove useful. One option is to "butter" the area of the crack-sensitive casting to be joined, using a
consumable of a less crack-sensitive material. This "buttering" involves surfacing the casting locally with a consumable
before fabricating the actual weld joint. With no joint present during the buttering operation, the restraint on the
solidifying surface pass and the underlying HAZ of the casting can be quite small and defects (fusion zone and HAZ hot
cracks) may be avoided. This surfaced area can be built up slowly to a thickness where it can then be prepared as a joint
for subsequent welded attachment. Additional information on buttering can be found in the article "Hardfacing, Weld
Cladding, and Dissimilar Metal Joining" in this Volume. As another option, an insert of a less hot-crack-sensitive alloy
can be inertia or friction welded onto the mating surface of the hot-crack-sensitive casting. This insert could then be
prepared for subsequent fusion welding to the required structure. These options are contingent upon the availability of consumable materials that are acceptable in the service environment.
SFA - 5.13
A7.3.1 ENiCr-C Electrodes
A7.3.1.1 Characteristics. Undiluted weld metal of this composition exhibits a structure consisting of chromium carbides and chromium borides in a nickel-rich matrix. The nickel base and high chromium content give these deposits good heat and corrosion resistance. Care should be taken when cooling hardfacing deposits because of a tendency to stress crack. This alloy possesses excellent resistance to low stress abrasion.
SFA - 5.21
A7.1.8.2 Applications. A general purpose hard facing alloy which can be used where limited stress-relief cracks (checks) are acceptable but severe abrasion is not encountered.
Where direct fusion welding is not appropriate, as in the case of an extremely hot-crack-sensitive casting, other
approaches might prove useful. One option is to "butter" the area of the crack-sensitive casting to be joined, using a
consumable of a less crack-sensitive material. This "buttering" involves surfacing the casting locally with a consumable
before fabricating the actual weld joint. With no joint present during the buttering operation, the restraint on the
solidifying surface pass and the underlying HAZ of the casting can be quite small and defects (fusion zone and HAZ hot
cracks) may be avoided. This surfaced area can be built up slowly to a thickness where it can then be prepared as a joint
for subsequent welded attachment. Additional information on buttering can be found in the article "Hardfacing, Weld
Cladding, and Dissimilar Metal Joining" in this Volume. As another option, an insert of a less hot-crack-sensitive alloy
can be inertia or friction welded onto the mating surface of the hot-crack-sensitive casting. This insert could then be
prepared for subsequent fusion welding to the required structure. These options are contingent upon the availability of consumable materials that are acceptable in the service environment.
SFA - 5.13
A7.3.1 ENiCr-C Electrodes
A7.3.1.1 Characteristics. Undiluted weld metal of this composition exhibits a structure consisting of chromium carbides and chromium borides in a nickel-rich matrix. The nickel base and high chromium content give these deposits good heat and corrosion resistance. Care should be taken when cooling hardfacing deposits because of a tendency to stress crack. This alloy possesses excellent resistance to low stress abrasion.
SFA - 5.21
A7.1.8.2 Applications. A general purpose hard facing alloy which can be used where limited stress-relief cracks (checks) are acceptable but severe abrasion is not encountered.
Thanks & Best Regards,
M Veera SAMY
BVQI
Date: Fri, 21 Jun 2013 09:49:43 +0530
Subject: [MW:17992] Cracks on Hard Facing Overlay
From: hirens...@gmail.com
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Ramin Kondori
Jun 21, 2013, 4:33:44 AM6/21/13
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Dear Sevak:
Mr. Swamy mentioned the methods of fabrication to avoid cracks of overlays on sensitive base metal which is not the case here.
Chromium Carbide Deposit will crack whatsoever the method is. That's inherent to this material but the point is you shall manage these cracks. If you decide to avoid these cracks, maybe you can manage it for a while but suddenly you will see a big wide crack tearing your workpiece apart. So you have to accept its presence and control it in your favor.
You should be critical on the crack size (width and length), quantity per square feet and their direction. It means that ideally it is better to have many short perpendicular cracks rather than a few long parallel cracks.
Chromium Carbide Deposit will crack whatsoever the method is. That's inherent to this material but the point is you shall manage these cracks. If you decide to avoid these cracks, maybe you can manage it for a while but suddenly you will see a big wide crack tearing your workpiece apart. So you have to accept its presence and control it in your favor.
You should be critical on the crack size (width and length), quantity per square feet and their direction. It means that ideally it is better to have many short perpendicular cracks rather than a few long parallel cracks.
How can you do that...?
For this purpose, you want cracks to be formed as soon as possible. Don't hold them back...!!!
Do not use much preheat unless your base metal calls for it (I don't think your base metal needs preheat), interpass temperature shall not exceed a certain limit (like Austenitic stainless steels). Some people actually use water to quench these overlays right after the arc is off and inspect the cracks after depositing each lb of filler metal and before they continue overlaying and it works...!!!
It's better to have a crossed pattern for weld directions. Normally cracks appear in transverse direction (with reference to weld direction) so if you want to avoid parallel cracks, you should weld in different directions. Chess pad pattern works well.
I think you got the idea...
--
pgoswami
Jun 21, 2013, 11:55:22 PM6/21/13
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Hello Hiren,
Hard facing alloys usually have little or low ductility
as compared to many other corrosion or erosion resistant alloys. However cracks
are not accepted as a rule. Hard facing containing cracks could be dislodged in
service, if the extent of cracking is severe.
Perhaps adjusting the composition would be the way to
go. The other technique could be use of austenitic(Ni based ) barrier
layer.
What' re the technical requirements ?? You refer this
article for general guidance.
Thanks.
Pradip Goswami, P.Eng,IWE
Welding & Metallurgical Specialist
Ontario, Canada
From: material...@googlegroups.com [mailto:material...@googlegroups.com] On Behalf Of cbe swamy
Sent: Friday, June 21, 2013 1:30 AM
To: material...@googlegroups.com
Subject: RE: [MW:17993] Cracks on Hard Facing Overlay
Dear All,
Where direct fusion welding is not appropriate, as in the case of an extremely hot-crack-sensitive casting, other
approaches might prove useful. One option is to "
Where direct fusion welding is not appropriate, as in the case of an extremely hot-crack-sensitive casting, other
approaches might prove useful. One option is to "
Ramin Kondori
Jun 22, 2013, 12:27:41 AM6/22/13
to material...@googlegroups.com
Dear Sevak:
 |
|
|
Check-cracking,
or checking as it's sometimes called, occurs in the metal carbide
families and can be seen as cracks that are perpendicular to the bead
length. They generally occur from 3/8 to
2 inches apart and are the result of high residual stresses of hard-facing weld metal as it cools. Other alloys such as the austenitic and
martensitic families, don't crack when applied with proper welding
procedures but for many of chromium carbide alloys, check-cracks appear when cooled to moderate
temperatures; this is normal.
Again, be careful if you try to stop this cracks, the residual stress will build-up and whatever you do, it will eventually crack, this time it will be a wide long crack that tears your work-piece apart...!!!
Check cracks propagate through the thickness of the weld bead and stop at the parent metal, as long as it's not brittle (like your case). In cases in which the parent metal is hard or brittle, you should select a buffer layer of a softer, tougher weld metal. Like what Mr. Swamy recommended, Ni-base or austenitic buffer family are good choices for a buffer deposit.
Regards
jsr...@gmail.com
Jun 22, 2013, 1:13:54 AM6/22/13
to material...@googlegroups.com
Dear All,
Hard facing deposits which contain carbides display cracks that are really stress relief checks as mentioned.
These cracks will go only to the depth of hardfacing & will not propogate to base metal & are harmless.
Only thing to be ensured that the crack is transverse and not longitudinal & base metal has not cracked.
J.Srinivasan
Hard facing deposits which contain carbides display cracks that are really stress relief checks as mentioned.
These cracks will go only to the depth of hardfacing & will not propogate to base metal & are harmless.
Only thing to be ensured that the crack is transverse and not longitudinal & base metal has not cracked.
J.Srinivasan
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From: Ramin Kondori <ramink...@gmail.com>
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Date: Sat, 22 Jun 2013 08:57:41 +0430
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Subject: Re: [MW:18000] Cracks on Hard Facing Overlay
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