Dear Rudolf
Any time...
Again, If the root pass is the problem, you either change the parameters to achieve desired properties (hardness, impact etc.) or you simply grind out that bloody root pass and proceed.Any time...
Personally, I would rather choose the first option. Applying a combination of 150-200C pre-heat, controlled heat input and PWHT (holding temp not higher than base metal tempering temperature) is a routine solution.
If you decided to go for root pass removal, just do not forget to be critical. The gouging heat input shall be kept to minimum and gouging products shall be completely removed by grinding (high-carbon metal or gouging HAZ).
Regards
On Wed, Jun 19, 2013 at 8:55 AM, rudolf saldanha <rudolf_jude@yahoo.com> wrote:
Hi, RaminThank you very much for your valuable feed back. I have included Back gouging in the WPS, although this was not done on the WPQT coupon, as the fit up and penetration was excellent, just did back grinding instead of gouging.As suggested, PWHT may be the only solution out.Root pass geometry was Double V 2/3 - 1/3 Bevelling 60 deg. with 3 mm root gap and 2 mm face.Thanks again,RegardsRudolfFrom: Ramin Kondori <raminkondori@gmail.com>
To: materials-welding@googlegroups.com
Sent: Tuesday, 18 June 2013, 19:50
Subject: Re: [MW:17973] PQR for Welding Weldox 700
I recommend include back gouging (grinding is better) in your WPS (if you have access in the actual work). Gouging shall be done with low heat input, followed by grinding.Dear Rudolf:Now that's the information I needed.
At the beginning I thought you have the usual HAZ toughness problem but this one is different.
There are a few reasons for such high hardness values in root pass, including:
That means you have to increase Heat input and/or preheat.
- Alloying elements in this filler metal (1.75% Ni and 2.0% Mn)
- Your thickness is 35mm so heat sink is high
- Root pass geometry causes stress concentration
But you can't increase preheat so much otherwise you will jeopardize HAZ toughness so PWHT will be essential. There is no other way...!!!
This is to remove this problematic root pass.Good LuckOn Tue, Jun 18, 2013 at 2:56 PM, Rudolf <rudolf_jude@yahoo.com> wrote:
Hi Ramin,Thanks for your reply. Yes you are right the impact values at 1mm and 5 mm at fusion line is over 150 joules. It is only at the weld metal that it has dropped to single digit. The hardness at root pass weld metal and HAZ is around 350 to 400 HV. The parameters are all fine. Checked with Esab.The parameters are given in my first query.Am really confused. Why and how it has happened. I have religiously monitored the inter pass temp with temp stick and digital thermometer. Continuously checked V and A using tong meter. Checked gas flow at regulator.Thanks and regardsRudolf
Sent from my iPhoneNormally, the problem with welding of Quench & Tempered steels like Weldox-700 is that impact toughness drops in HAZ (and/or fusion line). Of course that's when you select suitable filler metal and welding process and technique. Below table shows that you should not have any problem with weld metal specimens. In other words if you use recommended parameters, you should get these results (for weld metal only). If you have not, then you are missing something.Dear Rudolf:
Are you saying that your specimens did not fail in HAZ (or fusion line) and weld metal specimens failed...?
If "weld metal" impact test has failed, most probably it has something to do either with your filler metal or welding process (or power source settings, technique etc.).
Are you using recommended welding parameters...?
Please check with the ESAB page to ensure you are using proper power source settings (http://www.esabna.com/us/en/products_catalog.cfm?Product_ID=265).
Typical Mechanical Properties (Weld Metal)
As Welded 75% Ar / 25% CO2
Yield Strength: 110 ksi, 760 MPaTensile Strength: 120 ksi, 830 MPaReduction in Area: 54%Elongation in 2": 19%Stress Relieved 8 hrs. @ 1150°F (621°C) 75% Ar / 25% CO2
Yield Strength: 108 ksi, 745 MPaTensile Strength: 116 ksi, 800 MPaReduction in Area: 56%Elongation in 2": 19%
Charpy V-Notch Properties (Weld Metal)Testing Temperature 0°F (-18°C)
As Welded 75% Ar / 25% CO2 : 40 ft-lb, 54 JStress Relieved 8 hrs. @ 1150°F (621°C): 29 ft-lb, 39 J
Testing Temperature -20°F (-29°C)
As Welded 75% Ar / 25% CO2 : 36 ft-lb, 49 JStress Relieved 8 hrs. @ 1150°F (621°C) : 27 ft-lb, 37 J
Testing Temperature -60°F (-51°C)
As Welded 75% Ar / 25% CO2 : 26 ft-lb, 35 JStress Relieved 8 hrs. @ 1150°F (621°C) : 21 ft-lb, 28 J
That was about "weld metal" but HAZ is another issue here.
PWHT is necessary since it will restore toughness of the HAZ. I don't know why that manufacturer has told you that PWHT is not mandatory. When you have impact requirements, PWHT is essential for restoring toughness in HAZ of QT steels.
I have seen this issue before and by changing the process to Pulsed GMAW the problem solved.
Pulsed GMAW lowers the heat input and you have more control on transfer mode.
I recommend you to do the same.Good LuckOn Tue, Jun 18, 2013 at 11:48 AM, Rudolf <rudolf_jude@yahoo.com> wrote:
Dear Mr. RaminThanks for your valuable feed back. But am afraid I have checked with SSAB manufacturer of this plate and am told that PWHT is not mandatory unless the design calls for.However I agree with you regarding the transfer method.The heat input has been very low as the welding speed was good, but. This too fast may also be the reason for insufficient slag covering over the weld puddle and exposure to atmosphere.Another possibility may be the low heat input the heat has immediately dissipated to the base metal and the plate has served as a heat sink thereby leading to a hard micro structure.RegardsRudolf
Sent from my iPhoneTry to keep heat input around 1.0 KJ/mm. Lower heat input is better.The holding temp shall not exceed that of base metal during manufacturing.Dear Rudolf:But be careful...
Of course it will fail...
This is a Q&T steel...
Along with heat input control, a 35 mm Thick Weldox-700 plate shall definitely require stress relief after welding.
do not apply stress relieve at 600, 620 or so...
Check the plate certificate and you will find the heat treatment parameters there, the PWHT temp shall not exceed the tempering temperature of your weldox-700 plate.
You are using FCAW...Not saying that it is wrong but sometimes in Q&T steels, you have to use pulsed arc or spray transfer to get good impact results and for this reason, MIG works better (in case you failed with FCAW).
Good LuckOn Sat, Jun 15, 2013 at 6:02 PM, rudolf <rudolf.jude@gmail.com> wrote:
Dear Community Members.We have done a PQR coupon for welding Weldox 700E. The material Thickness was 35 mm. Double V Groove Butt Joint. 2G position. Code AWS D1.1The following parameters were followedProcess = FCAWElectrode wire = Esab Dual Shield II 110Gas = 80 % Argon 20% Co2Gas Flow = 20 lpmPreheat to 103 CInterpass temp around 150 CCurrent SettingsDCEP CVAmps 200 amps 24 Volts for root passAmps 180 to 160 24 Volts for hot, fill and capping.The heat input recorded was between .8 to 1.5 kj/mmThe wire feed rate was 10 m/minWe did a charpy test on weld metal however it failed.The results were average of 8 kj absorption at -40 CAt 1mm and 5mm from fusion line the absorption was 80 to 130kjIntend to do a re charpy test @ -18 C.Though the client has not specified Charpy requirements and specifications. Wanted to do it for future requirements if any.
Request you to please share your opinion,WHAT COULD BE THE REASON THE CHARPY @ WELD METAL IS SO LOW, and in the absence of specific requirements for CVN what should be the impact values.AWS D1.1 does not state any values for Yield strength above 355 MPA, but leaves the onus on the client to specifiy.Please advise.ThanksTo unsubscribe from this group, send email to mailto:materials-welding%2Bunsubscribe@googlegroups.comTo unsubscribe from this group and stop receiving emails from it, send an email to mailto:materials-welding%2Bunsubscribe@googlegroups.com.
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