Controling ferrite content in Duplex Stainless Steel

[duongwe]

dear all,

can someone help? when i qualify a WPS Duplex Stainless Steel and i need to control ferrite content. what do i do ?
please tell me some way for controlling ferrite content in Duplex Stainless Steel when i star to qualify a WPS.

 

[DiplingAndre]

Hi,
there are different methods.
You can use a point count (or computer based analysis) (see thread723-288690 ) which is imo the best way and you can determinate in exact areas like weld metal, heat affected area and base metal).

Next option is using a Ferritoscope (by Fischer) to determinate the Ferrite percentage and/or the Ferrite Number (FN). Its a very easy and simple tool to use. Just tip the probe ont the sample and you get the result. But you can onlyy measure weld metal and base metal on the outside (heat affected zone is haard to check because of the probe size).

The last option (I know) is the simplest, to use a WRC/De Long Diagramm. If you know the chemical composition you can calculate the FN with it.

 

[Kiwi2671]

duongwe,
Hope this helps,
Regards,
Kiwi

 

[weldtek]

The first post outlines methods for measuring % ferrite, but, controlling ferrite can be complex and difficult. There are many factors that affect ferrite in welds and HAZ's. In my experience two of the most important factors are heat input and cooling rate.
Successful results generally depend on low to moderate heat input and interpass temperatures, and to some degree, these will vary from process to process.

 

[duongwe]

Thanks all, but specially to Mr Weldtek.
but you can talk about further about heat input and cooling rate for controlling ferrite percentage , how does the method to carry out it?
Example: i have a pipe duplex with "3 inch, SCH 40S, A790", and i must control ferrite percentage not exceeded 57 percent so what do i use the method? and how?
Help me now.

 

[weldtek]

duongwe,
What specific base metal are you welding?
What process do you plan to use?
What joint detail will you use?
What filler metal do you plan to use?
In which position will the welding be performed.

 

[Guest102023]

Measuring ferrite content is not controlling it, as asked by the poster.

Use weld consumables from reputable suppliers, follow their recommendations, esp. heat input, technique, and shielding gas, and you will be OK. Each welding process has its own characteristic range of acceptable % ferrite, and a good technical specification will differentiate requirements for GTAW, SMAW, SAW, etc.

 

[duongwe]

i am welding with A790 (S31803) base metal, 2.4 ER2209 electrode, single V, GTAW process, 6G position. Help me!

 

[moltenmetal]

We had similar problems. Glad to hear we weren't alone!

Some on this site LOVE duplex SS grades and claim they're dead easy to weld once you're used to them. Previous posters have suggested that the best way to get good GTAW welds without elevated segregated ferrite is to tell the welders it's just another new grade of austenitic stainless steel- except to use this special filler rod.

We were welding small sizes (1/2"-2" butt welds mostly, sch10S). Following the weld consumable supplier's recommendations, we worried the welders about heat input and interpass temperatures- and got poor ferrite results, and haven't had a chance to use 31803 since. It was suggested by folks here that the welders were under-using filler metal as a result of trying to keep the heat input down, and I can see that as possible.

An argon shield gas mixture containing nitrogen is also recommended, as nitrogen is an essential alloying component in duplexes and can be lost during welding.

Best of luck- and make SURE you tell us what you did to fix this problem!

 

[weldtek]

duongwe,
Many owners specify S32205 due to the tighter chemistry controls and I think you may find that many material manufacturer's are producing materials to the tighter spec and dual certifying them as 31803/32205. The tighter control of Nitrogen can be a factor in maintaining acceptable ferrite levels in the HAZ.
Kiwi provided a link to the IMOA brochure. I suggest you review it as there's some good info there.
You shouldn't need any additions of Nitrogen added to the shield or purge gas.
Heat input is of major importance so if you perform testing on plate be sure to cover the 3G position, if you're testing on pipe in the 6G position be sure to test ferrite in the critical area.
We successfully tested a weld in plate 0.312" thick in the 3G position as follows;
ER2209 Avesta filler 1/8" diameter
90 -100 A, 13 V, 2-5 ipm travel Max heat input 29,250 j
Argon shield and purge
Impacts at -40F low 96 ft/lbs high 134 ft / lbs High in weld low in HAZ
Ferrite in weld low 40.28 high 41.53
Ferrite in HAZ low 48.89 - High 54.03
E562 Manual point count
This isn't to say you couldn't pass the test with different parameters, this is just one example. The joint thickness you'll be using is a little less so an adjustment in parameters may be in order.

 

[XL83NL]

hi duongwe,

I agree with the advise of weldtek, it's mostly about heat input.
also, telling your welder's it's DSS, but having them pay more attention to HI might worsen things up. when you tell a welder he just has to put down some weldmetal in e.g. a V-groove, he'll do it properly. making an Xray will 99 of 100 times show you it's a good weld.
now, telling the welder his next weld is a photo-weld might have the adverse effect, regardsless of the person welding.
so dont try to make a very big deal out of this. learn from the welder's experience, use their experience and info, ask them about the problems. on the other hand, if youre determined a certain weld has to made in a specific way (for example now with the DSS), just tell welder he has to do it such, and dont argue with him why things are that way.

now, I have a WPS here for a 1.5" Sch40 S32205 pipe, V-groove.
parameters;
max interpass 200 deg C
filler: LNT 4462 (AWS No ER 2209)
shielding and baccking; 99.9% argon
2.4 mm tungsten electrode
root pass; 65-75 DC+, 8-12 V,
2..n pass; 105-115 DC+, 10- 15 V
all GTAW welds.

As weldtek said, adding some nitrogen might be a good thing. Ive heard stories of qualifications welded with argon as backing, where the weldment, in a corrosion test, failed due to pitting. when the same piece was welded with 100% nitrogen as backing, it didnt fail in the corrosion test.

one last advise; 2 other things to worry about when welding DSS;
- hydrogenembrittlement. prevented by low hydrogen content and proper ferrite content in filler metal
- 475 deg C embrittlement; for application above 475 deg C, use multi layer welds

 

[weldtek]

One other important detail I overlooked was the ITP for the example in my previous post. It was 250 F.

 

[XL83NL]

Just talked to an experienced DSS welder: thoroughly cleaning before welding is very important!
Make sure there's no grease or dirt in weld.

 

[Duwe6]

and 'Thorough Cleaning' needs fresh, clean [preferably white] rags and a clean-drying solvent like naptha. Welder will need clean TIG /GTAW gloves once a week, or more often.

When his foreman fails to provide a welder the needed items, your results get pretty bad, pretty fast.