duplex steel weld adequate microstructure

[Liuk]

Hello,

There is very interesting requirements for duplex steel weld in EN ISO 13445-4 (PED: steel group 10 weld micro structure examination shall shows adequate microstructure.

What do you think what it means?

My problem: no any intermetallic precipitation, but there are some nitrides (ferrite content in limits of EN 13445-4, hardness range is 240-270 HV10). I have (as I think) enough big experience in duplex steel weld microstructure evaluation (of course level "test for welding procedure qualification). But this combination (nitrides and evaluation against EN ISO 13445-4) in the first time.

Could I evaluate this structure as adequate?

F.e. there is limit of nitrides content in Norsok standard, but it isn't used in this case.

Thanks in advance

 

[metengr]

The microstructure itself should contain near equal amounts of ferrite and austenite based on metallographic examination. Other tests (like ASTM A 923 Method C) can be used to determine if harmful precipitates are present.

 

[Guest102023]

Fabricating with duplex SS has several pitfalls, and requires a level of workmanship and QC monitoring that is big step up from what is necessary for austenitic SS such as 304.
I strongly suggest you retain qualified help from a welding engineer familiar with this class of steel, and use a testing laboratory that has experience with this material.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[EdStainless]

Many people, when they are starting out with duplex welding, find it helpful to test samples to the most restrictive specifications. I have seen weld coupons tested for mechanical properties, the microstructures examined for phase balance, chemistry testing, and a combination of A923 B and C. This would give you a full picture.
If you see any any secondary phases in the micro you are probably in trouble, but it does depend on a lot of things. Testing A923C is not a corrosion test, it is a measurement of the extent to which secondary phases degrade the corrosion resistance. The low temperature impact testing also helps you see this.
You need expert help if you want to do this right. And if you do it right there is no such thing as meeting one standard and not another, all of your duplex welds should be able to meet any of the requirements. If not hen you are playing a risky game of deliberately making sub-performing welds for some applications.

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P.E. Metallurgy, Plymouth Tube

 

[Liuk]

Thanks a lot EdStainless

It is great if we have clear requirements for microstructure acceptance f.e. "unaffected structure" acc. to ASTM A923 method A or "no intermetallic precipitation' and etc. But requirement "adequate microstructure" isn't transparent...

 

[EdStainless]

That is why it is critical to do a range of testing, so that you understand it more completely.

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P.E. Metallurgy, Plymouth Tube

 

[Guest102023]

EdS,
In my experience, duplex welds either pass A923C comfortably or fail badly. It is uncommon to have a borderline result.
Deposit ferrite balance is also dependent on the welding process.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"