Addition of Micro allying elemenst to carbon steel

[MatSci1254]

Hi,

I have received A106 GR B seamless pipe for one of our project.
while checking the material test certificate of this pipes and relevant purchase specification I noticed that

- purchase spec specify Micro alloy steel shall not be used without prior approval.

- Nb and V contenet reported on MTC is 0.02% and 0.06%

- as per ASTM A106 Nb is non regulated elemenet( ASTM A106 does not specify limit for Nb) and mximum allowed content for v is 0.08%

My questions are

1) Does ASTM spec allow intentaionl addition of Micro alloy element?
2) How can we detrmine whether these elemenst are intentionaly added elements or are residual elements.
3) also does API 5L (for grade B and X42)allows intentional addition of micro ally elements

I have check ASTM A333 for GR 6 material, this spec does not allow delibrate addition of micro alloy element other those specified for Gr 6

Appreciate you advise.

 

[metengr]

As you stated - ASTM A 106 material specification allows the following element(s) for Grade B

Vanadium - 0.08% by mass

The Nb content reported in the MTR is probably an “ intentionally added unspecified element (an element added in controlled amounts at the option of the producer to obtain desirable characteristics)”. The Nb was most likely added by the Supplier for controlling grain size. There is nothing in A 106 that prohibits the use of Nb.

To answer your questions - unless either the ASTM specification prohibits deliberate alloy addition with approval from the Purchaser or through agreement between the Purchaser and the supplier, you get what chemical composition falls under ASTM A 106 general requirements.

Please review
ASTM A 530
ASTM A 751

 

[blacksmith37]

As far as I know ,material specifications are based on properties, chem, etc; not the mills' intentions.

 

[redpicker]

The problem here is the purchase spec that prohibits the use of "Micro alloy steel" without providing a definition of what a "Micro alloy steel" is. How is a supplier supposed to know what is suitable and what is not suitable? As bliacksmit37 said, all you can go by is the mehcanical properties and chemical analysis.

As far as I know, 5L does not prohibit micoralloy in any grades, let alone Grade B and X42. Generally, microalloying is not needed in these grades.

I'd guess that the author of the specification has had trouble in the past with microalloy steels, but never discovered what the root problem was. That is, it was not the microalloy that caused the problem, but maybe a high yield to tensile ratio, or maybe issues resulting from the fact the steel was as-rolled instead of quench and tempered. Who knows? But, by just saying "no Micro alloy steel", the author has not done anything to prevent a re-current problem, just left the door open for disagreements and confusion as to what meets the specificaiton and what does not.

rp

 

[stanweld]

Nb and V will positively affect strength and toughness in the as hot worked and as welded condition. If Al was not added to tie up Nitrogen, the toughness properties of the HAZ will be adversely affected after PWHT due to secondary precipitation of niobium carbo-nitrides.

While the reported V & Nb contents indicate that they were added, they could have resulted from pouring the heat into a ladle or tundish that had previously (last cast) been made for a micro-alloyed steel; more than likely this was not the case. V & Nb will also be added if rutile fluxing agents are used.

 

[EdStainless]

If a non-specified element is present, intentional or not, and it then qualifies as another grade it is that other grade. You can't call it both grades. Alloy additions work, intentional or not.

If the Nb and V, along with everything else qualify this as a microalloyed grade then that is what it is. period.

This is why my analysis list is always about 20 elements long.
Weldabiltiy and heat treat response cannot be taken for granted.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[blacksmith37]

With the advent of "mini-mills" (100% scrap, electric melt) ,0ne can expect a general increase in unspecified residual elements. This also works to the mills advantage as a single heat will meet many specifications (depending on heat-treat/strength). Specifications often to not seriously restrict unspecified elements. This is partially deliberate because the specs do not want to restrict the mills from innovation. (That is a two sided knife).

 

[metman]

...never discovered what the root problem was. ...author has not done anything to prevent a re-current problem, just left the door open for disagreements and confusion as to what meets the specificaiton and what does not

MatSci1254,
Can you talk to the author of the Purchase Order and find out from her/him if this is an internal requirement or customer requirement? If you can find the source person who is requiring this, maybe they can explain where the concern arises from.

For example; some HSLA steels as in the case of ASTM A514 are susceptible to cracking if PWHT(thermal stress relief)is applied ---- and this is attributed to the influence certain micro-elements.

http://www.arcelormittal.com/platei...chure/ARCELORMITTAL A514 AND T-1_20080514.pdf

Or maybe you should let sleeping dogs lie since the material appears meet spec?

 

[stanweld]

FYI
I had occasion to review some CMTR's for SA-106 B recently from a US manufacturer. All heats had aluminum additions indicative of fine grain melting. The larger bore pipe had additions of V or Nb. Note that these pipes were stamped and certified to SA-106B, SA-53B, API 5LB and API 5LX-42.

 

[Guest102023]

Microalloy elements (V, Nb, Ti) are just some of the possible ingredients in the recipe, to make an analogy. When added to a true high-strength low alloy steel, these potent elements work in concert with thermomechanical processing (controlled rolling) to yield a strong product with very fine grain size and good low-temperature toughness. At the same concentration in ordinary hot finished products, they may or may not have much effect in raising strength, although they will not lower it.

I once had a major cracking issue on very thick (8") carbon steel in a very high restraint configuration that was PWHT. We never investigated the root cause, but I always suspected two things: stress relief cracking; and that steelmakers 'cheat' by adding these elements to thick heats to help them meet the mechanical minimums.
I'd like a steelmaking insider to comment on my suspicions. Certainly the HSLA are not amenable to PWHT, which is never done on X-grade pipelines, for instance.