Antimony in heat resistant steel castings

[Martinos]

I want to ask you for your opinions regarding antimony influence to heat resistant steel castings. We found antimony content from 0.05 % to 0.1 % (in extremely cases) in two our materials (1 austenitic, 1 ferritic). Fero-niobium (columbium) is suspected as a source (investigation is still in progress).

How detrimental could be effect of antimony up-to 0.1 % to this kind of steels?

In these two steels we have problems with tensile strength, yield strength and elongation (at 20 deg. C) as well.

 

[JackMats]

What is the service and how are your mechanical/corrosion tests?

If any problems were to occur I would envisage this would be with the ferritic due to embrittlement and subsequent cracking. What grades are they?

 

[Martinos]

They are vane rings or discs in turbocharger assemblies. Corrosion test were not carried out.

Mechanical properties of ferritic casting: Rm 290 MPa (shall be 450 MPa), Rp0,2 unmeasurable (shall be 400 MPa). Elongation unmeasurable (shall be 5 %). The fracture was very brittle.

Grades are special, ferritic is 1.4740 + W + Nb, austenitic is chromium-manganese heat resistant steel.

 

[metengr]

Antimony is a bad element when it comes to steels. It will segregate at grain boundaries at elevated temperature and cause embrittlement.

 

[arunmrao]

How was the melt charge prepared? Any suspect scrap or metal? Your suspicion of Ferro Niobium to be containing Antimony,may be correct.

But, I wonder then the content of Antimony in Ferro Niobium for you to record 0.05-0.1%. As metengr states, I agree, Antimony is not a friendly element.


"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[winstonsk]

Can you describe the fracture surface? Did it look shiny? Did it look dull? Did it sparkle in the light? Was there any necking whatsoever?

Do you have a lab with an SEM? If you can determine that the fracture was intergranular, then that would support Sb segregation to grain boundaries.

 

[EdStainless]

Did you conduct long term aging at high temp before you did the corrosion test?
I suspect that hot properties, and long term properties will both suffer.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Martinos]

@metengr, definitely ferro-niobium, because antimony content is correlating with niobium content... spectral lines were checked by specialist, it is not an influence of niobium spectrum, but real antimony content... it looks like we have antimony content higher for a while in all our alloys which are alloyed with ferro-niobium (firstly the measured antimony content 0.05 % max. was considered as a measurement error)...

@winstonsk: fracture brittle, shiny, sparkle in the light, no necking, SEM in external lab can be carried out for information, but after investigation of antimony sources and their rejection

@ed: no aging and corrosions tests, they are not required by customer standard or customer is doing it by himself

Anyway, this is big issue. As all of you wrote it looks like there will be a lot of troubles during service in VTG.

 

[WKTaylor]

Is Your heat of steel produce by a known/reputable vendor... or was it produced by a lesser-known vendor... or perhaps imported from a third-world source... or a less reliable Chinese source?

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[gruntguru]

Ouch. It sounds like you have sent some finished product into the market? I think a recall would be less expensive than the potential damage - financial and reputation.

je suis charlie