Changing of microstructure after fire 2

[Liuk]

Hello,

Could you give me some advice?

Now I examine structural steel (S235) sample from fired construction.

As I can see there is shperoidisation of perlite and some carbides along grain boundaries. Band structure is disappeared.

Is it really possible this changing after fire (Unfortunately I don't know time, but I think it wasn't too long)?

Thank you in advance.

 

[EdStainless]

There are books (and consultants) that address this subject.
Yes, structural steels can be damaged (microstructure and properties) in a fire.

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P.E. Metallurgy, Plymouth Tube

 

[Liuk]

Thanks a lot!

We have performed only hardness test (due to sample size). Hardness is around 125 HV10. Conversion in Rm (UTS) give acceptable result for steel S235, but as I understand in this case value of Rp0.2 (YS offset 0,2%) would be more significant...

N.B. Could you please give some reference if it is possible?

 

[mrfailure]

I'm not really sure what to say regarding the hardness test since you provided no details. Damage likely extended from the surface beyond visible changes in microstructure. You can get a good feel for this by taking a microhardness survey starting at the surface and also obtaining core microhardness so you can identify the extent of damaged material.

 

[Guest102023]

Agree with EdS, this is a specialized field and the investigation should involve a specialist who is trained to look for visible evidence at the scene as well as metallurgical. What you actually want is a fitness-for-service assessment to determine how much material must be condemned.

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

 

[FBraun]

Hello,

Yes, you can see a microstructural change like that after a exposure of the steel to high temperatures (ie. fire). I suggest you to read this article.

http://www.ommi.co.uk/etd/eccc/advancedcreep/V6i1x.pdf

Good Luck!

 

[Guest102023]

Hardness testing should always be done in concert with in situ metallography.

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