Meaning of lower critical temperature 3

[Xeros]

I have a question about NACE MR0175 - 2003 edition.

in accordance with para. 5.2 on NACE MR0175-2003 edition, Overlays applied to carbon and low-alloy steel or to martensitic stainless steels by thermal processes such as welding, silver brazing, or spray metallizing systems are acceptable for use in sour environments, provided the substrate does not exceed the lower critical temperature during application.

In this sentence, what is the meaning of lower critical temperature?

Best regards,

 

[Metalguy]

It's the temperature where steels start to transform to austenite (FCC), typically ~1330 F.

Gold is for the mistress - silver for the maid
Copper for the craftsman cunning in his trade.
"Good!" said the Baron, sitting in his hall
But iron - cold iron is the master of them all.
Rudyard Kipling

 

[metengr]

and....... the reason for not exceeding the lower critical transformation temperature is to avoid re-hardening the steel substrate, which would result in poor corrosion resistance and potential hydrogen cracking at the fusion line.

 

[strider6]

xeros

if you look into the standard, page 6 you'll find the definition of lower critical temperature:

Lower Critical Temperature: The temperature of a ferrous
metal at which austenite begins to form during heating or at
which the transformation of austenite is completed during
cooling.

S.



Corrosion Protection & Corrosion Control

 

[0707]

Go to

http://www.matter.org.uk/steelmatter/metallurgy/7_1_2.html

Best Regards


Luis Marques