[MW:26390] Differnce between A350 LF1 and LF2

Dear Experts,

Good Day!!

I have query regarding SA350 LF1 and LF2, as you can compare the chemical composition of two grades, there are no difference between two grades;

but you can see the major difference between impact test temperature, what is the reason for this major difference as in SA-350 there is no major heat treatment requirements.

also what is the reason for difference between impact test temperature of LF2 Class 1 and class 2?

thanks indeed if you share your valuable ideas.

Regards,

Himan Nikdin