I would specify the heat number as a reference.  That relates to the metallurgy which affects the impact properties.

Sorry, but your question is confusing. I believe what you are asking is what is the number of impact test samples that would represent a heat or lot?

If this is the question, you need to review the applicable product specification requirements or engineering specification for the product form.

Hi, metengr.
Our client request to us additional impact test.
But, The mill test report is described as follows,

for example)
 thickness Heat No.  Lot No.
    25mm      A         1
    25mm      A         2
    20mm      B         3
    30mm      B         4

Which one is represent for the impact testing? if the impact test specimen shall be prepare per each heat#, only two sents(for A,B)are needed.

Ok, maybe this might help. The term "lot" that is used for impact testing normally refers to x-number of pieces that are made from the same heat of material.

So, what you have from the mill test report is one impact test from each lot of material (lot 1 and lot 2) that were made from the same heat #A. The number of pieces in a lot can vary, and only one impact test specimen may or may not be representative.