Sachin,
Here is my interpretation FYI:
Martensitic stainless steel SA-240 S41500 - P No. 6 Grp 4 - Minimum Specified elongation 15%.
Matching filler meatal SFA-5.4 E410NiMo-15 - F No. 4 - Minimum Specified elongation 15%.
In Figure QW-466.1, you will look at "Materials with 3% to less than 20% elongation". The max. dimension of A, B, C and D in Figure QW466.1 are calculated based on 3% elongation.
In accordance with Note (1), the purpose of this bend test is to impose at least 15% "outer fiber elongation" on your specimens.
15=100x10mm/(A+10mm), then we get A=57mm.
That is to say, you need A=57mm max. to make at least 15% "outer fiber elongation".
Hope this helps out.
Jovi