Makio

Overused car springs from 80 or 90's Not tempered  here are other one more severe line in whole blade length but it's new steel 65mn disk for agro machine

This is harrow disk new not used 65 MN steel but look

Yes hardened it was from leaf springs 

Hardened of leaf springs in salty water cause olil didn't work

3 days in rust acid removal I believe fosforic and this is happening on 4 blades some are broken in half but before acid bath nothing to be seen xxx???

So guys this is my sparks of leaf springs from Yugoslavian car named zastava 101 so your opinion on sparks test about steel type?