grade 60 bars..markings

huangyhg

grade 60 bars..markings
how can you tell if rebars are grade 60 or not.  some have markings of "6" on them, but others do not, yet their mill certificates indicate grade 60.  (of course i could be shown certs for grade 60 bars used elsewhere..)
one contractor insists that grade 40 bars break when bending, is there anything to this?   
a pretty good explanation of rebar identification marks is at:
pt999,
reinforcing steel is marked this way.
there is two ways that bars are marked, one way is: when looking at the marks the top letter is the symbol for the producing mill (letter or symbol) the next is the bar size, a number such as six, meaning #6 bar, the next letter is the type of steel, the bar strength is indicated by a grade line (raised) parralel to the bar, no line means grade 40, one line means grade 60, and two lines means grade 75.
sometimes bars are noted right on the bar what grade it is such as 60, or 75, grade 40 would have no mark.
type of steel (third designation, below bar size):
s = billet meeting supplemental requirements si (a 615)
n = new billet (a 615)
r = for rail meeting astm a 617. grade 60 bend test requirement (a 616) [per aci 318-99]
a =  axle (a 617)
w = low alloy (a 706)