hardness measurement recommended on 9.5mm or thicker section -astm A276

[fhadzafar]

To evaluate the response to heat treatment, ASTM A276 recommends to measure hardness on samples with a minimum section of 9.5 mm. As hardness can be measured on lower section thickness reliably as well, then why section thickness is restricted to a minimum of 9.5mm by specification?

 

[MagBen]

9.5mm is for cooling rate (quench), not a limit size for hardness measurement.

 

[fhadzafar]

MagBen, please see, that legend (A) is marked with the column "type" and the note with legend is :

[highlight #EDD400](A) Samples for testing shall be in the form of a section not exceeding 3⁄8 in. (9.50
mm) in thickness[/highlight].

I've ASTM A276-04 available with me.

 

[mrfailure]

So this is actually the opposite of what you said: maximum section thickness is to be 3/8", not minimum. This is probably to ensure uniform HT properties for tested 400-series martensitic steels under Rockwell C surface testing.

 

[fhadzafar]

sorry for that, all readers; u r right mrfailure.
Hardness is a surface property then y section thickness should be limited to ensure uniform hardness (as its the only property given in this table). seconldy, martensitic steels have good hardenability as well. So they are expected to demonstrate a fairly uniform hardness throughout the section thickness. The upper limit on thickness might have something to do with this hardenability, that is expected of this alloy family..