Frequently Asked Questions

Q: How long do hardness blocks last?

A: Some blocks can last several years, though blocks can self-destruct in a short time from heavy use. Generally, soft blocks and high force testing can destroy a block in a matter of a month or so, especially if daily verification is required.

It is possible that a block become rendered useless due to changes in ASTM and ISO requirements. Such as the case of pre-NIST traceable HRC in 2000 and pre-E18-07a blocks calibrated without verified indenters.

Q: I asked for a 300 HV 0.5 micro-indentation test block and they sent me a 370 HV 0.5. I needed it to check a special part that I was manufacturing. Why can’t I get the exact value that I want?

A: Test blocks are used to verify the tester calibration, not your part. While it is desirable to get a block as close to your part hardness, it is not critical. Having said that, block are chosen from various heat treat lots to match the best possible. Also, different force and indenter combinations can affect the outcome of the block value you receive.

It is suggested that you look at the recommended hardness levels listed in ASTM and ISO documents.

Q: I am not sure what hardness scale to use. How can I find out?

A: A good place to start is part specifications within your company or your customer. Sometimes part specifications are listed with a common scale such as HRC, even though that scale can not be done on your part. This could be because the part is too thin or has a case hardness. ASTM and ISO charts give guidance on minimum thickness.

Be careful when using a tester by conversion or that can electronically convert hardness scales. Be sure to see if you are allowed to due that.