Microhardness testing questions
Microhardness testing questions
(OP)
I have been asked to measure the hardness of a 0.005" thick piece of C1050 grade steel. Since surface hardness clearly isn't possible, I mounted a sample and will do microhardness. The specification for this thin steel requires testing by Vickers using load 10kg and is supposed to show results in the range of 560 +/- 30 HV. The problem I'm experiencing is that the microhardness tester I have access to only goes up to a 1kg load. I've checked with some outside labs and they also can only test at 1kg.
My questions:
1. Could I use a lesser load such as 1kg or 500g to carry out the microhardness testing and still expect to receive similar results as if I used 10kg?
2. If not why and how could I get accurate hardness readings if using a 10kg load is not possible?
3. Could I simply get results first by Knoop and then convert to Vickers? It seems this may be the best option.
Thanks in advance for the advice. It is always most appreciated.
My questions:
1. Could I use a lesser load such as 1kg or 500g to carry out the microhardness testing and still expect to receive similar results as if I used 10kg?
2. If not why and how could I get accurate hardness readings if using a 10kg load is not possible?
3. Could I simply get results first by Knoop and then convert to Vickers? It seems this may be the best option.
Thanks in advance for the advice. It is always most appreciated.





RE: Microhardness testing questions
You are correct, probably the best option would be a Knoop test, report the KHN and report what the corresponding 10kg vickers result would be when converted per ASTM E140.
rp
RE: Microhardness testing questions
RE: Microhardness testing questions
I'll bet that they were doing 10kg VHN on a flat sample.
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Plymouth Tube
RE: Microhardness testing questions
ASTM E 384 requires the indent center-to-edge distance to be a minimum of 2.5 * diagonal. Using 530 HV, you could use 200 gf and meet the requirement.
It is possible that the hardness of your material is not constant from 200 gf to 10 kgf. The same is true for a low-force Knoop test.
RE: Microhardness testing questions
With thin materials such as yours the thermal history can cause variation due to grain size. We used small diameter 1095 wire and the grain size was across the scale where as the calibration block was very fine grain.
Things to ponder.
One of our uses for 1095 wire allowed us the use bending test to insure that in operation was within the elastic limit of the material.
On wires used for shear pins and other small pats we always used a first temper that produced a hardness higher than we needed. After testing we would draw the material down into the desired range.
You might be able to use a small anvil and stack two pieces to check the hardness.
Can your instrument do scratch hardness?
RE: Microhardness testing questions
Unclesyd,
I don't believe it's necessary for an absolute value so I will just provide the comparison.
Thanks to everyone for the input.