Conversion from Microhardness to Hardness 3

[stanislasdz]

How to convert microhardness 0.3 kg Vickers to standard Brinell hardness !!

Thanks in advance

 

[dbooker630]

You will need a copy of ASTM E140 for the conversion charts and equations. Some of the conversions are dependent on material being tested. There are also several precautions to consider based on the condition of the material.

If you know the material and HV value, perhaps one of us can convert it for you if you do not have the standard.

 

[TVP]

ISO 18265 is the international equivalent of ASTM E 140. Keep in mind that converting microhardness to macrohardness can be difficult if the microstructure is not homogeneous on the microscale. Indenting on a hard area of martensite or bainite with 0.3 kgf Vickers will result in high hardness, but if this is a multiphase microstructure (say ferrite + pearlite + bainite), then the macrohardness would be much lower due to the combination of the hardness from the different phases.

 

[weldtek]

TVP raises a very good point. To say for example, that a reading of 248 HV-10 is equivalent to 237 Brinnel is somewhat misleading, although if you look in a reference book that is in fact what you'll likely see. As TVP points out, because the Brinnel method makes a larger impression it averages harder and softer regions.
I think recognition of this limitation is reflected in the fact that while many specs limit hardness of welds and HAZ's in P1 materials to 200 Brinnel, they typically allow a maximum of 248 HV-10.

 

[DVWE]

Other things to consider, the titles of the tables in E 140.

"Approximate" key word!

 

[EdStainless]

If you convert this make sure that you note that it is a conversion. I have modified our practices to require always reporting in the native units, convert if you like but you have to report the original.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[dhan12]

Dear Friend,
Please keep in mind that this conversion is only applicable for Steel material as practicle exp. of my.
Drawing requirement should be strictly Microhardness Testing not the BHN. because it will hamper your quality requirement.

 

[AidanMc]

I have a related question about this and figured I could add it to this thread instead of starting my own.

In ASTM E140, there are both tables and conversion equations. We have an issue with our microhardness tester and I was curious if it is because of round off error. For example, 708HV is converted to 60.5HRC by the tester which would round up to 61. When converting by the tables in E140 708HV should be 60.478HRC, which rounds down to 60HRC... on the other hand, the equations would give 60.575HRC and that would clearly round up to 61HRC.

If I had a spec where the limit was 60HRC, would the 708HV pass that spec?

Aidan McAllister
Metallurgical Engineer
Automotive Enthusiast

 

[redpicker]

AidanMc,
Technically, no, if the spec limit was 60HRC, you would be obliged to test the material with a Rockwell 'C' tester to determine conformance. Any conversion is an approximation, so if you tested the material in HV to meet a requriement stated in HRC, at best you could say you approxiamtely meet the requirement (or approxiamtely do not meet the requirement). If all you are trying to do is approximately meet the requirement, then does it really matter if your result is 60 or 61? Both numbers approximately meet the requirement.

rp

 

[israelkk]

redpicker

Well said, I gave you a star.

 

[AidanMc]

As I'm still new to this whole working world thing, I'm curious how that works on small parts then? Does that mean that if I have a part small enough to call for Vickers or even a Superficial Rockwell test, the customer should have supplied the requirement in those units rather than in HRC?

Aidan McAllister
Metallurgical Engineer
Automotive Enthusiast

 

[dbooker630]

AidanMc,

There are thickness and process requirements to consider when specifying a hardness scale or allowable conversion. For example, using your 60HRC number, the stock should be at least .030" thick to use a direct HRC test at that expected hardness. But if your .030" stock was not through hardened but carbonitrided instead, a different hardness scale like an HR15N or file hardness would be more appropriate.

 

[redpicker]

I'm curious how that works on small parts then? Does that mean that if I have a part small enough to call for Vickers or even a Superficial Rockwell test, the customer should have supplied the requirement in those units rather than in HRC?

Technically, yes, the customer should specify the requirement in a manner that is actually possible to determine conformance. Perhaps missing the mark a little, but specifying hardness of a 0.020" thick section in Rockwell 'C' is kind of like specifying a length in Watts. Of course, customers are always right and if they want you to do a Vickers test to verify their 0.020" section meets the 60 HRC requirement, then that is what you do. As mentioned upthread, however, you should report the results in the hardness scale you performed the test in and say "converted to XX HRC in accordance with ASTM E140".

rp

 

[AidanMc]

Thanks everyone, that helps me out some. Yes we do make sure to show both the converted hardness as well as the actual hardness as read in Vickers.

Aidan McAllister
Metallurgical Engineer
Automotive Enthusiast