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Hardness conversion - Austenitic vs all other steels

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dgallup

Automotive
May 9, 2003
4,712
I was just reading ASTM E140 Standard Hardness Conversion Tables for Metals. Table 2 gives conversions for non-austenitic steels (Rockwell B hardness range) and Table 5 gives conversions for austenitic stainless steel also in the Rockwell B range. The differences are not huge but significant:

HRB 100 = 240 Brinell non austenitic
HRB 100 = 253 Brinell austenitic

Not being a metallurgist, I was wondering what the reason is for the difference? Is the austenitic stainless steel work hardening more in the Brinell test thus giving a higher reading?

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
 
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Your guess is right. Austenitic stainless steel can exhibit more work hardening tendencies, and also the load applied is 3000kgs ,using a 10mm ball indenter for Brinell hardness.

 
The different hardness tests, even though you are using a ball indenter for both HRB and HBW, have differences in how they are performed, so you get differing results. In general, non-austenitic steels have lower work hardening rates that are different from austenitic steels, but differences in the elastic modulus, as well as other differences in how the tests are performed will also contribute the observed differences.

Remember, at best, the E140 conversions are an "estimate" of what the hardness would be if tested on another scale. The different groupings (carbon/low-alloy, austenitic, non-ferrous) are attempts at improving the estimate, but that is all it is, an attempt to obtain a better estimate. If you have a Rockwell "B" reading, but need to know the hardness in Brinell, your best bet is to perform the Brinell test.

rp
 
redpicker is correct- if you carefully read the operating instructions for some of the modern portable hardness testers, the default calibration from the factory is based on ferritic steel, and any alloy with a different Young's modulus will require recalibration of some of these testers.

"Whom the gods would destroy, they first make mad "
 
Thanks guys. I was unaware until yesterday that there are a different hardness conversions between austenitic and all other steels. It came up because we have a material callout for on a component drawing for 303 with a hardness of 100 max Rockwell B. Our supplier said his supplier was quoting 253 max Brinell hardness. Using the standard steel conversion chart this material looked like it could be above our spec. Digging a little I found ASTM E140 with the austenitic conversion chart. I realize these thing are approximate but we are just talking about the upper limits of specs on an order sheet, the material will be checked when it comes in and in all likelihood will be quite a few points under the limit.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
 
We have fought over this for years.
Now when we have to do a hardness in a scale other than the one that is called out in the spec (usually due to the matterial being too thin) we report both the actual reading and our conversion.
Of course we have built our own conversions as well.


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Plymouth Tube
 
How different is the Young's modulus between austenitic and ferritic steel with comparable alloying? I feel like I was always taught that they were almost equal, and that the differences were so small that it wouldn't manifest in a macroscopic test like hardness testing?
 
Hardness measurement is never precision, so just use it as a reference or an indicator, not very good for design purpose. for thin gaged material, you could hit the anvil the dents, superficial is better; for very thin material, micro testing (Knoop, Vicker) is more appropriate. however, when the dent scale decreases, the representative could lose. Conversion is a rule of thumbs
 
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