Indentation hardness correlation to yield and tensile strength of mild steel 2

[Ingenuity]

I understand that indentation hardness testing (using small hand-held equipment) in the field has a linear correlation to tensile strength.

For steel sections typically used in buildings and bridges, for example, say a wide flange mild steel section, is there a comparison table available between hardness values (Rockwell, Vickers, Brinell etc) to YIELD and TENSILE strengths?

If so, it is sufficiently accurate to determine if the steel is say grade 36 ksi or grade 50 ksi without having to take a field sample and lab test?

 

[Nereth1]

Almost every hardness comparison chart I've seen on google has the comparison to UTS listed there. I have never seen a direct comparison to yield though, but if you know roughly what you are looking at you can probably make an educated guess.

In terms of reliability - there is error in the hardness test, then there is error in the conversion to UTS, and further error in estimating yield off that. Whether or not if it is sufficiently accurate depends I think on the criticality of your application. Personally I have used scratch tests to tell the difference between our Australian grade 250 and 350 steels for first passes in non-critical situations.

 

[metengr]

I have seen some correlation graphs between hardness and yield strength. The problem is the actual yield strength can vary in steel depending on plane stress versus plane strain conditions, so that is the reason for a soft comparison. You would be better off having an estimated tensile strength from hardness and using a knock down factor of 0.75 for yield strength.

 

[mrfailure]

I've seen so many rules of thumb relating hardness to yield strength; there is too wide a variance for me to feel comfortable using any of them. As for UTS, the approximation is published in ASTM A370 and is used in published charts referred to above for ferritic steels.

 

[Ingenuity]

Thank you all for the detailed replies.

 

[Nereth1]

Mrfailure,

Saying that the hardness to UTS comparison works specifically for ferritic steels is an interesting distinction. Let me preface this by saying I'm not a metallurgist, but does that mean it doesn't work on steels with significant non-ferrite fractions? In that case, why is the comparison posted up to 40, 50, 60+ Rockwell C? I would think that steels of those harnesses would have very little ferrite involved?

Thanks

 

[mrfailure]

What the comparison really means is that you cannot apply it to austenitic (generally 300-series) stainless steels. The term ferritic is not referring to ferrite content, but the fact the steel is ferro-magnetic.

 

[CoryPad]

Excellent information above. In addition to ASTM A370, ISO 18265 has tensile strength vs. hardness for a variety of steels. SAE J413 shows yield:tensile ratio for steels from low to high tensile strength. Some rules of thumb for the ratio:

0.6 for annealed or hot wrought material
0.8 for cold worked material
0.8 for martensitic material < 35 HRC, < 1000 MPa tensile strength
0.9 for martensitic material > 35 HRC, > 1000 MPa tensile strength