Hardness value for ASTM 213 316L and ASTM 240 316L

[replica]

Dear all,

I did the hardness measurement on the 316L boiler tube and always found that the average values are higher than 192HB as specified in ASTM 213 316L. The value can be ranging from 213HB to 280HB. Are these values acceptable? Similarly when I did the hardness measurement on the plate ASTM 240 316L, the value is also higher than 217HB as recommended. The hardness value is not specified in ASTM 240 316L for plate material but the information from the manufacturer stated that the value of plate is max of 217HB. I am using Krautkramer Microdur 10 Hardness Tester and wondering why the value is always high. Can the hardness increase during grinding prior to hardness testing? Any idea on why the value is high?. To my knowledge, the as supplied plate can be hot rolled or cold drawn. So could it be work hardened?

Any comment is highly appreciated.

Regards,

 

[metengr]

The higher hardness could indeed be remnant forming strains where the tubes were not supplied in the solution annealed condition before final processing. Seen this before. Regarding plate, similar remnant forming strains could be present resulting in the higher hardness. If you understand replication work, surface grinding will be very superficial and will be removed upon subsequent polishing steps.

 

[replica]

metengr

Thank you very much. So it is possible to have higher hardness when the remaining forming strain does not fully removed during solution annealing or it was not supplied in solution annealed condition. I also experienced high hardness when the microstructure exhibited high amount of slip bands in the austenite grains.

 

[metengr]

Correct. Merry Christmas and Happy New Year.

 

[EdStainless]

Did you test on a curved surface? What correction did you use?
Aren't the requirements in the spec listed in Rockwell B?
Did you do a tensile test?

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P.E. Metallurgy, Plymouth Tube

 

[replica]

EdStainless

No, the surface was ground and polished to flatten it. We did the hardness test prior to in situ replication work and try to relate the hardness and the microstructure. The value of our result is in HV and it was not converted. The requirement in ASTM 213 316L is 192HB or 200HV or 90HRB. We make sure that the surface roughness is less than 30% of the depth of penetration as specified in the procedure. However we anticipate that our uncontact impedence method (UCI) is sensitive to young modulus (E) and the equipment is calibrated to carbon steel. The young modulus for carbon steel is different from austenitic stainless steel so the equipment has to be calibrated using stainless steel. Unfortunately we did not do this because it is very difficult to find the calibration block which is similar/almost to the material to be tested every time we want to do the test. Is this really matter? Is the different huge?

No, we did not do tensile test.

Happy new year to all....

 

[EdStainless]

Yes it matters, 300 series SS will have a modulus that is roughly 5% less than CS.
And yes, it would be good to look into your surface prep, on such soft material it can have a significant impact.
Are SS reference samples really that hard to find?

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P.E. Metallurgy, Plymouth Tube

 

[replica]

EdStainless

I have no idea because we only calibrate our equipment based on carbon steel calibration block. I think SS reference block is not difficult to find compared to other high alloy material. I never try to do this calibration work but will try to do this with the standard SS calibration block. Thank you EdStainless.

 

[metengr]

If you read the owner's manual and have used the Krautkramer Microdur 10 Hardness Tester (which is an excellent and versatile portable hardness) tester, you can adjust for stainless steel material by calibration offset values using steel calibration blocks.

 

[replica]

Thank you metergr....I am not aware of that...