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Microhardness conversion 17-7PH

Microhardness conversion 17-7PH

Microhardness conversion 17-7PH

(OP)
Is there a special conversion for microhardness of 17-7PH to macrohardness that deviates from ASTM E140?  

RE: Microhardness conversion 17-7PH

Yes, but you will need more information.
Why are you trying to convert?
What is the strength level?

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Plymouth Tube

RE: Microhardness conversion 17-7PH

Not sure what the question is asking.   

RE: Microhardness conversion 17-7PH

You can't use generic conversions for steels or austenetic alloys and expect them to work for 17-7PH.

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Plymouth Tube

RE: Microhardness conversion 17-7PH

ASTM E140 Tables 1 and 2 conversions apply to "non-austenitic steels".  Yet 17-7PH is considered a "semi-austenitic" steel.  That does leave the applicability an open question.

 

Aaron Tanzer
www.lehightesting.com

RE: Microhardness conversion 17-7PH

(OP)
Reason for the question is that I have been told that the correlationS in ASTM E140 are not valid for 17-7PH. This is analogous to the situation with uns s31803 which requires a special correlation built by TWI (0.091HV-2.4=HRC). Microhardness is converting to HRC 45-47 by the ASTM E140 table, but the tensile coupon failed to meet minimum UTS of 210ksi. Part was too thin for Rockwell hardness measurements.

Thanks for your help.  

RE: Microhardness conversion 17-7PH

The best you can do is have a reference block of 17-7PH material, preferably in a similar metallurgical condition, on which you can perform both micro- and macrohardness tests.  This won't be 'official' however, so you will need some lawyerproof weasel words to qualify your converted results.  

I am wary of using E140 under the best of conditions, and always insert such verbiage.   

RE: Microhardness conversion 17-7PH

Kev, have you tried using superficial Rockwell?
We have been known to generate our own unofficial conversions in house.
However missing UTS is another issue.
How low were you?
this is RH950 right? are you sure that the cooling was done right? Fast enough, cold enough, long enough?

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Plymouth Tube

RE: Microhardness conversion 17-7PH

(OP)
Ed,

The parts are too thin for superficial (4mils). We got 206ksi UTS.
Yes RH 950. We followed the spec procedure and refrigerated for the prescribed time. Tensile was subsize, which might have been the problem. Coupon was 4X1. I requested an 8 X 1. Yeah, thought about doing an inhouse correlation.  I just wish I could do it for these parts. I am not sure how much affect the chemistry will have on that correlation. The correlation might deviate considerably from the correlation from heat to heat given the same heat treatment. I'll probably build one, but it will take a few different heats of material to see whether I can get a consistent correlation.

thanks.  

RE: Microhardness conversion 17-7PH

Just throwing this out, but with parts so thin, perhaps the furnace overshot slightly on heating and lowered the UTS?

rp

RE: Microhardness conversion 17-7PH

kevlar49,

When you say coupon was 4x1, do you mean that a rectangular section was tension tested, and not a standard tensile specimen (dogbone)?  The standard subsize section in ASTM E8 allows for a 4 inch overall length, width of the reduced section equal to 0.25 inch, and gage length equal to 1 inch.

RE: Microhardness conversion 17-7PH

(OP)
tvp,

I meant raw stock dimensions. Tested a dogbone, but the blank it was cut from was 4X1.  

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