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.
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.
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.
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?
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.
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.
