Hardness - Print Callout
Hardness - Print Callout
(OP)
Hello,
I have a quick question. We currently purchase a forging from an outside vendor. Our forging print calls out "Hardness 50-60 HRC", during a PPAP for our customer we discovered that the core hardness on several forgings was 61-63 HRC but the surface hardness was within the print specification. Our Supplier responded to the corrective action that by only specifying "Hardness" they were only obligated to measure surface hardness. My feeling on it is that if it doesn't specify core, surface, etc. then the callout should be applied to the entire part. Am I wrong in this?
I have a quick question. We currently purchase a forging from an outside vendor. Our forging print calls out "Hardness 50-60 HRC", during a PPAP for our customer we discovered that the core hardness on several forgings was 61-63 HRC but the surface hardness was within the print specification. Our Supplier responded to the corrective action that by only specifying "Hardness" they were only obligated to measure surface hardness. My feeling on it is that if it doesn't specify core, surface, etc. then the callout should be applied to the entire part. Am I wrong in this?
RE: Hardness - Print Callout
RE: Hardness - Print Callout
This implies that they must destroy a part (and charge you for it).
On the other hand a difference of a 2 points HRC isn't much.
Have you pulled tensiles or done impacts?
Are the properties what you wanted?
Do you have notes about limits of decarb?
This sounds very loose on you end.
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P.E. Metallurgy, consulting work welcomed
RE: Hardness - Print Callout
It sounds like your print didn't adequately describe the part you need, so you received something slightly different than your expectations.
RE: Hardness - Print Callout
RE: Hardness - Print Callout
RE: Hardness - Print Callout
A finished part (with associated core hardness spec), or a forging (with ill-defined hardness)?
RE: Hardness - Print Callout
RE: Hardness - Print Callout
RE: Hardness - Print Callout
RE: Hardness - Print Callout
In my copy they have instructions on added material for testing, FIG. 1
RE: Hardness - Print Callout
my interpretation of what has happened:
- part was forged
- part was (through) hardened
- part was annealed/tempered to specs at surface
the annealing must have been too short to soften the core properly. (is there another explanation?)
also:
- hrc is a crude measurement. the last calibration puck i saw had +/- 2 hrc on it (if i recall correctly).
- depending on the application, alloy and it thermo-mechanical history the part might ideed be useless. at hrc 60+ most materials get pretty fragile. that thing might even crack on you spontaniously.
- most commonly for wear protecton the part is in the hrc 40ies and surface hardened.
- for larger parts its impossible to achive identical properties in core and at surface because of solidification/grain structure mechanisms. the core is weaker. (thats why high end parts are machined from "solid" rather than forged.)
- be very cautious to extrapolate hardness to other mechanical properties (like uts or wear attributes).
- has the testing been done professionaly (surface prepped to specs) or did somebody just cut it appart and stick it in the machine?