Investment cast 17-4 HT'd to double H1150 1

[imswc19]

My customer references ASTM A747 Gr. CB7Cu-1 in their material spec. Parts are required to be HT'd to the dbl H1150 condition. I accompany each lot of castings with a set of 4 test pins (3 1/2" long, threaded on both ends...).

I've been having a problem lately getting the yield strength to pass. My minimum req'ts are as follows:
UT - 125K, Y - 100K; Elong 15%, RA 35%. My results for yield has been in the 90-98K range and tensiles sometimes hover near the minimums as well.

Castings and pins are first solution annealed at 1900F as per the spec. We've even experimented with the H1150 M alternative, which is allowed by our customer. This is where the first age is at 1400F for 2 hours followed by an 1150F for 4.

Any ideas or new resources would be helpful.

 

[israelkk]

According to ASTM 747 Gr. CB7Cu-1 the Yield Strength at 0.2 % Offset, is 97ksi min, Ultimate 125ksi and Elongation 10%. No requirement for RA. Therefore, your minimum requirements should be as the ASTM specify and nothing no more and no less. However, the yield that you receive is not to the spec.

The ASTM specifies the elongation with reference to 2" long tensile test specimen. The tensile test specimens and tensile tests should be according to ASTM A 370. I would make sure that the heat treating furnaces are accurate and calibrated and that the tensile test specimens are exactly as they should according to ASTM A 370. Also check the testing machine for accuracy and calibration.

 

[EdStainless]

Are the castings much different in size from the pins? Are they heat treated together?
It may be that the pins heat much faster and therefore spend more time at temp than the load.

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Plymouth Tube

 

[imswc19]

Israelkk - Thanks for the quick response. First let me say again that they "Reference" the ASTM spec for the mechanical req'ts. I will approach them as to where the 100K min yield came from as well as the elongation.

I didn't want to bore you with the details of the test pins. The actual area that is first machined and then pulled and analyzed IS per the A370 spec. My HT'er is ISO and his equipment is in spec. My lab is independent and are ISO and NADCAP and I'm certain their equipment is up to snuff.


Ed - the castings have a max cross section thickness of about 3/4" at the core. The castings weigh about 2 lbs and the pins about a tenth of a pound ea.

They are heat treated together.

 

[GRoberts]

You could try holding the temperature (1150F) at the lower end of your temperature tolerance. With the small amount you are low, it could help a bit.