718 Impact Properties 2

[kingsley47]

Is there anything that can be done to help improve the low temperature impact properties of Inconel 718? By low temperature I am talking about -150 F.

 

[TVP]

The fracture toughness of Alloy 718 depends significantly upon the thermomechanical process history. Can you provide details? Weldment, spring, fastener, shaft, etc.? Heat treat process variables?

 

[kingsley47]

Heat Treatment:
Solution Anneal @ 1870-1925 F for 2 hours

Multiple Choices for Ageing Procedure

1)1400F +/- 15F for 10 hours, then furnace cool @ 100F/hr to 1200F +/- 15F for 18 hours

2)1400-1450F +/-15f for 6-8 hours followed by an optional secondary precipitation hardening treatment @1325-1375F for 2-4 hours

The 718 will be used to make hex head bolts @ 1.75" which will be used as a component for a subsea blowout preventer on an oil well.

 

[metengr]

The information below is from Special Metals, which has impact energy data at -75 deg F for various Inconel alloy 718 heat treatments.

If I were you, I would contact Special Metals directly. They should have even lower temperature impact data. I have personally worked with several individuals from Special Metals on ASME B&PV Code committee, and they are very knowledgeable about their product line.

http://www.specialmetals.com/documents/Inconel alloy 718.pdf

 

[SJones]

Will you need -150 deg F subsea on an oil well? API 6A718 starts at -75 deg F but, if it's not necessary to go lower, why try?

Steve Jones
Materials & Corrosion Engineer

http://www.oilandgaspeople.com/cv/11499664

http://www.linkedin.com/pub/8/83b/b04

 

[TVP]

I agree with metengr, you definitely need to discuss this with Special Metals or Cartech (another producer of Alloy 718). The raw material production route needs to be specified, in addition to the part production method and the final heat treatment. If you are actually fabricating the bolts, you need to determine several things, including (1) will the heads be upset forged, (2) will the underhead transition be fillet rolled, and (3) will the threads be rolled before or after heat treatment. Are you designing to a strength level in excess of 160 ksi (1100 MPa)? Will these bolts be primarily loaded in shear or tension, or both (static tension, dynamic shear)?

 

[kingsley47]

-75 F is the actual testing temperature. I'm not sure where I pulled -150 from (too much L7 bolting).

The melting practice could be either AOD or VOD followed by VAR or ESR.

We will be forging the heads and machining the underhead fillet. The threads will be rolled after the forged blanks have been solution annealled. The UTS has a minimum requirement of 175 ksi and as far as the loading goes, I do not know whether the bolts will be loaded in tension or shear.

Based on the information I was able to obtain from the special metals pdf I feel confident that I will be able to meet the customers required mechanicals. Thank you all for your help.

 

[TemperedMartensite]

I would check with ATI Allvac - they have a continuous rolling mill that can achieve very fine microstructures - pluse they have a grade for the oil patch.

 

[TemperedMartensite]

By the way - API 6A 718 frowns against all melt methods other than VIM/VAR - be prepared to answer tough questions if you choose even VIM/ESR.