the load (roughly) is ~700 MPa (difference of the expansion coefficients X the change of temperature during a shot X Young modulus) plus the pre-load: these are tie bars across 2D CFC tiles
we cannot change the material now: this is a large experimental device and the rods already in are 100s, no plan of touching all these tiles
however we can change the shot characteristics so that the energy dumped on these tiles is less - actually so far we limited it to keep the temperature below 700C, but under new "management" I've been pushed into investigate their use under higher heat loads
Looking at what data I have says that 718 is not suitable for the temperature and stress you state. As you get above 760°C the physical properties of 718 fall off rapidly. I have two stress to rupture curves, though they are a little different, both indicate that your required stress levels are too high.
I checked with two of my high temperature users and both said your intended use is a little too high for the material.
Special Metals, the producer of Inconel 718, has a great deal of technical data available for their website. Use the following link for more information:
Looking at heat treating/softening an Inconel 718 part down to HRC 32. Still developping a procedure, will involve some machining as well so I am thinking about heat treating then machining then age hardening?
Special Metals has a great deal of technical information available on their website, including a 33 page document on Machining. Use the following links for more information:
Davidgr;
Are you looking to have a final hardness of 32 HRc after machining and subsequent solution annealing/aging heat treatment of Inconel 718?
The link provided by TVP provides various options regarding heat treatment of Inconel 718. The heat treatment options depend on end-use;
for example the lower (1700-1850 deg F) solution annealing temperature/aging will provide the highest rupture strength, tensile strength and yield strength.
the higher (1900-1950 deg F) solution treatment temperature/aging will result in lower tensile and yield strength but will have increased ductility and low temperature tensile strength.
There is a third heat treatment that follows NACE MR0175 guidelines for oil field applications. The hardness range for the solution annealed/aged Inconel 718 is between 30-40 HRc.
yes looking for final hardness around 32 HRC for end use after machining. Ive taken a look at the phase diagram but am wandering if all machining should be done in one shot after heat treating before age hardening or whether to machine in 2 stages going back to heat treating, going from 1/2 inch to 1/4 inch thick, need to account for potential notch sensitivity and control distortion.
