H11 Tool Steel vs Inconel 718

[flash3780]

A general curiosity, really, but corrosion resistance aside, what are some reasons one may choose to make a component out of Inco 718 over H11 tool steel when looking for a high-strength alloy for service below 750F? Machinability? Cost? Availability? Weldability? Fatigue resistance?

I was looking at a design for a satellite component the other day made from Inco 718, and I was thinking to myself that there are probably less expensive material choices out there that would perform better (esp. absent of air). I'm pretty sure the operating temperature was well below 750F, which is where I'd usually start thinking about a high-temperature alloy. Comments?

 

[arunmrao]

Inconel 718, is a NiCr precipitation hardenable alloy with high creep strength upto 700C.

H11 is a straight hot working tool steel,there can be no similarity in my opinion

 

[flash3780]

I understand the differences in the composition, I was leaning more towards suitability for moderate-temperature, high strength applications where corrosion is not a concern.

It seems as though H11 (or other high-strength steels) would be a better material choice than high-strength, nickel-based alloys in these sort of situations. Comments?

 

[metengr]

The major difference will be elevated temperature strength properties at intermediate temperature service between the two alloys.

You can do this on your own - Google the two materials and look for elevated temperature tensile properties.

 

[swall]

IN-718 is non magnetic, if that is a consideration in your application.

 

[TVP]

Fracture toughness: Alloy 718 will have significantly higher fracture toughness for a given yield/tensile strengh. So, if it is a static-type component, without requirements for high temperature strength, fracture toughness, corrosion resistance, or magnetic properties, then a steel alloy would be cheaper, easier to fabricate, more readily obtainable, and have better weldability. For what it's worth, steel grades like 4340 and 300M are more commonly used than the tool steel grade H11 for high-strength aerospace components.

 

[TemperedMartensite]

There are lots of application below 750F where superalloys come into play. 718 has a nice combination of strength, toughness, corrosion resistance, and low magnetic permeability.

If I had to pick one my guess is that it is the magnetic permeability which made it required for a satelite component. This is why 718 is used in other position sensitive devices (such as drill collars). The alternative may not have been H11 but a titanium alloy.

As a rule of thumb - no one designs in a superalloy unless they absolutely have no other option.