4140 as spring steel?

[brashear]

I need a steel to withstand 670MPa of cyclic loading stress (spring component for experiment, maybe 500 cycles). I cannot change the geometry of my part to achieve lower stress. I'm looking at 41xx chro-moly as a possiblity, but I think it does not like to be repeatedly bent so close to its yield. Is chro-moly a bad choice for a spring?

5160 is another option, but quenched and tempered only has 700MPa yield strength.

Any other candidates? Thanks.

 

[brashear]

I forgot to mention that that stress cycle varies from 670MPa to ~0MPa (amplitude 335MPa).

 

[unclesyd]

Come back with the type of spring and dimensions along with the environment it will see.

Though sometimes used the 41xx series isn't considered a good spring material.

 

[brashear]

I'm not sure how the dimensions of it effect the choice of material.

It's a cantilevered beam that acts as a spring when loaded at the end. It's used in an experiment as a variable-constant spring. By moving the support, the effective length of the beam is changed, and the spring constant is changed.

Basically I have to achieve a deflection of 300mm at a length of 1m without it breaking. Any material and any dimension works. 670MPa is just the stress I got with the modulus for steel

It's a laboratory environment inside a building.

could 7075 aluminum work? I get a max stress of 400MPa, compared to its yield of 460MPa. Again, I'm only going to use it less than 500 cycles varying between 400MPa and 0.

 

[CoryPad]

4140 quenched and tempered to an ultimate strength of ~ 1000 MPa should not have a problem providing 500 cycles of 0 MPa to 670 MPa. It isn't an ideal spring material, but it should work for this application.

 

[BrainFailure]

Brashear:

How are you calculating your applied stress? If you are using a spring hand book then you are getting shear stress. Material properies are given in tensile stress. To convert from tensile to shear multiply by 0.58.

7075 will definately not work. At the max stress you are exceeding the ultimate strength.

If your wire diameter is less then about 3mm then just use plain music wire (ASTM A228). You will save a lot of money. Music wire is typically the same as 1080 steel that is work hardened. MatWeb lists the tensile strength as 1590-2750 Mpa.

Juvinal recomends estimating the 1000 cycles strength as 0.9 times the Ultimate strength.

 

[BrainFailure]

Oops. Sorry I thought you were talking about a helical spring.

Try going to McMaster.com and type in "Blue Spring Steel" in the search field. It will give you a lot of choices for 1095 springs steel (UTS = 1215 Mpa).