Compressive yield strength of 4140 versus A2 tool steel hardened to RC 55-60

Tensile strength correlates pretty closely with hardness in most steels, so there's not going to be a lot of difference between various materials at equal hardness. Rc55 is about as hard as 4140 gets as quenched in small sections, and it's not generally used without tempering to a lower hardness.

Uconeer is an excellent free units converter with a hardness conversion function that includes hardness to tensile strength.

This is an online converter... Crucible has a lot of good data on tool steels, though finding it on their website is not always easy. Ned Simmons

Hi Ned,

Thanks for your reply.

Will the tensile strength generally be comparable to the compressive yield strength ?

I have a chart showing the tensile strength of 4140 at RC 52.5 at

240,000 PSI and a Tensile "fittted" strength of 230,000 PSI. I'm not sure how this relates to compressive yield strength though.

Do you think the 4140 and A2 would have comparable compressive yield strengths at RC55?

I would like to find a cam material that has a compressive yield strength of at least 260,000 PSI after heat treatment. The cam rotates so slow I think the application could be considered static.

I think I remember reading in Timoshenko's book on the strength of materials that hardened steel can handle Hertz contact stresses of over

450,000 PSI in static applications owing to the fact that at the center of the ellipse of contact, the material is compressed not only in the direction of the force but also in the lateral direction. I don't think it mentioned what type of steel or how hard. I do not presently have a copy of the book.

Thanks aga> > > Hi everyone,

Ned,

I forgot to mention my maximum Hertz contact stress is about 260,000 PSI so I would think the compressive yield strength of the material should be at least this amount or a little higher for safety. However, Timoshenko seemed to be suggesting that this might not be the case, unless I misunderstood what I read.

Also, thanks for the links you gave.

John

John2005 wrote:

Clarification: Timoshenko only suggested this for static applications, not applications with dynamic forces that need to be accounted for.

John

John2005 wrote:

The yield is obviously going to be somewhat less than ultimate tensile, but the spread will be less percentage-wise than at lower hardness.

My graph for 4140 shows a tensile of 260 ksi, and a yield of 235 ksi at RC52.

I think so, but I bet A2 will be tougher at that hardness. Rc55 is at the low end of A2's toughness peak, Rc58-60 may be a better range.

I'm getting that feeling of deja vu all over again. I think I recommended SAE 52100 before and will do so again.

Quoted yield at Rc60-66 is 295ksi

Ned Simmons

There's some interesting test data here on 52100 and a hi-tech (and preumably high-dollar) alternative to 52100...

Ned Simmons

Hi Ned,

Thanks for the additional feedback,

John:

Yes, I did go through this before and decided on A2 hardened to at least 55RC, but my machinist suggested to use 4140, I guess because they feel it machines easier or because it's more readily available or cheaper from a material standpoint.

I could not find much data on the compressive strength of 4140 at RC55, so I posted in hopes I could get a little data for comparison. It was also suggested by crucible to use S5 or S7 Tool steel with A2 as a good second choice. I think I decided on A2 because it had good dimensional stability and seemed to have a compressive yield of over 300,000 PSI at

55RC according to a chart.

At the online hardness conversion link you gave, it calculated the tensile strength of steel at about 303,000 PSI at 55RC. Perhaps the

4140 would work OK and be better from a cost standpoint, but I also feel the A2 would be tougher, and the same would probably apply to S5 , S7, and SAE 52100.

I will also keep the SAE 52100 in mind and will suggest that as an alternative.

Thanks again for your help, both times :-)

Take care and happy holidays.

John

Ned Simm> >

Although Ned seems to know about your application, you may be more successful by explaining what the application is to the rest of us.

than those numbers you've posted. The successful application of various types of tool steels is generally very dependant on the type of conditions and wear mechanisms the part will experience while in use.

Additionally, if this is a stamping application, there may be significantly greater forces working on your part during tryout or in the case of a crash. You should be aware that a 20% increase in material strength is trivial compared to a 1000%+ increase in force in the worst case. Dies are over-built for a reason.

Also, machining is a major concern in tool steels. Certain steels are significantly more difficult/expensive to machine and you should listen closely to your machinist/toolmaker when they explain why they're making recommendations about material choices, especially if you're paying by the hour/cutting tool.

Regards,

Robin