A2/D2 Tool steel over-tempered strength data

[ERT]

Hi all,

I am designing metal forming equipment where some machine components needed to have very high tensile strength (and therefore high fatigue strength). The components in question need to mount forming dies into restrictive spaces, so what I need is the highest strength steel that is generally available.

AISI D2 tool steel is my first choice, but I want to over-temper so that the ductility is increased. Ductility is an issue as there is not much room for large fillet radii; plus also I need to tap threads and I do not what brittle threads.

I think that tensile strength is the key performance parameter, rather than shock resistance in this application.

My question is - does anyone know of a good tool steel reference for ultimate tensile strength (or fatigue strength) versus hardness in an over-tempered condition? I would be interested in either A2 or D2, or any other recommendations.

I did manage to find two data points for A2 in "Tool Steels", Roberts, Hamaker, Johnson. They give ultimate tensile strength (UTS) of 269,500 psi and 54HRC if tempered at 1000 F. And for tempering at 1100 F they give: 47HRC; UTS is 232,600 psi; yield strength is 184,000 psi; elongation is 5% and reduction of area is 13.9%.

Of course, I found lots of data for 58+HRC and I found several references for compressive strength but the tensile data for over-tempered condition appears sparse. Therefore, I wonder if the data is actually that simple to chart UTS vs HRC. Can UTS be determined without specifying the exact heat treatment process - single vs double temper; temper time and temperature?

Any comments or references are appreciated.

Regards,

ERT

 

[Goahead]

Why resorting to tool steel if hardness is not a design requirement?
You may find many high strength steels with the properties you require without overtempering.
If your small radius fillets are stressed you can improve their fatigue resistance by shot peening.

http://www.welding-advisers.com/

 

[swall]

Probably premature to make a recommendation without more details about your application, buy here goes anyway. You might consider Aermet 100. It is high strength, has good toughness and fatigue resistance. Not cheap, though.

 

[TVP]

I agree with both of the previous replies-- another grade of steel will be a better choice than A2 or D2 tool steel. Can you provide some additional details on the specifics of this application? A quenched and tempered steel like 4340 or Aermet 100 would be my first choice. If the strength needs to be higher than 4340, maraging steels would be another option.

 

[Maui]

Yes, it is possible to specify the relationship between hardness and ultimate tensile strength without a detailed knowledge of the heat treating parameters used to process the parts in question. For martensitic materials, the general correlation between ultimate tensile strength and hardness can be viewed in the following link:

http://www.crucibleservice.com/eselector/selectortables/selecttables pdf files/HardConvTbls.pdf

Hardness in Rockwell C appears in the left hand column, and the corresponding tensile strength appears in the far right hand column. This chart should be appropriate for hardened A2 and D2 steels.


Maui

 

[ERT]

Hi all,

Thanks for all your input on this.

Yes, I agree that 4340 is a better choice based on what I explained.

Another reason we like A2/D2 is stability during heat treatment.

Regards,

ERT

 

[unclesyd]

I don't believe that you a beat D2 Tool Steel for stability and wear resistance.
We have literally thousands of components with multiple threaded holes that are continuously recycled after service at 600F and cleaning at 900F. The screws are H-11 and they too are reused multiple times with no thread problems. With some processes were routinely use SS White abrasive blasters to clean the threaded holes.
Many of these components are over 40 years old have have been recycled thousands of times.
My Tool Steel Book is on loan and my regular compute is on the fritz, but here is the just of our heat treatment. Air cool from 1850F then tempera at the peak of the secondary hardening range, cryotreat, them temper again at the same temperature. We use several variation on this process depending on the end use.