4340 vs EN24

[FennLane]

I have been looking at the specification for 4340 for some time and the UTS values quoted by most US based suppliers is often quoted at 1800MPa - around 27ksi.

This is much higher than values typically quoted for EN24 (817M40).

The chemistry of the two materials is very similar and I believe that they share a Werkstoff Number 1.6565.

It is difficult to heat treat EN24 to much beyond a W condition of around 1230MPa and still maintain a reasonable Impact Strength (35J).


I keep seeing articles that claim American made steel is much cleaner annd hence better - I could accpet this from a fatigue point of view but where does the strength increase come from?

The cost difference between US produced 4340 and UK produced 817M40 is between 3 and 4 times.

 

[FennLane]

I meant to say 270 ksi - not 27ksi

 

[metengr]

FennLane;
If I understand your post correctly, the real issue is comparing mechanical properties of a known steel chemical composition between different material specifications and making sure you are comparing 'apples to apples'. In this case, since you did not reference a standard specification for the 4340 steel it can be supplied in a fully hardened condition or in a quenched and tempered condition. For proper comparison, heat treatment condition must be specified or known for a steel to provide a suitable strength comparison. You have addressed the fatigue performance differences.

 

[mrfailure]

You should look for the appropriate specifications for the product form you are planning to use the material in. I recommend first using the summary of specifications for 4340 in the Worldwide Guide to Equivalent Irons and Steels p. 694 - 697. This also will give you ideas for other internationally-available equivalent materials.

Aaron Tanzer

http://www.lehightesting.com

 

[FennLane]

I am thinking about using 4340 or 817M40 and am trying to deal with the detail of why manufacturer published data seems to indicate that the 4340 can be heat treated to strength levels which are around 30% higher than this that can be acheived with 817M40 when heat treated in a similar manner.

I am only trying to make drive shafts of around 30mm diameter and know how to heat treat the material we finally select.

We plan to start with a Normalised and tempered material so the starting condition is not relevant to my question.

Looking at the TATA Steel website shows 4340 as having a strength of 1000MPa ie a U condition up to 50mm diameter and this is entirely consistent with 817M40.

Bohler Uddeholm show similar vales to TATA.

Many of the US based websites show values of around 1800MPa and I am trying to learn how they obtain these strength values.

I am surprised to learn that 4340 can be commercially obtained in a fully hardened condition which must make ot relatively difficult to machine.

 

[mrfailure]

FennLane,

Before looking for material, you should assess what the design requirements are for your application. What tensile and yield strengths and hardness, for example, are required by the design. Then you can compile a list of materials whose minimum strength requirements will meet requirements. Make sure to use specification requirements and not "typical" values often reported when considering - i.e. minimum specified strength should exceed your application requirements. Once you have done that, you will be able to choose the most cost-effective steel meeting your requirements.

My references show EN24 and 817M40 are now obsolete alloys. Make sure you really can obtain these materials when considering.

Aaron Tanzer

http://www.lehightesting.com

 

[FennLane]

Thank you for the input.

I have to say that 817M40 is alive and well and still readily available throughout the UK at least, it is still sold as EN24.

EN24 as a designation was renedered obsolete in 1970 when a revised version of BS970 was introduced. I had just left my job as a Metallurgical Technician to start my Undergraduate Degree course.

It amuses me that EN24T and all of the other common steels referred to in the UK by the 'Emergency Numbers' first introduced in WW2 still hold sway and are in day to day use.

I have to say that I am not really looking for help with the design of the components but a reason why 4340 is commonly quoted as having very high strengths, which I find difficult to accept and understand.

I have to say that I believe that some of the claims made for 4340 are optimistic and I am looking for someone with practical experience.

If the claims are true I would be inclined to pay the price premium for insurance in terms of fatigue life.

 

[mrfailure]

1800 MPa seems awfully high for 4340, even if it is a "typical" value. The largest minimum specified UTS I found under a summary of 4340 specifications was 1070 MPa. I would focus more on specified yield strengths if the goal is maximizing fatigue strength.

Aaron Tanzer

http://www.lehightesting.com

 

[redpicker]

I am a bit confused at the "US based websites show values of around 1800MPa" comment. That is rather unusually high for 4340. For a Tensile Strength value, it represnets the maximum the matierial could achieve and I would not use the material in a structural or high stress application at that strength level.

Likewise, the 1000MPa value seems a bit low for the tenslie strength for what is essentially the same material. As a yield strength, this is about the highest I would consider the material useful for structural and/or high stress applications.

I suspect the comment "claim American made steel is much cleaner annd hence better" is misunderstood. Most 4340 produced in the US is E4340 (0.025% max P & S). I believe the EU uses 0.030-0.040 as maximum for these reanges for most of their low-alloy specificiatons (as does the US). While one should do adequate research into the requirements of the materials and the manufacturing specifications, I would expect the two materials to be essentially equivalent.

rp

 

[mrfailure]

I agree with you RP that the materials are equivalent and about the same compositions. Differences in various international standards really are from heat treatment, processing, and product form.

Aaron Tanzer

http://www.lehightesting.com

 

[gearcutter]

FennLane,

I'd be interested to see all those sites, which you are referring to, which show 1800MPa as this is most unusual for 30mm diameter bar. Could you please post some links.
Here in Australia 4340 is commonly supplied as 950-1200MPa.



Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[CoryPad]

Grade 4340 supplied according to AMS 6414 has an ultimate tensile strength of 1800 MPa and is available not only in the USA but also in Europe:

http://www.tatasteeleurope.com/file_source/StaticFiles/Business Units/Engineering steels/AMS6414.PDF

4340 in this condition will not have high impact strength.

EN24 can be obtained in multiple conditions that are similar to 4340, such as here:

http://www.westyorkssteel.com/en24.html

The strength/toughness tradeoff is similar between EN24 and 4340 (and other low-alloy steels).