Thought some other people might be interested in some info I gathered on the comparative strenght of the steels used in aftermarket Land Rover (and other) axle products.


Material (other names) / Application / Ultimate Tensile Strength (MPa / psi)

EN25 (X9931) / McNamara axles? / 1300 / 190 000

EN26 / X9940 / 1380 / 200 000

AMS-6418 (MIL S - 7108 / 4625M4 / HY-TUFF) / Maxi-Drive and Strange axles / 1655 / 240 000

4140 / 1230 / 186 000

4340 / New longfield / 1380 / 200 000

300m (4340m) / New longfield star/ 1980 / 288 000

Data mainly from Timken Steels and Smorgon Steel - both are suppliers of these steels. Interestingly, Maxi-Drive quote a lower strength of 1550MPa for their axles, but strange engineering (another axle manufacturer), quotes 240 000psi (as does Timken).

I am not 100% sure that McNamara use EN25 and not EN26, but since EN25 is what Maxi-Drive used before they switched to AMS-6418 it is probably right. Although the maximum values are the same, most steel suppliers state that EN26 should be used where higher strength than 4340 is required.

Shear is usually 75% of tensile strength for all these steels.

From the looks of the numbers, AMS-6418 is a pretty impressive steel, a fair bit stronger than 4340 and almost as strong as 300m/4340m. Of course a lot depends on how the axle is designed, how well it is machined and heat treated, but I think this is a usefull comparison of like for like.

Here is what BillaVista says about steels like AMS-6418/HY-TUFF...

THE HIGH SILICON, NICKEL CHROME STEELS
These are usually known by trade names such as Hi-Tuff and Stress Proof. They contain up to about 3 % silicon and are, as the names suggest, tough as hell. They are popular for stock car and off-road racing axles—and the alloys are very suitable for these applications. They are not as good as 4340 M or even 4340, but they are also a damned sight cheaper and, especially where the minimum weights imposed are high, the fact that a part with the same strength and fatigue resistance can be made lighter by using a better steel may be a lot less significant than the cost difference. However, these steels are tough only because of the high silicon content, which is mainly in the form of longitudinal fibers or strings of silicon. This limits the efficient (and safe) use of the alloys to parts with minimal section changes and virtually no transverse machining (we don't want to cut the longitudinal strings that make the stuff tough to start with, do we?). They also don't like being bent very much because that may rupture the silicon strings. Mind you, I have made a lot of street car antiroll bars from Stress Proof with excellent results and pretty severe bends—but in this case the bends are almost, by definition, in lightly stressed areas.

Looks like he is wrong about the strength of HY-TUFF compared to 4340 though.

have you seen the mindless debate i found my self in on d-web. these guys are terrified of the hybrid cocept. i want to do the toy swap, and i like the idea of the 4340 toy birfs. my biggest concearn is the wear longevity in the full time 4wd. the strength is great, but will they last more than 2 years?look here and beware (http://discoweb.org/forums/showthread.php?t=3860)

I'm not sure UTS is the only factor to look for in an axle or CV.
Fracture toughness (resistance to crack growth)
Impact strenght
Elongation
Are all relevant parameters, I think.
Will try to get some useful data from our excellent materials database at work tomorrow. (I'm more into cast Irons, which I do not expect in axles or CVs :shaking: )

Tobias

More data would be great Tobias. This was just a first quick look.

Running a few quick calcs last night - it looks like McNamara 30 spline 1.31" axles (if made from EN25) are actually the same strength (or even a bit weaker) than Maxi-Drive 24 spline 1.24" axles (Using the quoted MPa values from MD for HY-TUFF). If someone can measure the root diameter of the toy axle I can do a more accurate calc.

The data about silicon strings in AMS-6418, and transverse machining being bad for them that I quoted from Billa Vista above, may be the reason that Maxi-Drive axles were not waisted to the spline root diameter along their length. However I think they are now though.

What is it that we are worried about?
CV's: Shock loads (Charpy V) , wear (Hardness, strength ?)
Axles Stength, twisting a large amount before breaking (elongation )

Or what?
Depending on what we want we should be looking at different alloys.

For instance aircraft landing gear used 4340 and similar way back, but when they are strong they are brittle. The need impact strength as well, so other strengthening methods than martensite was needed. Austempering and recently particle hardening have developed. These alloys give good/better strength with much improved ductility, impact strength and fracture toughness.

I believe AMS-6418 is such an alloy. Possibly also 300m. Another alloy that definitely is one of these "superalloys" is AirMet100.

Tobias

That is the only place that I have heard those statements about the long Si strings and problems with section changes.

It sounds to me like someone may have read about the long Si strings and drawn some possibly misleading conclusions re section changes. But it is not something that I have researched, so I may be wrong. I just can't see the strings being at all long compared to well designed blends/large fillet radii, used at section changes to minimise stress raisers.

Another thing, the main chem difference between 300m and 4340 is the addition of 1.6% Si (and 0.05% min V). Hi-tuff has 1.5% Si. But I don't hear these people running down 300m.

Hi-tuff is intended to be used between 1500 and 1650 MPa. Interesting that Mal uses 1550 MPa. 0.2% offset stress is greatest (1340 MPa) at about 1550-1560 MPa tensile. But the Izod impact strength jumps considerably when tempered for >1600 MPa. Some Izod values for hi-tuff are:

28J at 1450 MPa
34J at 1560 MPa
42J at 1600 MPa
45J at 1630 and 1650 MPa

Interesting info John, thanks. Interesing about the silicone - I thought it sounded strange too, especially since Maxi-Drive axles have been reported to plastically deform a lot wothout actually failing.

Here is some info for 1045H and 1541H that may be of more interest to people in the US - since most US aftermarket axles are 1541H - including Moser who makes axles for Keith/Rovertracks.

Material / Application / Ultimate Tensile Strength (MPa / psi )
SAE1045H / Many std axles / 930 / 135 000
SAE1541H / Many US aftermarket and truck axles (Including Moser/Rovertracks) / 1200 / 175 000

I am not 100% sure of the 1541H value though. Do you have a more accurate one Keith? Interestingly, it sems that most US aftermarket axles are made from 1541H, because it is supplied already induction (case) hardened, but is still soft enough to machine the splines in without re-hardening. This saves a lot of $$$ over other axles which are machined in the annealed or normalised state and then through hardened. The use of pre-hardened steel is probably one of the main reasons that the US axles are not waisted along their full length.

The figure below is from timken steels - interesting how much surface finish affects the steel.

http://www.timken.com/timken_ols/steel/images/online/pdm/pdm063.gif