wolfe racecraft has some cromoly subframe connectors and I was wondering if there is any advantavges or disadvantages to the cromoly over the regular mild steell ones they have

Thanks guys

 

i beleive (spelling i know) chromoly is stronger and lighter...cost more...it might be more of a personal preference, but i like chromoly so that is what i would go with...

Jon

 

I hear its lighter too thats why I started looking at them. The only thing is they are a tubular design and I really wanted boxed for strength but if they are lighter it might just be worth it.

 

I also think you would have to have the chromo SFC's TIG welded ($$$$$) vs. being able to have the mild steel SFC's MIG welded.

 

well the debate about boxed over tubular is on going, but i read a book on structural bracing and construction, it wasnt a car book but more of a construction book, and they say that tubular is actually stronger b/c of the circular design (takes the pressure evenly, and equally) when a boxed design can break, crack, if the presure is applied in a specific way...now i aint telling you one is better then the other, im just saying i read this awhile back when i was in college before i even had a Fbod and just remember reading it...so that is why i opted for tubular...

 

Hmm I didn't think about that, I'll have to run by Wolfe and see if they do installs if thats the way I decide to go

 

That's because have you ever tried putting a moment on a circle? From the little I remember of engineering (and trust me most of that stuff was over my head) but it is very difficult. Thinking about it a little now...it would seem that the SFC would only be subject to sheer, which is definately stronger then tension when materials are concerned. Also depends on the design and where the load is being distributed, but SilverStreak, you are right in that it does help to distribute the load throughout the whole part. Fortunately for me, I have a buddy that's close to being certified with mig, excuse me, TIG.

 

Chromoly is substantially stronger than mild steel, so chances are your tubular SFC will be stronger and lighter than the boxed.

 

Cool thats what I was hoping to hear

 

Spohn also makes Chromoly SFC. The mounting plates are mild steel though and can be MIG welded. The only reason to TIG weld is if you weld the whole side of the tube.

 

Chromoly can be tig or mig welded just have to use the proper wire. Tig and Mig are just different processes. FYI, You will get a stronger weld with tig and chromoly usually needs preheated before welding.

 

Correct, Chrome Moly is a grade of steel (4130, 4140). MIG or TIG welding can both be done. Some pre-heating and proper cooling may be nessecary when welding these grades of materials.

 

Stronger, lighter, more expensive, and not always necessary! That's chromoly.

 

Chromoly is amazingly light and its also stronger. Why wouldnt you get it

 

Because maybe he understands the material properties and the purpose of the part.

 

In some cases I feel Chrome Moly Steel is overkill for certain applications it is being used in and is a sales pitch. I think mild steel strengh is under estimated buy the consumer.

Like I said SOME cases

 

Sorry if it looks like I am raining on the Crome-Moly parade now.

If a design made of steel (any steel) is not strong enough to do its job you upgrade to a higher quality alloy rather than make it heavier. However, all steels have the same density 2.83 lb/cubic inch. Steels also have the same stiffness, known as Young's Modulus (~29.7 million psi). Chrome-Molybdenum (check out 4130 properties or mild steel have the same density, mild steel is just weaker. Switching to the stronger steel does nothing to the performance of the part if the weaker steel was already strong enough. Most people use the terms stiff and strong interchangeably and that creates a lot of confusion.

So why is the Crome-Moly design lighter? Because they just use less steel. What are the effects? They can use less material because its stronger. That part everyone understands. What they do not realize is that a subframe connector, strut tower brace, or any brace is a stiffness design, not a strength design. The mild steel version stiffens the car more because there is more steel. You are adding a SFC primarily to stiffen the car, secondarily it also strengthens it because you now carry loads in the structure more efficiently.

Mild steel has a yield strength of ~40,000 psi. The annealed 4130 above is 66,700 psi. You could heat treat it to raise its strength and some alloys respond to heat treatment better than others, but in the region of the welds you would have destroyed the heat treat. You also have to remember the fabricator welded it together in the first place so the part would be riddled with low strength areas. So very roughly you could make the 4130 part 2/3 the weight of the mild steel version and it would have equal strength to the mild steel version. But because the mild steel version is bigger the 4130 version is also 2/3 the stiffness. Oh yeah and you paid more. Since the SFC is not much of the total mass of the whole car it makes little sense to use the high strength version.

Just as an aside, why are all steels so similar in density and stiffness? The alloying content of a steel is always less than 2% of the total, the rest is iron. Iron with a sprinkling of carbon makes it a steel.

Someone might ask about stainless steels. They always seem to be the Cadillac of steels. Stainless steels are regular steels with huge amount of alloying metals in them, mostly Chromium and Nickel (both highly resistant to corrosion). Due to this huge alloy content the metal matrix is actually more flexible and stainless steels are about 10% LESS stiff than carbon steels.

Why not Titanium for those with a lot of buck? Titanium is almost exactly half as stiff as steel but is quite often stronger than even very expensive steels. A common Ti alloy is Ti-6Al-4V which means 6% Aluminum and 4% Vanadium. It has a yield strength of 120,000 psi. If you jump your F-Body off of ramps this might be good but it would not stiffen your car as much as the mild steel SFC.

If you really want to buy the higher priced part, go for it but try to get one that weighs the same as the lower cost mild steel version or you will not get what you wanted, a stiffer car.

 

I know its over kill. The advantages though are weight and strength.



BJM thats WAY too much to read when ive been up all night its 4:40am here. Maybe ill come back and read it later

 

Boiling down what I said. The mild steel version is better because its stiffer. In this application you need stiffness. A stronger alloy is worse in this case because they make it lighter. The mild steel version does its job better.