mild vs. chromoly

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what are the advantages of using chromoly steel over mild other than weight. i know cost definitely isnt one of them.  pros and cons of each would be greatly appreciated.  also, how much weight savings should i expect switching from mild to chromolythanksmatt
Reply:pros and cons depend greatly on what your using it for
Reply:This is kind of a trick question. First, there is no weight savings if you use the same size material. 1.5"x.120 weighs the same for both materials. 4130 is definitely much stronger, so there is the possibility to drop down a wall thickness on a tube and still retain the same strength. Another big plus for chromo is that it has very good spring qualities. It will flex, and go back better than mild steel. Many times, I will mix the tubing up, using the 4130 for main parts, and the mild for small gussets. Mild has the better cost, and is easier to work, especially if you don't have very strong bending equipment. Mild is also much less likely to crack, it will likely bend long before it tears. They both weld equally well, and remember that chromoly will work harden significantly when you weld it, bend it, drill it. If you let a drill bit just spin instead of cut it, it will get unbelievably hard surfaced rather quickly. Then, you'll be starting over with a different bit, or grinding.And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:you are correct about the wieght. ok let me rephrase that. to get comparable strength qualities out of both materials, say 1 1/4" .083 wall mild steel tubing, how much weight am i looking to save.  the application is for a frame for an SAE mini baja car.  if you are unfamiliar with the competition, it is basically a large go cart built from scratch by a university team to compete at the end of the school year.  each team is limited to a 10hp briggs and stratton, so in order to go faster, weight must be cut
Reply:Total weight saved will depend on lots of things (how much tubing is used, is it all the same OD and wall etc)When it comes to stiffness, all steels are basically the same- 1018, 4130, 4340 all have (near as damn it) the same modulus of elasticity, something to bear in mind. Taking the entire design into account swapping from mild to 4130 is more involved than just dropping the wall thickness because 4130 is 'stronger'. It all depends how 'evolved' the current design isA GROSS GENERALISATION... with a wall of 0.083 mild you could be looking in the region of 0.035 (select areas only) - 0.065 depending on tube location and design. Other common wall thicknesses would be 0.049 and 0.058EVERTHING will become more critical regarding workmanship
Reply:Chrome-moly--has 65 times the impact strength that mild, low carbon steel does.That's 'why'.....you see sprint cars that have flipped end over end....and suffer littledamage to the tube frame.A good tube structure will, as others  mentioned, act as a sort of spring--it's that tough.Blackbird