4130 Contradictions

[jumpin jellybean]

it all comes down to proper bracing and design just my .02 will you see me doing this or even this nope don't think so remeber it is design that will give you what you need to be safe just my opionon

[masterfabr]

BINGO! We have a winner!

[jumpin jellybean]

what I win

[masterfabr]

Originally Posted by jumpin jellybean

what I win

You win the priveledge of blocking all poo that comes my way!

[jumpin jellybean]

I am sending you a virus for all people that fling poo it is a very bad virus I will just accept these badges as my prize

[K-fab]

Jellybean wins that cookie that Master's owed me for so long...

[masterfabr]

K-fab, you apparently didn't enlarge the badges.

[grant_wt]

Parts of your cage that are designed to be in compression will never crack. The more you can design so that bars are being compressed, the less problems you will have with cracking.

All steels have an endurance limit, which is the pressure that the steel will form cracks if loaded to that pressure a million times (or so). For 1080 the endurance limit is approximately 30-35KSI. For normalized 4130 the endurance limit is 40-45KSI. So in theory the 4130 is slightly less susceptible to cracking.

Part of the problem and why 4130 cracks is that it is tig welded and not mig welded. Tig welding is best from the fact you have less problems with weld undercut and improper reinforced root. The welds are a lot more uniform, which makes them stronger. However, the welding process takes a lot longer, causing more heat typically to be introduced to the part. This causes additional warping and internal stresses inside the weld, which can quickly cut away from your 40-45psi endurance limit. It may end up that a good mig weld without undercut and proper reinforcement is more resistant to cracking than a comparable tig weld (I know that there will be some people that hate to hear this!!).

Also, a ductile material will tend to relieve itself of these internal pressures by slipping (Stretching), whereas a brittle material will relieve these by forming a crack.

However, internal stresses caused by welding (especially tig) can be dealt with by stress relieving the steel. I doubt that any buggy manufacturers actually do this though on complete frames, but a Baja or professional CORR vehicle just might. This would require heating the complete frame to ~1100°F for 25 minutes and it would cost quite a bit to do in an oven big enough for a complete frame. But once this was done, a tig welded 4130 frame would have an endurance limit of 40-45KSI without internal pressures, and the benefit of perfect welds.

Lastly the real benefit of 4130 is that it can be heat treated to be much stronger than 1020. 4130 is capable of being heat treated to 180-200ksi ultimate strength, or an endurance limit of ~80KSI. That is that 4130 would resist cracking at stresses 2.5 times that of steel, allowing you to use thinner material and decrease the weight of the vehicle by up to half.

Moral of the story: If you go all the way with the stress relieving and heat treating you are going to be able to build a frame that is twice as light, and still as strong. If you don't do that, you wont be able to shave much weight, if any, without making the frame weaker and more susceptible to cracking.

Might just be able to save more weight by making your design such that you minimize tubing!!

Just so you all know, I am a 4th year engineering student that, while I have read and learned a lot, I still don't (and never will) know everything. And I still make mistakes. But this is my .02

Grant

[masterfabr]

Originally Posted by grant_wt

Parts of your cage that are designed to be in compression will never crack. The more you can design so that bars are being compressed, the less problems you will have with cracking.

All steels have an endurance limit, which is the pressure that the steel will form cracks if loaded to that pressure a million times (or so). For 1080 the endurance limit is approximately 30-35KSI. For normalized 4130 the endurance limit is 40-45KSI. So in theory the 4130 is slightly less susceptible to cracking.

Part of the problem and why 4130 cracks is that it is tig welded and not mig welded. Tig welding is best from the fact you have less problems with weld undercut and improper reinforced root. The welds are a lot more uniform, which makes them stronger. However, the welding process takes a lot longer, causing more heat typically to be introduced to the part. This causes additional warping and internal stresses inside the weld, which can quickly cut away from your 40-45psi endurance limit. It may end up that a good mig weld without undercut and proper reinforcement is more resistant to cracking that a comparable tig weld (I know that there will be some people that hate to hear this!!).

Also, a ductile material will tend to relieve itself of these internal pressures by slipping (Stretching), whereas a brittle material will relieve these by forming a crack.

However, internal stresses caused by welding (especially tig) can be dealt with by stress relieving the steel. I doubt that any buggy manufacturers actually do this though on complete frames, but a Baja or professional CORR vehicle just might. This would require heating the complete frame to ~1100°F for 25 minutes and it would cost quite a bit to do in an oven big enough for a complete frame. But once this was done, a tig welded 4130 frame would have an endurance limit of 40-45KSI without internal pressures, and the benefit of perfect welds.

Lastly the real benefit of 4130 is that it can be heat treated to be much stronger than 1020. 4130 is capable of being heat treated to 180-200ksi ultimate strength, or an endurance limit of ~80KSI. That is that 4130 would resist cracking at stresses 2.5 times that of steel, allowing you to use thinner material and decrease the weight of the vehicle by up to half.

Moral of the story: If you go all the way with the stress relieving and heat treating you are going to be able to build a frame that is twice as light, and still as strong. If you don't do that, you wont be able to shave much weight, if any, without making the frame weaker and more susceptible to cracking.

Might just be able to save more weight by making your design such that you minimize tubing!!

Just so you all know, I am a 4th year engineering student that, while I have read and learned a lot, I still don't (and never will) know everything. And I still make mistakes. But this is my .02

Grant

The only thing I will add to that is that a TIG weld can be done as fast on thin tube as MIG by a good welder .Nice post BTW.

[K-fab]

Originally Posted by masterfabr

K-fab, you apparently didn't enlarge the badges.

ROFLMAO!!! No I didn't until just now.