Chromoly

[FlatTire]

Anybody have any experience with Chromoly frames? I always hear about cracking on cars built from chromoly tubing. Is this because of they are MIG instead of TIG welded? or is it due to too much flex/fatigue. Does AWS have a weld procedure to do this? I was taught in school that chromoly should always be TIG welded.

[Kromulous]

Most likely due to not stress relieving the steel, or welded areas. Tig is best, small localized heat, but it can still crack.

AWS should have plenty of info on it, i wonder if AMS does as well, i will take a look around if i get some time. Filler wire would be critical i would think, and maybe the gas.

[billetbirdcage]

Anybody have any experience with Chromoly frames? I always hear about cracking on cars built from chromoly tubing. Is this because of they are MIG instead of TIG welded? or is it due to too much flex/fatigue. Does AWS have a weld procedure to do this? I was taught in school that chromoly should always be TIG welded.

There are tons of moly cars out there Mig welded and no problems. Rockets don't have the problem your referring too. In circle track the only moly cars that are TIG welded for the most part are sprint cars then rest are MIG welded.

I could make another 2 page post on this but pretty sure I have before and it's been covered.

[fox1162002]

If you mig weld moly it is best to take a torch and turn the welded area blue this resets the molecules in the moly. Most chassis places have the ovens turned up on the heat before they powder coat them.

[fastford]

There are tons of moly cars out there Mig welded and no problems. Rockets don't have the problem your referring too. In circle track the only moly cars that are TIG welded for the most part are sprint cars then rest are MIG welded.

I could make another 2 page post on this but pretty sure I have before and it's been covered.

this is true, also mig welding with mild steel wire creates a flexible weld that will not crack near as easily, drag car builders discovered this years back.

[billetbirdcage]

If you mig weld moly it is best to take a torch and turn the welded area blue this resets the molecules in the moly. Most chassis places have the ovens turned up on the heat before they powder coat them.

While the first part is true, the temp to anneal moly is around 1200 degree's and a powercoat oven won't get close enough to that to do anything.

It's about spreading the heat thru the rest of the tubing when welding so the weld or more importantly the thin moly right beside the weld to not cool too fast or it will harden and become brittle. Welding slow and allowing the heat to soak up the tube will increase the cool down time and fix the issue. That basic reason TIG is preferred cause it's going to take you a lot longer to weld the joint.

Think of it this way, heat up a 1" x 1" x 1/2" think piece of metal red, it will take a half an hour to cool off by air cooling but heat a 1" x 1" piece of sheet metal .020 thick and it will cool very quickly. Welding with too much heat so you weld real fast will only allow the heat to go up the tube of the joint say 2" and beyond that you can grab the tube so it will cool really fast. However, If you weld with lower heat and therefore have to weld slower the heat will go up 6" of the tube and it will take longer for it to cool thus not heat treating the moly as hard.

Hope that makes sense

Fastford is correct IMO, use regular steel filler.

[fox1162002]

I was just passing on what Mark Richards told me at Rocket when I bought my first Rocket. I weld everyday mig, tig, & stick and was just passing on what I've learned over the years.

[25drtrkr]

There are tons of moly cars out there Mig welded and no problems. Rockets don't have the problem your referring too. In circle track the only moly cars that are TIG welded for the most part are sprint cars then rest are MIG welded.

I could make another 2 page post on this but pretty sure I have before and it's been covered.

I'm pretty sure Grt offeres a tig welded chassis as an option.

[billetbirdcage]

I'm pretty sure Grt offeres a tig welded chassis as an option.

yes, they did (might still do) and IIRC it was a 3500.00 option for moly and TIG welding. I remember talking to one of the welders when they did the first one (thinking it was Clint's car) and they had 40 hours in welding it.

That's the reason I said "MOST" cars are MIG'ed

[billetbirdcage]

I was just passing on what Mark Richards told me at Rocket when I bought my first Rocket. I weld everyday mig, tig, & stick and was just passing on what I've learned over the years.

Only my first paragraph was directed at you, I added the rest just to explain a little more. I wasn't intending on demeaning you in any way, just stating that your typical powdercoat ovens usually only get around 400 degree's which isn't hot enough to have any effect on the moly.

I did agree that heating up the area and letting it cool down is a viable option if you don't have experience with welding moly for a chassis but is sort of unrealistic for production of a chassis as it would eat up a lot of time. They make temp sensitive paint that you can put on the area and it will change colors when you reach the desired temp to anneal the area. You can always do this if your worried that you may not be welding it so it doesn't become brittle.

Peace

[50j]

Tig welding takes a lot longer but is much nicer IMO. You have more control over the amount of heat used as you go around a tube, and can start hotter or turn the heat up for inside joints and back off some as needed in other areas. NHRA certified drag cars can not have Mig welded chrome moly.

[Bubstr]

When working with Molly, the first mistake many make is not knowing the letter N at the end of the properties number is more forgiving to any type of welding. N stands for Normalized. This is a process in the heat treating.

The discussion on how and why to weld high carbon, chrome Molibnium steel has been going on since the 40s. The problem is ruining the heat treat near the weld with heat during the welding process. You end up with hard and softer right where the heat line is. This promotes the cracking so many talk about. The general consensus is to limit the area effected by the heat and still get good penetration with the weld. Up until the mid 60s F1 cars where brased with a torch and held up surprisingly well. Military and experimental Aircraft switched to torch and mild steel and if you build a experimental AC today, you better learn how to use a torch according to the FAA. Stick welding was never a good option, because it was too hard to control the heat. Tig is the most accepted weld, because the heat is so controllable. Not saying Mig can not work if you know about wire size and speed. Heating a welded joint is only one part of normalizing it. How fast it gets cooled is the other. The best possible results come from a good welder, using good equipment, keeping the heat in a area small as possible and still getting good penetration..

If we are realistic, the only advantage CM has over steels that are easy to weld is a small weight savings if you use thinner wall tubing in Molly. Same wall thickness weighs the same, but molly has a little more rigidity.

[let-r-eat]

I've worked with many different makes of metal over the years. Moly is a good option but I'd only TIG. The reason being the filler. The chassis is only as strong as the joints. They are the weak link. Why would you mig them with mild steel? You are defeating the purpose if rigidity is your goal.

Quench and temper is a whole other story.

[MasterSbilt_Racer]

Not to pick on the guys above, but saying moly is more rigid is not really correct. All steel alloys have basically the same spring constant, or modulus of elasticity. The only advantage is simply a higher stress before yield occurs.

This comes in handy in areas such as the cage where strength is important. Otherwise, the rest of the chassis should be designed with rigidity in mind. If you replace mild steel with thinner wall moly, you may maintain or increase strength, but stiffness of the chassis was actually reduced.

[let-r-eat]

Not to pick on the guys above, but saying moly is more rigid is not really correct. All steel alloys have basically the same spring constant, or modulus of elasticity. The only advantage is simply a higher stress before yield occurs.

This comes in handy in areas such as the cage where strength is important. Otherwise, the rest of the chassis should be designed with rigidity in mind. If you replace mild steel with thinner wall moly, you may maintain or increase strength, but stiffness of the chassis was actually reduced.
Last edited by MasterSbilt_Racer; 08-13-2015 at 11:48 PM.


Like the modulus of elasticity of spring steel? That is a perfect example to explain the post I was making. Take a broken spring leaf and weld it together with mild steel. What happens?

I did use the word rigidity in the proper context. A mild steel filler on a moly tube is doing basically the same thing as it would on a leaf spring but on a much smaller scale.

Just clarifying my post.

[fastford]

nope, your wrong, im no metal urgist, but there is a lot of difference in a hardened leaf spring and moly tubing, but this whole conversation was hashed over on here several years back and im not going through it again. you keep welding yours with a tig and moly filler and ill keep welding mine with a mig and mild steel and we will see who gets the most stress cracks at the weld....

[let-r-eat]

http://www.lincolnelectric.com/en-us/support/welding-how-to/Pages/chrome-moly-detail.aspx



Why am I wrong fastford. You think I'm talking out my ass?

[fastford]

I don't know what your talking out off, and don't care. that article has been out a while, ive seen it before and I think er80-02 is a form of low carbon mild steel filler, not sure. im not saying tig is no good, just saying that ive done both and have found less stress cracks with tig and mild steel wire. I suppose tig and proper filler like mentioned above , would be just as good, but no better and a lot slower. JMO, no offence.

[50j]

ER70S-2 works well on chassis and is flexible enough not to crack at the joints.

[MasterSbilt_Racer]

Not to pick on the guys above, but saying moly is more rigid is not really correct. All steel alloys have basically the same spring constant, or modulus of elasticity. The only advantage is simply a higher stress before yield occurs.

This comes in handy in areas such as the cage where strength is important. Otherwise, the rest of the chassis should be designed with rigidity in mind. If you replace mild steel with thinner wall moly, you may maintain or increase strength, but stiffness of the chassis was actually reduced.
Last edited by MasterSbilt_Racer; 08-13-2015 at 11:48 PM.


Like the modulus of elasticity of spring steel? That is a perfect example to explain the post I was making. Take a broken spring leaf and weld it together with mild steel. What happens?

I did use the word rigidity in the proper context. A mild steel filler on a moly tube is doing basically the same thing as it would on a leaf spring but on a much smaller scale.

Just clarifying my post.

A leaf is hardened to raise the yield point. Your repaired leaf would behave the same up to the point the mild steel starts to yield. A chassis isn't supposed to be a spring. It shouldn't see stresses that cause deflections that high.

[let-r-eat]

A leaf is hardened to raise the yield point. Your repaired leaf would behave the same up to the point the mild steel starts to yield. A chassis isn't supposed to be a spring. It shouldn't see stresses that cause deflections that high.


That is correct. But my point was that it is only as strong as the weakest link.................The mild steel...............which compromises the strength.

The chassis will be stronger with moly filler properly annealed.

[Bubstr]

Welding with softer material as a filler is not as big of thing as it seems. the softer filler mixes with the harder and strength is maintained by the thickness. All steel is rated by diameter and wall thickness, to compare one to another. If your weld is thicker than the wall, you gain a lot of strength in that place. This is why you see cracks, next to the weld, rather in the weld. No matter what some may think, these cracks are the result of two things on Molly. #1 molly transfers force better than milder steels. #2 you can loose the integrity of the heat treat where you heat for welding. It still comes to using just enough heat to get good penetration. Unless your very good with a MIG, a TIG is a better bet for heat control. Not saying you couldn't do it some other way. Just keep that blue heat line narrow.

When it all comes down, I'm not sure that something that bends rather than breaks isn't a better option for a lot of purposes. We can straighten or replace, with out loss of integrity. Just my opinion on the last part.

[fastford]

bubstr, I agree with your thoughts on bending is better than breaking, im old school, ive been welding long before the all mighty internet, but I have to admit, ive learned a lot from it. My youngest son is a senior in high school and has enrolled in welding. his teacher is an old friend of mine and considered to one of the best welders around, I told him maybe he can teach his old man a trick or two.......

[Windy]

chrome moly chassis vs. D.O.M. ...instead of starting a new thread id like everyones opinion on which chassis/material to buy for a new modified..my car owner just bought a new elite,car/d.o.m. ..built by the allison brothers..there are a lot of good chassis out there,beak built, huges, dw + to many to list....my preference is the rocket by ruhlman..its a rocket off thier jig,plymouth pro tube moly and brian puts the front clip on and it comes out to the black ft. end rocket settings..i know theres some other d.o.m. thats supposed to be better like db8 or somthing like that..????..i still would think the rocket by ruhlman would be the best..years ago i helped build some cars..one in particular we raced and at about 75 to 80 races it turned into a boat anchor especially the 2nd nite you raced it like fri., it was fair and sat., you couldnt hit the broad side of the barn with it..it was fairly stiff with underslung frame rails....most people i talked with that i thought knew more than me said the d.o.m. was flexed out..????..AND that brings me to the most important question with the day an age of the 5 thousand dollor an + bare mod chassis wouldnt the pro tube moly chassis be the best buy..ive worked with the ruhlman car and its awsome fast..also with a swartz mod and a bad fast and a grt..ive worked with rockets since the 90,s when francis started running them and i like them but its a cost vs., a lasting thing now with the cost of the chassis and parts being so high you will have close to 20 somthing in the roller with most everything ..looking for your experienced opinions,not wanting arguements or smart--- comments about modifieds please..just honest opinions and experiences..thank you all in advance..WINDY..~V~..

[SuperEight]

Personally I'll never use a "Moly" chassis and I've included pictures to demonstrate. Moly breaks, usually next to the weld. Lots of people claim you can treat them and get them to be safe, but for me its a risk not worth taking.

[hammond motorsports]

On Chrome moly just make sure you use the correct gas and wire . Using a std gas and wire the chrome moly will crack .

[fastford]

On Chrome moly just make sure you use the correct gas and wire . Using a std gas and wire the chrome moly will crack .

would you please share what wire and gas you use? I still use 75/25 gas.

[Bubstr]

I believe nascar requires mild steel chassis yet. They hit things harder than most cars. Now NHRA requires CM tig welded only, but I suspect SEMA had something to do with that rule, to keep pro chassis builders in business.

[Bubstr]

would you please share what wire and gas you use? I still use 75/25 gas.

What I'd like to know is the annealing process. 4130 is heated to around 2000 deg then slowly cooled over a 24 hour period then finished in a oil bath, which is why CM is dark and oily, to mark that N on 4130N. Each number means something. the 4 means high carbon steel the others say how much nickle and molybdenum and the N means normalized.

[hammond motorsports]

tri mix gas Argon, Helium, Carbon Dioxide and I use a spoolarc 83 wire from ESAB . I have used this combo from the early 90s to today . Never had any cracks in my chrome moly welding

[fastford]

thanks hammond, I will check into this. I have had some chassis take some hard licks and the welds held fine welded with 75/25 and mild steel wire, but im always looking for a better way. also do you preheat the weld area or just weld at room temp? thanks.