welding chromoly to mild.....any issues?

[Jonny Hotnuts]

Making take up tubes, the ends are chromoly and was going to use a stout mild steel tube for the body.

Is there any problems in welding the two materials?

[Loose Goose-Terry#1]

 
Be very careful!!! You will have to preheat and then anneal with a gas torch before and after welding to help prevent the weld from cracking. Also, I found that if you weld using stainless steel or nickel rod there is less tendency for the weld to crack (this is what I've had the best luck with). Tig, Heli-Arc doesn't work as well as electric arc welding in this case and Mig won't work at all. DO NOT use a mild steel rod to join the two materials together (the weld is sure to crack either as soon as you are finished or when it is stressed from use or vibration). I have heard of people joining the two materials together using an oxi/acel torch (but a friend of mine used this technique and was killed when his home built airplane crashed ) I don't recommend it unless you are very, very good and you don't destroy your metal's physical properties. Also, braze welding is a consideration...but that should be all that it is because the strength just isn't there for highly stressed areas 

Good Luck

Terry

[SPARKY]

IS there anyway you can make a mechanical joint ??

[Harold Bettes]

Howdy,

Have heard of CrMo and mild steel joints using a pre and after heat of weldment to decrease the generation of martinsite which is very brittle. The stuff that I was exposed to used Eutectic 660 or 680 (don't remember which) as filler rod using Tig. The rod has high nickel content and is super smooth to use as a filler. 

The big issue seemed to be what mild steel was used was important. I seem to remember that the mild steel was probably C1030 and not C1018. As I understand it the higher content carbon was easier to attach to the CrMo (C4130 in this case).

Sorry I don't have any very definitive data for you, perhaps this might trigger someone else's memory because mine is kaput!

Regards to All,
HB2

[Howard]

I use aeutectic 680 to join metals when I'm not sure of the alloys. Have had no problems with it.
Howard

[interested bystander]

I'm assuming the mild steel is for BODY mounts off the chromoly main chassis. You are wire welding it using wire that has a 70 in it's spec, right?

Every Saturday nite circle track racer welds up his car with that WIRE and we use ER70s-2 rod to weld 4130.

I may be wrong and there may be a difference but both wires tell me the TENSILE is 70,000 psi.

Common sense tells me it's plenty OK.

You're not building a spacecraft.

Hope you continue to keep your build journal; going.

[willieworld]

Every year usually in the spring I weld a couple of pieces of tubing together and I put them in the press and squeeze them till something lets go.
Its a test for me to test my welds to make sure that my welds are strong.
I've tried many different kinds of rod including stainless and have found that the flagged er70s2 in a 1/16th rod works the best for me. I weld alot of mild steel tubing and alot of chrome moly tubing. Most of the mild steel is .120 wall and most of the chrome moly is .065 or .083 wall. Every year when I put these welded tubes in the press the tube that is fishmouthed usually gives up near the weld. Which should be actually the weakest spot on the material because of the leverage. This year since I seen this posting about chrome moly and mild steel welding I decided to weld a piece of  chrome moly to mild steel, which I've done 1000 times and never gave it much thought. After all its all steel.But it set me to thinking that I should try the chrome moly to mild steel this year, which I did.
I used a piece of 1 5/8 .120 wall mild steel, which for you car guys would be frame rail size. I fish mouthed a piece of chrome moly thats 1 1/2 by .083 wall. welded them together with the er70s2 rod. Nothing special just an ordinary everyday weld. Put it in the press and as usual the fish mouthed piece broke near the weld. I did notice that it took a lot more pressure than it usually does with the mild steel.
I do alot of NHRA cars and their rules are chrome moly to be tig welded only. This test was to test my weld only. I am going to post some pics so that you can look and draw your own conclusions. But I would say that if you are tig welding, you could weld chrome moly to mild steel. What would help spread the load and keep the material from ripping near the weld would be a couple of gussets stitched welded and not welded solid.Or you could just build a motorcycle and don't worry about a roll cage or seatbelts or firesuit or fire system or......
Seriously though I hope this helps you guys out.
Willie Buchta

[willieworld]

more pics

Willie Buchta

[Geo]

Thanks Willie!

We are just getting started on the cage for the car. 

I would have a bike but I like seatbelts and firesuit and fire system and air conditioning and tunes and...

Geo

[Harold Bettes]

Willie,

Thanks for sharing the pics and the data on what you were welding. 

Could you please do the same type weldment (CrMo and mild steel) but with after weld heating of the welded area with a gas torch and after it cools off and gets easy to handle....then place it in the press and see what happens?

Hope things are going well for you out there. As a kid I spent a lot of time in nearby Patterson and spent weekends in Modesto cruising the streets.

Thanks in advance and we all thank you for the help in sorting this out.

Regards,
HB2

 

[willieworld]

yea harold i will but if im to do it right i will have to buy some heat stick so i can get the right temperature i will try and do that tomorrow  but i can tell you now the same thing will happen thats my guess  willie buchta

[Harold Bettes]

Willie,

Dummy me, I didn't even think about some heat crayons.

I only visualized in my mind heating the entire heat affected zone to a dull red and let 'er coast back down to room temperature.

I do think that this is a great opportunity for folks to see how stuff works and that is very difficult at best to get information in any other venue but this one. And with photos yet!

Regards,
HB2

[Rex Schimmer]

I don't think that on most of the stuff that we are usually welding pre heating is required. I would say if you are doing something 1/4 inch thick or more you might want to pre heat, also the size of the part has a lot to do with it. The idea behind pre heating is to get the surrounding metal hot enough so that it does not become a heat sink for the welded area. If the surrounding metal is think, large and cold it will cool the weld area to quickly and then start a crack. When we did thin walled stuff that was not to big we would bury it in a sand box an let it cool real slow. I have seen chassis builders anneal weld joints on drag cars but have never seen any testing. Willy's testing is real world and probably as good of information as we could find anywhere.

I did a couple of motorcycle frames years ago using the back bone, head piece and down tube from a Husky and then built the engine cradle, seat frame and the rear part of the frame, all from 3/4 inch x 049 4130 normialized tubing and welded it all with a gas torch. I read up in some aircraft book how to do the chrome moly with a gas torch and it was pretty easy, I was a pretty good gas welder, and I never broke either of the frames both of which I desert raced and moto-crossed for a couple of years. As I remember you use a slight carborizing flame and then when the weld pass is complete you pull the torch away from the weld puddle very slowly and watch it solidify, then let it cool in very still air. Gas welding is still recognized as an acceptable method for aircraft tube repair and fabrication.

Rex

Rex

[willieworld]

Today I got around to welding the other tube together, same material, same rod, same heat. The difference was after I finished welding it, the weld cooled I took the torch and heated the chrome moly from the weld to about 1 inch out to a dull red. When that cooled I took it to the press and put the squeeze on it. As you can see from the pictures I took it out of the press a couple of times and took some pics. The first pics you'll see the metal starting to distort. The second set you'll see the cracks starting. And then the third set you'll see the metal with a good tear.As you can see in the pics the chrome moly held together longer and the mild steel distorted much more in the second test then in the first. But, I can tell you this, the first test took much more pressure to break the tubing than the second test. The first test the tubing distorted a certain amount and then just ripped. The second test the tubing bent and distorted much more before it ripped, but it took alot less pressure from the press to do it. So my conclusion other than my second weld held flawlessly, was that if you don't heat it after you weld it, its much stronger but more brittle. If you heat it after you weld it the chrome moly acts much more like mild steel would. My personal preference is mild steel. Availability, cost, easier to bend, easier to weld. If I was going to use chrome moly in a door car I wouldn't heat it after welding. But if it was a dragster or an altered or a motorcycle chasis and it was chrome moly I would heat it after I welded it. But look at the pics and make up your own mind. I hope that I have helped someone out there.
Willie Buchta

[willieworld]

more pics
Willie Buchta