[RRich]

How do you tell if it\'s crome moly?

A friend wants me to weld an ice chest holder onto his dune buggy. The guy he bought the buggy from said it's made of CM tube. It has been TIG welded, but that's no garantee it's CM. The guy TIG'd everything.

All I have is MIG - It needs to be attached to the frame in a critical place. This stuff does have a seam, and does not have the telltale spiral of DOM.

Any easy way to tell the difference?

Thanks in advance, Rich

 

[Jim_Lou]

Re: How do you tell if it\'s crome moly?

It doesn't matter if you're going to TIG it. You can use the same high-strength (80,000 psi?) filler rod for either chrome-moly or something as mild as 1018. Oddly enough, you don't use 4130 filler to TIG 4130!

Last summer I took a short class taught by a guy who works for Lincoln Electric and travels with their demo circus. That was one of his main points; 4130 filler produces inferior results when TIG welding 4130!

Ask your welding supplier for a filler to TIG 4130. If he hands you 4130, have him try again.

 

[RRich]

Re: How do you tell if it\'s crome moly?

Sorry, I must have said it backwards.

All I can do is MIG it, I don't have the luxury of TIG yet - (someday hopefully - but a good plasma torch will be first.)

I'm afraid trying to MIG it in that spot may weaken the CM frame too much - if it really is crome moly. Some of the other claims the PO made have proven not to be true, he may have lied about the frame being CM too.

Is CM as magnetic as regular steel?
Is there an acid test, spark test etc to see if it really is CM?
How does one know?

 

[1652]

Re: How do you tell if it\'s crome moly?

see if this helps you

or this

(good to have on the shop wall anyhow)

 

[RRich]

Re: How do you tell if it\'s crome moly?

Great - I've been looking for the spark test chart for quite awhile. Thanks. Had most of it committed to memory, but it helps to have one hanging on the wall for reference.

The flow chart is good too.

But - neither identify crome moly - .

Q - how do you make the charts small enough to print - I can only print the left sides.

 

[1652]

Re: How do you tell if it\'s crome moly?

In reply to:

Q - how do you make the charts small enough to print - I can only print the left sides

[/ QUOTE ]

Try this: when you select print, in that other dialog box that opens up, look for "layout" tab (or something to that effect), and change selection from "portrait" to "landscape"

HTH

 

[RRich]

Re: How do you tell if it\'s crome moly?

Worked like a charm - had to use legal sized paper!

Thanks.

Too bad it's not that simple identifying CM from mild steel.

If I weld it with MIG, won't it weaken the CM tube? Then next time he jumps it - or I do - the frame could buckle or break there. Welding in a support underneath would cause the same problem -- if it really is CM.

 

[Jim_Lou]

Re: How do you tell if it\'s crome moly?

Chrome moly will turn that dull gray color naturally. Scrub an area with Skotchbrite and see what happens. I don't know if that's definitive, but it will give an indication.

I just found my notes from that seminar. The high points:

Preferred TIG rod is ER80 SD2.

Also acceptable is 4130 VM. It must have the VM suffix for TIG use, and is 5 to 7 times as expensive as ER80 SD2.

The ER80 filler can be used to weld 4130 to 1018, or 1018 to 1018.

It's very important to have no moisture in the area of the weld. The arc can disassociate hydrogen from the water and cause hydrogen embrittlement in the joint. For that reason it's recommended that you preheat the area slightly - 150* or so - to remove any trace of moisture.

For more information on TIG welding 4130, go to www.tigdepot.com. That's the site run by the seminar instructor.

I've never heard of MIG welding 4130, but I asked that question on the tigdepot site. I'll post the answer when I get it.

I do know that you can oxy/acetelyene weld 4130. As a matter of fact, there are old timers who will tell you that that is the ONLY way to weld it - TIG gives inferior results. You use plain 4130 filler. I don't know if the ER80 filler will work. That's what I would use if I didn't have the TIG machine.

I also posed the question of identifying the base metal on the tigdepot site. I'll post that answer too.

 

[Jim_Lou]

Re: How do you tell if it\'s crome moly?

Rich, here's what Mr. Tig had to say:

Jim,

If you are not sure of the metal then try the spark test on the grinder. Regular steel will have long sparkles and because of the 30 points of carbon the 4130 will have shorter sparkles coming from the grinder. If you
are concerned about which filler then use the ER80S-D2 for either steel or 4130.

You can get the same properties with MIG welding but we have found that the consistency and failures cause by the operator or his machine make it high risk to use the MIG process.

Good Luck,

Mister TIG

 

[Mark2003]

Re: How do you tell if it\'s crome moly?

There is an acid test to determine the percent chromium in steels. You need a drop of concentrated nitric acid, 47% nitric acid and 35% nitric acid. When placing one drop of each of these, the reaction of each indicates the chromium content.

0.1% chrome has a vigorous reaction from all three.
5% chrome has no reaction with the concentrated, turns dark brown then becomes clear with the 47%, and the 35% turns the spot dark brown.
12% chrome has no reaction from any of the solutions.

The intermidiate chrome contents have varying reactions.

To determine the molybedenum content, a drop of 10% nitric acid is placed on a piece of filter paper and placed in contact with the metal. A 6-volt battery is then connected across the metal and filter paper. The color of the paper after several more steps and solutions indicates that the metal contains 'Moly'.

 

[517]

Re: How do you tell if it\'s crome moly?

Now this looks like one heck of a book. Perhaps your local engineering faculty has a copy in their library?

Rapid spot testing of metals

 

[1756]

Re: How do you tell if it\'s crome moly?

Rich,

Sorry I couldn't get back to you right away, but here is what my resident expert had to say. He didn't have a lot to add to the other posts, but ...

-The etch method is the best way to identify 4130.

-Tube connections in general are ugly from a structural analysis standpoint because they create a lot of stress concentration areas. Trying to get full strength joints with a material like 4130 is more difficult.

- TIG is usually used, one reason because the tubing is usually thin, but MIG can be used as well. Workmanship is an important factor.

- Preheat should be considered, especially with MIG, to keep the hydrogen out of the joint.

- Welds shouldn't have sharp re-entrant angles - may need to be ground at the toes to smooth the tansition and minimize the potential for fatigue cracking.

He didn't like using 4130, said the .3% carbon content is kind of high and there are other strong steels that are easier to work with (4130 is used for a lot of small tubing & aircraft uses - we have mostly a lot of big structural stuff where I work)

 

[RRich]

Re: How do you tell if it\'s crome moly?

Lots of interesting stuff!

Thanks everyone.

What I did:
It's just an ice chest rack, but it had to tee into the frame. I didn't want to weaken the frame there.
I took the rack's round legs, which were about 3/4" mild tube, teed them into a rounded mild steel section that conformed to the roundness of the frame, - which at that point was 1 1/4 CM tube. That "footing" was I think made from 1.5" tube - about 1/3 section. That gave it a footing to distribute the load, rather than just a tee type joint.
Then I welded that footing to the frame rail.

My friend brought home some gas rod he got from work he said they use on CM. I used oxy/acetelyne with a slightly carbonizing flame, heating the entire area several inches around it fairly hot - to a very dull red, then welded it. I made sure that there was no strain on the area - axle stands all around under it to prevent any bending or distortion.
I kept the torch playing on the surrounding area afterwards letting it all cool down slowly.
The actual welding was easy, I expected it to fight me but it flowed very nice. It almost felt like brass the way it flowed. I didn't use a lot of filler, trying to meld the two base metals together. The filler mostly went on top.

While I was doing it I saw 4 more cracks in the frame in the front - the TIG welds there were cracked along next to the weld. I used the oxy acet to fix those too, again pre-heating the entire surrounding area first, and cooling it very slowly.

I think one very important aspect was the pre and post heating. The TIG welds probably weren't preheated. To hot too fast, then too cold too fast caused the welds to break away from the base material.

The way it acted and felt I have a feeling it's stronger now than before. Time will tell, if it's breakable, he will. But then, since I get to run it sometimes, I probably will.

Thanks again for all the inputs - it has been very educational.

That's why we are here - to share info and help one another.

Thanks again, Rich

 

[Jim_Lou]

Re: How do you tell if it\'s crome moly?

Dull read preheat is more than is necessary. All you need to do is insure that the metal is warm enough that there isn't any trace of moisture on it. With gas welding I doubt that preheat is necessary at all. You can see the moisture from the flame condense on the cool metal, and then retreat as the metal gets warmer.

Post heating can cook the carbon out, which is one of the important components of 4130 - .30% carbon, but a carburizing flame might have prevented that or roughly compensated. It should be fine.