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post #1 of (permalink) Old 03-05-2004, 07:41 PM Thread Starter
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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
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post #2 of (permalink) Old 03-06-2004, 07:22 AM
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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.
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post #3 of (permalink) Old 03-06-2004, 08:16 AM Thread Starter
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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?
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post #4 of (permalink) Old 03-06-2004, 09:01 AM
 
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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)
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post #5 of (permalink) Old 03-06-2004, 10:35 AM Thread Starter
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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.
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post #6 of (permalink) Old 03-06-2004, 11:21 AM
 
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Re: How do you tell if it\'s crome moly?

</font><blockquote><font class="small">In reply to:</font><hr />
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
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post #7 of (permalink) Old 03-06-2004, 12:26 PM Thread Starter
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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.

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post #8 of (permalink) Old 03-06-2004, 01:19 PM
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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.
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post #9 of (permalink) Old 03-08-2004, 07:29 AM
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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
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post #10 of (permalink) Old 03-08-2004, 12:20 PM
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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'.



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