Chromoly.... tink of death??

Date 08-25-2005 05:30

You could drive people nuts just walking around and occasionally hitting a couple of drill bits together.

On a more serious bent, one of those dye check kits sounds like a good starting point here.

Is some sort of NDT done?
Bill

By jarsanb (***)

Date 08-25-2005 12:38

In a lot of cases where this happens, it's from a lack of fusion area at the tack welds. The "tink" noise sounds loud but the seperation may not be noticable just by looking at it. Still should be removed before welding over tack. In other situations, sometimes tacks are made without filler, and those may crack through the face.

By - Date 08-25-2005 12:38

4130 is a Heat-Treatable Low-Alloy Steel, not a chromoly steel. Regardless, the 4130 has high hardenability and are susceptible to hydrogen cracking in the weld metal and HAZ if sufficient preheat and interpass temperatures are not maintained. It is a good chance that your "TINK" is hydrogen cracking in the weld or HAZ. I think I would suggest some sort of NDT to determine if this is not the case.

Chuck

By MDG Custom Weld (***)

Date 08-25-2005 18:49

Dye penetrant will only show a crack that has made it's way to the surface in some fashion. A mag particle test will be able to show something that has not propagated to the surface. This testing method would be recommended only second to x-ray, which in most cases is cost prohibitive. I'm sure you should be able to find a local shop or testing lab that will perform any of these test for a fraction of the cost you will incur if you do have a field failure. As Chuck stated 4130 is not really CrMo steel and pre/post weld heating are critical. What filler did you use when you welded these.

By jwright650 (*****)

Date 08-25-2005 19:06

A parker probe is not that expensive if you plan to check welds in the future, it can help persuade the powers to be to spend the money on NDT equipment and training, if they know you will use it on future projects. Minimal training can make you proficient enough to evaluate your findings with that equipment. Basically the steel powder filings are lightly dusted over the weld and stick to where the magnetic flux leakage is occuring(the crack). If it holds powder it is possible that there is a problem. Here's the one I have...
http://www.parkreshcorp.com/da400.htm
http://www.parkreshcorp.com/da400kits.htm
Just a thought
John Wright

By Lawrence (*****)

Date 08-25-2005 20:37

*Tinks* happen for a lot of reasons.

First of all... you are dealing with 0.095 materials... A visual inspection with a 10X glass should reveal any cracks.. You are very unlikely to have subsurface flaws in stuff this thin.

If you have multiple tacks, check each one. Distortion can certainly break a tack in a situation like the one you describe.

If you have closely butted surfaces (like 0.095 sheet) sometimes movement in the base material (substrate) caused by tacking and welding will simply cause the two surfaces to rub together, if they are fitted together very tightly, that movement can come all at once and make that *tink* sound without anything at all breaking.

Are these control arms total custom fabrications or are there manufactures assembly/repair documents that you can consult for tacking/welding sequence, filler metal selection (already wisely mentioned), possible interpass temperatures and post weld stress relief?

Yeah I know, the value of Pre-heat and stress relief of 4130 is a can of worms with important people on both sides of the issue, especially on material below 0.125 inch. With carbon content of between 0.25 and 0.35 Most specs require a 600 Degree Maximum often with *no minimum* for pre-heat and interpass temp. D17.1 refers to D1.1 Annex X1 so you might want to look into that.

I'm just not sold on the value of expensive NDT equipment on material less than 0.125 in thickness... Most aerospace standard practice manuals require visual inspection aided as required by Red Dye check (Right on Bill) or FPI.

Finally, it often ends up doing more harm than good when well intentioned folks try to bring thin sections of 4130 to pre-heat with a rosebud or even an oven. If the torch is left too long in one spot (and it doesn't take long) damage is done.. Also; The second the torch is removed from that pre-heat operation, the thin material is at the mercy of the atmosphere and cools off way too quickly from the thinnest areas while lingering in complex geometries often causing unplanned distortion. The same thing can happen just walking between the oven and the workbench or just wrapping your work in a blanket.

A lot of words to say; Start by trying to find the simplest method within accepted guidelines. And with 4130 there may be some pretty wide guidelines.

By - Date 08-26-2005 02:18

Lawrence,
You make some very good points. Please allow me to voice my opinion. The carbon content of 4130 is 0.28-0.33%. For thicknesses up to 0.5" the recommended "minimum" preheat and interpass temperature is 300F. For HTLA steels (4130), 4 things determine the preheat and interpass temperatures: 1) the carbon content and alloy content, 2) condition of any heat treatment, 3) section thickness or amount of joint restraint, and 4) available hydrogen during welding.
Because of their high hardenability, it is necessary to preheat these steels properly for welding in order to avoid hydrogen cracking and to obtain a sound weld. Controlled preheat and interpass temperatures are necessary to prevent excessive hardness in the weld metal and HAZ. Actually, 4130 is one of the HTLA's with the lowest carbon content. Only 4027 and 4320 have lower carbon contents than the 4130. A few others have the same, but not lower, so preheat and interpass temperature is very important, probably moreso than PWHT. In the 4130, the most deciding factor for preheat and interpass temperature is the thickness, more than the carbon content.

Chuck

By Lawrence (*****)

Date 08-26-2005 14:23

Chuck,

Isn't the 300 degree F preheat in essence insurance against any moisture on the surface of the parent material? What else could be happening in the matrix at 300 F ? Thats what I've always read and been told, but now I get to ask somebody who actually knows :)

The thin section 4130 thing has always been a mystery to me as far as why the material suppliers and the technical texts such as ASM Vol 6 stick to there guns on preheat but the people who actually produce the welds on thin section 4130 almost never follow these suggestions. From both widebody, military and private Aviation, to high performance bicycles and motocross frames to NASCAR rarely if ever do anything more than warm the part to 100-150 F to make sure no moisture remains.

Here are a few examples
http://archive.metalformingmagazine.com/2001/01/Lincoln.pdf

This "Welding Journal" article offers NASCAR type procedures for 4130 that suggest that preheat was "not desirable"
http://www.aws.org/wj/apr03/AWfeature.html

I'm on the fence here... The thread is interesting and it still sort of surprises me that some pretty big fish out there seem to flout established guidelines and even go out and publish procedures that appear to contridict sound technical data.

By - Date 08-26-2005 15:12

Lawrence,
With due respect to the AWS Journal article, it refers to 4130 as a chrome moly. It is not, it is an HTLA. The minimum preheat of 300F is not primarily for moisture removal, although that could be considered a good thing. For thicknesses up to 0.5", the 300F is for both preheat and interpass temperatures. Regardless what it is being used for, low hydrogen welding procedures MUST BE USED with sufficient preheat and interpass temperatures to prevent hydrogen cracking. Let me say this...The combined carbon and alloy content of the HTLA's are sufficiently high to promote the formation of martensite, which may make the 4130 more susceptable ot hydrogen cracking. HTLA's are very prone to hydrogen cracking. The best approach to welding HTLA materials is to use the recommended preheat and interpass temperatures to slow the cooling rate of the weld enough to permit the formation of softer bainite instead of the much harder martensite, which will be more prone to hydrogen cracking. Whether one follows the recommended preheat and interpass temperatures of these AISI Steels is up to the individual. But, one should know the possible detrimental effects if he/she chooses to neglect those recommendations.

Chuck

By kawgomoo (*)

Date 09-08-2005 03:15

crazy crazy..... well first ndt is pretty much out. we are not that kind of shop. pretty much the same as building nascar chassis. but we dont have any rules. we use er80s-d2 1/16th filler, amperage set at about 160-170. pulsed by pedal. small gas lens and 3/32 red tungsten. when i weld the metal usually turns a gold/purplish. this is desirable. sometimes it gets kinda flaky and grey which worries me. usually when the metal is warm from welding on other parts of the arm.. does this seem to be a problem. i look for cracks but see none. the tink seems to be small tack welds breaking as i approach them during the course of welding. i dont use filler when i tack, cause i hate hitting that blob.

also smart asses in the shop have taken a liking to throwing nuts and butt connectors on my table while im welding.... tough being the FNG ;)

By - Date 09-08-2005 12:56

Autogenous tacking (tacking with no filler metal) can be a possible cause to the "tink" sound you hear. It is very possible that the tack is cracking and you can't see it with the naked eye. There is not a lot of strength in an autogenous tack. Like you said, it might be your shop buddies just messing with you by causing the sound. Regardless, if you are welding over the autogenous tack with filler metal, and the part has not moved, it probably won't hurt you.

Chuck

By jon20013 (*****)

Date 09-08-2005 13:39

I would agree 100% with your statement Chuck. No matter when one hears that "tink" it always manages to send shivers up the backbone and make ones neck hairs stand on end but in the application being discussed it probably doesn't matter too much and, as you say, welding over an autogenous tack would probably not have any adverse effect.

By Lawrence (*****)

Date 09-08-2005 14:53

One little technique note to add to the good advice already given.

The oxide color (Blue/Gold) is of negligable importance to the soundness in a 4130 weld for the most part with the following checks.

1. Do not weld over colored oxide, either tacks or subsiquent passes in multi pass welds. Remove oxide color with a wire brush or light abrasive.

2. Removal of oxide will make for a more corrosion resistant joint and is a reasonable expectation for paint prep.

Your Flakey Grey stuff ought to be avoided. Generally this is an argon shielding matter on the face of the weld. Incorrect Torch angle or argon flow (too much or too little) can cause poor coverage. For the most part the melt thru on 4130 is not gas backed and ought to be nice and shiney. Another cause for this coloration could be continuing to weld after dipping your electrode into the weld pool or filler wire... If your electrode is not in perfect condition *stop* and make it perfect.