TIG Chromolly with Silicon Bronze?

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I saw a couple pictures of a NHRA Drag car by a very respectable chassis builder with bronze colored welds on his chromolly tubing in the car.Now I think he made a root pass with ER70 and went in with the silicon bronze and filled it the rest of the way. The tubing is 1 1/4" chromolly and I think the wall thickness is .083".Anyone have any input on this? I have never seen ER70 chromolly welds look this good in my life, these look like fat aluminum welds. Plus they are bronze colored beads, so Im pretty damn sure its SB. SB itself is too weak to weld anything structural with it, from what I hear... Anyone use it?Thanks guys, this is a great place indeed, I have learned a lot allready.
Reply:For us gas welders, RG60 is considered the best rod to weld chrome moly with.
Reply:i've always used 70-s on moly tubingall my cars pass inspection  ...zap!
Reply:I'll have to check my rod catolog and check out the specs on RG 60.Thanks guys.
Reply:I also saw some photos posted of a car being built that the welds were very bright bronze colored.  I asked in that post what they were using and the claim was that it was a new shielding gas cup configuration that was creating the color.  I didnt buy the explanation because I seriously doubt that a shield cup could creat any difference in the weld color.  I kind of figured they were using some type of stainless or bronze filler in an attempt to make the welds look better.
Reply:Many steel bicycle frames are brazed together using a nickel alloy.  Nickel alloys develop a bit of a gold tint from the heat.
Reply:brazing chrome moly is a no noChuckASME Pressure Vessel welder
Reply:Elaborate?
Reply:Brazing chromolly makes it brittle from what I read in a welding book. Brittleness = cracking, and cracking leads to utter failure. Best way to join chromolly is TIG, but thats besides the point, I was wondering if any of you use Silicon Bronze on your chromolly.
Reply:yup what Neil saidChuckASME Pressure Vessel welder
Reply:This is not to discount the Chopper or Neil posts.Brazing cro-moly is not uncommon.  As stated above especially in the bicycle industry.  It is done with and without lug.  Bronze is used for non-lugged construction and silver is used for lugged construction.  It is still common even with the popularity of tig.     My very first project was a track racing bicycle frame.  Track bicycles are subject to incredible amounts of stress from dead starts and crashes.  Never a crack through a full season of racing and a crash.  The Bicycle was built with lugged construction and 45% silver brazing alloy.  I raced the bicycle in the 1996 Olympic Trials at Trexlertown, Pa.
Reply:everyone uses ER70S2 rod - if you do not prep it properly with steel wool and acetone - and if you get it too hot, it will not have the bronze appearance.If you prep it properly and use JUST enough heat it will have the bronze appearance.  Do not use any rod other than ER70S2 or ER80D2 (I think that's it).  That's all that is used and the 70 is more common.I know this - because i just welded my SFI 25.5 chromoly cage.
Reply:I have to ask everyone ... what is the point of spending the money on expensive chromoly tubing only to weld it with anything less than what it's supposed to be welded with - chromoly! Yes Lump , 80d2 . There is a difference between what will hold the bars together and what will enable a roll cage to do what its designed to do. Bicycles are totally different I'm afraid. On the other hand , if your willing to get into the car yourself after your brazing by all means break a leg!  Johnny
Reply:It is generally not recommended that chromemo be welded with chrommo for brittleness reasons.  Eg., for gas welders, RG60 is the recommended rod to weld chromo with because it makes a ductile weld that will not crack.  www.tinmantech.com says something about it.
Reply:There are also many different chromium/molybdenum alloys that vary in hardness. The filler metal you use should be dependant on the final strength/hardness desired and wether or not your part will be heat treated. Welding changes the molecular structure of chromemoly and it must be heat treated to regain its original hardness.  (maximum hardness is not always necessary and/or practical, thus heat treating is not always required) For racing purposes check the rules and regulations of your local sanctioning body, such as NHRA, for the rollcage and structural minimum specifications for your application. They will tell you what is required for materials and what welding methods are acceptable .We offer correct, cheap and fast. Pick two.Weldanpower G800XMT 304Syncrowave 250Millermatic 135Maxstar 91Heliwelder 4A/DDR 224/HPA/BHFT Plasma
Reply:Kind of.  Welding causes all non-austenitic steels to become hard/brittle.  Mild steel and ChroMo included.  The heat treatment is done to make the weld ductile again, not to harden it.  If heat treatment is not going to be performed, it is recommended a weaker 60-70ksi filler is used with gussets to improve the ductility of the joint in as welded condition.
Reply:Was the car fram anodized, that may why the weld color changeThanks
Reply:Keep in mind that that bronze color ur seeing may well be the same straw yellow tint ya see on a lot of steels after welding but before any kinda cleanup.cm tends to show it very well.see if ya enlarge the picks and see a light red and blue fade on both sides of the weld(although should be very small zone and hard to see on a pic if not impossible).if thats the case its just a straw color caused by the heat of the weld that hasnt been cleaned off.Assuming that is indeed what it is(and we all know what that leads to) i was taught that that nice even color band was as good of a indicator as a nice smooth bead that i was welding in the correct temp and speed as well *** letting the end of ur bead cool down with post flow..if ur moving ur tip and puddle to fast then ur also moving ur sheilding gas away from ur bead to fast and the color will change as well as allowing cotamination to ur weld before it had cooled enough
Reply:wlii I am inclined to think it may be th ga s cup 7 the fliow rae of the argon,also silicon bronze is not for chro moll,9can't handle the  strength/load .I have seen this type of appearing weld you are talkin about many times over the years ,first of all the the surface ha s to be surgically clean/shiney,gas flow rate ,ififst saw this type of weld s on funny cars back inthe 60's770's,wondered how was that did,shet that is really beautiful,i got to do that toothe welder i have now does that same type of weld on plain ole hot roll 1/4 plate(it's in the gas cup&flow rate,also the right alloy rod,Hartman engineering made some of the most beautiful welded road race karts you ever seen,copper /bronze coler welds polished welds&VERY STRONG too,the shifterkarts that are made byZIP Karts IN England are all brazed/silversoldered ,VERY STRONG ,strong enough for a superkart at at 140mph,the weld is more ductile/flexible,yes it's sstrong enough for a100hp shifterkart at 150hph it'll hold ,I've used tig rod from rockmount&got the same results,also harris brand(er70-2for chro molly)there are aerospace alloy maretials avail at a slightly higher cost but there is no compromise in quaility either.whateveryou do do not use silicon bronze rod  for structure&chro molly,sil/bronze is better suited in high vibration areas&light guage consrtuction/light stress,not for chassis roll barsframes,simply stay with a tig filler rod for chro molly it mat take awhile but iit is righthere  with what you got,now go back to weldin   CYA, rick beaver