Is pre-heat needed on a TIG weld of 4130 tubing?

Tue, 31 Aug 2021 10:03:25 GMT

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I'm planning to make a bicycle frame of a mix of 4130 and mild steel.  I read somewhere that you need to pre-heat welds on 4130 to prevent hardening in HAZ due to quick cooling of parts that are not pre-heated.  Is this true and could you also accomplish the same thing with a post-heat of the HAZ?
Reply:Nope....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:No. Er70s or some er80s-d2.  The debate has been covered many times.  I swear by the 80s-d2 and have seen many of my cages survive the nasty of the nasty.Miller Dynasty 200DXMiller Spectrum 250DMiller Millermatic 200Bunch of old blue dinosaurs....
Reply:It needs to be super clean. Not too cold. At least room temperature. Use ER70S-2 as the tubes are very thin. Thinner than that used in planes and race cars. The dilution of the weld by the 4130 is 40 to 50 percent due to the tubes' thinness. For standard 0.9 mm tubes, use .035" filler and make the fillets about twice as big as that. For hardened 4130 bicycle tubes, make the fillets maybe three times the filler thickness, but at least twice thickness. The hardened tubes will stress the welds (or right next to them) more greatly. A larger fillet will help spread the stress.I used to get British tubes that came with thick, wax-like grease and a lot of metal shavings. Those require a lot of prep. Some other makes come with a thin film of light oil and little to no metal shavings. The oil still needs to be completely removed though.TIG welding doesn't induce the weld stress that MIG welding does in thin 4130 tubes. MIG welding should get post weld stress relieving, but it's not needed when the tubes are TIG welded.Last edited by Ag-Cat; 03-01-2017 at 12:01 AM.
Reply:Er80 is actually er70 with a slight addition of 4130. It was formulated to provide increased strength in the weld to better match the based metal. Preheat prior to weld and stress relief is always recommended for weldments greater than 3mm in thickness. Less than 3mm is optional.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Replyreheating will never hurt, ever. With that said on something as thin as bicycle tubing you must be very careful. It isn't necessary in your application if you use er80s-d2
Reply:In the mid 1980's, I was a materials engineering student in Belgium. We had many projects that were sponsored by bicycle companies and bicycle component companies. Before I went to Belgium I had tried my hand at brazing bicycle frames, but I didn't have much money to practice.Before the 1980's, preheat and post weld heating steel was mostly dependent on the steel type without much regard for thickness or thinness. Theories and concepts were changing to where certain steels would call for different heating requirements based on their thickness. The thinner they were, the less heat required. some steels, like 4130, would get to a thickness or thinness that required no pre-heat at all.Most of my reading material at the time was very dated. I bought a new boo, that might have been published around 1981. it was about race car welding. In it, it was stated that thin wall 4130 didn't need pre-heat or post weld stress relieving for, "careful TIG welding." That was a new concept to me in 1985. I knew about gas welding 4130. MIG welding still called for post weld stress relieving.In the university lab we had been brazing steel bike frames. I wanted to try TIG welding, based on the new book I had. At the time I had never heard of a commercial chrome moly bike frame being welded. There were no tube sets meant for welding back then.In brazing we found that manganese-moly Reynolds 531 was more temperature sensitive than 25crmo4 (4130) chrome moly Columbus SL tubing. That helped me determine that 531 wasn't going to be suitable for welding. When we were brazing we would test the tubes for hardness and strength.I tested ER70S-2, ER70S-6 and ER80S-D2, or whatever their equivalents were in 1985. All were acceptable and stronger than the tubes. ER70S-2 allowed me to make the best looking welds.Years later at an American university, welding bike frames with ER70S-2. ER80S-D2 and ER312 were found to have no significant difference in frame strength.In 1987 I went to Italy to study bike frame building. I found out there were two well known Italian frame builders that had been welding Columbus SL since the 1970's. One of them had a father that was an aircraft welder. I originally wanted to hone my old world brazing skills there.I would get old broken, disposed or cheap bikes to practice welding. I like to clean new tubes with mineral spirits (sometimes auto brake cleaner) followed with alcohol, inside and out. I then like to warm the joints with a torch before welding, to remove moisture and maybe whatever trash might have gotten on them.4130 will weld to mild steel just fine. If you are using 4130 tubes meant for bicycles, they are thin. The mild steel tubes, if bike tubes, will likely be thicker. Then there are people that weld up custom bike frame with heavier 4130 and mild steel tubes.
Reply:I would assume Er70 would weld thin wall frames just fine. I just go with AWS guidelines and use ER80. When my customers want documentation I default AWS guidelines.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:as stated above not cold I check with a propane torch if you see the moisture flash off then do every one if its warm and dry go for it.Syncrowave 180 SDMillermatic 250XSnap On MW 120 Econopac 50Victor O/A with some Smith Attachments 30 X 50 shop with a 400 Amps