Welding mild steel to chromoly?

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Hi there, I'm a newbie welder and I'm wondering if anyone can tell me if it's OK to weld mild steel to chromoly? I'm making a 'T' shape out of chromoly pipe and want to put some gussets in around the join or junction of the 2 pipes. I was planning on using mild steel for the gussets. Would that be OK? The 2 materials wouldn't react against each other???Many thanks.
Reply:Originally Posted by siringoHi there, I'm a newbie welder and I'm wondering if anyone can tell me if it's OK to weld mild steel to chromoly? I'm making a 'T' shape out of chromoly pipe and want to put some gussets in around the join or junction of the 2 pipes. I was planning on using mild steel for the gussets. Would that be OK? The 2 materials wouldn't react against each other???Many thanks.
Reply:Rojo, you assume he is using electric welding  , Anyway yes its fine to weld those materials together, use the mentioned filler if electric welding and RG-45 if OA welding. If Electric welding be sure to temper the weldment when finished. Shy away from Mig if you can.-Aaron
Reply:There is some very important information missing here.1. What thickness is the the 4130 tube?2.We need to be more specific on the process, GMAW, GTAW, SMAW????(Mig, Tig, Stick)3. If you were Oxy-fuel welding it, you would want to use RG60, as RG45 is a sever under match.(Yes, the steel is likely only 36,000 psi, but it still matters.)It is generally considered bad practice to attempt any kind of at home heat treatment, especially with a torch.If the tube is thinner than .125" wall, then using RG60 or ER70s-2 is acceptable, and requires no post-weld treatment. Heat treatment should be left to places that are certified to do so, and is really only needed on thick sections of 4130 where 4130 filler rod was used.Best of luck, you can search Lincoln's website for an article on this.
Reply:Hi and thanks for the replies.It's all light stuff I'm welding. The 4130 has a wall thickness of only 0.058 and the mild steel is roughly about the same thickness. I am using a Mig as that's all I have. Would Tig be better?Thanks again.
Reply:Originally Posted by siringoHi and thanks for the replies.It's all light stuff I'm welding. The 4130 has a wall thickness of only 0.058 and the mild steel is roughly about the same thickness. I am using a Mig as that's all I have. Would Tig be better?Thanks again.
Reply:It's all light stuff I'm welding. The 4130 has a wall thickness of only 0.058 and the mild steel is roughly about the same thickness. I am using a Mig as that's all I have. Would Tig be better?
Reply:Originally Posted by siringoHi and thanks for the replies.It's all light stuff I'm welding. The 4130 has a wall thickness of only 0.058 and the mild steel is roughly about the same thickness. I am using a Mig as that's all I have. Would Tig be better?Thanks again.
Reply:Originally Posted by RojodiabloMig is fine, unless you have to present it to God for testing.I agree. If it is life lending crucial, then maybe even the .058 is questionable. But for everyday projects?? Have some fun, and post up some pictures.
Reply:Originally Posted by makoman1860Yes Tig would be a better option if you are looking for a more durable weldment in a one-of situation like this.  Revhard, RG45 is NOT an undermatched filler for 4130 in the N condition in the tubing size he listed. Testing has shown 90-100 ksi tensile strength of the fillet using RG45 filler on 4130 in a properly reinforced weld of typical aircraft tubing. This is due to the intermixing of the materials in the weld pool.  Also your notes on heat treat conflict with most of my engineering texts and approved procedures used by the aerospace community for many years. I have noticed your views are popular with the motorsports crowd, im not sure why the difference between aerospace/engineering and motorsports groups on the same material? Maybe its the expectation of the completed assembly, racing guys seem to get away with murder due to low cycle times of the parts, we dont get away with anything!-Aaron
Reply:Originally Posted by revhardHeat treating is needed on heavy parts and/or 4130 rod parts as mentioned. I am pretty sure your engineering texts do not advocate heating it to a precise temperature of "red"  hot at home with an oxy-fuel torch and air-cooling at an undisclosed ambient temperature.I am fully aware of how important post-weld heat treatments are on 4130, but doing stuff at home without parameters has often led to situations far worse than my suggestions.I have aerospace certification on 4130, as well as destructive test results, and seemingly limitless training oppurtunities. This does not mean that I think I'm right all the time, just that I have passed very high standards doing what I have learned. Look at John Force's crash. The welds and parameters were cleared of any fault, and they adhere to the same basic procedures when building a tube chassis. Destructive tests are quick ways of learning what works and what doesn't.I believe you that RG45 is fine, and so is RG60. It's a moot point on my behalf.TIG would be better, but I agree that it depends on what you are doing.
Reply:Originally Posted by makoman1860.058 questionable?? What are you used to, water pipe??
Reply:Yes, heat treatment is fantastic in the right hands. I'm sure you have more than a few minutes on the torch and test procedures. There are a ton of things that guys do wrong.I was merely suggesting that a rookie maybe shouldn't play with heat treatments.I have seen what just some simple heating and cooling can do to 4130, and it can be very bad. Raising the carbon content is a new one on me. With TIG it's impossible, with OAW there is a component that can introduce carbon, but I have only heard of that working during fusion welds.(carbonizing flame)Anybody that is familiar with dynamic loads will not discount 8000hp drag cars. If you have ever seen tire shake, you would know that 510mph has nothing to do with it.More than one way to skin a cat, and we can agree that TIG or OAW are the 2 best methods, regardless of opinions on them.
Reply:Originally Posted by revhardYes, heat treatment is fantastic in the right hands. I'm sure you have more than a few minutes on the torch and test procedures. There are a ton of things that guys do wrong.I was merely suggesting that a rookie maybe shouldn't play with heat treatments.I have seen what just some simple heating and cooling can do to 4130, and it can be very bad. Raising the carbon content is a new one on me. With TIG it's impossible, with OAW there is a component that can introduce carbon, but I have only heard of that working during fusion welds.(carbonizing flame)Anybody that is familiar with dynamic loads will not discount 8000hp drag cars. If you have ever seen tire shake, you would know that 510mph has nothing to do with it.More than one way to skin a cat, and we can agree that TIG or OAW are the 2 best methods, regardless of opinions on them.