Hello,
I was wondering if anyone knows the procedure for welding 4130 heat treat to x 42 pipe. I'm using 325 for preheat, 6010 root and 7018 fill and cap then allowing it to cool in floor dry. I am having cracking issues in the root. If anyone has a better procedure or any info on this your help would greatly appreciated.
Tony
There could be several reasons, but since you mention letting it cool, I am guessing that you are having hydrogen problems from the 6010 root. The 4130 is very sensetive to hydrogen, and the 6010 is not a low-hydrogen rod. Your best bet is to switch to a low hydrogen rod &/or process, such as GTAW or GMAW. You can also maintian the preheat after welding is done to allow they hydrogen that does get into the metal to escape. Try keeping it around 400-500F for 6-8 hours after welding, depending on the wall thickness. PWHT would help as well if you are able to PWHT before cooling below the preheat temperature.
Ok, I have talked to a welding engineer and he said and I quote "4130 is real funky stuff"... He said that the electrode selection was fine and the pre heat was fine, but the post heat treatment was incorrect. He said that the weld joint needed to be normalized. This consists of bringing the joint up to 1350 degrees, 100 degrees each hour per inch of weld, leaving it at 1350 for two hours, then bring the temp back down 100 degrees each hour per inch of weld. This is only for mild type of steel to a heat treated 4130. The post heat treatment is not necessary for mild type of steel to aneeled 4130.
Tony
There really wasn't enough detail in the orignal post to determine all the possibilities. The main one being materail thickness. 4130 can be welded all day without PWHT if it is relatively thin, such as thin-wall tube. PWHT is beneficial (although not alway practical) for all thicknesses and heat treat conditions, but increses in necessity with increasing thickness and original strength of the 4130. I still wouldn't weld on 4130 with 6010 though. The PWHT temperature may or may not suit you material. High strength 4130 may be tempered at a much lower temperature than 1350, so a PWHT that hot may compromise the strength of your whole assembly depending on teh 4130's origina heat treat condition. Also, a 1350F PWHT would not be "normalizing", but serves only a "stress relief" or "tempering" type PWHT as it should be below the lower critical temperature of 4130. "Normalizing" would be above the upper critical temperature, and typically around 1500-1600F.
There are other factors that could be leading to root cracking.
What is your root gap, root face, angle of bevel, thickness of material, heat input, level of restraint?
Are you maintaining an appropriate interpass temp?
How many hours are you leaving the pipe in the floor dry (not my preffered method of slow cooling).
What is the configuration of the part, ie. does it encompass the outside diameter of the pipe or does it weld onto the end of the pipe, ie a cap.
What condition is the 4130 in? Is it Q and T annealed, etc.
All of these things can change the behaviour of the weld. Simply applying preheat to a joint and welding it up may not be suffecient to prevent cracking
Well it was actually a test. The x42 was 6" 7/8 wall. The face was 3/32. the bevel was 60 degrees and the gap was 3/32. The preheat was 325 and interpass was around 500. I let it cool in the floor dry untill I could pick it up with a bare hand. The 4130 was a solid piece that had to be made into pipe. The reason for this was I had to weld 4130 flanges to x42 pipe. When the inspector did the bend tests, the coupon only cracked at the root, he even cut another one because he said he had never seen that before. I found out later that I was givin the wrong 4130 and I belive the tensile was around 120000. The flanges where 4130 was aneeled with tensile no more than 108000. Since then I have welded these flanges with 6010, 7018 fill and cap. They were tested yesterday and held 12500 pounds of pressure. I was also told when chooseing an electrode for dissimilar tensile strengths to use the one lowest in tensil, so you are not over welding the joint. What is your take on this? Why would you not choose to let it cool in floor dry?
I have another question, I am about to weld about 150 joints of grade b pipe to hammer unions, I am in a shop situation and able to roll the pipe. I want to wirefeed these joints and know that lincoln has special wire for this, but what I don't know is what to use for the root pass. I am thinking 6010 root and fcaw fill and cap. Any ideas?
Tony
Congrats on passing the test.
Undermatching filler metal makes absolute sense when welding two dissimilar tensile strength materials together. The reason for this can be summed up simply, if the strength of the weld metal exceeds the strength of the weakest member the weakest member will break before the weld metal. In practice this means the extra expense associated with matching filler metal gives no net benefit to the overall strength of the joint and is therefore unnecessary.
We weld 4140 4 in. square bars to 4140 4 in. square bars and utilize matching filler metal so that it can later be heat treated. Everything is Q and T. For this we use GTAW.
As for floor dry, it does work but I don't think it always gives a very consistent cooling rate.
Grade B to a hammer union. These are both basically plain carbon steel and shouldn't present much of a problem. They do have a little higher tensile strength than the 6010 does but it is very common to use 6010 for your root in this type of application. Where you are going to run a FCAW fill and cap you might want to try a GMAW root. Of course you should have a written weld procedure for any welding you do and the procedure should list the appropriate filler metals. I have had succes with E70S-X for the root on many in shop open root applications and in some cases it has been required by the EOR. I might even think about a GMAW root and fill and cap if I was going to roll it or possibly even metalcore. I would of course test this before I did any work on a production part.
Forum
