Welding 4130N to Mild steel?

Date 05-06-2005 11:31

Might better check the governing rules at the track your friend frequents. I'm hearing from other car forums http://www.nastyz28.com/ubb/Forum23/HTML/002553.html that NHRA and others are moving towards all C/M cages/frames (even in the slower classes) and allow only GTAW(TIG) joints in the "as welded" (no grinding on the welds) condition.
John Wright

By Masta Date 05-06-2005 23:40

No issues with rules, I'm more concerned with the metalurgy(sp*) involved regarding welding steel to cro-moly.

Thanks

D.

By - Date 05-07-2005 09:53

Actually, 4130 is an HTLA (Heat-Treatable Low-Alloy) steel. Although it is sometimes called a "chrome-moly", that is not the case. The 4130 lacks the minimum required moly content (0.45%) and exceeds the maximum carbon content (0.20%) to be considered a chrome-moly steel product form.
4130, being an HTLA steel product form, has high hardenability and is susceptible to hydrogen cracking in the weld metal and HAZ. Low-hydrogen welding procedures must be used with sufficient preheat and interpass temperatures to prevent hydrogen cracking. This is not the case with mild steel. The relative high caron content of the HTLA steels compared to the mild steels also tends to contribute to solidification cracking in diluted weld metal, because it increases the temperature range over which solidification takes place. An appropriate PWHT should be done to the 4130 for maximum metallurgical properties, if that is the desired scenario.
To join the 4130 to the mild steel, an ER-80S can be used, but not "without issue". The matching filler metal composition for the 4130 is covered by AMS specification 6457A. ER-80S is compatible with mild steel and is not normally post weld heat treated, so you must make your decision on what filler metal you should use to join the HTLA to mild steel while taking into consideration the metallurgical characteristics of both.

CM

By Masta Date 05-07-2005 22:15

I am finding many differing opinions about post heat treating 4130. The lincoln electric site staes that 4130N that is under .120 wall thickness does NOT need to be heat treated. They also call for the use of ER-80S filler material to be used when welding 4130N. I have spoken to many cage builders and only one post heat treats. I will be using the "TIG" process to weld the cage. So where can I find a true, definative answer. Roll cages save lives, safety is paramount, I want to do this correctly but the info is so sketchy, almost based on opinion, not fact. I need some hard facts keeping in mind that we need to have the best possible weld under the given conditions and given "hobby-like" consdieration to how this will be completed. We're not in a cost is no object situation.

Thanks

Darren

By - Date 05-08-2005 02:40

I suggest you read up on the HTLA grades of stainless and decide what you should do. It appears you are getting numerous recommendations. I will say again that the matching filler metal for 4130 is listed in AMS 6457A. ER-80S is certainly usually used with no PWHT, but you are joining an HTLA to carbon steel. 4130, with thickness up to 0.5 in., will require a preheat and interpass temperature of 300F. This temperature is necessary to to prevent excessive hardness in the weld metal and HAZ. With a wall thickness of 0.120 in., a PWHT can definitely cause distortion, but I don't know if I fully agree that that thickness does not need to be heat treated. A sufficient preheat and interpass temperature can most certainly be considered a form of heat treatment. It does not necessarily have to be a "post weld" heat treatment. I cannot begin to make a suggestion on what you should do because I've never been closer than the TV to a "cage". All I can do is offer you some facts and suggest you make your own decision.

CM

By Masta Date 05-08-2005 02:58

I appreciate your very technical responses, I'm a self taught Tig welder with zero theory under my belt. I have my pressure vessel ticket but other than that I'm a self taught hack so excuse my ignorance please. So what you are saying is that we could preheat, weld and then leave it and that would be sufficient? Why exactly does 4130 need to be PWHT? My fear of PWHT is the fact that it is in a confined space, and how do you know, without expensive infrared guns, when you have reached the proper temp? Is it possible to not heat enough? or too much and do damage? How serious will it be if I don't heat treat pre or post? Thanks so much for your time, this is when I really enjoy being a welder, when I'm learning.

Thanks

D.

By kawgomoo (*)

Date 05-08-2005 08:12

i think er80s-d2 is what you are looking for. er70s2 then er70s6 are acceptable in that order.....

er312 stainless is good for welding dissimilar metals to 4130. typically stainless, but i dont see why it wouldnt work with mild to 4130 as well.

lincoln's homepage has an article about this very topic.

By happybearwelder (*)

Date 05-08-2005 14:31

I personally dont like to do TIG welding with carbon steel fillers. Porosity problems, some of which you cant see. I can do it I just dont like to. If it were me using TIG, I to would choose the 312 SS. I have done 4130 with MIG using er80s6 and beat, twisted, and bent the heck out of it with no weld zone problems at all. ER70S6, 80S6 and 312SS all work well with both metals and are all tougher than mild steel. I have never had it subjected to the type of stress encountered during a racing crash.
I was involved as a judge in a Mini Baha put on by engineering schools three years ago. If you ever get the chance to be a judge, take it. It's genuine hoot. Any how, They require 4130 tubing cages properly braced with at least, good looking welds (bird poop not allowed). We had several rollovers, end over end, and sideways, and with 106 cars entered, and at least 106 diffrent non professional welders, no cages let loose. All the students I questioned used er70s6, and used both TIG and MIG. Granted these only weigh a couple of hundred pounds and run 10 HP engines, but they really took a beating.
Now you know what I know (which aint much). Hope this helps

By - Date 05-08-2005 16:38

A couple of the posts have mentioned a 312 SS filler, and that is OK if lower strength is permitted. Lower strength filler metals can reduce the risk of cracking in some applications. To be perfectly honest, and based on your limitations, I would think a higher strength filler (ER80S-B2 for TIG) could serve you properly. This is not a "recommendation", but a "suggestion". The ultimate decision is up to you. The very thin diameter material you are using is going to make it hard to do any kind of preheat, but you will need to try. The recommended preheat and interpass temperature for the thickness you are using is 300F. for both the preheat and interpass temp. I believe that if you use that temperature when joining an HTLA of that thickness to a carbon steel, and you let it cool down very slowly, that you will not encounter any problems using an ER80S-B2 filler.

CM

By Masta Date 05-08-2005 18:54

I will be using ER-80S when I Tig it, although I have also heard of using SS filler, In this case I would rather not. I will look at a preheat setup and if practical I may go that route. Again thanks to all who have replied, I hope you don't mind having a canadian use the American Welding Society boards :-)

By jwright650 (*****)

Date 05-09-2005 10:55

[quote]I hope you don't mind having a canadian use the American Welding Society boards :-)[/quote]

This BBS is used world wide, and ALL are welcome, as far as I'm concerned :)
John Wright