High Carbon Steels

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I am trying to weld 4140 annealed to 1020 cold rolled. I do preheat but I don’t know the exact process to take to do so. Any advice?Thanks,James CollinsMechanical Engineer
Reply:Not a welding engineer, so I can't help too much.  But in my experience, you'll need to pay at least as much attention to the cooling aspect.  You'll want it to cool over as long a period of time as possible.  I've had many problems welding these materials together, and I have since decided to change materials for my particular part.  We had many problems with the weldment breaking at the joint, with the weld pulling from the 4140 side.Best of luck, and let us know how it works for you in the end.
Reply:I agree! I need to choose a different material. If you have any suggestion let me know. I was going to use a tool steel however, I think that will pose the same problems.
Reply:MJ, you might be able to weld that 4140 to 1020, but you should anneal (overtemper) the 4140 first to minimize the cold cracking tendancy.   Use preheat (300-500F) and postheat (800-1250F).  4140 is considered considered a high hardenability heat-treatable low alloy steel which typically contains .38-.43% carbon, .75-1.0% manganese, .15-.35% silicon, .8-1.1% chromium and .15-.25% molybednum.  I'd use mild steel filler.During welding, a portion of the weld HAZ will transform to austenite.  If cooled too rapidly, a martensitic or martensitic and bainite grain structure with high internal stresses will result.  The presence of hydrogen will greatly worsen this situation and promote even worse cracking tendancies, so postheat is essential.As far as tool steels go, you are right.  The welding problems will be similar to 4140.  There are seven major tool steel groups.  Without discussing them all, steels in the high-speed "M' group (M1, M2, ...M47) have much more carbon (.8-1.25%) than 4140, are free of  manganese, silicon and nickel, but contain vanadium and tungsten.  The higher carbon allows heat treat hardenability up to 60 (Rockwell C-scale).  Most suppliers provide tool steels in the annealed condition, but if it has been previously heat treated, you'll have to anneal it before welding.  For M-2, I'd suggest 950-1100F for preheat and postheat and 1600-1650F for annealing, 1000-1100F for tempering after quenching if you re- heat treat, which you probably are not interested in doing.  Air, oil or salt bath are suitable quench medias.  Without bothering to re heat treat for increased hardness, postheat and a slow cooldown rate should prevent cracking., OlPilot(Aero Engineer/Aircraft Maintenance Engineer)
Reply:It's good to hear from a fellow metallurgists. Thanks for the info. We are already doing the pre-heat and post-heat with the slow cool down. In the past it has worked...the place that is working on the parts has changed welders and the qaulity has gone down; But I have fixed that problem. So, thanks for all of the info guys.
Reply:I have used mild steel wire to build up 4140 dies with the mig process with great results. I do give them a pre-heat of a say 400 degrees at most. I have and have not post heated 4140 it states you should post heat to around 500.J P Streets Welding LLC
Reply:Jerry offered: I have and have not post heated 4140 it states you should post heat to around 500. could you tell us what your referencing when you say "it states"?thanksRaymond Ryel