Welding forged tool steel?

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My questions concern forged tools.  I’ve wondered what makes metal “tool steel” - composition-wise - when it’s used for common forged items?  Examples: a cold chisel.  a splitting-maul head (a quality one, not “chinese junk”)Is it carbon content level that makes them "tool steel"?  Would the two forged examples I gave likely be made from steel with differing compositions?And my welding-related question, stemming from the above:  If I want to weld these kinds of items to a mild steel rod or bar (for functional or artistic purposes), would I need something other than all-purpose mild-steel MIG wire?  Would ordinary wire produce a weak weld, due to a compositional difference with the forged “tool steel” object?Another thought: I can preheat the forged object using either propane/air or oxy-acet.  Would this be helpful for a better weld?Thanks.
Reply:High impact resistant stuff like a chisel or a hammer is usually made from W type tool steel (water-quenched). I would probably tig it with 312 stainless filler because it might want to crack, or find a specific W type filler. You could probably mig it with ER70s-6 just fine if it's for an 'artistic' application. If it was structural or an impact type load I'd go with something better.Welding/Fab Pics: www.UtahWeld.com
Reply:Not just carbon content, but alloying elements as well, magnesium, phosphorus, silicon, chrome, vanadium, etc. you can weld it with 70s-6 mig wire just fine, but it is not as strong as the tool steel. It is generally not near as impact resistant after welding.
Reply:The difference between tool steel and "regular" mild steel, often referred to as A-36 is the carbon content.  Tool steels and many alloys contain higher carbon content than mild steel.  Don't need to get into percentages of carbon for each, just suffice to say the tool steel is higher...we're talking fractions of a percent carbon here.You can forge tool steel and mild steel, the tool steel usually requires a slightly higher forging heat, say yellow to orange, whereas mild steel can be forged down to cherry red.As for welding, you can weld mild to tool and vice-versa.  The tensile strength of your weld, for example, is most likely higher than either mild steel (A-36) or the lower carbon tool steels.  I have stick welded mild steel and tool steel together with no problems.  If the stock is very thick, you might consider pre-heat, but that's another subject.  Stock like 1" or less probably doesn't need pre-heat, but thicker stuff might.  You'll need to weld a little hotter without any preheat.  Search the forum on guidelines for preheating your stock.
Reply:Tool steel is kind of vague but implies something a bit more than just Iron, Carbon and some Manganese.  Like a bit of Chromium for deeper hardening.  Maybe some Vanadium for fine grain.  Etc. On the low end, look up the composition of W-1 as opposed to O-1 and go from there. Anything in the "tool steel" range shouldn't be welded really cold and prefers a low hydrogen process to prevent cracking.  Hardwire MIG, TIG or something like 7018 stick.  Not a big deal for decorative stuff as long as it holds together."USMCPOP" First-born son: KIA  Iraq 1/26/05Syncrowave 250 w/ Coolmate 3Dialarc 250, Idealarc 250SP-175 +Firepower TIG 160S (gave the TA 161 STL to the son)Lincwelder AC180C (1952)Victor & Smith O/A torchesMiller spot welder
Reply:I had some 1/4" square rod which I cut into about 1" pieces for a small project. I had terrible fits trying to (tig) weld that stuff, it just didnt want to weld. Turns out it was 'keyway' stock. I dont know what it is composed of, but the 3' + - piece leftover was EXTREMELY stiff, felt like it would break before bending. It got tossed,  ,  , good for keyways, but nothing else.-corne-What is the sound of one knee jerking?
Reply:Originally Posted by cornemuseI had some 1/4" square rod which I cut into about 1" pieces for a small project. I had terrible fits trying to (tig) weld that stuff, it just didnt want to weld. Turns out it was 'keyway' stock. I dont know what it is composed of, but the 3' + - piece leftover was EXTREMELY stiff, felt like it would break before bending. It got tossed,  ,  , good for keyways, but nothing else.-corne-
Reply:The op is generally correct. The higher the carbon content the harder the metal but harder to weld.The posts from other are also correct in saying different alloying elements add to it.Im fairly sure it is not standard to weld such materials in critical applications however it can be done.I remember I used to weld this hardened round solid bar to my bench for certain forming jobs however it would always crack very easily. Pre heat and post heat is a good idea. Besides that im in the dark as to what filler to use so take note of what suggestions get made.All the best