Carburizing flame for welding steel.

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Tank sizes and withdrawal rates for oxy-acetylene aside; I found something interesting today in one of my books: Welding Engineering, Author, Rossi, Boniface, E (1954)I quote: "Although the neutral flame is most generally used for all heating and welding operations, there are special uses for both the carburizing flame and the oxidizing flame. With the carburizing, or excess-acetylene flame, free carbon is deposited in a very fine form. Use of this free carbon in welding has been taken advantage of in welding steel, for a thin layer of highly carburizing iron is formed which will melt at a lower temperature than the iron itself. The presence of this mixture, therefore, is conducive to fusion and shortens the period of heating so that the rate of welding is faster than with the neutral flame. However, as the carburizing effect of the flame is increased, the flame temperature drops and the amount of carbon deposited increases. For this reason, only small amounts of excess acetylene are used in welding."I didn't know this. have any of you heard of this before?Last edited by maarty; 08-30-2009 at 05:42 PM.
Reply:After a week of my first welding class my instructor got more into the science of metallurgy and stuff like that. It can be usefull sometimes.
Reply:I always thought that the neutral flame was the way to go. For a lot of reasons I think it is. But I never would have thought that an acetylene rich (carburizing) flame could lower the welding temperature of steel, and therefore allow it to be welded faster.
Reply:An increase in carbon will always lower melting temp.  Cast iron has a lower melting temp than carbon steel.  I have found in older texts the recommendation of using carburizing flame for steel pipe that has a higher than normal carbon content.  The aim was to maintain carbon content.
Reply:I understand wanting to maintain the carbon content, but to actually lower the melting point of the steel with a carburizing flame, is new to me.
Reply:Pretty common knowledge among "dark siders". The whole idea of that method was developed by Linde, and hence was oficially called the "Linde steel welding process"  and was commonly used by pipefitters. It should be noted that the process was developed for use with a specific filler, Oxweld 32-CMS. Use with any other filler may actually raise the CC of the weld pool too far and should be avoided. This is one of those cases where a little information can be dangerous. So basicly, yes you can use the 2-3x reducing flame with 32-CMS filler and perform the Linde process. However 32-CMS filler does not exist, period. It hasnt been made in 20 years or so. RG-65 has replaced it, and some retailers sell it as 32-CMS, but the chemistry is different and should not be used with the Linde welding process. Other than that specific use, RG-65 is considered an engineering performance equivelant for 32-CMS. Happy Welding!-Aaron
Reply:Thanks Makoman!
Reply:Based on the iron/carbon equilibrium diagram (see below), the addition of about 4% carbon could lower the melting point of iron from about 2800 F to 2070 F, which is very impressive, but  I wonder how much carbon is being added by the carburizing flame, because if the weld chemistry ends up over about 0.4% (1040 steel) you begin having issues with weld hardenability and cracking.http://www.sv.vt.edu/classes/MSE2094...es/kimcon.html  click on the dots to see the solidification phase (structure) under equilibrium conditions.
Reply:Originally Posted by pulserBased on the iron/carbon equilibrium diagram (see below), the addition of about 4% carbon could lower the melting point of iron from about 2800 F to 2070 F, which is very impressive, but  I wonder how much carbon is being added by the carburizing flame, because if the weld chemistry ends up over about 0.4% (1040 steel) you begin having issues with weld hardenability and cracking.http://www.sv.vt.edu/classes/MSE2094...es/kimcon.html  click on the dots to see the solidification phase (structure) under equilibrium conditions.
Reply:I use a carburizing flame to heat treat my chipping hammers and some cold chisels prior to re-sharpening.  Adds a little hardness to them.  Once they reach dark cherry red, I quench them in old motor oil.  Not an exact science for heat treating, but works for me.  They stay sharper longer.