I'm not a REAL welder but have done some daubing on occasion(G) in TIG, MIG, SMAW and oxyacetylene. I worked in the nuclear business for many years around some mighty fine welders and even some Welding Engineers (BS in Metallurgy, etc). We welded seats on stellite-lined valves and added inconel buttering to the nozzles on the RPV (reactor pressure vessel) among other things, and everything had to be dead-nuts to pass the X-ray and other NDEs (non-destructive examinations). Tom and RWTF have it right, cleanliness and smooth flow are the 2 main keys to a good weld.
We (and I in my own experience) have found that the heat-treatment is critical in not ending up with hard spots in the weld, usually at the point of weldment. If not preheated, the larger mass of unheated steel will act as a heat sink and, as soon as the welding heat is removed, will SUCK the heat right out of the red-hot welded area and quench it. One effective procedure is to pre-heat the entire area of the weld to 500F or higher before ever striking the first arc, and to extend the cool-down period by wrapping in insulation. This not only avoids the quenching action that causes hard spots but also minimizes the warpage caused by the uneven pinpoint heating of the weld.
HTH, regards, Joe
