On Jan 2, 1:42 pm, "Phil" wrote:
If you have any doubt as to the hardenability of any piece of steel , just
light up your TIG Torch and get it close enough to your steel specimen and
melt a small fly speck spot , turn off the welder and touch that spot with a
file , even on low carbon steel like 1018 you may find that the file will
give up just about as easy as the hardened 1018 will , hardness and loss of
ductility pretty much parallel each other , I have seen 4130 parts that
couldn't be filed or cut with a hacksaw , not good .

That applies to just about any steel with any arc. It has
something to do with the extremely intense heat and electron flow of
the arc. I spent years welding up broken castings and worn
crankshafts, and to avoid those hard start-spots (which crack easily
and play hob with the milling and turning cutters after welding) we'd
start the arc on a scrap bit of steel held against the part and run
off that onto the work. The only hard places after that were in the
transition zone, especially in cast iron, which has around 4% carbon.
You had to keep that zone as thin as possible, so we used nickel
filler and applied it a low amperage to minimize dilution of the
parent metal.

DAn