In article ,
Michael Horowitz wrote:

In preparation for doing some simple OA welding on a rudder, I've been
practicing on some 4130 scrap. Since there is filler where it's not
structurally important, I"ve been filing the excess material. All
except one and it's as hard as if I were trying to file stainless.

Is this an indication that I was using an oxidizing flame on that
sample? - MIke

If you fill with 4130, the weld will be hard -- and brittle. That is why
you use regular welding rod on 4130 -- the thicker material in the weld
relieves stress and keeps things good.