There are a few posts on the subject. Take a look at the information already listed. Though I don't agree that it is required for a sound gouge, John Wright I believe indicates that that a AWS document does suggest preheating when gouging material required to be preheated when welding. I too would like to see some evidence that this is necessary.
http://www.aws.org/cgi-bin/mwf/topic_show.pl?pid=98682;hl=gouging%20preheathttp://www.aws.org/cgi-bin/mwf/topic_show.pl?pid=75738;hl=gouging%20preheathttp://www.aws.org/cgi-bin/mwf/topic_show.pl?pid=5059;hl=gouging%20preheatIn the cases in which you DID not preheat before, did any cracks occur? If yes, then preheat, If NO- Why preheat ? Any localized hardened areas that are very thin and near the surface of the material will be subsequently remelted during welding and thus any residual stress removed.
I too would love to get a answer for this question. I have based all of my opinions on other information I have read ofver the years and am not an expert. I would like to see some "FACTS".
A simple "Gouge and PT/MT may answer all of your questions. There are also variables related to the size of the gouge, size of the rods, number of passes etc all that could affect the size of a hardened area left by arc gouging.
I would imagine if you are doing tool and die work you may have access to a hardness tester of some type. A hardness profile on the gouge befer welding after welding with and without preheat would be a pretty good source of information. The highly hardenable materials would be much more sensitive that carbon steels and HSLA materials I have worked with.
Gerald Austin
www.weldingdata.com