Some chromoly questions

The Hurdy Gurdy Man · 2003-12-08T07:28:50+00:00

(Please note: I've crossposted this to both and since it's valid both places, and possibly ofequal interest to readers of both, so set your follow-ups accordingly ifyou're concerned about it!)So as my welding classes are coming to a close, I happened across somefactoids in my welding text that have me wondering about the wonders ofchromoly steel. The main one, though, is this whole thing about post-weldstress relieving using a torch. Just about every book I've read onfabrication suggests the same post-weld process, except for one; that bookis "Performance Welding" by Richard Finch. Now previous discussions onthe subject of Mr. Finch have led me to believe that he's not alwaysplaying with a full deck of cards, but my welding textbook for class saidsomething that actually matches his opinion on the subject.Finch writes that post-weld stress relieving of a weld in chromoly steelusing a torch is completely worthless because proper stress relievingrequires a six hour long process that simply can't be achieved with atorch. My textbook makes a vaguely similar assertion in that it says thatproper stress relief of a welded joint can take anywhere from one hour tosix hours for the heating segment of the process, with the point ofdiminishing returns on the increase in strength starting at around the sixhour mark. However, its implication is that SOME amount of stressrelieving will still have a benefit, but that the percentage ofeffectiveness is based on the total amount of time the part to be stressrelieved is soaked in the heat.Here, then, is my first question. Who is right on this subject? Is itworthless to even attempt post-weld stress relieving of a chromoly part,or can an appreciable amount of strength be regained through using a torchand allowing the part to cool in still air, or better yet, buried insand? Does anyone know of a chart that might exist someplace that showsthe relationship between gained strength and duration of applied heat?That first question...