pre and post heat treatment for TIG welding

I've heard a number of experienced welders say that a TIG welded joint requires post heat treatment and recommend an OA torch to bring the joint up
to a dull red and hold it for less than a minute and then slowly allow the weld to cool. On the other hand, the guy that wrote the book Performance Welding claims that he oversaw the TIG welding of 1800 Aerostar engine mounts that had no pre or post weld heat treament and had experienced no cracked joints. I'm sure that there are opinions and anecdotal evidence to support both sides of this issue. Are there any Pros out there that can comment on this?
Stu Fields
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First of all, are you welding 4130 ("chrome-moly")? If so, you'll probably get comments, but nothing you hear is going to be conclusive, Stu. This is a very controversial issue and it has been for 50 years or more.
If it's something else, what alloy are you welding?
-- Ed Huntress
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The old standard was to post weld heat treat tube joints in 4130 Chrome-moly steel, but the current standard is to use ER80S-B2 filler rod. This eliminates the need for the post weld heat treat.
Pre-weld heating is only needed on high carbon steels, tool steels, castings (iron, aluminum or bronze) and large sections of conductive metals like aluminum or copper.
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Ernie: I just stumbled on a page from American Filler Metals where they say that careful control of pre heat, and interpass temperature, amd post heat is essential to avoid cracking using AFM ER80S-B2 This doesn't seem to be in line with your posting?
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I imagine they would say that . I am speaking from experience welding chrome-moly with ER80S-B2. Also preheat, interpass temp and post weld cooling will be dependant on thickness.
If welding thin wall tube for bicycles, then no heat treat is needed. If however you are welding 3 inch thick 4130 plate for structural bridge components, then yes there will be strict heat control guidelines as stated in AWSD1.1. My copy of D1.1 is at school or I would give you the page number.
I remember that chart from studying for my Certified Weld Inspector card.
Also if you are welding 4140 gun components then I would be more careful of heat control since the higher carbon content could encourage cracking.
4130 and 4140 are both Chrome-moly steel, they just different carbon contents. While it may seem like 0.3% and 0.4% carbon both seem low, you have to take into account the "carbon equivalency" of the chromium and molybdenum. This makes the carbon more influential on the steel than say a 1040 simple mild steel.

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Ernie: Thanks for the clarification. BTW your original post was cited in the Experimental Helo Magazine. I expect to get some feedback from "knowledgeable" backyard welders. Thanks again.
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