Andrew R Stewart 

I believe the question is whether the steel's modulus of elasticity lowers due to the heat of poorly done welding. I just did the unusual, for me, and tried to find the answer via surfing the internet. here's what I found. I've omitted the names and such for their privacy.

The mechanical properties of steel will certainly change with heat treatment and microstructure but this statement pertains to the properties that are governed by plasticity, e.g., strength, hardness, ductility, toughness, etc. In stark contrast, the elastic properties, such as the Young's modulus and Poisson's ratio, hardly change at all, or if they do, the change will be very small. The modulus is essentially insensitive to microstructure, heat treatment, strain rate, prior history and even small changes in composition, as it is a function of the elastic "flexing" of the atomic bonds. Thus, compare a low strength mild steel, with a yield strength of 300 MPa, with an alloyed maraging steel that could have a corresponding strength of 2000 MPa, and contrast this almost order magnitude increase in strength with the fact that the Young's modulus of the two steels is essentially unchanged.
Bottom line: The elastic properties such as the elastic modulus are essentially insensitive to heat treatment and microstructure.

This jives with what I seem to remember being told a long time ago by one of my mentors. Any heating then cooling of steel is heat treating to some degree. We tend to only use the term when talking about controlled temps, time and cool down processes which result in a pre decided spec. But bad welding is just not controlled heat treating too. I have more thoughts but I should go back and read the linked thread first. Andy

PS- Well after 122 posts and on page 5 of Trakhak's linked thread I found the relevant post about the story. I gleamed no new info for it though.