Dan Minette wrote: >> -----Original Message----- >> From: [EMAIL PROTECTED] >> [mailto:[EMAIL PROTECTED] On Behalf Of Nick Arnett >> Sent: Thursday, June 29, 2006 10:19 AM >> To: Killer Bs Discussion >> Subject: Re: Physics Prof Finds Thermate in WTC Physical Samples >> >> On 6/29/06, Dan Minette <[EMAIL PROTECTED]> wrote: >>> >>> >>> Good find on the phase diagram Charlie. To pick a nit, if the >>> consistency and structural integrity at that temp was actually the >>> same as well- chewed gum, I don't think that blacksmiths would >>> have >>> required big hammers and big >>> arms. :-) Hyperbola aside, I presume that you have no difficulty >>> with the multiple references to about a factor of 2 reduction in >>> yield strength at that temperature. >> >> >> Even if it is soft, it's still heavy... and the hammers aren't just >> for shaping it, they are for annealing, which requires kinetic >> energy. > > I thought I might have been wrong about the annealing process, so I > looked it up. One decent reference, which is supported by other > more > technical references, is > http://en.wikipedia.org/wiki/Annealing_%28metallurgy%29 > > To quote: > > <quote> > Annealing, in metallurgy and materials science, is a heat treatment > wherein the microstructure of a material is altered, causing changes > in its properties such as strength and hardness. There are several > phases in the annealing process, with the first being the recovery > phase, which results in softening of the metal through removal of > crystal defects and the internal stresses which they cause. The > second phase is recrystallization, where new grains nucleate and > grow > to replace those deformed by internal stresses. If annealing is > allowed to continue once recrystallization has been completed, grain > growth will occur, in which the microstructure starts to coarsen and > may cause the metal to have less than satisfactory mechanical > properties. <end quote> > > I think you are referencing work hardening....which increases the > strength of the steel at the price of ductility. That has to do > with > stress/strain. A good reference on this is > > http://www.engineersedge.com/material_science/work_strain_hardening.htm > > I know I'm a bit pedantic about this, but I've had to spend a good > deal of time worrying about the tradeoffs between hardness and > brittleness. I had long talks on this with a colleague who has a PhD > in metallurgy...so the differences are fairly big in my mind. > OK....we are back in territory I know a bit about. Before I started doing electrical work I worked for 7 years in a manufacturing facility with it's own machine shop and heat treat facility. I was QC inspector so I frequently performed Rockwell and Brinnel (No Joke) hardness tests and was working-enviroment-aware of the results of Charpy impact tests. I had to be taught a minimal bit of metalurgy in order to understand what I was doing.
Dan is correct. Annealing is a heat treating process wherein metal is made as soft and uniform as possible before it undergoes another heat treating process that hardens it to a desired state. (Most of the metals I worked with were 1018 &1020 carbon steels, 4130 & 4140 alloy steels, 12Chrome & 17-4PH stainless steels and just a few others. The company made chokes and valves to withstand 2000 - 40,000 PSI. They machined from bar stock, castings, and forgings.) We routinely case hardened (nitride hardening) machined stainless at 1200F without weakening the part and our heat treating used 2000F on alloy parts *to make them harder*. But then this was an industrial setting and a specific formula was being followed to get specific results. AFAIK the sub-100F temperatures *could* produce the weakening seen at WTC, but I can't say that I know that it *would*. The metals we were using probably would not have weakened at such low temps (to be honest I think the 1018 -1020 carbon steels could have, and further I believe the structural components of building steel are a similar metal with similar properties, say 1040 carbon steel.) But it all depends on the specific metal being used in the structure *and* if it were a quality product. I note that there has been some discussion of the Titanics sinking being related to the poor quality of the metal used in its hull. To have a rational non-chaotic discussion on this subject I believe one needs to understand the meanings of Hardness, Ductility, Yield Strength, Tensile Strength, and Shear Strength in at least a general manner, and to undertand how non-destructive testing and destructive testing are done (At least in regards to materials science). xponent Metal Maru rob _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
