The way steel is made hasn’t changed a whole lot over the years, ya know? The industrial revolution was a way cool thing back in times long ago. We got all kinds of cool stuff – the biggest thing being embracing technology.
Even with the group hugging of technology, there are instances when technology outpaces end user material requirements. That is EXACTLY what has happened with time and temperatures and separate annealing of stainless steel bars.
I have this request come to me all the time. If I had, oh, a dime for every time I’ve been asked to have the mill “add times and temps to this MTR”, I would be living the good life, sitting back sipping a beverage on a beach, covered in SPF bazillion, watching the waves lap lazily on the beach (I’ve put some thought into this sippin’ beverages kind of day, huh?).
In this instance, the MTR didn’t have a time nor a temp on the MTR. So, the gal in receiving gave me a jingle and told me I needed to get the MTR revised, or she was going to quarantine my bars!
I realize this is 2020, but I’ve had my fill of quarantine-ing and social distancing. And my bright shiny bars do not deserve such treatment.
Today’s blog post is “How without times and temps, bars will meet ASTM 484”.
It’s a process, literally, called PROCESS ANNEALING.
The question is asked because within ASTM 484, there’s a table that indicates the temperature requirements that material is to “finish”.
And that temperature isn’t in this list of standards and specifications! OH HEAVENS!!!
ASTM 484 is a pretty exhaustive standard specifically indicating what has to be in the material and how much (chemistry), what has to happen to that material (the producing process) and a bunch of other stuff that if I had it in front of me, I’d be happy to elaborate. But to get to the good stuff, there is a table that says that material has to be annealed at X degrees for X amount of time. I’d show a clip of it, but because of copyright stuff, I think best that I don’t, ya know whadda mean?
The MTR indicates that the material is also compliant to ASTM A479
ASTM A479 has a good number of basic stuff for purchase orders for the material, what is “conforms” to and it’s all gotta be to the current rev (slang for revision level) to meet the standard. I mean, stuff like how its ordered on the PO, testing required, etc., etc. And guess what else?
YES! HEAT TREATING!
For the record, making steel is a hot mess and not in the Sunday morning after Saturday nite kinda way. Its really a hot process. So its gonna meet, generally speaking A484.
So we’ve got the heat part explained, what about the time part (patience, my friends, I’m getting there).
Over the years, I’ve learned that standards or requirements of material meeting is a process. Literally a process. I’ve often reminded folks how it was once told to me “It’s not brownies out of a box!” (Shout out to my aluminum bud, Laurie).
First – what is annealing and why is it necessary?
A separate annealing was performed back in the day when material “finished” at a lower temp than the table would allow. The problem with that – carbides precipitated out causing all kinds of problems with grain, corrosion resistance, and more I’m sure.
So, the answer to that problem was to plop the bars back into oven, bringing the bars back to temp quickly, then quenching the bars super fast to keep the material re-precipitating any other stuff that would influence “phases”.
Within ASTM A479 there’s an appendix paragraph (thank goodness for after the show shows, right?) that says basically, “Hey look!! We embrace technology, and you can also do this by PROCESS ANNEALING that’s always maintaining over the required temperatures followed up with quenching via hot rolling. That appendix paragraph, Folks is X1.1 (I’d put a snip in the blog, but I’ve addressed that already).
To give you tho a bit of the official jargon — ASTM basically acknowledges that while in process, austenitc stainless steels are annealed when its so freaking hot that the chrome carbide bits are pretty much liquefied and quenched lightning fast quick so the chrome carbide bits STAY OUT of the grain boundaries (yeah, don’t cross this line, Chrome Bits). This is a no intergranular attack zone right here, Pal!
Which translates to – the entire time this material is being produced, its hitting above those required temperatures. Really. THE. ENTIRE. TIME.
How long is that—I’ve not been to a mill but if its 30 seconds or 3 hours, it doesn’t matter. What matters is THE. ENTIRE. TIME.
I’m so happy!!!!
But I’m about to get happier because –
ASTM A479 also says you gotta meet ASTM A262 which is a corrosion test for process annealing proving that this material will not be “susceptible to Intergranular Attacks” (sounds like a B grade old Vincent Price horror flick). And the mills test for that because, they can’t ship material to ASTM 479 without it.
You’ll have some that will want the temps at 1850 degrees (usually an internal material requirement). Send the MTR off to the mill and ask if the material was produced at that temp. If they can, they will, if not, Tricia has still added the 1900 degrees as its widely accepted, and can usually get approved by material deviation requests.
Mostly tho, 1900 degrees is the magic number.
Customers really don’t want a separate annealing.
And why if the end result is the same?
I leave you with this: “There are three things that extremely hard: steel, a diamond , and to know oneself.” — Benjamin Franklin