Yet Another Quenching Question

J

J.S. Carter

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Jul 4, 2007
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915
My question is once you get past the pearlite nose and down to close to Ms (say 500º F) Could you just allow it to remain in the air? or, better yet, transfer directly to your preheated 400º tempering oven before Ms? (is this "Marquenching") Wouldnt this promote a more efficient martensite growth, by giving it a slower cooling rate begining at Ms?:confused:
So in process it would look like this ::
1) Take to critical
2) Quench in fast quench, leave in quench for 3-5 seconds.
3) transfer directly to preheated tempering oven at 400º F for say 15 minutes then gradually lower the temp every 10-15 minutes to Mf
4) perform tempering process.
 
So in process it would look like this ::
1) Take to critical
2) Quench in fast quench, leave in quench for 3-5 seconds.
3) transfer directly to preheated tempering oven at 400º F for say 15 minutes then gradually lower the temp every 10-15 minutes to Mf
4) perform tempering process.
Click to expand...

1: Critical is not your target, you need to go higher to austenisation.

You forgot to mention about soak...

I dont know about the efficiency about martensite formation, all I know martempering is used for dimensional stability, to let the steel enter MS both surface and the core at the same time, so deformation chance is reduced...
 
I apologose I wasnt speaking about any one steel, just basic simple carbon steels mostly, I was looking at the W1 TTT chart and RC Riecharts thread and this popped into my head. :foot::rolleyes:
So then that would be considered marquenching then? I was trying to think of the best way to encourage full martensite growth. And by leaving it at Ms for an exponentially longer time then just dipping it in quenchant and leaving it there. Then run it through it's transformation very slowly to Mf (dropping 50º to 100º F every 10-15 minutes) to enhance the chance and time for full martensite growth.
 
What you are suggesting is called an interrupted quench, and it takles a bit of practice to get used to.

Don't bother transferring directly to a preheated oven. Instead, interrupt your quench at around 50 degrees higher than MS and let it air cool. That's the part that takes the most practice. However, even though you may be a bit late, and interrupt at like 50 below MS that's no big deal. As long as you're good and clear of the pearlite nose and significantly higher than MF you're good.

During the air cooling phase, the steel is forming martensite from the austenite. You can use this oppertunity to hand straighten the blade (with a well gloved hand, of course, 400 is still hot enough for some real nasty burns!) as it's quite moveable for the first dozen or so seconds while it cools. Once you feel the resistance mount up, leave it alone, or you may break it, but while it's hand moveable, straighten 'er out!

Don't forget to allow the steel to reach MF BEFORE tempering! Otherwise, you're wasting your time tempering, as you'll have to do it again, and with some of the more complicated stuff, you run the risk of retaining austenite.

Air cooling through the martensite transformation range is quite slow enough. Once you dip below MS the fate of the steel is written (unless you heat it back up over this point). The transformation to martensite is temperature dependant at that point, not time dependant, so slowing it down only serves the purpose of allowing the steel to temper itself as it forms martensite, as well as to keep warpage down.

I watched Mr. Cashen do a demo on interrupted quenching of 1084 at Ashokan '07 and he reccomended interrupting the quech at around 6-7 seconds (using parks 50 as a quench). I've played with it a bit myself and found I must be counting too fast because I don't generally get quite the coolness I am looking for (as judged by the smoke coming off the blade) until I get to 8 or 9. Bear in mind that this is for 1084 with parks #50, and so, it may not be DIRECTLY translatable to your combination, but that should give you an idea of time and temperature scale for similarly simple stuff.
 
Quench to ms then air cool to mf will be plenty slow. The salt bath with high temp and low temp salts is exactly that. quench from the high temp to the low temp say around 400 and air cool the rest of the way.

Going from a quenchent directly to a 400 degree oven is probly not a good idea.
 
I try to be clear when I speak, both so that anyone reading / listening can understand exactly what I say, and so that those who want to correct me can show me exactly where I am mistaken. I have learned an awful lot that way, so I consider it a success on both fronts!
 
Thank you Dan and Will. I understood both and Dan thanx for the extra effort I more clearly understand why i shouldnt do it (I could induce kept austenite by not allowing a full cool down to Mf) so there is no further benifit with extending and slowing down the martensite transformation. Got It! :thumbup:
 
Critical is any temperature that a major change happens, either on heating or cooling. MS is a "critical" point as much as Ar1. The point you are originally shooting for, Ar1 is the temperature at which whatever microstructure the steel was in dissolves and forms austenite. This point, for very simple steels (10xx, W1, W2) is only a little hotter than the curie pooint of iron, thus, the magnet is a way a lot of people try and cheat it.

However, more complex steels can have this austenizing temperature at a much higher level, in which case, the magnet is practically useless, as the curie point of iron doesn't change, regardless of what's in the steel
 
Maybe I should clarify, my post was in response to this:

"1: Critical is not your target, you need to go higher to austenisation."

I took this to be a misunderstanding between critical and curie.
 
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My bad sorry, I'm just used to myth talks around internet, when they talk about "critical" they always mean non-magnetic. critical is a too foggy term, maybe we have to use "aus temp" to be clear....
Sorry for my mistake, I hope I didnt misguided anyone....
 
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