Martensite formation speed?

Future Samurai · May 30, 2020

Greetings BF!

I just want to start out by saying that I’m not new to making knives or heat treating them. I’ve been a lurker for a long time, and have benefited greatly from the advise and information on here.

Anyway, I had a question that popped in my mind. I work pretty much exclusively with W1 tool steel and 1095 (hey, I like the stuff). Also, I love water/brine quenching. I don’t like really like oils; smelly, messy, and possible fires are things I could do without.

Now, for the steels I work with, brine is amazing because of the time you have to beat the pearlite nose. Now I understand that MartensiteStart is around 450-500F range, and MartensiteFinish is around 250F (ballpark).

I always interrupt my quenches to avoid cracks, but sometimes it gets a bit tricky when I get below 500F. So my question was...

Hypothetical quench:
-Austenize at 1450-1475 for 5 mins
-Into the brine for a second (to beat the nose) This will get you to below 900F.
-Pull the blade out wait a few seconds, and then plunge into the brine once more for 1-1.5 sec (to get to Ms temp).
-Blade should be about 450F now.

The big question is, once you hit Ms, does the speed you hit Mf matter? Do you have a certain amount of time for martensite to form?

My wild theory is that you could do two plunges into brine and let the blade air cool to Mf. If this is possible, you’d have a fully hardened blade without the unnecessary stresses that are often associated with water/brine.

I’ve tried to look for a question like this, and never really found one, so I just had to ask myself

Thank you all that read this, and a reply would be greatly appreciated.

Thank You!

DevinT · May 30, 2020

You will loose some hardness due to increased retained austenite.

Look into marquenching followed by water quenching.

Hoss

Future Samurai · May 30, 2020

DevinT said:
You will loose some hardness due to increased retained austenite.

Look into marquenching followed by water quenching.

Hoss

I’ve heard about RA. I didn’t know it was an issue once you hit Martensite start. So I take it that it does matter how quickly you go from Ms to Mf? The faster you go through transformation, the more Rockwell hardness? I’m not a metallurgist by any means, this is why I ask this.

Since I don’t use an oil after the initial quench, I guess I could just keep doing things how I’ve been doing; dipping into the brine in very quick bursts to decrease stress as much as possible.

Thank you for the quick reply!

A.McPherson · May 30, 2020

Go to knifesteelnerds.com and read up on RA, lots and lots of good info there...

More than I can ever really absorb to be honest.

DAMNENG · May 31, 2020

From everything I've read and the courses I've taken, Martensite is only TEMPERATURE dependent, all others are time and temperature dependent.
Jim A

Future Samurai · Jun 1, 2020

DAMNENG said:
From everything I've read and the courses I've taken, Martensite is only TEMPERATURE dependent, all others are time and temperature dependent.
Jim A

Hey Jim! Thanks for the reply.

Yes, I believe you are Correct. I visited the website the gentleman above posted the link of. I managed to read a few articles about quenching and the deep scientific stuff that goes along with it.

I also read that Martensite formation is temp dependent not time dependent. So I guess that means there is no set speed of cooling once you break the Ms point. As long as you’re not quenching to a temperature above Mf and holding it there, I guess it makes sense that you could air cool. After all, air will cool the blade from 450F to below 250F.

So I guess the big question is, since Martensite formation is temp dependent, even though air cooled after Ms, it will attain max hardness?

This could mean this little experiment I’m thinking up could work with 1095/W1. Just use the brine to get it to Ms (shouldn’t take more than 2-3 secs).

Thanks!

Larrin · Jun 1, 2020

Future Samurai said:
Hey Jim! Thanks for the reply.

Yes, I believe you are Correct. I visited the website the gentleman above posted the link of. I managed to read a few articles about quenching and the deep scientific stuff that goes along with it.

I also read that Martensite formation is temp dependent not time dependent. So I guess that means there is no set speed of cooling once you break the Ms point. As long as you’re not quenching to a temperature above Mf and holding it there, I guess it makes sense that you could air cool. After all, air will cool the blade from 450F to below 250F.

So I guess the big question is, since Martensite formation is temp dependent, even though air cooled after Ms, it will attain max hardness?

This could mean this little experiment I’m thinking up could work with 1095/W1. Just use the brine to get it to Ms (shouldn’t take more than 2-3 secs).

Thanks!

https://knifesteelnerds.com/2018/12/03/cryogenic-part1/

Larrin · Jun 1, 2020

Future Samurai · Jun 1, 2020

Larrin said:

Wow! I don’t know where you got that pic but it’s pretty much exactly what I was looking for. Thanks Larrin.

So it looks like I could finish it with icy water/brine to get the least amount of RA I can. Sadly, Cryo quench for me is pretty much out of the question, simply don’t have that kind of equipment. Perhaps I could even try cold Superquench.

Looking at the chart, looks like quenching to warm/hot water and very cold water has a significant difference on RA percentage.

How long would be optimal to let sit at freezing water temp? Risk of cracks?

Future Samurai · Jun 1, 2020

Larrin said:

Wow! I don’t know where you got that pic but it’s pretty much exactly what I was looking for. Thanks Larrin.

So it looks like I could finish it with icy water/brine to get the least amount of RA I can. Sadly, Cryo quench for me is pretty much out of the question, simply don’t have that kind of equipment. Perhaps I could even try cold Superquench.

Looking at the chart, looks like quenching to warm/hot water and very cold water has a significant difference on RA percentage.

How long would be optimal to let sit at freezing water temp? Risk of cracks?

Larrin · Jun 1, 2020

Future Samurai said:
Wow! I don’t know where you got that pic but it’s pretty much exactly what I was looking for. Thanks Larrin.

So it looks like I could finish it with icy water/brine to get the least amount of RA I can. Sadly, Cryo quench for me is pretty much out of the question, simply don’t have that kind of equipment. Perhaps I could even try cold Superquench.

Looking at the chart, looks like quenching to warm/hot water and very cold water has a significant difference on RA percentage.

How long would be optimal to let sit at freezing water temp? Risk of cracks?

I got it from D DevinT

Anyone can get a dewar for liquid nitrogen and most cities have access to dry ice as an alternative.

The optimal time in ice water would be long enough for the blade to reach the cold temperature throughout. 60 minutes is pretty standard for a cold treatment though that is likely longer than necessary.

Future Samurai · Jun 2, 2020

Larrin said:
I got it from D DevinT

Anyone can get a dewar for liquid nitrogen and most cities have access to dry ice as an alternative.

The optimal time in ice water would be long enough for the blade to reach the cold temperature throughout. 60 minutes is pretty standard for a cold treatment though that is likely longer than necessary.

Well then, thanks very much to you both for all of your answers. I guess the only thing left to so now is experiment. Perhaps I could even pop it into the freezer once it comes out of the quench at room temp, not Cryo, but colder than ice water for sure.

I will see what I can do tomorrow, and will be reporting results on this thread most likely.

Thanks to all!

Future Samurai · Jun 4, 2020

Update:

So I did a little experimenting. I HT'd two knives, but I only have footage of one. Here's a small breakdown.

Steel: 1095 (NJsteelbaron)
Thickness: 2.4mm (3/32")
Edge thickness: about as thick as a dime (3/64")
Austenization Temp: 1450-1475ish
Soaking Time: 5-7 minutes on both blades
Quench medium: I decided to add blue dawn to my brine and turn it into SuperQuench.

Mixture: 1 gal water, ~1lb of salt, dish soap (This stuff is CRAZY fast, yet remarkably stable)
Why SQ? Well a few reasons:
-Gets past the nose fast enough
-Minimize Retained Austenite as much as possible
-Thus attain as much hardness as I can.
-I like having fun

*By the way how do I post pictures from my desktop, I can't find a way to do it.

Quench operation (as I had planned out before in previous posts):
-Straight from the fire; 2-2.5 seconds full dip into the SQ
-Interrupt the quench
-From here continuously peck in and out of the water to relieve as much stress as possible through the Martensite formation phase
-Neither blade pinged/cracked/warped

1st blade: cooled to the temperature of the 70F Superquench, then clean off scale and quickly snap tempered to the 350-400F range. My 65HRC file barely bit. Stuck it in the freezer overnight, the file is just about skating. Without a RC tester all I can conclude is this one is sitting 64.5-65.5 HRC.

2nd blade: Also cooled to 70F, cleaned of scale. I did NOT temper this one, just to see if it would rip itself apart. File test? forget it. Skating like there's no tomorrow. On purpose, I decided I would take it as far as I could. I stuck it in the freezer for 8 hours. It's still in one piece, probably harder than before since the first blade showed signs of slight hardness increase. As far as the hardness on this one, I honestly can't even estimate. I have no file that's hard enough to touch. But based on the carbon content and what I've seen, it could be in the realm of ~68hrc.

What I'll do next: sharpen these little suckers, put on test handles and test them, until their breaking point. The un-tempered one will probably fail quickly, but it will be interesting to see, as it's been 24hrs since it was quench and it hasn't cracked.

While I find out how to upload pictures, here is a crappy video of my quenching method:

P.S. Anybody know where I could get a 70hrc file or something like that? lol

Stacy E. Apelt - Bladesmith · Jun 5, 2020

P.S. Anybody know where I could get a 70hrc file or something like that? lol

"something like that" is called a hardness tester.
Above Rc 60 files and chisels are pretty useless for accurate testing. A proper Rockwell tester is needed for any analytical testing to have accurate numbers.

You won't need to test 1095 at Rc70 anyway, sas its maximum hardness is Rc66.

Natlek · Jun 5, 2020

Future Samurai said:
P.S. Anybody know where I could get a 70hrc file or something like that? lol

Pferd make them ........and many others .Look for hardchrome file ....
I think that you will like this picture

Future Samurai · Jun 5, 2020

Stacy E. Apelt - Bladesmith said:
P.S. Anybody know where I could get a 70hrc file or something like that? lol

"something like that" is called a hardness tester.
Above Rc 60 files and chisels are pretty useless for accurate testing. A proper Rockwell tester is needed for any analytical testing to have accurate numbers.

You won't need to test 1095 at Rc70 anyway, sas its maximum hardness is Rc66.

Hey Stacy, it’s awesome to have you on my thread! Thanks.

I’m kinda tight on the moneys right now lol. I’ve tried finding places with good RC testers. Know anywhere I could get them tested?

Future Samurai · Jun 5, 2020

Natlek said:
Pferd make them ........and many others .Look for hardchrome file ....
I think that you will like this picture

Hey! Thanks.
Well I don’t really know French, but it’s looks like a ratio of quench speed compared to normal room temp water. I know “Eau” is h20, and “vitesse” is speed.

So I guess brine is 1.16 faster than normal water and more even because of the large decrease in vapor jacket.

Soude is baking soda? (I googled that lol) Looks like that stuff even faster at almost 1.2 times. Never thought about that. However I don’t know if it would provide the same protection from the vapor jacket as regular salt.

Perhaps one of the more knowledgeable guys on here could help me on that

Natlek · Jun 5, 2020

Future Samurai said:
Hey! Thanks.
Well I don’t really know French, but it’s looks like a ratio of quench speed compared to normal room temp water. I know “Eau” is h20, and “vitesse” is speed.

So I guess brine is 1.16 faster than normal water and more even because of the large decrease in vapor jacket.

Soude is baking soda? (I googled that lol) Looks like that stuff even faster at almost 1.2 times. Never thought about that. However I don’t know if it would provide the same protection from the vapor jacket as regular salt.

Perhaps one of the more knowledgeable guys on here could help me on that

Agitating water help with vapor jacket a lot .........but , instead of a square container you need a round one

Martensite formation speed?

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