does 440c reach temperature at non magnetic? & Cryo Question

T

tacticalrescue

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Mar 13, 2016
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i had some 440c and decided to take a shot at hardening it. ive only worked with non-stainless so far and when i took the 440c knife out there was very little scaling at all.....i tested with magnet and it was not sticking. im just hanging it and letting it air cool. no plates or anything....it passed the file test but im still so shocked i didnt have the amount of carb i am used to....is this a normal aspect of stainless?
 
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i have a 440A blade that isnt performing well and i was going to dip it in some dry ice and iso alc for about an hour. the original heat treatment was done a year ago or so.....can i simply cryo and temper? or must i start over with Heat treatment and quench again?

thanks for your time
 
the non magnetic work decent for standard carbon steels. 440c to get the full benefit needs a lot more precise heat control and the ability to hold it. from my understanding 440c needs to reach and hold 1900 degrees for 1/2hr to heat treat correctly. non magnetic is some where around 1400 degrees.
 
Evan Miner said:
the non magnetic work decent for standard carbon steels. 440c to get the full benefit needs a lot more precise heat control and the ability to hold it. from my understanding 440c needs to reach and hold 1900 degrees for 1/2hr to heat treat correctly. non magnetic is some where around 1400 degrees.
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awesome. thats what i was wondering.....i noticed today the the blade is definitely a bit "stiffer" i could bend it a lil before and now its nice and "hard?"(possibly it has just refined the grain? as i did heat it up and cool down three times). i did not hold it at heat very long or anything.....is it possible to have hardening effects at only 1400?

thanks for the reply
 
to my understanding there is always some degree of hardening when you heat an air hardening steel and let it cool it's just to what extent it hardens. as for refining grain I'm no expert on the topic but it could have done some grain refinement if you didn't get the temp above 1900. most of my heat treat recipes have been ones that after a lot of use of the custom search on here I found to be the most common and we'll known method for the steel in question. and then tweaked a little bit pending on the results I had got on a few test peices. I'd recommend like most people here if your not set up with at least a heat treat oven of some sort I'd stick to the simple carbon steels or send out for heat treat
 
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Stainless steel is completely different from carbon steel. It does not anneal, grain refine, or harden by the same methods. You need to sit down with a book on HT and read a lot more. I have followed your posts and questions. It seems you haven't read much about HT in general. I would read the metallurgy part in the stickys, and the try and get a good book on metallurgy and HT to read as well. The stickys has a ton of other good info that you probably need to read, also.

FYI, the magnet trick is to see when the blade reaches the Currie point. The HT target for simple carbon steels is about 50-75°F higher than that. For stainless steel you need stainless HT foil to wrap and seal the blade and a HT oven that reaches around 2000°F and can hold that accurately for 30-60 minutes. The HT has programmed steps along the way.

The Bladeforums custom search engine is in the stickys, too, and will find most every question in past discussions.
 
Please read the answer to the other thread you just posted.


thread merged.
 
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Stacy E. Apelt - Bladesmith said:
Stainless steel is completely different from carbon steel. It does not anneal, grain refine, or harden by the same methods. You need to sit down with a book on HT and read a lot more. I have followed your posts and questions. It seems you haven't read much about HT in general. I would read the metallurgy part in the stickys, and the try and get a good book on metallurgy and HT to read as well. The stickys has a ton of other good info that you probably need to read, also.

FYI, the magnet trick is to see when the blade reaches the Currie point. The HT target for simple carbon steels is about 50-75°F higher than that. For stainless steel you need stainless HT foil to wrap and seal the blade and a HT oven that reaches around 2000°F and can hold that accurately for 30-60 minutes. The HT has programmed steps along the way.

The Bladeforums custom search engine is in the stickys, too, and will find most every question in past discussions.
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i always search at least 30 minutes before posting. there is almost too much info on this site and ive read so much my eyes are bleeding. im more curious how a knife i didnt get up to temp is passing file test, little to no carb, and a noticeable harder feel (less bend). most things ive read would say thats not how it works....furthermore on cryo i have read so many opinions and jay Fischer being my foremost on the subject it is helpful regardless to hear some more peoples personal experience with it. could u please unlock my post or point me toward a post about cryo 1 year after HT on 440. most of all on this subject i read alot where people are mixing up high carbon and stainless HT methods so i always ask to be sure.
 
I'll merge the two threads. No need to have two threads on the same issues.

Stainless steel has two things happening in HT. One is the carbon-iron structure changing phase into austenite and then converting back into martensite or pearlite. This happens around 1450-1500°F. With high alloy content, this will happen to some degree even in air cooling. To fully HT stainless steel, it has to be taken through the phase change and then to the solution point of the alloying - around 1900-2000°F. Since the alloying is often as high as 20-40% of the steel, this makes a big difference. Without the right process ending in the high temperature step, the carbon may end up improperly distributed between the carbide formers and the iron, resulting in a poor or useless blade.

As to cryo:
When the steel has high alloying, the tendency for retained austenite after quench is increased. The martensitic finish point (Mf) is also much lower. In stainless steels, the Mf is around -100°F. The cryo or sub-zero treatment allows the steel to finish the conversion to martensite. It also allows some changes in the type of carbides formed. It results in a harder and tougher steel matrix. Almost all high alloy and stainless steels benefit from cryo.

Cryo/sub-zero is part of the cooling curve of the quench. It should be done in a more-or-less continuous drop. Done a day later it will get poor results. Done a year later it will get no results. The RA will be long stabilized by then.

BTW, fill out your profile. Knowing your age, location, occupation, hobbies, etc. will help with better answers and offers for help from local makers.
 
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Stacy E. Apelt - Bladesmith said:
I'll merge the two threads. No need to have two threads on the same issues.

Stainless steel has two things happening in HT. One is the carbon-iron structure changing phase into austenite and then converting back into martensite or pearlite. This happens around 1450-1500°F. With high alloy content, this will happen to some degree even in air cooling. To fully HT stainless steel, it has to be taken through the phase change and then to the solution point of the alloying - around 1900-2000°F. Since the alloying is often as high as 20-40% of the steel, this makes a big difference. Without the right process ending in the high temperature step, the carbon may end up improperly distributed between the carbide formers and the iron, resulting in a poor or useless blade.

As to cryo:
When the steel has high alloying, the tendency for retained austenite after quench is increased. The martensitic finish point (Mf) is also much lower. In stainless steels, the Mf is around -100°F. The cryo or sub-zero treatment allows the steel to finish the conversion to martensite. It also allows some changes in the type of carbides formed. It results in a harder and tougher steel matrix. Almost all high alloy and stainless steels benefit from cryo.

Cryo/sub-zero is part of the cooling curve of the quench. It should be done in a more-or-less continuous drop. Done a day later it will get poor results. Done a year later it will get no results. The RA will be long stabilized by then.

BTW, fill out your profile. Knowing your age, location, occupation, hobbies, etc. will help with better answers and offers for help from local makers.
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that answered my enquiry perfectly. thank you so much for your knowledge. i will fill out the form:) all the best
 
In addition to the stickies, there's a lot of good info on the steel companies web
sites....And....some of the distributors will mail out spec sheets if you ask...
 
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