N690 heat treatment question

D

dansity

Joined
Apr 4, 2022
Messages
6
Hello!
First time I ever have worked with stainless steel I chosen N690 to begin with. Obviously I have checked all the videos and articles about is. Big day come, wrap in stainless foil, 1050C kiln dip in for 8min (2.7mm steel), quench with aluminium plates then into the freezer -20C. Normalization cycle 2x150C 1hrs.
I think this is how the book says, i did try to be preciese. File was skating on the steel and it was eating up my belts like crazy. I was happy with the hardness. Where is the issue?
Today the knife fell off from my magnetic knife holder in the kitchen. Then I noticed it is barely magnetic. It is but the pulling force is weak. Not like my other shop bought stainless knifes up there. There must be something to my heat treatment proccess I have screwed up and before I proceed with my second knife I want to know what could be the issue. I do have a sencond knife heat treated, normalized but not yet ground. I also want to know what can I do with an already treated steel if my proccess was wrong how can I fix it. Thank you,
 
dansity said:
Hello!
First time I ever have worked with stainless steel I chosen N690 to begin with. Obviously I have checked all the videos and articles about is. Big day come, wrap in stainless foil, 1050C kiln dip in for 8min (2.7mm steel), quench with aluminium plates then into the freezer -20C. Normalization cycle 2x150C 1hrs.
I think this is how the book says, i did try to be preciese. File was skating on the steel and it was eating up my belts like crazy. I was happy with the hardness. Where is the issue?
Today the knife fell off from my magnetic knife holder in the kitchen. Then I noticed it is barely magnetic. It is but the pulling force is weak. Not like my other shop bought stainless knifes up there. There must be something to my heat treatment proccess I have screwed up and before I proceed with my second knife I want to know what could be the issue. I do have a sencond knife heat treated, normalized but not yet ground. I also want to know what can I do with an already treated steel if my proccess was wrong how can I fix it. Thank you,
Click to expand...
read this ........................

N690 Magnetism after heat threatment

Hi all, my blade from N690 material is after heat threatment - quenching no more magnetic. Is this normal?
www.bladeforums.com www.bladeforums.com
 
fitzo said:
Welcome to BF!
Here's a bit of N690 heat treat info from Alpha Knife Supply to compare your procedure.
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Thank you. I pretty much followed the same as written. I found some extra info where the soak time was dependent on the blade thickness so i did not soak for 20-30 min as mentioned, only 8min as i had a very thin (2.7mm) preground metal. The steel was glowing red when I pulled it so I'm assuming it was enough. I still have no idea where I could have got it wrong.
 
DevinT said:
That’s an indication of retained austenite. Austenite is non magnetic.

Lower your austenitizing temperature and use cryo if possible immediately following the quench.

Hoss
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Thank you. Sorry for being slow, so you recommend even tho all recommendation suggests 1050C in the kiln I should try a bit lower temperature?
 
dansity said:
Thank you. Sorry for being slow, so you recommend even tho all recommendation suggests 1050C in the kiln I should try a bit lower temperature?
Click to expand...
The best way to reduce RA is to use cryo, a lower austenitizing temperature helps. The faster you go into your sub-zero treatment after the quench, the more austenite is transformed into martensite. Longer tempering cycles will reduce some RA.

Hoss
 
fitzo said:
D dansity Have you verified the accuracy of your furnace setpoint lately?
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Only on lower temperatures as I don't have another thermometer capable of measuring 1000C. My multimeter has a sensor and I have used that to verify it at ~500C. It was something like +/- 5C
 
DevinT said:
The best way to reduce RA is to use cryo, a lower austenitizing temperature helps. The faster you go into your sub-zero treatment after the quench, the more austenite is transformed into martensite. Longer tempering cycles will reduce some RA.

Hoss
Click to expand...
Thank you. I was rather quick going into my freezer but obviously a domestic freezer is in no pair with liquid nitrogen. Maybe I should try dry ice and alcohol before i invest into a nitrogen vessel
 
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