Inconsistant heat treating results M390

O

Oooompie

Joined
May 7, 2005
Messages
8
Hi Guys – I would please like to know from the experts how is their consistency in heat treating M390 with regular hardness testing. Do you achieve constantly the same hardness or in a certain range.
For me it has been very disappointing using this steel. I normally heat treat 2 linerlock blades in 1 Knufoil stainless steel foil envelope and not touching each other at all. I use the instructions as per Böhler’s recommendations of between 1070°C/1960°F and 1150°C/2100°F. I also use 2x 2 hour tempers at 500°C/930°F and my results vary between the two blades 60 – 62 RC respectively or 58-60 RC respectively. How is this possible when both are in the same packet being treated in a custom furnace with 2 thermocouples and controllers to ensure correct temperature.
On my latest I used the 1070°C/1960°F soaked for 30 minutes, quenched in oil, temper at 480°C/900°F for 90 minutes, sub zero cryogenic treatment for 30 minutes, temper at 500°C/930°F for 90 minutes, sub-zero cryogenic treatment for 30 minutes.
I had the blades tested 1 is 58-59RC the other is 60-61RC from 2 different RC meters respectively. How is this possible? Böhler states in their instructions obtainable hardness is 58- 62RC. Are results never consistent in treating this steel like the old conventional steels (440C, 12C27, ATS34, N690 etc) with which constant results of 59-60RC is achieved. Can any of the regular users of this steel comment on their regular hardness testing results. Your response will be highly appreciated.
Regards - Neels
 
Might want to contact Bohler.

A lot of things could be going on there, M390 is VERY sensitive to temperature so the equipment has to be dead on accurate and consisitant (tested real temps) as even a variation of 30 degress can make a big difference.
 
Ankerson said:
Might want to contact Bohler.

A lot of things could be going on there, M390 is VERY sensitive to temperature so the equipment has to be dead on accurate and consistent (tested real temps) as even a variation of 30 degrees. can make a big difference.
Click to expand...

Thank you for the reply. Temperature is spot on. I am using two independent thermocouples with a calibrated digital thermometer. 30°C is a lot. Do you use M390 and what hardness do you achieve regularly?

Ankerson said:
Might want to read this also.

http://www.bucorp.com/files/Phil_Wilson_Testimonial.pdf
Click to expand...

Thank you. Very interesting reading.
 
Oooompie said:
Thank you for the reply. Temperature is spot on. I am using two independent thermocouples with a calibrated digital thermometer. 30°C is a lot. Do you use M390 and what hardness do you achieve regularly?



Thank you. Very interesting reading.
Click to expand...


I am more of a consultant to point people in the right direction if they are having problems, Bohler can really help you and you can email Phil Wilson as he is the expert on the steel so he can provide more insite on what might be going on.

info@seamountknifeworks.com
 
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Oooompie said:
Thank you Ankerson. It is appreciated.
Click to expand...

No problem, just want to make sure you get the correct information that will help you be successful as M390 isn't the easiest steel to work with to get it into that higher HRC range. :)
 
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According to your post the last step is cryo ? The last step after cryo should ALWAYS be TEMPER !!
 
I don’t have good results with my method on these high alloy grades with more than one blade in the foil pack. Maybe they insulate each other or maybe the way the come out of the pack is just different enough to cause a change in the cooling rate. M390 is very quench rate sensitive. You have to get it out of the foil pack and into the quench very fast.
Thermo couples will drift over time and there is no real way to know what you have unless you get one made special and calibrated to the temperature you are trying to read. I have had two brand new couples reading 40 degrees different at 1000. Which one is right? Here are some things to try….
Surface grind the flats before heat treat. Remove all scale and go at least .008 to get into good material. This will help the quench and also give you good hardness readings. This is very important with this steel.
Start at a lower temp, 1550 or so and ramp up to the high slowly.
Increase the final temp to 2140 just in case you are reading low there. Hold at least 30 min. A little longer and a little hotter is ok, pretty hard to blow the grains on these PM steels.
Keep the quench moving down, final in cold water after you can hold it in your hand and then direct into the LN2. Hold for at least two hours in LN2
Temper at the low end. Start at 350F, hold for an hour and then check hardness. Adjust up till you get what you want.
Hardness readings can vary over the blade one point easily just due to the machine and other factors.
Shoot for 60/61 average on this steel. 62 is possible but if I told you how I do it you would have to host me to a Plains Game hunt up near Kruger Park. Phil
 
mete said:
According to your post the last step is cryo ? The last step after cryo should ALWAYS be TEMPER !!
Click to expand...

Thank you Mete. I will remember that temper last.

Phil Wilson said:
I don’t have good results with my method on these high alloy grades with more than one blade in the foil pack. Maybe they insulate each other or maybe the way the come out of the pack is just different enough to cause a change in the cooling rate. M390 is very quench rate sensitive. You have to get it out of the foil pack and into the quench very fast.
Thermo couples will drift over time and there is no real way to know what you have unless you get one made special and calibrated to the temperature you are trying to read. I have had two brand new couples reading 40 degrees different at 1000. Which one is right? Here are some things to try….
Surface grind the flats before heat treat. Remove all scale and go at least .008 to get into good material. This will help the quench and also give you good hardness readings. This is very important with this steel.
Start at a lower temp, 1550 or so and ramp up to the high slowly.
Increase the final temp to 2140 just in case you are reading low there. Hold at least 30 min. A little longer and a little hotter is ok, pretty hard to blow the grains on these PM steels.
Keep the quench moving down, final in cold water after you can hold it in your hand and then direct into the LN2. Hold for at least two hours in LN2
Temper at the low end. Start at 350F, hold for an hour and then check hardness. Adjust up till you get what you want.
Hardness readings can vary over the blade one point easily just due to the machine and other factors.
Shoot for 60/61 average on this steel. 62 is possible but if I told you how I do it you would have to host me to a Plains Game hunt up near Kruger Park. Phil
Click to expand...

Thank you Phil. As a regular user of M390 I appreciate you taking the time to answer me.
I do not cut open the foil packed but quench in the packet as recommended by the manufacturers of Knufoil. http://www.knight-group.co.uk/stainless-steel/knufoil-user-manual.pdf
I used to cut it open and did experiments and there was no difference in hardness heat treating without the foil or heat treating and quenching in foil. I will however not do air quenching in foil as it is slower to reach "black heat" than oil quenching. When using carbon Damascus I quench in water as recommended by Knights Knufoil.
The heat treating recipe that I used and described above was supplied per special request By Böhler in SA as I wanted to use their lower recommended temperature. I have used their higher temperature before and have achieved in one of the two blades 62Rc. In this case one is 61Rc and the other 59Rc after discovering which of the two meters is correct.
It is a very interesting topic and a challenge to get constant results and with your recipe and description above It will make it easier to perfect the process. I thank you for sharing your information.

Phil unfortunately the Kruger park is a 1050 miles away from Cape Town but if you come to Cape Town one day to admire one of the new seven wonders of the world (Table Mountain) I would love to have a chat over a glass of our finest red Cabernet Sauvignon wine. Thank you.
 
Ooompie, I do an forced air quench with the PM steels, if Bohler is advocating an oil quench in a closed pack with this steel then OK.... Seems like in a closed foil pack that there could be uneven cooling around the two blades. As I mentioned this steel is very quench rate sensitive. Anyhow just an observation that maybe could explain the difference in hardness between the two blades. thanks for the invitation on the wine. If I get there someday I will take you up on it. Phil
 
Thank you Phil. I will try it without foil.
Do you profile your blades, heat treat and then grind or do you rough grind, heat treat and then complete the grind?
I am considering doing the first mentioned. Then with the high tempers you do not stand the risk of overheating.
How do you find grinding a steel with 4% vanadium at 61Rc?
Regards
Neels
 
Phil was very good to give his heat treating recommendations to me for a friend, Rob Riddly to go by. Her has done say 20 or so folder blades for me and has managed to stay at 60 RC. I grind all of my blades, yes they are only folder blades up to say 4" long maximum after heat treat. I love how that steel seems to work, finish, and then cut. I sure wish I was still going out hunting ! My previous experience and information back from the fellows using these folders tells me it's one of the best steels around at this time. Frank
 
Neels, if you are asking about temper I use 350 to 450F. Yes the high end 950 to 1000 will maybe give you a hardness bump if you hit it just right but you will not see much especially if you have already transformed the RA in the Ln2. I rough grind, heat treat and finish grind after on the PM steels. I agree M390 is very clean, and nice to grind with the right abrasives. I also will take a very nice 320 grit belt finish. Best to send me an e mail through my web site for more detail. I was up in Limpoppo in 2010 for a week hunting and did get to Kruger Park. Incredible place.
 
Phil - Thank you for revealing all your secrets and experiments here for us all to improve our heat treating skills.
I find that you must of course not skimp on belts when grinding M390. Only new belts will cut.
It is great that you have been to Limpopo and the Kruger Park Hope you had a good hunting trip.
Regards
Neels Roos
 
That's right ! The rule is don't get emotionally attached to grinding belts .When they stop cutting throw them out ! A belt that isn't cutting cleanly is also one that more easily burns insted of cutting and why those new knifes can have poor edges.
 
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