Pure Curiosity regarding M4 knife steel

R

Retired Spook

Joined
Mar 23, 2023
Messages
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No, I have no plans on grinding M4 into a knife insomuch as I have exactly zero knife grinding/making experience, but I have been reading, and I am curious.

I was curious about TiALN coating for knife blades and a person I spoke to at a company that does this recommended M4 (and some other) knife steel due to the fact that the blade is heated to 700-degrees for around 3-hours under vacuum during the TiALN process, at that could ruin the heat treat on other steels. Also, I have read that M4 can be challenging to grind once it has been hardened.

My question is, were you to grind M4 into a knife, harden or have it hardened, and then have it TiALN coated, to what level of finish would you grind the blade before hardening / having it hardened?
 
You are talking about two separate issues.
First, yes, if you are considering a coating process at 700F, you should choose a steel with a significantly higher tempering temperature.
Alpha Knife Supplies lists some basic suggestions for heat treatment protocols for each steel. M4 is listed as 2 or 3 cycles at 1000F, so it should be minimally affected by the coating process.

As far as how much to grind before/after heat treatment, everyone has their own preference and in many cases it depends on the type of steel and whether it is especially prone to warp. For M4, sent out for professional heat treatment, you could take the edge to around 0.025-0.030" first. For most blade styles that might be about 80-90 percent of grinding before heat treatment. On the other hand some prefer to do all the grinding after heat treatment...
 
Many of the high alloy steels have a high tempering window where secondary hardening occurs. If you look at the data sheet for 3v it even recommends a 1000°F tempering temperature.

Many of the custom makers have moved away from the high temperature temper and use cryo and a lower tempering range.
 
Retired Spook said:
No, I have no plans on grinding M4 into a knife insomuch as I have exactly zero knife grinding/making experience, but I have been reading, and I am curious.

I was curious about TiALN coating for knife blades and a person I spoke to at a company that does this recommended M4 (and some other) knife steel due to the fact that the blade is heated to 700-degrees for around 3-hours under vacuum during the TiALN process, at that could ruin the heat treat on other steels. Also, I have read that M4 can be challenging to grind once it has been hardened.

My question is, were you to grind M4 into a knife, harden or have it hardened, and then have it TiALN coated, to what level of finish would you grind the blade before hardening / having it hardened?
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i began knife making 25 years ago using M2-M4 almost exclusively.
i guess i never "Learned" that it was a PITA to work on .. i just did it.... drilling holes in it has always been "Fun" but do able using the correct type of bits (Carbide)
it does take a nice edge "and holds it well" but i think it does not hold a edge as well as some other "Blade steels" since it is a (Tool steel) protecting it from corrosion is a worry
that normal blade steel helps to avoid..
i still have a stack of that blade steel around just "In case" someone was to request it..
it heat treats by high temp salts and cryo to my understanding and it "Hot hard " up to like 800 degrees .... tough yes but maybe a bit brittle in a thin cutting edge..
 
Seedy Lot said:
Many of the high alloy steels have a high tempering window where secondary hardening occurs. If you look at the data sheet for 3v it even recommends a 1000°F tempering temperature.

Many of the custom makers have moved away from the high temperature temper and use cryo and a lower tempering range.
Click to expand...
im one of those makers but if i planned before hand that the blade was going to get this style of coating i would run the high temp temper. most the time steel tempering 500-800f is kind of no mans land as alot of not great things can happen in that range as far as hardness and toughness. going with the high secondary temp range means that after the 950-1000f temper that the 700f is not a big deal
 
I was only curious as to what level of grinding to take M4 before heat treating so as to reduce finish grinding hardened M4 steel, as much as practical, given that M4 was recommended as a suitable steel to receive TiALN coating.

This is just a curiosity for me.
 
Retired Spook said:
I was only curious as to what level of grinding to take M4 before heat treating so as to reduce finish grinding hardened M4 steel, as much as practical, given that M4 was recommended as a suitable steel to receive TiALN coating.

This is just a curiosity for me.
Click to expand...
I make so far lot of knives from HSS circular saws which mean hardened steel , some are 67 -70 HRC ,M35 and M42 steel ..Grinding bevels is not problem , hand sanding is problem . When I say problem I mean it take little longer then some other steel , but you can get whatever finish you want at the end . Even mirror finish if you use some diamond paste ........................
Why you want TiALN coating ? While it is extremely hard/durable with time scratch will be there and they look ugly .I have some knives from HSS saw with TiN coating ........cool look :thumbsup:
 
Retired Spook said:
I was only curious as to what level of grinding to take M4 before heat treating so as to reduce finish grinding hardened M4 steel, as much as practical, given that M4 was recommended as a suitable steel to receive TiALN coating.

This is just a curiosity for me.
Click to expand...
Peter's heat treat recommends keeping the edge of air quenched steels to have a minimum thickens of 0.015 inches.
 
i grind a partial bevel about 1/2" up the blade and grind the rest post HT it for sure takes more time then the XHP ive been using. was a small run of 2 head knives a few parers and some 5.5 inch mini chefs
 
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