Case hardening process

[rslaback]

A while back I inquired about hard jaw covers as the vise here at work has a set of soft aluminum V jaws that I machined installed and I know eventually some gorilla is going to come along and damage them with some big hunk of random steel that they want to beat on. Nothing seemed readily available so I determined I would need to make my own. I'm a few hours in and so far so good with the exception of a snafu on the mill power feed at exactly the wrong time.



I know that I want to case harden them but I haven't done that since 9th grade metals class back in the 90's. Tell me if this sounds right:

1. Heat steel to 1650F in the oven at work. Hold that temp for 10 minutes or so.
2. Test temperature with crayon.
3. Quench in fast quenching oil. Leave in for 10 minutes or so.
4. Move back to oven at heat to 450F.
5. Remove from oven and allow to cool in still air until room temperature.

 

[Junkman]

I have no idea how steel is hardened; however, I know there is a company in Southbridge, MA, that provides hardening services to local industries. I have toyed with the idea of having a part on my snowblower hardened, but I don't know if they take in private customer work.

 

[gte718p]

Proccess seems right but one important step, choose the right material. Not all steels harden equally. If it doesn't have enough carbon it is not going to harden.

For the tempering, I would just turn off the oven and leave overnight or until it is cool.

 

[PCustoms]

Temps and process should be dictated by material.

What kind of steel was is?

 

[MushCreek]

That sounds like the process for oil-hardening steel, but that would be to through harden, not case harden. We use to case harden regular steel by putting the hot steel in a special powder called Kasenite. Case hardening makes a hard surface with a softer, tougher inner structure so it won't shatter.

 

[racecougar]

What material are you working with?

 

[rslaback]

It's just A36 which is why I need to case harden it. Sounds like some of you are confusing through hardening of high carbon steel and case hardening of a piece like this.

 

[PCustoms]

It's just A36 which is why I need to case harden it. Sounds like some of you are confusing through hardening of high carbon steel and case hardening of a piece like this.

Not sure it's us that are confused.

Also not sure I've ever seen anyone harden (case or through) A36. I suppose it can be done, but I don't see anything in a quick search indicating final hardness. Might be worthwhile to get some better material

 

[Firebrick43]

It's just A36 which is why I need to case harden it. Sounds like some of you are confusing through hardening of high carbon steel and case hardening of a piece like this.

Case hardening is adding carbon to the surface. Traditionally is was bone meal but there are other products such as cherry red.

Cherry Red Hardening Compound

Instant case hardening compound Surface hardening for lower carbon steels hardness depth up to 0.010 inches (approx. 10 thousandths)

blacksmithsdepot.com

You place the part in a stainless steel foil packet with the carbon medium of choice with a sheet of paper or two to burn burn off the oxygen and load it in a furnace for a specified amount of time for the depth you desire, usually several hours then you quench and temper.

Commercial Heat treaters use a similar process but either add the carbon via natural gas in an electric oven with inert atmosphere (no oxygen means the NG doesn’t explode) or in a molten salt (usually cyanide) bath

With A36 the method you described doesn’t work as there is not enough carbon in the steel. You most definitely are the one getting processed confused

There are other processes that can leave a hard out skin w/soft core such as induction or flame hardening but they are very tightly controlled processes unlikely to be done successfully at home and require a steel that has enough carbon already in it. The heat has to be extremely localized and powerful and then instantly quenched.

 

[rslaback]

Not sure it's us that are confused.

Also not sure I've ever seen anyone harden (case or through) A36. I suppose it can be done, but I don't see anything in a quick search indicating final hardness. Might be worthwhile to get some better material

Maybe. Just sounded like some of the responses were concerned about the carbon content in the base steel.

Case hardening a piece of low carbon steel like A36 is possible. To do it you are heating it in a high carbon environment and effectively adding carbon to the outside surface which is then hardened while the inside stays soft and tough. I believe in class back in the day we used a carbonizing flame from the actetylene torch. Now it's more normal to use external powders or charcoal.

 

[racecougar]

Do you have access to a carburizing medium like bone charcoal or Kasenit? You'll need to increase your soak time (oven time) significantly (a couple hours rather than 10 minutes). Will your work allow that?

 

[PCustoms]

Maybe. Just sounded like some of the responses were concerned about the carbon content in the base steel.

Yes, as that's needed for the process.

Case hardening a piece of low carbon steel like A36 is possible. To do it you are heating it in a high carbon environment and effectively adding carbon to the outside surface which is then hardened while the inside stays soft and tough. I believe in class back in the day we used a carbonizing flame from the actetylene torch. Now it's more normal to use external powders or charcoal.

Sounds like you've got it all figured out already.

 

[rslaback]

Case hardening is adding carbon to the surface. Traditionally is was bone meal but there are other products such as cherry red.

Cherry Red Hardening Compound

Instant case hardening compound Surface hardening for lower carbon steels hardness depth up to 0.010 inches (approx. 10 thousandths)

blacksmithsdepot.com

You place the part in a stainless steel foil packet with the carbon medium of choice with a sheet of paper or two to burn burn off the oxygen and load it in a furnace for a specified amount of time for the depth you desire, usually several hours then you quench and temper.

Commercial Heat treaters use a similar process but either add the carbon via natural gas in an electric oven with inert atmosphere (no oxygen means the NG doesn’t explode) or in a molten salt (usually cyanide) bath

With A36 the method you described doesn’t work as there is not enough carbon in the steel. You most definitely are the one getting processed confused

I missed the powder. That's why I'm here asking questions. Perhaps I just got overly frustrated with the comments that seemed to imply that I need to make these parts from high carbon steel which I know definitely isn't the case. Case hardening is usually the way to go in a tool in order to give you wear resistance without making it brittle like a file that just snaps when dropped.

 

[rslaback]

Do you have access to a carburizing medium like bone charcoal or Kasenit? You'll need to increase your soak time (oven time) significantly (a couple hours rather than 10 minutes). Will your work allow that?

Sure will. Thanks for the reply.

 

[Firebrick43]

I don’t believe kasnite is on the market any more. Kasinite or cherry red can be drizzled on a part heated in a forge or heated with a torch but it’s depth is going to be very very shallow and superficial compared to a SS pack in a furnace for an extended time

 

[rslaback]

I don’t believe kasnite is on the market any more. Kasinite or cherry red can be drizzled on a part heated in a forge or heated with a torch but it’s depth is going to be very very shallow and superficial compared to a SS pack in a furnace for an extended time

Can you tell me more about the SS packet process? I'm willing to give that a go. I love learning and trying new things.

Found this as well for the skeptics:

 

[Firebrick43]

Can you tell me more about the SS packet process? I'm willing to give that a go. I love learning and trying new things.

Found this as well for the skeptics:

It almost identical to the video at 19/20 minutes mark. You just pour a little bit of hardening compound out in the foil and place your part on it and then pour some more on it. A few pieces of paper and wrap the foil tight and put it into the furnace.

Some guys will cap a small piece of square tubing and fill the tube with the compound with the part in the center completely to the top and put a heavy piece of steel on top to seal. The packing prevents mill scale like he experienced especially when doing it for several hours. He mentioned it sort of at 20:50

 

[rslaback]

It almost identical to the video at 19/20 minutes mark. You just pour a little bit of hardening compound out in the foil and place your part on it and then pour some more on it. A few pieces of paper and wrap the foil tight and put it into the furnace.

Some guys will cap a small piece of square tubing and fill the tube with the compound with the part in the center completely to the top and put a heavy piece of steel on top to seal. The packing prevents mill scale like he experienced especially when doing it for several hours. He mentioned it sort of at 20:50

So preheat the part to 1650 and allow that to soak in. Have a piece of stainless foil laid out that will cover the jaws. Lay out a bed of powder in the foil. Move the jaw to the bed. Add more powder on top of the jaw to full cover it. Add some paper to burn up the oxygen. Fold the stainless foil over to make a packet and fold and crease the edges to seal it. Put it back in the oven at 1650 for most of the day. Remove and water quench.

Also, is tempering required after this or can you pass on that since the case is already so thin?

Finally, when it comes out after the long heat will the powder that was not directly touching the steel still be reusable or does it melt or change and it is scrapped?

 

[Firebrick43]

No preheat, just wrap it or put it in a sealed steel container and throw it all in a 1650. It will all heat to that temp. Foil is nice as you can make any size pack quick and it’s easy to rip and dump to quench.

 

[MushCreek]

Kasenite is apparently long gone, so Cherry Red seems to be the only option.

 

[badmatt]

Just make a set of jaws out of something easily hardenable. A2/A6, cheap and easy to deal with.

 

[RoninB4]

....

 

[MoonRise]

Mostly covered by others, but I'll chime in anyway.

A36 is low carbon steel and it does not have enough carbon in it to harden via quenching.

Case hardening is where you heat a piece of typically low(er) carbon steel in a carbon-rich environment for a relatively long period of time (hours typically) so that the carbon can diffuse into the surface of the steel and actually change the steel alloy at the surface by a few thousandths of an inch (typical case depth is usually 5-40 thou for a 50 HRC hardness). The steel is then quenched (to harden it) and then may be tempered (to reduce brittleness and increase 'toughness').

There is a dance between the base alloy and the case hardening process and the tempering to get the desired final material properties of core hardness and toughness with the case hardness and depth.

Case hardening some A36 could give you a 'skin' of about 50 HRC but the core will still be plain A36. Put those vise jaws on and then crank it tight and there's a good chance you will still deform/dent the jaws if the workpiece isn't flat on the jaws (someone putting a round workpiece in and cranking the vise tight and then wailing away on the round bar to bend it over the vise jaws perhaps).

Alloy medium carbon steels might be a better material choice. That would let you case harden the skin while still having a tough but strong core (compared to A36 with a typical yield strength of only 36 ksi).

Example: case hardening some 4130 and then quenched and then temper at 900F and you can end up with a core hardness of ~36 HRC and a core yield strength of over 100 ksi with a case hardness of ~50 HRC or harder. 3x or more stronger core than the soft A36.

Or use a higher alloy steel or a tool steel and adjust the heat treatment process to get your desired blend of surface hardness and core strength and overall toughness.

I think that even case hardened A36 vise jaws are going to be too soft to hold up to gorillas in the shop. IMNSHO

 

[rslaback]

If/when these fail I might try to make a set out of 4140. There are ends that will be welded onto these to prevent them from sliding laterally on the base jaws so I was concerned with weldability as well as ease of finding a piece of high carbon steel angle to save machining time.

 

[FTG-05]

Kasenite is apparently long gone, so Cherry Red seems to be the only option.

Not an uncommon process in the gunsmithing field:








Easy-to-use compound case hardens plain and low carbon alloy steels. Carburizes surfaces quickly to uniform depth while retaining the toughness of the core. Also protects delicate, highly finished work, and helps eliminate the need for remachining. Simply apply the hardening compound to your metal parts, heat to the required temperature, then quench in oil or water for a professional grade, heat-treatment. Helps keep the edge sharp on expensive drill bits, milling and grinding tools, punches, firing pins, hammer davits, trigger pins, sears, and cocking pieces. Water soluble for easy clean-up. Complete instructions included. SPECS: 1 pound (453.6g) can.

 

[rslaback]

No preheat, just wrap it or put it in a sealed steel container and throw it all in a 1650. It will all heat to that temp. Foil is nice as you can make any size pack quick and it’s easy to rip and dump to quench.

Making the container out of square tubing is going to be easier than a stainless pouch but I do have some stainless foil if that is superior. Either way, is it necessary for the container to have a lid or as long as the powder is covering the part that is all that matters?

 

[Firebrick43]

Making the container out of square tubing is going to be easier than a stainless pouch but I do have some stainless foil if that is superior. Either way, is it necessary for the container to have a lid or as long as the powder is covering the part that is all that matters?

It allows oxygen to get to the part and create mill scale. Not much if if doing a quick shallow case like tubal came did but if it’s in there for hours there will be significant mill scale without a tight fitting lid

 

[bwringer]

...I think that even case hardened A36 vise jaws are going to be too soft to hold up to gorillas in the shop. IMNSHO

To be fair, diamond-faced adamantium would be too soft to hold up to any self-respecting shop gorilla.

Vise jaws are consumables, so whatever process the OP ends up with, it will need to be easily repeatable.

 

[rslaback]

It allows oxygen to get to the part and create mill scale. Not much if if doing a quick shallow case like tubal came did but if it’s in there for hours there will be significant mill scale without a tight fitting lid

I assume that if I make the container, line it with paper, fill it and shake it until I can't get any more compound in and then weld a lid on that would also work?
It will make my quench process take a bit longer as I cut off the end of the container when I pull it out. I assume since I have the option to also allow it to air cool that that won't be a problem. Is that correct?

 

[Firebrick43]

I assume that if I make the container, line it with paper, fill it and shake it until I can't get any more compound in and then weld a lid on that would also work?
It will make my quench process take a bit longer as I cut off the end of the container when I pull it out. I assume since I have the option to also allow it to air cool that that won't be a problem. Is that correct?

We never welded it on because it would mean you would probably need a second heat by the time you got the welded on lid off. We just set a chunk of 1/2 plate on top. But if you don't mind bringing the part up to temp again to quench once the lid is off its perfectly fine.

If you let it air cool it wont be hardened.

 

[rslaback]

We never welded it on because it would mean you would probably need a second heat by the time you got the welded on lid off. We just set a chunk of 1/2 plate on top. But if you don't mind bringing the part up to temp again to quench once the lid is off its perfectly fine.

If you let it air cool it wont be hardened.

Well, I gave this a shot today and it bombed. Turns out the oven wasn't able to get above 1250 today so it was all a waste. I will have to try again on the newer oven instead of the antique one that I was using. Any idea what the yellow crusty foam is from that spewed out today while it was heating. My only guesses are from either an oily coating inside the vessel or something from the Cherry Red itself.

I'll order more compound and repack the tube now that the paper has burned out.

 

[FTG-05]

My bet: Yellow = Sulphur.

 

[PCustoms]

Well, I gave this a shot today and it bombed. Turns out the oven wasn't able to get above 1250 today so it was all a waste. I will have to try again on the newer oven instead of the antique one that I was using. Any idea what the yellow crusty foam is from that spewed out today while it was heating. My only guesses are from either an oily coating inside the vessel or something from the Cherry Red itself.

I'll order more compound and repack the tube now that the paper has burned out.

How's the party look, or more importantly, how does it test?

 

[PugetDude]

Old timer at a machine shop in the Missouri Ozarks used to swear by heating a knife blade to cherry red, then plunging it into a container of sugar, then leave it to cool overnight.

.

 

[Firebrick43]

Well, I gave this a shot today and it bombed. Turns out the oven wasn't able to get above 1250 today so it was all a waste. I will have to try again on the newer oven instead of the antique one that I was using. Any idea what the yellow crusty foam is from that spewed out today while it was heating. My only guesses are from either an oily coating inside the vessel or something from the Cherry Red itself.

I'll order more compound and repack the tube now that the paper has burned out.

You don't have to pack it completely full, just cover the part. That will prevent the spill over.

Do you know why the oven couldn't get above 1200?

 

[rslaback]

How's the party look, or more importantly, how does it test?

They are black and slightly mottled. A file skates over them but a center punch does leave a slight impression.

 

[rslaback]

You don't have to pack it completely full, just cover the part. That will prevent the spill over.

Do you know why the oven couldn't get above 1200?

I think just age. We don't normally heat that high so it hadn't been tested. I did get the newer one in a different building up to 1650 tonight though so I should be good.

The way the parts sat in there they were only about 1/4" from the top so I had it packed full. I do think on this next try I will lay them down in a container because it was an absolute bear to get them to pull out of that vertical vessel.

 

[MoonRise]

They are black and slightly mottled. A file skates over them but a center punch does leave a slight impression.

If a file skates on the part surface and doesn't dig in, then the part surface is harder than the file (most likely).

The center punch leaving an impression/depression/mark is because you 'overwhelmed' the surface hardness (you applied a concentrated surface compressive stess higher than the combination of the several thou thick case hardened skin and the still A36 core could withstand without yielding).

Good luck with the retry in the better oven.

 

[rslaback]

If a file skates on the part surface and doesn't dig in, then the part surface is harder than the file (most likely).

The center punch leaving an impression/depression/mark is because you 'overwhelmed' the surface hardness (you applied a concentrated surface compressive stess higher than the combination of the several thou thick case hardened skin and the still A36 core could withstand without yielding).

Good luck with the retry in the better oven.

I know that it is at least somewhat hardened which makes me question the temp read out of the first oven. But I also figure that giving it another go isn't going to hurt anything.

 

[PCustoms]

I know that it is at least somewhat hardened which makes me question the temp read out of the first oven. But I also figure that giving it another go isn't going to hurt anything.

Did you make new jaws or are you planning to put the same ones back through?