My first charcoal pack

[Mark Elliott]

I had a bunch of small tools (a drill bit, two square reamers, and a tap)  that I wanted to heat in the oven to make sure they were heated evenly.   So,  I decided to put them in a charcoal pack to prevent carbon loss.  I packed them in a #1 crucible with crushed hardwood charcoal and heated them to 1600F for about a hour and a half.   Then I dumped the whole thing in a bucket of room temp water.  To my surprise,  there was not the mess I was expecting.   The parts came out hard and had quite a nice color case on them.   If that had been my goal, I would have been very happy with it.  The only problem was that that reamers warped.   Given how I plan to use them, I don't think that will be an issue.   Now, I won't be so hesitant to do that again.   Next time, I will remember to cover the crucible. 

[Acer Saccharum]

Congrats!

You've got to exclude oxygen from the pack. A well fitted cover is essential for best results. But it sounds like you done good despite lack of cover.

It's very difficult to harden long thin things without warping.

[Ed Wenger]

That's awesome, Mark.  I need to pay you a visit and see your set up!


     Ed

[Mark Elliott]

That's awesome, Mark.  I need to pay you a visit and see your set up!


     Ed

I welcome visitors most any time.    Just let me know you are coming.

[Naphtali]

If I am intruding on the thread, please ignore my reply.
***
What is the difference between pack hardening and case hardening?

[Mark Elliott]

A charcoal pack is a way to case harden.   However, in my case,  I was doing it just to prevent carbon loss in water hardening drill rod that I was heating slowly in a heat treat oven.   Given as small as my parts were and as long as it took to come up to hardening temp, all the carbon required to harden the surface could have cooked out.  As a by-product,  I got a nice color case.   

[Acer Saccharum]

some commercial operations case harden in ovens filled with methane gas. So this is case hardening, but not packed in charcoal.

[James Wilson Everett]

Mark,

I have done pack hardening as you describe.  However, now I do it in a somewhat different way for two reasons.

1.  As I dumped the entire pack into water, red hot metal parts & charcoal, I got a rather bad flash steam burn on my wrists above my gloves - yikes!

2.  I too noticed some part warping from this type of quench.

Now I do the pack heating, them allow the pack to cool.  Next I reheat each individual part and quench in a controlled manner.  The metal surface is now high carbon steel so it can be reheated and quenched and tempered just like a spring.

For long cutting tools, such as a square armory reamer, I quench the part vertically without any swirling or stirring.  This results in a lot less warping (not zero warping, just a lot less).  When you swirl or stir the part in the water during the quench, one side cools more quickly, leading to warping.  Just plunge the part straight and vertically into the water.  When you dump into the water from the pack, you have no control over how the hot part is quenched.

For the slight amount of warping I still see I lay a sheet of abrasive paper on the top platen of my table saw and rub the part on the abrasive until the warp disappears.  This does take a bit of patience!  I think that you can reheat the reamers, straighten them and then re-heat treat them.

Keep up your great work!

Jim

[Acer Saccharum]

Good advice on letting the pack cool, then heat treating parts individually. Much more control! (but this is for tools, NOT for color case hardening)

[JCKelly]

I agree with Wilson  Quench long things straight in to the water, and they may come out straight.
If they belly-flop, warping is guaranteed.

My metallurgy professor used to work at Springfield Armory. He told us this about bayonets.

As far as water quenching, but NOT for colors - you will get a more uniform quench with less distortion if you quench in water with about 10% by weight salt (NaCl, table salt or whatever). A guy who worked a while in the Mideast said he told people just enough salt to float a potato.

This brine is even faster than with straight water and also gives less chance of cracking.
Perhaps you thing this counter intuitive, can give the long metallurgical reasons if anyone wants.

[Dennis Glazener]

The parts came out hard and had quite a nice color case on them.   If that had been my goal, I would have been very happy with it.  The only problem was that that reamers warped.

Mark,
Not sure if the reamers are small enough to do this with but its how we used to make precision "spuds" to slip into bores to indicate benchrest barrels when sitting them up to chamber. We would turn, polish the spud then put it in the quill of a drill press. Sit a can of water/oil under the quill turn the drill press on, then heat the spud to desired color then pull the drill press handle down plunging the spud into the water/oil. Never had one warp when I did it that way.
Dennis

[Ben Quearry]

Dennis
That is a fine idea (30+ years in the Tool & Die trade and I have not seen that one!). We should all be thankful for the wealth of information our members share.

Ben

[jerrywh]

 Mark.
  If your intention is to preserve the surface carbon in the tools you only need to leave them in the oven for 30 minutes after they reach 1500° before quenching. Warping is always a problem with long pieces. I have case hardened a lot of lock plates over the years and they usually warp some even if they are blocked but if they are blocked the warpage will be minimum. I am interested in studying how files are hardened. However they do it is the secret to no warpage.
  I should learn all this just before I die. 

[Mark Elliott]

I gave up on a uniform heat treatment with the charcoal pack.   I reheated the reamers in a carborizing flame using a small rosebud tip; straightened them and quenched them directly in water inserting them vertically.  There was still some warpage, but not as much.   The charcoal pack was a successful experiment on color case hardening but a failure as to a way to uniformly harden small parts.   The quench is always going to be problematic.   

[James Wilson Everett]

Mark,

As you have found, it is s very easy to read in a book how such things are done.  It quite a bit more complex when a person actually does it.  Congratulations on your pack hardening and encouragement to continue your work.  My often repeated thought has always been - "Wow, this is a lot more difficult than I thought at first!"

Jim