Case Hardening a Hammer

[ArielSalaverria]

Case hardening (or surface hardening) is the process of hardening the surface of a low carbon steel, by adding carbon into the material's surface, forming a thin layer of a harder/hardeneable alloy.

This way we obtain some 1/10s of mm of hardened steel, without modifying the core hardness.

For this example I'm going to use to hammers my nephews made in high school. Since I'm they favorite uncle, they gave them to me to use

This method allows us to make manual tools with relatively ease by using a softer steel or to get new life to older tools that already lost their original supericial hardness.

To start I'm gonna need a container, so I use this square section iron pipe.

I add powdered vegetal charcoal mixed with 10% of regular kitchen salt.

Then I put one hammer head inside.

Some more charcoal/salt mix.

Then the other head.

And keep adding powder til the pipe is filled.

Then I weld close the cannister.

 

[ArielSalaverria]

After the can is closed, I put it on the oven at 900C for 2 hours.

Once the 2 hours passed, I retrieve it from the oven and open the welded end.

As they come out of the can.

After I get the surface carburized, I HT at 850C, with a second HT at 350C.

The used steel was SAE 1030, and after this entire process I got an aproximate hardness of 56Rc


Finished pieces.

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Thanks for looking!


Ariel

 

[Sam Salvati]

Very cool Ariel!

 

[WadeH]

Very cool indeed.

 

[mete]

"Pack Carburizing" it's called. Make sure you temper high enough to get 56 HRc or a bit less so as not to get brittle.

 

[Keith_H]

Neat! My shop class made chipping hammers, (I didn't because I wanted to focus on my kmg clone) They "heat treated" the mild steel hammers by heating them up to yellow/orange and dunking in a nasty bucket of motor oil. Stunk up the shop. This is a cool way of hardening.

 

[ArielSalaverria]

"Pack Carburizing" it's called. Make sure you temper high enough to get 56 HRc or a bit less so as not to get brittle.

Exactly! :thumbup:

Ariel

 

[dustfurn]

Exactly! :thumbup:

Ariel

Thanks for the little tutorial. Quick question, what purpose does the 10% salt serve?

Thanks,
Dustin

p.s. I always look forward to opening any thread you create Ariel. Always very very informative.

 

[ArielSalaverria]

Thanks!

It facilitates the carbon penetration on the metal.

Ariel

 

[mete]

Commercially the 'salt' they use is Barium Carbonate.I havenn't heard of using salt [NaCl].

 

[dustfurn]

Commercially the 'salt' they use is Barium Carbonate.I havenn't heard of using salt [NaCl].

What is your opinion on this, Mete? Is there any physical (chemical) reason adding NaCl (or barium carbonate, for that matter) would improve the rate or depth of carbon absorption?

Thanks,
Dustin

 

[mete]

Pack Carburizing:

In this process, the part that is to be carburized is packed in a steel container so that it is completely surrounded by granules of charcoal. The charcoal is treated with an activating chemical such as Barium Carbonate (BaBO3) that promotes the formation of Carbon Dioxide (CO2). This gas in turn reacts with the excess carbon in the charcoal to produce carbon monoxide, CO.Carbon Monoxide reacts with the low-carbon steel surface to form atomic carbon which diffuses into the steel. Carbon Monoxide supplies the carbon gradient that is necessary for diffusion. The carburizing process does not harden the steel. It only increases the carbon content to some predetermined depth below the surface to a sufficient level to allow subsequent quench hardening.

Carbon Monoxide reaction:

CO2 + C ---> 2 CO

Reaction of Cementite to Carbon Monoxide:

2 CO + 3 Fe --->Fe3C + CO2
From http://info.lu.farmingdale.edu/depts/met/met205/index.html
An activating chemical is necessary to make it more efficient.I don't know of any other than BaCo3.

 

[SteelSlaver]

So how do I do it to make the cool colors like on some case hardened gun parts. And could I do it to a knife blade or the fittings. Thanks Jim

 

[Fox Creek]

Antique recipies include all sorts of materials, charred leather (carbon and phosphorus(?), Calcium Carbonate (Limestone, source of CO2), etc. I think the Barium Carbonate is the modern, scientific method.

IB2, Color Casehardeing, as is practiced by gun makers is a whole 'nother specialty and involves quenching the hot parts in an agitated, aerated quench to maximise the color effects.

 

[ArielSalaverria]

A lot of salts can be used, we used to employ cyanides salts back in the day when I was working on the train company. Needless to say this was a process that needed to be done with extreme care.

What the regular kitchen salt does is get the penetration process faster than if you were not using it. So by using it, you reduce the time you leave the piece in the oven at hot temperatures.

Ariel

 

[mete]

COLOR case hardening is done with organic materials in the mix typically leather. It's not easy to do, it's a job for specialists..I have a rifle that has a beautiful case hardening. But beware some new guns have the colors painted on !!!