Case Hardening

[jlpservicesinc]

Mike, it's experienced and then the difference to what is read, or shared, or learned based on this information.  (outside the box thinking is my favorite)


Last weekend I actually demonstrated the forging of a hammer eye handled punch, some fire management stuff, and the addition of carbon at elevated temperatures.

The carbonizing process with some 1/4" nail rod, forging a nice small knife.  

I said out loud that mild steel won't harden in plain water and one of the long term smiths spoke up and said "Of course it will".   I was dumbfounded but it doesn't take much.  So disagreed with the gentleman.  I honestly thought it wouldn't be challenged but there always has to be a wise guy in the crowd. I have no idea who anyone is other than a few people I know from being involved at other events. 

So heated it to orange and stuck it in the water swirling it around...  NOPE. still soft as mild steel is, being able to bend it easily both down and back to straight. 

I then heated the same metal to a good welding heat in the carbonizing zone of the fire.

 

A few cycles( no sparks) and this time cooled at a bright orange and it snapped right off and the file skated. 

I recently have done a bunch of reading on carbon and how steel has a very high affinity for it at elevated temperatures.  This answered my earlier question as to why it worked though it's not supposed to from a laypersons standpoint. 

[pnut]

I may be wrong but the way I picture hot steel (around welding temp) is like a sponge absorbing free elements and compounds easily. I admit I don't have experience but that is how I picture it in my mind. It helps me wrap my head around it a little easier. Thinking about it this way it makes perfect sense that mild steel would absorb carbon in the carbon rich zone of the fire. I think I'm beginning to understand the most basic things about steel finally;-)

Pnut (Mike) 

jlpservices, sorry for my ignorance about this but thinking about it a little further I realized I am not familiar with the area of the fire your talking about. I am familiar with the oxidizing, neutral, and reducing zone. Is the carbeurizing zone the same as one of these. If so which one.

Thanks for the info in advance. 

Pnut (Mike)  

I think I figured out that the reducing and carburizing zones are one and the same. If that's not right please let me know. 

 

Edited May 10, 2019 by pnut
found the answer.

[jlpservicesinc]

Pnut, Don't be sorry. Its this kind of information that us old timers are here for. 

 carbonizing and reducing is the same.  I don't really like the use of  " reducing" for a solid fuel forge so use carbonizing instead. 

Pilfered of the interweb. 

This is in reference to a gas flame.

"The reducing flame is the flame with low oxygen. It has a yellow or yellowish color due to carbon or hydrocarbons which bind with (or reduce) the oxygen contained in the materials processed with the flame. The reducing flame is also called the carburizing flame, since it tends to introduce carbon into the molten metal."

I gave the demo on the process in reference to the zones of a solid fuel forge and oxidizing, neutral and carbonizing zones of the same fire based on air flow. All 3 zones are controlled simply by the amount of air pushed into the fire. 

A carbonizing or even a neutral zone will let the metal reach a higher temperature with no sparks until removed from the fires protective shielding for forge welding and such. 

I showed also that the metal if kept in those safe areas even when over heated won't release the carbon until pulled out to the O2 rich air.  Was neat.