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Metal Hardening

819 Views 8 Replies 3 Participants Last post by  Dex
Hey everyone, been thinking about some things lately. One of them is ways to make certain metal parts harder. I have found info on cryo treating, shot peening, and induction hardening. I would like to know what anyone thinks on these processes. Specifically, induction hardening, I stumbled across it l8ly (fords new truck commercial lol) and want more info. Cryotreating on average makes a part 100 % stronger, shot peening is about 300 % stronger. I have found no average for induction hardening, and was curious if any one has any direct experience, or info etc.
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I've heard of shot peening and crytreating but not the other.

Not sure how any of them work, etc. Crytreating I think makes th metal less maleable and more brittle but very strong.

(Like cartilidge is to bone)
I am a sheet metal mechanic, so it is my job to understand the properties of metal, so I understand what maleable means :)

Cryo treating is a process where the metal to be hardened is frozen using liquid nitrogen, then slowly heated up to about 350 degrees farenheit. The metal is cycled like this about 3 times over roughly 72 hours. Basically it is just an extension of heat treating, and usually provides about 100 % increase in fatigue strength, and wear, with some improvements in tensile strength as well. It works best on ferrous metals, like steel, that have already been heat treated. Good to use on highly stressed parts, with no negative side effects.

Shotpeening is a process where millions of tiny steel balls are shot at the part at high velocities. This causes the metal to be compressed, and refines the grain structure on the surface. Basically it is micro forging the metal into a harder layer, which makes it harder for a crack to start. It changes the structure of the metal about 0.005-0.010 of a inch deep. Typical improvements in the fatigue strength are in the 100-300% range. Very good at preventing breakage, typically used on airplanes.

The purpose is always to increase the strength of metals, and this occurs when heated metal is cooled rapidly. The result is a metal with small grains and increased resistance to penetration--hardness.

so with that, I am interested in induction hardening, because I have found through research, induction hardening is capable of improving wear resistance, strength, and fatigue, however I am not sure on what level. Look at shot peening, 300 % increase at a depth of 0.010 of an inch. Induction hardening can do the same thing to depths beyond 0.375 (3/8) of an inch. If not more, I am just curious if anyone here has more info??
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Wow. learn something everyday. Thats crazy.
I know, I can't even imagine how much stronger induction hardening is, but it should be crazy ;)
I believe induction hardening is used to increase wear resistance (like nitriding or hard chrome), not to increase strength.

Rotary engine intermediate and end housings are induction hardened on the minor axis. Housings are cast iron.

Edit: depth of induction hardening is nowhere near 3/8 inch, at least in that application. I had a few surface ground when I was racing those things and it disappears after about .040

It's visible as a dark blue line.
Well as I understand it, you can control the depth, it is very capable of going to 3/8 of an inch, but doesn't have to. Thats the neat thing about it. I know it is capable of increasing wear resistance, strenth, and fatigue, but to what extent, I am not sure. While researching this further I also came across plasma nitriding, sounds very interesting, and reduces friction :) but it looks like I am going to have to search more, I will post some links when I find some good sites.
Dex said:
I know it is capable of increasing wear resistance, strenth, and fatigue, but to what extent, I am not sure.
What kind of metal are you alluding to? What kind of application?

A mentioned above, intermediate/end housings on the Mazda rotary are (grey, I think) cast iron. I don't believe any type of cast iron (maybe nodular, but I don't think so) responds to any of those kind of treatments the way steel does.
Actually, I am genuinely curious, perhaps I have a use for it later in my life, I am researching stuff, gonna try to make my tranny a little stronger etc, but I really just want to know.
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