Tempering talk

Deweyknives said:
What is the differance between several tempering cycles or one long one? I assume reaching ambient temp is benaficial in between, but why? What does it do for the steel? If you do two or three cycles at 400 degrees and the blade is 60RC after the first temper[just picking numbers here], what is another cycle at 400 degrees doing to improve the steel without changing the hardness?
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If your blade has retained austenite in it, multiple temperings, with a cool-down in between, can stabilize it, and maybe even convert it to martensite.
 
Also most of the time when we say a blade is 60RC that's an average, there might be points on the blade that are 60.5 or 59.5. From what I'm to understand, tempering longer helps to homogenize these results?
 
Again we have a difference between simple and complex steels .A simple steel such as 1080 will benefit little by multiple tempers but a complex one like S30V will !!
 
Hey Kevin,

Thanks for the post..... I am still fairly new to the blade forum but have always loved the science of materials especially as it pertains to carbon steels.

Here's the build-up to my question; atom size can be thought of as function of the orbitals of electrons (how they rotate around the nucleaus, of course based upon how many protons and neutrons are in the center of the atom). Nice arrangements of atoms of similar element can occur because they all fit very well together. Hence there are pockets of graphite / carbon within steel which has not been hardened because the pockets of graphite more easily exist within the iron matrix (kinda like differing ethinic sections of a city) / no atom is expected to mingle with different kinds of atoms. It is when the carbon becomes solute within the iron structure at higher temps (possible because the electrons of each element have been raised in terms of energy level / orbital / excitation) that carbon and iron move towards homogenation. Once again, this seems to be a function of the electron orbitals.

Hence, here's the question; is the hardness of steel created because of the stress in bonds between atoms of dissimilar element having to occupy a space which does not easily accomodate different (size) electron orbitals? Is the resulting tension in electron bonds between elements the driving factor of hardening? Is tempering then the allowing of the migration of carbon atoms to a more organized state via the addition / induced motion of electrons in the carbon atom by the addition of heat energy?

Thanks in advance for the reply. I know it may seem somewhat convoluted, but the pictures in my head don't always make it out on the paper so good!:p

Norm....
 
Dewey, would you rather have a girl over three times for one hour of lovemaking, or once for three hours. The similarities are more than meet the eye. All that - get her hot, keep going steady at that heat, don't get it too hot or you'll get to the final point too soon, cool down before you can do it again,......vs.... Keeping it up for three hours straight.

Dang, I think I need a cigarette.
Stacy
 
Cordovan, wedging atoms of carbon between atoms of iron strains the crystal and hardens and strengthens the iron. But it has little to do with electrons .There are various strengthening mechanisms in metals but they have to do with the formation and movement of dislocations which are imperfections in the crystal lattice. Interstitial alloying elements [small carbon atoms] wedge in between iron atoms. Substitutional alloying elements [similar in size to iron - Ni,Cr etc ] substitute for an iron atom in the matrix.Precipitation such as carbides strengthen things too especially when there is coherency with the matrix. Cold working disrupts the matrix producing many dislocations ....BTW ,carbides are only a metastable form in steel.The stable form is graphite ...Electrons ???I'm only a metallurgist not a physicist !
 
I am with mete, metallurgy is fine, physics is a little too deep, distortion of the lattice due to interstitial atoms and dislocations is more than enough to bring about the effects. Unless you are shooting for a free machining grade (like 06) it is best to keep graphite out of your steel, it is a little too stable and doesn't really contribute much to these processes, that is why it makes maching easy, it sort of sits there and allows surrounding structures to be removed easier.
 
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