Oil Breaking Down Steel

sog

Hi all, i am new here,

There is a person at Bladeforums rubbing oil on an expensive damascus blade knife. He stated that he gets a black substance appearing in the oil. I think that the steel is being broken down at the molecular level.

A phd. in molecular physics stated that steel has no molecules. He later recanted and explained: The steel used in knives is a complex mix of many phases and the general matrix is a crystal structure held together by metallic and not molecular bonds. The lay defination (sic) would never be used to discuss properties because as noted that it (sic) why the actual materials defination were defined, so you speak of molecules, ions, crystals, etc. .

Any competant physicist care to comment?

You may be interested in the site: http://www.bladeforums.com/

sog

Astronuc

What kind of oil. There may be a chemical reaction in the oil, or something in the steel. Magnetite (Fe₃O₄) is black.

Steel is a metal alloy and as such doesn't have 'molecules', but rather grains of metal (mostly Fe) with additions of Ni, Cr, C, . . . . Atoms of some of the other elements (mostly metals) replace Fe atoms to form solid solution, while others (like C) are interstitional, and in some alloys there are intermetallic phases with definite stoichiometry.

turbo

There is another possibility, too. It seems that a lot of the Damascus blades seen in knife magazines these days have strong color contrasts. I own a few Damascus-blade knives, including a beautiful trout-and-bird knife made by Jerry Rados, and none of my knives have a strong color-contrast. Perhaps the blade had been colored to enhance the contrast between high and low spots, and the oil is removing some of the colorant.

Bystander

And, the other thing when oiling metals --- oil has a lower surface tension than most metals (wets the surface), and loosely bound oxides are easily dislodged --- finely divided metal oxides in oil? Black.

turbo

Good point. The acid-etching that brings out the damascus patterns may leave residues that can be neutralized (but not removed) by a water-based buffering solution, then the oil floats them free when combined with a bit of gentle rubbing.

sog

Doesn't iron have molecules?

How about carbon?

If not then all of the molecules are lost and are new ones formed?

turbo

Alloys like steel have a crystalline grain structure. Yes, there are molecules of materials in the steel, but on the microscopic level, these are aranged in crystal structures that depend on the heat, mechanical deformation, and chilling during formation. You can also Google on quenching and annealing.

Mech_Engineer

It sounds to me like you are confusing molecules with atoms. The point is that there are no steel "molecules," instead the atoms in steel are arranged in crystalline grains with little to no repeating geometries.

Molecule- The smallest division of a compound that still retains or exhibits all the properties of the substance.

The point that both Astronuc and your friend with Phd in Molecular Physics are making is 100% correct. You can't have a single molecule of steel, because no such unit structure of atoms for the metal exists.