sic transit gloria mundi
WHICHWATCH Wrote:...My best legal "fine print" is to tell you that this is a complicated subject around which enitre college curricula are built. I'll do my best to provide a primer, which is probably all I am capable of.Steels are such a widely used material because they are inexpensive and highly flexible in management of their properties. Properties can be changed dramatically through relatively small amounts of alloying elements and processing/heat treatment sequences.Stainless steels usually have significant amount of nickel and chromium added which provide the corrosion resistance. 316 is a widely used grade known for its manufacturability and corrosion resistance. It also contains molybdenum, which provides better corrosion resistance than grade 304. 316L is a lower carbon alloy of 316 that improves manufacturability as well as certain properties.While most carbon steels and some stainless steels can be strengthened by heat treatment, 316 and 316L are part of a family called "austenitic stainless steels" that can not be heat treated. Their properties can however be altered by cold working during manufacture.Hardness is usually defined as "resistance to penetration of the surface". Hardness of materials has probably long been assessed by resistance to scratching or cutting. Mohs is a scale that reflects the ability of one material to be scratched by another. However, relative hardness tests such as Mohs are limited in practical use and do not provide accurate numeric data or scales particularly useful for modern day metals and materials. The usual method to achieve a hardness value is to measure the depth or area of an indentation left by an indenter of a specific shape, with a specific force applied for a specific time. There are three principal standard test methods for expressing the relationship between hardness and the size of the impression, these being Brinell, Vickers, and Rockwell.I am not aware of great analyses quantitatively linking hardness values to "scratchability". As Mike said, "scratchability" can also depend on surface texture, the degree to which a surface has been polished, etc. I can easily imagine that on a watch we might see a scratch which technically hasn't really "penetrated" the surface in any meanigful way, but has rather merely disrupted the surface to an extremely shallow extent which can be removed by simple polishing. In fact, this type of "hairline" on a watch is probably more common than a classic scratch which actually deforms and moves metal, resulting in a small "bead"of metal pushed up at the end of the trough representing the scratch.So where does that bring us? To the end of my knowledge, for one thing. I'm certain there is a more knowledgeable metallurgist out there, and perhaps he can do a better job on this subject than I have done. Personally, I think the subject of "scratchability of steel surfaces in horological applications" would make a wonderful subject for a graduate students' PhD research.
Regards, Shing | email iwcforme1976 (at) gmail (dot) comtime does not change us. it just unfolds us. max frisch.all that really belongs to us is time; even he who has nothing else has that. baltasar gracian.
Last edited: 8 December, 2012 - 16:07