Quote:
Originally Posted by DavidJayUden
So, Don and Kyrie, is the metal part, once heated and straw colored, in any way preserved, hardened, strengthened, tempered or in any other way "improved" by the straw process? Or is it just colored?
dju
|
Yes sir, and this takes us back to the nature of the material used to make firearms, especially in the late 1800s to the mid to late 1900s; low carbon steel.
Low carbon steel was the wonder material of the late 1800's; cheap and easy to make, soft enough that it was easily workable without wearing out cutting/abrading tooling, and capable of being surface hardened by surface carbonization (usually case hardening), or by changing the crystal structure of the steel harden it.
Low carbon steel is soft enough to be easily shaped, but left soft has poor resistance to abrasion. Relatively large gun parts that would be subjected to abrasive contact with other parts were case hardened to have a thin "skin" of high carbon steel (which is what the surface carbonization process does). This surface hardness was generally "file hard" meaning a file would not bite, but would skip across the hardened surface. Taking a file to a part that has been surface hardened feels like trying to file a piece of oiled glass.
The process that produces straw and fire blue colors is different from surface carbonization, but like the case colors produced by surface carbonization, the straw and blue colors are a by-product of the hardening process and not a goal in and of them selves. More on this later, when I get some time....
Hardening only the surface, and leaving the core material soft, leaves the part capable of take shock without cracking or shattering (preserves the immense ultimate strength of the core). The surface hardness allowing the bearing parts to perform many cycles with little to no appreciable wear. Surface hardened parts of a Luger include the frame, barrel extension, and the toggle links. In a model 98 Mauser rifle, the major parts subjected to surface carbonization include the receiver and bolt body.
Case hardening produces, at the quench, surface colors. These colors are usually just muddy brown or grey, but it was discovered the additition of different elements to the material used in the case during surface carbonization would produce different colors - some of those colors were just stunning.
These colors produced at the quench would quicky just fade to muddy brown/grey, and people worked to find a way to fix the colors so they did not change. That effort was successful, and "case colors" were born.
The production of different colors at the quench became (and still is) something of an art form, with the specific materials added to the pace being a closely held secret. Companies that provided case hardening services were commonly located close to slaughter houses, as animal bone was one of the major components of the pack. Things added to the pack to produce colors like green, yellow, and royal blues included some passing strange things, including salts produced from urine.
The lock plates of Spanish side lock shotguns are classical examples of some of the colors possible as a side effect of case hardening and are true works of art. And, in this world of contradictions, it's not unusual to find the inside surface of such lock plated have had the case colors buffed off. Go figure.
In any event, the colors produced by surface carbonization are a by-product of the conversion of the surface of the part to high carbon steel. Discovering how to make beautiful, and fix, these colors doesen't make the part much more corrosion resistant, but does increase the price point at which the firearm can be sold.