|August 19||Index||August 21|
|August 20 is the __th day of the year (__th in leap years) in the Gregorian calendar. There are __ days remaining until the end of the year.|
|1775||The Spanish established a walled fortress, the Presidio San Agustín del Tucsón, starting what eventually became Tucson, Arizona. The English name Tucson was derived from the Spanish name Tucsón, which in turn was derived from the O’odham name Cuk Shon. Cuk Shon means “(at the) base of the black [hill]”, referring to the volcanic mountain located there.
Cuk means “black” and shon means “base, root, foundation, beginning”.1
|1913||Harry Brearley (February 18, 1871–July 14, 1948) created the first stainless steel in Sheffield, England. Stainless steel is also known as “inox” or “inox steel”, from the French word “inoxydable”. It is defined as a steel alloy with a minimum of 10.5% chromium content.
Brearley was an English metallurgist researching new steels for arms manufacturing in the years immediately before World War I. Excessive wear was a problem in gun barrels, so Brearley began researching new steels that could resist high-temperature wear—gun barrels get hot. He started experimenting with adding chromium to steel, which was known to raise the melting point from that of standard carbon steel. He was trying to quantify the effects of steels with 0.2% carbon and and chromium in the 6% to 15% range.
To examine the new alloys, Brearley had to polish and etch the samples. A dilute solution of nitric acid in alcohol works well to etch carbon steel, but he found the chromium alloys were extremely resistant to the chemicals. Brearley’s casting number 1008 (12.8% chromium, 0.44% manganese, 0.2% silicon, 0.24% carbon and 85.32% iron), considered the first stainless steel, was created on August 20, 1913.
Stainless steel, also called corrosion-resistant steel or CRES when the alloy type and grade are not given, does not corrode, rust or stain with water like carbon steel does. However, it is not 100% stain-proof; it will stain in low oxygen, poor circulation, or high salinity environments. Stainless steel is used where steel’s strength and resistance to corrosion are both required. There are different grades of stainless steel to suit different environments.
Carbon steel rusts easily when exposed to moisture or humidity. The rust, a film of iron oxide, is “active” and accelerates the rust process, forming more iron oxide. The iron oxide has a greater volume than the carbon steel, so the iron oxide expands, flakes, and falls off, “eating away” at the steel. In comparison, stainless steel contain chromium, which causes a “passive” film of chromium oxide to form on the surface. Due to the chromium oxide having the same volume as the steel, it remains on the surface. The chromium oxide film prevents further corrosion and blocks corrosion from spreading into the steel’s internal structure. Passivation, as the process is called, can only occur if the chromium content is high enough and oxygen is present.
In addition to chromium, nickel is often added to stabilize the structure of the stainless steel (sometimes manganese, which is cheaper than nickel, is added for the same purpose). Consumers commonly run across terms like “18/8 stainless steel” or “18/10 stainless steel”. 18/8 stainless steel is the most widely used stainless steel. 18/8 stainless (also known as EN-Standard X10CrNi18-8, SAE grade 301, or UNS S30100) is a composition of 18% chromium and 8% nickel. 18/10 stainless steel is commonly used in cutlery and high quality cookware. 18/10 stainless (also known as EN-Standard X5CrNi18-10, SAE grade 304, or UNS S30400) is a composition of 18% chromium and 10% nickel.
|1942||Born today: Isaac Hayes (August 20, 1942–August 10, 2008)|
|August 19||Index||August 21|