Apple yesterday was awarded a patent on improving stainless steel by applying a thin layer of nitride to improve its resistance to scratches and impact without changing the look and feel of the metal. The patent, number 20100273538, is described as being “cost-effective” and yet could improve the hardness of the stainless steel considerably.
The process involves taking regular stainless steel, which is formed by fusing chromium and nickel into an alloy with the steel, and placing it in a superheated salt bath (between 520-580 degrees Celsius, or around 1,000 degrees Fahrenheit) and allowing the steel to absorb the nitride over the course of 45-90 minutes. The resulting coating should around 15 microns thick, and yet increase the hardness of the steel from a typical Vickers Hardness rating of 140 to around 1,000.
Because the process produces an obvious benefit at a reasonable cost and doesn’t change the aesthetic qualities of the steel, the invention could have wide applications beyond where it is already being used, such as in the iPhone 4. Apple’s web page for the iPhone describes the steel band in the product as being “created from our own alloy” and “five times stronger” than standard steel, both of which fit in with the specifications of the newly-awarded patent.