Short answers, pulled from the story.
Stainless steel resists corrosion because its chromium content of at least 10.5% reacts with oxygen to form a microscopically thin chromium oxide film on the surface. This film blocks further oxygen from reaching the steel beneath and is self-repairing: if scratched, exposure to oxygen restores it.
Harry Brearley of the Brown-Firth research laboratory in Sheffield, England discovered a martensitic stainless steel alloy in 1913 while searching for a corrosion-resistant material for gun barrels. The discovery was publicly announced in a January 1915 newspaper article in The New York Times. Parallel work was also occurring: Krupp engineers Benno Strauss and Eduard Maurer had patented the austenitic 18/8 type on the 17th of October 1912.
The five families are austenitic, ferritic, martensitic, duplex, and precipitation hardening. The first four are defined by their crystalline structure, while precipitation hardening is defined by the heat treatment used to develop its properties. Austenitic stainless steel is the largest family, making up about two-thirds of global production.
Harry Brearley originally called his alloy "rustless steel," and Ford Motor Company continued using that term in promotional materials as late as 1932. A local cutlery manufacturer who worked with Brearley gave it the name stainless steel, which eventually came to dominate worldwide.
Stainless steel is 100% recyclable. An average stainless steel object is composed of about 60% recycled material. The average carbon footprint across all grades is estimated at 2.90 kg of CO2 per kg of stainless steel produced.
Inhaling fumes while welding stainless steel carries a probable increased risk of cancer, particularly lung cancer. According to Cancer Council Australia, all types of welding fumes were classified as a Group 1 carcinogen in 2017. Stainless steel welding is suspected of producing carcinogenic fumes from cadmium oxides, nickel, and chromium.