Short answers, pulled from the story.
Stainless steel must contain at least 10.5% chromium by mass to form a passive film on its surface. This specific percentage allows the material to protect deeper layers from oxidation when exposed to oxygen.
Harry Brearley worked at the Brown-Firth research laboratory in Sheffield, England during 1913 when he discovered corrosion-resistant alloy for gun barrels. His discovery resulted in a martensitic stainless steel later known as AISI type 420 with an announcement appearing two years later in a January 1915 issue of The New York Times.
Krupp engineers Benno Strauss and Eduard Maurer patented austenitic stainless steel on the 17th of October 1912. They called it Nirosta which became known as 18/8 or AISI type 304.
An average carbon footprint of 2.90 kilograms of CO2 exists per kilogram of stainless steel produced. Emissions from raw materials account for 1.92 kilograms while electricity contributes 0.54 kilograms and direct plant emissions add another 0.44 kilograms to the total.
Inhaling fumes during welding creates probable increased risks of lung cancer according to extensive research involving cadmium oxides, nickel, and chromium. All types of welding fumes were classified as Group 1 carcinogens by Cancer Council Australia in 2017.