Stainless steel as the common ferritic and austenitic stainless steels due to their low chromium content. Duplex stainless steels have a mixed microstructure of austenite and ferrite, the aim usually being to produce a 50/50 mix, although in commercial alloys the ratio may be 40/60. They are characterized by high chromium (19–32%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels. Duplex stainless steels have roughly twice the strength compared to austenitic stainless steels. Their mixed microstructure provides improved resistance to chloride stress corrosion cracking in comparison to austenitic stainless steels Types 304 and 316. The properties of
Stainless steel 1936 was also built using a spot-welded stainless steel hull. Due to its thermal stability, the Bristol Aeroplane Company built the all-stainless steel Bristol 188 high-speed research aircraft, which first flew in 1963. However, the practical problems encountered meant that Concorde employed aluminium alloys. The use of stainless steel in mainstream aircraft is hindered by its excessive weight compared to other materials, such as aluminium. Surgical tools and medical equipment are usually made of stainless steel, because of its durability and ability to be sterilized in an autoclave. In addition, surgical implants such as bone reinforcements and replacements (e.g. hip