ABSTRACT
There are three general classes of stainless steels normally used for diaphragm design. These include the austenitic chromium-nickel alloys exemplified by type 316, the straight martensitic chromium alloys such as type 410, and the precipitation-hardening alloys such as types 17-4 PH and 17-7 PH. The ability to resist corrosion is the first consideration on which the selection of stainless steel is made for instrument design. Stainless steel's resistance to oxidation or scaling is due to the formation of a nearly impervious, tightly adherent, chromium-oxide-rich film on the surface. The chromium stainless steels, having lower coefficients of thermal expansion, give better Service under such conditions than chromium-nickel steels with similar scaling resistance. Nitronic stainless steels are austenitic alloys similar to the 300 series alloys, but provide higher strength at all temperature levels. The precipitation-hardening stainless steels have gradually replaced the 410 stainless steels in many applications despite their higher costs.
