Stainless steels Flashcards
Characteristics
> contain minimum of 11.5 wt% Cr in solid soln
thin film of chromium oxide on free surfaces, passivating the steel
same density and young’s modulus as plain carbon steels, high electrical resistivity, low thermal conductivity
Effects of alloying elements on phase stability
> C, Ni, and Mn are austenite stabilizers and expand gamma loop
Cr is ferrite stabilizer
depending on amounts of alloying elements, stainless steel can be austenitic, ferritic, martensitic or duplex
Types of stainless steels
- austenitic: 3XX or 2XX
- martensitic: 4XX or 5XX
- ferritic: 4XX
- precipitation hardenable: 6XX
- duplex
Precipitation hardenable SS
> high strength and corrosion resistance
strengthening is not from carbon or martensite, but from gamma prime precip like Ni3Ti and Ni3Al
Ni3Ti, Ni3Al, Ti and Mo contribute to strength
Duplex SS
> equal amounts of ferrite and austenite
17-30wt% Cr, 3-13wt% Ni and Mo for pitting corrosion resistance
great ductility, toughness and strength
as temp v, strength ^, but ductility doesn’t ^
high rate of work hardening prevents necking and gives higher ductility
comp: C: 0.02 %; Cr: 26%; Ni: 4.7%; Mo: 1.4%; N: 0.2%