Stainless steel and wrought alloys

• An alloy which can be manipulated/shaped by cold working • So it can be drawn into wire

• Wires for orthodontics • Partial denture clasps

• Iron >98% • Carbon <2% *Above 2% carbon is regarded as cast iron or pig iron • Chromium 0.5-1% to improve tarnish resistance • Manganese • Nickel, cobalt

• Cutting instruments (<0.8% C) • Forceps (<0.8% C)

• Undergoes two solid state phases changes with temperature

• Temp >1400C (low carbon solubility 0.05%) • Temp <900C

• Temp in between 900 and 1400C • Has higher carbon solubility 2% • During this temp the Iron lattice expands which is what you’d expect

• Interstitial solid solution of Iron • Face centred cubic lattice • Lattice has iron in rows and columns and some C atoms interspersed • Exists at high temp >720C

• Very dilute solid solution of Iron • Exists at low temp

• Fe3C • Exists at low temp

• Eutectoid mixture of Ferrite and Cementite

• Two metals that form a common latice structure • Are soluble in one another • Two types of solid solution

-Random ( both types of atoms in lattice structure arranged in random fashion) • Ordered ( Can predict type of atom based on its location)

• Several lattices together • Can be random or ordered

• Atoms of different sizes (prerequisite) • Solute atoms occupy the interstitial (holes between atoms) in crystal lattice of the solute • E.g. Fe and C

• When Iron cools rapidly the grain structure is Austenite • Ferrite and Cementite exist if you slow the molten alloy down extremely slowly (not interested)

• Rapid cooling of metal to adjust the mechanical properties of its original state

• Should give us Austenite according to phase diagram • But in practice gives us Martensite

• Has distorted lattice structure due to carbon being unable to diffuse normally within array of iron atoms in each grain • This is hard and brittle • Don’t want this

• Iron 72% • Carbon <2% • Chromium 17-19% • Nickel 7-9%

• If there is at least 12% chromium

• Corrosion resistance due to chromium oxide layer it forms on surface • Vital as oral environment high risk for corrosion due to saliva, liquids with acidic pH levels • But it can be attacked by chlorides • Also lowers Austenite to Martensite temp and rate • Decreases % C at which Eutectoid formed

• Lowers Austenite to Martensite transition temp • Improves fracture strength • Improves corrosion resistance

• Martensitic • Austenitic