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