Stainless Steel

it is a wrought alloy

can be manipulated / shaped by cold working i.e. it can be drawn into a wire

orthodontic wires and partial denture clasps

> 98% iron <2% carbon 0.5-1% chromium (to increase tarnish resistance)

when the carbon content is above 2%

cutting instruments >0.8% C medical instruments e.g. forceps <0.8% C

in a solid state it can exist in 2 crystalline forms (2 phases) depending on the temperature

900 < temp < 1400C = face centred cubic lattice (FCC) with a higher carbon solubility (2%) temp <900 or >1400C = body centred cubic lattice (BCC) with a low carbon solubility (0.05%)

• austenite • ferrite • cementite • pearlite

interstitial solution, FCC; exists as high temp i.e. >720 C

very dilute solid solution, exists at low temp

Fe3C exists at low temp

eutectoid mixture of ferrite & cementite

2 metals that form a common lattice structure, are soluble in one another and form a solid solution

substitutional & interstitial

a) random - where both types of atoms in the lattice structure are arranged in a random fashion b) ordered - can predict the type of atom based on its location

2 atoms are markedly different in size e.g. iron occupies all the lattice sites and the carbon fits in the spaces in a random fashion

grain structure locked in to make austenite

ferrite & cementite but also large grains with poor mechanical properties which is not ideal

should give austenite but in reality gives martensite

has a distorted lattice structure as C is unable to diffuse normally within the array of Fe atoms in each grain meaning it forms a hard & brittle material - don’t want

heating followed by quenching which allows martensite to become a versatile alloy but not for dental application

pearlite (ferrite & cementite)

martensite (distorted lattice)