Stainless Steel Revision Questions

Question 1

Wrought alloy

Answer 1

alloy which can be manipulated by cold working

Question 2

Allotropic

Answer 2

in solid state can exist in 2 crystalline forms:
body cenetred cubic crystalline structure (<900 degrees, >1400 degrees)
Face centered cubiic lattice structure (900-1400 degrees)

Question 3

Austenite

Answer 3

intersitital solid solution, face centered cubic lattice structure - has inrows and columns, some C atoms interpsresed
exists at high temps

Question 4

Ferrite

Answer 4

very dilute solid solution

exists at low temps

Question 5

Cementitie

Answer 5

Fe3C - exisits at low temps

Question 6

Pearlite

Answer 6

eutectoid mixture of ferite and cementite

Question 7

Slow and fast cooling of austenite

Answer 7

slow cooling = pearlite (ferrite and cementite)

fast cooling = martensite (hard and brittle) - tempering produces pearlite

Question 8

Maternsite

Answer 8

disotred lattice structure as result of carbon being unable to diffuse normally with array of iron atoms in each grain
forms hard and brittle material

Question 9

Ferrite

Answer 9

soft and ductile

Question 10

Cementite

Answer 10

hard and brittle

Question 11

Corrosion resistance

Answer 11

due to chromium oxide layer formed but can be attacked by chlorides

Question 12

Chromium

Answer 12

lowers austensite to martensite temp and rate and decreased % carbon at which Eutectoid form

Question 13

Nickel

Answer 13

improves UTS, corrosion resistance

Lowers Austenite to martensite transiiton temp

Question 14

S.S wire soldering

Answer 14

use gold or silver <700 degrees

risks the grains recrytaliising which affects mechnical properties (quenching avoids this)

Question 15

Weld decay

Answer 15

Temp raised between 500-900 degree
it pushes Cr and C atoms to grain boundaries
casuses S.S to become brittle