metals pt 2

Question 1

Whats a eutectic phase equilibria

Answer 1

liiquid» solid+solid

Question 2

whats a peritectic phase equilibria

Answer 2

liquid + solid» solid

Question 3

whats a monotectic phase equilibria

Answer 3

liquid» solid + liquid

Question 4

eutectoid phase equilibria

Answer 4

solid»solid +solid

This reaction forms the basis of the heat treatment

Question 5

peritectoid phase equilibria

Answer 5

solid + solid»> solid

Question 6

whats a steel

Answer 6

alloys based upon the Fe-C or Fe-Fe3c binary phase diagram which can contain anywhere from trace amounts of C up to 1.2wt% C

Question 7

list the solid phases in Fe-Fe3C phase diagram

Answer 7

Ferrite (alpha), ferrite (delta), Austenite (gamma), Cementite (Fe3C)

Question 8

Whats do the last 2/3 numbers stand for
XXXX(X)
10201

Answer 8

2.01 wt%C

XX(X)/100

Question 9

Hyper or Hypo eutectoid greater than the eutectoid

Answer 9

hyper is greater

compositions that are more than the eutectoid

Question 10

In hypereutectoid steel what is the proeutectoid phase

Answer 10

cementite

in hypo its ferrite

Question 11

Most phase transformations in steel develop from which phase

Answer 11

austenite

Question 12

type of phase transformations in steel

Answer 12

-reactions near equilibrium conditions
(austenite to pearlite)
- reactions removed from equilibrium conditions
(austenite to martensite and bainite)

Question 13

whats to TTT diagrams show

Answer 13

represent the precipitation kinetics for the transformation of products associated with the decomposition of austenite (gamma)

Question 14

List the steel transformations on the TTT diagrams

from high to low temp formations

Answer 14

Coarse pearlite  (slow cooling, coarse)
fine pearlite 
fine pearlite and upper bainite 
lower bainite 
martensite   (fine , rapid quench)

Question 15

effects of temp on strength

Answer 15

lower temp, smaller intermellor spacing, more boundaries higher strength

Question 16

Martensite (alpha dash) is hard and brittle in the as-quenched form, how is it utilised in this form

Answer 16

DUAL PHASE STEEL

-microstructure consisting of islands of martensite in a ferrite matrix gives rise to high rates of work hardening

Question 17

how are Dual phase steels fabricated

Answer 17

theyre heat treated in the two phase region (ferrite alpha and austenite (gamma)). The temp with in the ferrite phase fixes the amount of ferrite formed and the composition of ferrite and austenite

Question 18

slow cooling of austenite gives what

Answer 18

pearlite

Question 19

moderate cooling of austenite gives

Answer 19

bainite

Question 20

rapid quench of austenite gives

Answer 20

martensite, reheated gives tempered martensite

Question 21

Indicate the particular heat treatment applied to asquenched

martensite, thereby making it useful for engineering applications

Answer 21

tempering

Question 22

what does tempering martensite do, list the reactions that occur

Answer 22

heated to a temp below the A1 to make it softer and more ductile
reactions:
-seggregation of carbon atoms
-precipitation of carbides
-decomposition of retained austenite to bainite
-precipitation of alloy carbides in alloy steel which give rise to secondary holding

Question 23

In TTT diagrams, transformation kinetics will change what

Answer 23

1- alloying element- more of these will retard the transformation kinetics, increasing hardenability
(produces a shallower gradient on the graph from the jominey test)
2- austenite grain size- bigger size, makes transformation kinetics slower, increases hardenability,

Question 24

what is hardenability

Answer 24

the ability of steel to partially or completely transform from austenite to some fraction of martensite under heat treatment. (hardening it)

Question 25

name and describe the test used to measure the hardness of steel

Answer 25

jominey test
-one end of the specimen quenched, plot hardness vs distance from quenched end
hardness decreases further from quenched end

Question 26

How does the size of a specimen effect hardenability

Answer 26

cooling rate will be highest at the surface, and diminish as you go towards the centre
the cooling rate at the centre could subsequently be low enough to no longer allow for our condition of a minimum of 50% martensite at the surface (remember our critical diameter).
we would have exceeded the critical diameter for the steel under these conditions.
1. we could increase the cooling rate by using a more aggressive cooling medium,
2. we could use a different composition through increased alloy additions.

Question 27

whats is the critical diameter and what is it a factor of

Answer 27

diameter for a steel composition and quench that would harden to 50% martensite at centre
function of the ideal diameter and the severity of the quench

Question 28

ideal diameter

Answer 28

the diameter that would harden to 50% martensite in an ideal quench 
function of base diameter and multiplying factors 
DI=base diameter x multipling factors

Question 29

what is the base diameter a function of

Answer 29

grain size and carbon concentration

Question 30

brittle fractore

Answer 30

low energy
rapid
clevaged , facetted surface

Question 31

ductile fracture

Answer 31

high energy
slow
ruptured, dimpled surface

Question 32

what is stainless steel

Answer 32

a class of corrosion resistant steels based on a minimum of 12wt% Cr in solid state

Question 33

what is stainless steel resistant to

Answer 33

• attacks by strong acids
• atmospheric corrosion
• aqueous corrosion
• high temp oxidation

Question 34

describe austenitic steels

Answer 34

• low yield strength
• high work hardening rate
• expensive
• excellent formability (undergoing plastic deformation without being damaged )

Question 35

ferritic stainless steels

Answer 35

• high yield strength
• low work hardening rate
• less expensive
• good formability

Question 36

stainless steel not effective in what conditions

Answer 36

• basic conditions

- presence of cl-

Question 37

problems with stainless steel

Answer 37

corrosion along grain boundaries
- temps that induce intergranual corrosion are called sensitising heat treatment, it results in the formation of Cr23C6 on grain boundaries, cr increases corrosion rate, associated with c concs

Question 38

solutions to corrosion of steel

Answer 38

• reduction in C concentration