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Flashcards in metals pt 2 Deck (38):
1

Whats a eutectic phase equilibria

liiquid>> solid+solid

2

whats a peritectic phase equilibria

liquid + solid>> solid

3

whats a monotectic phase equilibria

liquid>> solid + liquid

4

eutectoid phase equilibria

solid>>solid +solid
This reaction forms the basis of the heat treatment

5

peritectoid phase equilibria

solid + solid>>> solid

6

whats a steel

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

7

list the solid phases in Fe-Fe3C phase diagram

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

8

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

2.01 wt%C
XX(X)/100

9

Hyper or Hypo eutectoid greater than the eutectoid

hyper is greater
(compositions that are more than the eutectoid)

10

In hypereutectoid steel what is the proeutectoid phase

cementite
in hypo its ferrite

11

Most phase transformations in steel develop from which phase

austenite

12

type of phase transformations in steel

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

13

whats to TTT diagrams show

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

14

List the steel transformations on the TTT diagrams
from high to low temp formations

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

15

effects of temp on strength

lower temp, smaller intermellor spacing, more boundaries higher strength

16

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

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

17

how are Dual phase steels fabricated

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

18

slow cooling of austenite gives what

pearlite

19

moderate cooling of austenite gives

bainite

20

rapid quench of austenite gives

martensite, reheated gives tempered martensite

21

Indicate the particular heat treatment applied to asquenched
martensite, thereby making it useful for engineering applications

tempering

22

what does tempering martensite do, list the reactions that occur

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

23

In TTT diagrams, transformation kinetics will change what

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,

24

what is hardenability

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

25

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

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

26

How does the size of a specimen effect hardenability

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.

27

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

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

28

ideal diameter

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

29

what is the base diameter a function of

grain size and carbon concentration

30

brittle fractore

low energy
rapid
clevaged , facetted surface

31

ductile fracture

high energy
slow
ruptured, dimpled surface

32

what is stainless steel

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

33

what is stainless steel resistant to

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

34

describe austenitic steels

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

35

ferritic stainless steels

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

36

stainless steel not effective in what conditions

-basic conditions
-presence of cl-

37

problems with stainless steel

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

38

solutions to corrosion of steel


- reduction in C concentration