2.2

Cold Work

O, W, A, D

O series

Oil Hardening
O1, O2, O6, O7

W series

Water Hardening
W1, W2, W5

A series

Medium Alloy Air Hardening
A2, A4, A6, A8, A9, A10, A11

D series

High Carbon, High Chromium
D2, D3, D4, D5, D7

Shock Resisting

S series
S1, S2, S4, S5, S6, S7

Hot Work

H, P

H Series

H10-H19 Chromium Types
H20-H39 Tungsten Types
H40-H59 Molybdenum Types

P series

Molded
P6, P20, P21

High Speed

M, T

M series

Molybdenum Types
M1, M2, M3-1, M3-2, M4, M6, M7, M10, M33, M36, M41, M46, M50

T series

Tungsten Types
T1, T4, T5, T6, T8, T15

Special Purpose

L series
L2, L6

Carbon steel Hardening Properties

Hardenability: Biggest back curve/worst hardenability
Hardness: Sharp drop as Temper Temp Increases
Abrasion Resistance: Wear volume grows the most over time

Alloy Steel Hardening Properties

Hardenability: Middle Largest Back curve/middle hardenability
Hardness: Slow decline
Abrasion Resistance: Medium wear volume amount

Tool Steels

Hardenability: Smallest Back curve/best hardenability
Hardness: Goes down a little, then back up, then sharp drop
Abrasion Resistance: Least amount of wear volume

Safety in Hardening

Risk of Damaging from hardneing (quench cracks)

Eutectic Structures

spread out carbide structures

Eutectic Networks

Long multiple chains of carbide structures

Severe Banding

One long carbide chain structure

Why are eutectic things made?

Caused by lack of hot work or problems in processing or alloying
Makes the tool steel crack easier

Hardening Characteristics

Safety in Hardening
Depth of Hardening
Size change in hardening
Resistance to decarburization

Depth of Hardening

through hardening, Hardenability

Size change in hardening

Very important for design

Resistance to decarburization

Scale oxidation of surface during heat treatment

Use Characteristics

Resistance to heat softening
Wear Resistance
Toughness
Machinability

Resistance to heat softening

If enough heat is generated during operations that could cause tempering, softening of tool steels

Wear resistance

Difficult to quantify, dependent upon scientific application or wear criteria

Toughness

All tool steels have little or no toughness, some are just worse than others

Machinability

Difficult to quantify, very subjective

Body centered Tretraganol

BCT
Elongated compared to BCC
BCC has low carbon content, BCT has carbon stuck in it because of rapid cooling
Martensite is this

Acicular

needle like structures
BCT 100% Martensite

Martensite has:

High tensile & high hardness
lowest ductility & lowest impact strength

Heat treatments

Tempering
Stress Relieving
Spheroidizing
Austempering
Martempering
Normalizing
Annealing
Hardening

Tempering

After hardening process
Gains more impact strength/ductility & lose less tensile strength/hardness (trade off is much less)
800-1000 F; air cool

Stress relieving

used alot throughout industry
residual stress: stress leftover from a process (ex: cold working); Aims to get rid of this
900-1250 F
1 hr/inch of thickness; air cool

Spheroidizing

Improves machinablitiy & resistance to fracture
used if we tempered much to long
1200 F; 96+ hrs
Raise to temp right before austenite transition temp and then hold it there for very long
releases carbon from BCT, change to BCC ferrite + cementite spheroids
Makes "spheroidized Martensite"
-No actual martensite in it; composed of BCC ferrite + cementite spheroids

Austempering

Stops quench cracks & hardens material
cool in two steps
-first cool in molten salt (high liquid temp)
-then cool in water
Makes bainite
-looks like very tempered martensite(very hard)

Martempering

2 stages of cooling
-Molten salt bath with lower temp than austempering
-cool in water
Makes untempered martensite
*in order to get martensite, Austenite must be made first*

Flame hardening system

Martensite on just the surface
Selective hardening- works best with medium carbon steel
martensite on outside, ferrite & pearlite on inside

Difusion

Change chemistry of surface while solid
low carbon and low alloy steels
Must have this to occur:
*-difference in concentration*
*-material with low carbon*

Carburizing

Pack metal in carbon or carbon based gas and heat it up so that the metal soaks up carbon
two types:
-pack
-gas

Nitriding

-Just like carburizing, but use nitrogen instead
dont go nearly as hot (nitrogen can get in without steel being FCC(can stay BCC))
Nitrides end up on surface (very hard & unwearable)
Dont need to temper
Brittle white layer that must be removed after nitriding process
takes longer than carburizing
thickness is smaller than carburizing
no grain growth in nitriding, only in carburizing

Manganese (identification)

13xx
15xx

Nickel (identification)

23xx
25xx

Nickel-Chromium (identification)

31xx
33xx

Molybdenum (identification)

40xx
41xx Chromium & Molybdenum
43xx Nickel & Chromium
46xx
48xx

Chromium (Identification)

51xx
52xx Chromium

Chromium-vanadium (identification)

61xx

Multiple Alloy (identification)

86xx, 87xx, 92xx, 93xx, 94xx, 94Bxx

Carbon Steel

SAE 1006-1095 General Purpose
SAE 1108-1151 Free Machining
SAE 1513-1572 High Manganese
A611, A619, A620 ASTM Grades

Aluminum

Aids nitriding
Restricts Grain Growth
Removes oxygen in steel melting

Sulfur and Phosphorus

Adds Machinability
Reduces Weldability, ductility, & toughness
Increases resistance to corrosion & oxidation

Chromium

Increases hardenability (big effect)
Increases high temp strength
Can combine with carbon to form hard, wear resistant microconstituents

Nickel

Promotes an austentic structure
Increases Hardenability (mild effect)
Increases toughness

Copper

Promotes tenacious oxide film to aid atmospheric corrosion resistance

Manganese

Increases hardenability
lowers hardening temp
promotes an austenitic structure
combines with sulfur to reduce its adverse effects

Silicon

Removes oxygen in steel making
Improves toughness
Increases hardenability

Molybdenum

Promotes grain refinement
Increases hardenability
Improves high temp strength

Vanadium

Promotes grain refinement
Increases hardenability
Will combine with carbon to from wear resistant microconstituents

Boron

Added in small amounts to increase hardenability by alot
if too much added, reduces ductility(makes brittle)

Lead

Added only to aid in machinabiility

Nitrogen

Acts like carbon in strengthening

Carbon equivalency

When carbon equicalent is \>.3%, weldability can be a problem
%C+%Mn/6+%Ni/15+%Cr/5+%Mo/4+%V/4+%Cu/15
Promote hardening similar to carbon

Normalizing

heating a steel to the fully austenite region, soaking at this temp, & air cooling to room temp
makes grain size & alloy distribution more uniform
900-1400 F

Annealing

Heating a steel to its austenitizing temp and then cooling it at a slow enough rate to prevent the formation of a hardened structure
cool at 100F/hr - 30F/hr
Increases machinability

Hardening

Quenched after austenitizing temp is reached
high strength and toughness

as tempreing temp \___, hardness \____

increases, decreases

Microstructures

Ferrite
Austenite
Cementite
Martensite

Ferrite

Soft, ductile, magnetic

Austenite

Soft, moderate strength, non magnetic

Cementite

Hard, brittle

Martensite

Hardest

Hardenability

Ability of a steel to be hardened
alloys chemicals added in affect it, also temp and grain size

quench mediums

Quickest cool/most severe

Low carbon steel

Medium carbon steel

.3%-.6%

High carbon steel

.6%-2%

Grain growth

heat turns grains back to normal; fixes distortions
cooling depends on way cooled

Corrosion

deterioration of a material or its properties because of reaction with its environment

problems caused by corrosion

weight gain/reduction, mechanical properties affected

why corrosion occurs

Environment reacting with metal and material properties

Requirements for corrosion to occur

anode (higher energy, active)
cathode (lower energy, passive)
metal path
electrolyte that will carry ions
difference in energy between anode & cathode

electrolyte

liquid or other medium that carrys current

electrochemical corrosion process

changes of state aided by electron/ion movement(conduction)

Galvanic series chart

magnesium Anodic
zinc
lower carbon steel
tin
stainless steel

Metallurgical conditions

Chemical segregation
presence of multiple phases
inclusion
cold work
nonuniform stresses

chemical segregation

one part of a cast chills faster than the bulk

presence of multiple phases

grain boundaries are more active (anodic)

inclusions

most act like anodes (except wrought iron, it reduces corrosion)

cold work

bend has anode, rest of metal is cathode

nonuniform stresses

high energy creates an anode

environment corrosion

chemical nature
-reducing
-oxidixizing

operating conditions

intended service life
temperature
velocity-speed of liquid going through piping system
concentration
impurities
aeration

types of corrosion

uniform
pitting
crevice
galvanic corrosion
stress corrosion
intergranular attack
dealloying

uniform

same corrosion throughout metal
Ex: .05 in/yr

pitting

localized corrosion
happens in specific locations

crevice

metal to metal/nonmetal contact
makes divet near where contact is made

galvanic corrosion

2 metals connected electrically in an electrolyte
anode and cathode

stress corrosion

corrosion due to cracking
environmentally assisted cracking