03 Presentation Chapter 3 Material

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1

CHAPTER 2

Materials of Chemical

Equipments



2

What is Materials Technology?

Materials technology is a relatively comprehensive disciplinethat begins with the production of goods from raw materials to

processing of materials into the shapes and forms needed for

specific applications.

MaterialRaw material Equipment

State changing

Energy,

Additives

Processing/Manufacturing

Energy,

Additives

Raw material into material :



3

Material Engineering : Material Science – Material TechnologyScience :

•Material Structure•Material Propeties•Relationship between Internal Structure & Propeties

Technology : – Processing from Raw Material into Material – Application – Design and new development.



4



5



2.1 Metal and Alloy Metal

• Iron and Steel

• Steel structure• Carbon Steel & Cast Iron

• Crystal Structure

• Mixture & Impurities



Iron and steel

Applications:

Cutting tools, pressure vessels, bolts, hammers, gears, cutlery,

jet engine parts, car bodies, screws, concrete reinforcement, ‘tin’

cans, bridges...

Why?

• Ore is cheap and abundant

• Processing techniques are economical (extraction, refining,

alloying, fabrication)

• High strength

• Very versatile metallurgy - a wide range of mechanical and

physical properties can be achieved, and these can be tailored to

the application



Disadvantages:

• Low corrosion resistance (use e.g. titanium, brass instead)

• High density: 7.9 g cm-3 (use e.g. aluminium,

magnesium instead)

• High temperature strength could be better (use nickel instead)

Basic distinction between ferrous andnon-ferrous alloys:

• Ferrous metals are ‘all-purpose’ alloys

• Non-ferrous metals used for niche applications,

where properties of ferrous metals are inadequate

Iron and steel



9

Steel structure

• Ferrite : (Ferrum), soft, easy to beprocessed at low temperature

• Austenite ( Roberts Austen), easy to beprocessed, non magnetic

• Zementite Fe3C : hard

• Ledeburite ( A. Ledebur): Structure at

Eutectic point, hard to be processed• Pearlite : Layer structure like pearl

layers





Carbon Steel and Cast Iron

A. According to their Chemical Components :

Iron Carbon Alloy:

(>95%)Fe +(0.05% ~ 4%)C +(~1%)(impure steel and cast iron)

B. According to the Carbon Content:Steel C%=0.02~2%

Cast Iron C%>2%

Engineering Pure Iron C%<0.02%

Pure Iron Steel Cast Iron

0.02 2 4 C%0



Isomeric Transformation of Pure Iron

is the phenomenon that the crystal configurationchanges with the temperature in the state of solid.



t < 910 Cubic Lattice in Bulk Center,℃

called “ -Fe”

t > 910 Cubic Lattice in Face Center,℃

called “ -Fe”

The transformation accomplishes in 910℃without temperatur changing.

Classification



The structure of iron-carbon alloy steel

The structure of iron-carbon alloy steel

The structure of metal

The micro-structure of metal

Grain Boundary

Grain

micrograph



Different structure cause different

performance of materials.



Steel metallurgy

Iron is allotropic / polymorphic i.e. exhibits different crystal

structures at different temperaturesMost importantly: bcc <-> fcc transformation at 912°C (for pure

iron)

Solubility of carbon in ferrite (α-iron, bcc): 0.02 wt%

austenite (γ-iron, fcc): 2.1 wt%

What happens to carbon when crystal structure transforms from

fcc to bcc?

Fundamental issue in metallurgy of low alloy

steels







Pearlite

NB Pearlite is a MIXTURE of phases (on a very fine scale)

Alternating layers of ferrite and cementite formedsimultaneously from the remaining austenite when

temperature reaches 723qC





Fe 1.3 wt% C: Cementite precipitates at austenite grainboundaries, remaining austenite is transformed into

pearlite







24

High mechanic performance if structure of grain arehomogeneous and „ tight“



25

Crystal of Ferrite Steel (

Atom Carbon in thestructure Ferrite

-Fe)



26

Atom chrom in the structure Ferrite

Crystal of Ferrite Steel ( -Fe)



27

Atom silicium in the structure Ferrite

Crystal of Ferrite Steel ( -Fe)



28

Crystal of Austenite Steel ( -Fe)

Atom Carbon in thestructure Austenite



29

Ferrit, lowmechanicendurance

Ferrit+ Perlit :0,35% C,temper steel

Perlit : 0,8% C,mold steel, bycooling of

Austenite

Structure of different metal crystal under microscope



30

Micrograph of Perlite & Zementite

1,3%C , tool steel

Micrograph of Austenite steelX10CrNi18.9

Structure of different metal crystal under microscope



α-Fe γ -Fe

910℃

The transformation



Iron-iron carbide equilibrium diagram



Austenite

A3

A1

Ferrite

Austenite+

Ferrite

Pearlite

+

908

722

Tem

perature

Iron-iron carbide equilibrium diagram

Percent carbon of weight

0 0.80.2 0.4 0.6



• The lattice structure of steel varies from one form toanother as the temperature changes.

• This is illustrated in the above diagram. Between roomtemperature and 722ºC, the steel consists of what isknown as “ferrite and pearlite”.

• Ferrite is a solid solution of a small amount of carbondissolved in iron. Pearlite, which is shown in thediagram, is a mixture of ferrite and iron carbide. Thecarbide is very hard and brittle.

• In the previous diagram between line A1 (lower criticaltemperature) and A3 (upper critical temperature) thecarbide dissolves more readily into the lattice that is nowcalled “Ferrite and austenite”. Austenite is a solidsolution of carbon and iron that is denser than ferrite.



Above line A3 the lattice is uniform in property with theaustenite the main structure. The actual temperature forthis austenite range is a function of the carbon content of the steel as shown in the figure.



The basic types of C existing in iron-carbon alloy:

Carbon and its existing form in steel

Dissolution

Chemical Combination

Blending



• C dissolute in the lattice of Fe to form

Solid Solution

—— Fe-C Solid Solution.

Solvent —— the element without changing in

lattice Fe is the solvent

Solute —— the element dissolving in solvent C is

the solute

Dissolution



Two kinds of common-used Solid Solution

Solubility of C

At room temperature 0.006 %

723 ℃ 0.02 %(maximum)

Ferrite(F):

The solid solution formed by C dissolving in -Fe is calledFerrite.

Characteristics:

Because the gap between atoms is small, the capacity todissolve C is weak.



Low strength

Low hardness

Good plasticity

Good toughness

aMP saMP b

170~90,280~200 == σ σ

aMP HB 0.8~5.5=

%40~30=δ

2/5.2~8.1 mMJ ak =

Properties



The solid solution formed by C dissolving in γ -Fe is called

Austenite, it is denser than Ferrite.The lattice of C keeps in that of γ -Fe, i.e. Cubic Lattice

in Face Center.

Characteristics:

Because the gap between atoms is large, the capacityto dissolve C is strong.

Solubility of C

723 ℃ 0.8 %

1147 ℃ 2.06 %(maximum)

Austenite(A)



High strength

High hardness

Good plasticity

Good toughness

No ironic magnetism

Properties



The transformation between F and A:

723 ~ 910℃Ferrite (F) Austenite (A)

Both F and A have good plasticity and they

are the structural basis of steels’ characteristicof excellent plasticity.

The irons that dissolve C will take the

transformation between -Fe and -Fe in

different temperature.



Chemical Combination:

C and Fe form the metallic compound ——Iron Carbide(Fe3C) whose crystal structure is called Cementite indicated

by “C”.

C + 3Fe Fe3C•Characteristics:

a)The carbon content of Cementite is high, the massproportion is 6.67%.

b)Hard and brittle (HB=78.4MPa)

c)Almost no plasticity and toughness

Cementite



a) Low break-down strength ( b≈35 MPa )b) The Cementite is semi-stable compound, it will

decompose into Fe and C at certain conditions, theextricated C exists in the form of graphite.

Fe3C C + 3Fe

Cementite



The alloy whose components are blending together

in the state of liquid can solidify into two types of mechanical mixtures:

a) Mixture formed by two solid solutions;

b) Mixture formed by a solid solution and

metallic compound.

Mechanical Blending (Mixture)

For example:

Pearlite (P),Ledeburite (L) is a kind of Mechanical Mixture.

Pearlite (P) = Ferrite (F) + Cementite (C)Ledeburite (L) = Austenite (A) + Cementite (C)



46

Damascus sword:

which Westerners first encountered during the Crusades

against the Muslim nations



What Is Real Damascus Steel?

Genuine Damascus blades are known to have been made in that city — and later elsewhere in the Muslim Middle East and Orient—fromsmall ingots made of steel (a mix of iron and carbon) shipped fromIndia; those starting materials have been called wootz ingots or wootzcakes since around 1800.

The steel contains around 1.5 percent carbon by weight, plus lowlevels of other impurities such as silicon, manganese, phosphorus andsulfur.DAMASCUS STEEL SWORD from the 17th century shows a classicdamascene pattern of swirling light and dark bands. The inscriptiontells us that this excellent blade was made in 1691 or 1692 by Assad Allah, the most renowned Persian sword smith of his time.



Assemble the ingredients to load into thecrucible, including high-purity iron, Sorel iron,charcoal, glass chips and green leaves. The

quantity of carbon and impurity elements thatend up in the ingot is controlled by theproportions of iron, Sorel iron and charcoaladded to the mix.

Heat the crucible. During this process, theglass melts, forming a slag that protects theingot from oxidizing. The leaves generatehydrogen, which is known to acceleratecarburization of iron. The carbon content of the iron is raised to 1.5 percent, a goodproportion for forming the hard iron carbideparticles whose accretion into bands gives

Damascus blades their characteristic wavysurface pattern. The leaves and glass can beleft out, but ingots made without them aremore prone to cracking during hammering.



When the crucible has cooled, remove theingot, which bears a resemblance to thewootz cakes used by the ancients.

Heat the ingot to a precise temperature.Pendray is using a gas-fired furnace withthe propane-to-air ratio adjusted to

minimize the formation of oxide scaleduring forging. Typically, a surface oxidelayer of about half a millimeter in thicknessforms, and the final grinding operation mustbe sufficient to remove it.



Forge the ingot (deform it slightly with hammer blows while it is still hot). When the ingot gets

too cold to deform without cracking, heat it upandforge again. Four separate stages of the ingot areshown here; each stage is the result of severalcycles of heating and forging. A total of about 50cycles may be needed to bang out the blade shapefrom the ingot—a highly labor-intensive process.Pendray uses a modern air hammer. A handheld

hammer works, too, but it takes longer.

Cut the blade to final shape and hand-forgeto add finer details.



Remove the excess steel and thedecarburized surface metal. Pendray isusing an electric belt grinder for this step.

Cut grooves and drill holes into thesurface of the blade to createMohammed's ladder and rose

patterns, if desired. Forge the bladeflat again and polish the surface to givethe blade its near final form.



Etch blade surface with an acid to bring out the pattern; the softer steeldarkens, and the harder steel appears as brighter lines.



The impure elementsThe main impure elements are:

Mn is useful element.

Si is useful element.

S is harmful element.

P is harmful element.O is harmful element.

N is harmful element.

H is harmful element.



Mn < 0.8% (the common existing impure element)

Coming from the deoxidizing and desulfurizingagent in the process of smelting.

Function: eliminating S and O2.

• They won’t effect the properties of steels if the

content of both are little.

Manganese (Mn):

Mn > 0.8% ( the alloy element intentionally)

Function: Mn can disolve in the ferrite to formthe solid solution strengthening the effect of

ferrite.



Si < 0.5% (common existing impure element)

Coming from the deoxidizing agent and ore.

Function:

Ability of deoxidation is stronger than Mn.

2FeO + Si 2 Fe + SiO2

Si can dissolve in the Ferrite and improve the

strength and hardness of steels.

The existing form:

Forming solid solution with Ferrite.or Remaining in the steels in the form of

deoxidation product (SiO2)

Silicon (Si):

S l h (S)



Sulphur (S):• Originating in the fuels in ore or which are used in the

process of smelting (Coke).

• The existing form: FeS (S doesn’t dissolve in Fe)

• Function:

The low-melting-pointed compound (985ºC) formed by

FeS and Fe makes the steel unit crack in the process of hot-working, this phenomenon is called “Hot Brittle”.

Controlling of the content of S:

Common Steel : S 0.055 0.07%

High Grade Steel : S 0.03 0.045%

Super High Grade Steel : S 0.02 0.03%



Phosphorus (P):• Originating in the ore.

• Function:P in steels can dissolves in -Fe and improves the

strength of steels in normal atmospheric temperature

& brittleness, but dramatically reduces their plasticity

and toughness, this phenomenon is called “ColdBrittle”.

• When the content of P in the steel is P=0.3%, the

impact toughness ak = 0.

• Controlling of the content of P: P 0.06%



Oxygen (O2)

• Originating in the air.

• Existing form:

O2 always exists in the steels in the form of non-metallic

inclusion, such as FeO, SiO2 , MnO, MgO, Al2O3 , etc.

• Function:

These oxidations is in the steels as solid grains which

are hard but brittle and damage the continuity of basic

structure of steels sharply reducing the mechanical

property of steels.

• Eliminating the O2 in the process of smelting.



Nitrogen (N)• Originating in the air.

• Function: – Low Carbon Steels with high-content of N2 are

particularly lack of resistance to corrosion.

– Easy to form the air bubble to be loose.

– Cause the phenomenon of “Age-hardening”.

• Methods:

Adding Al and Ti to form AlN and TiN as if making the

N fix in the steels (called N-fixed Treatment), this will

eliminate the age-hardening.



Hydrogen (H2)

Originating in moist feed in steel-melting stove, pouring

system and the moist air, etc. Function:

– Making the steels to be brittle (H-Brittle)

– Making the steels to be seriously defective (Fish-eye)

Methods:

• Improve the environment of smelting.

• Clear up the moisture content in the feed.

• Purify the steel liquid.



2.2 Properties of Materials

61

Mechanical Properties

Physical Properties

Chemical PropertiesManufacturing Properties



Mechanical Properties:

62

Definition:The capability of materials to resist external forces,but does not deformation beyond allowance or wreck.

Main Performance Index:

Five Index:

Elasticity,Plasticity,

Strength,

Hardness,

Toughness



Mechanical properties

Ferrite: soft and ductile Cementite: hard andbrittle

M h i l P ti



Mechanical Properties:Elasticity

64

Elastic State(curve o-b)1.proportional limit:

2.elastic limit:

Tensile curve of Low Carbon steel

ε

ab

o

M h i l P ti



Mechanical Properties:Elasticity



Strength

66

• ultimate tensile stress σb• yielding point σs,• creep limit σn• creep rupture strength σD• fatigue limit (strength) σ-1

p

p

shrinkage

dolo

4Ao= πdo2

P

AoStress= (MPa)

Strain=llo



1. Yielding State

(near point c)

o

s s

F

P =σ

2. Intensification State (curve c-d)

T. S. (Tensile Strength)

o

bb

F

P =σ

o F

P 2.02.0 =σ

Conditional Yielding

Mechanical Properties:When it is stretched to a certain degree,

there will be shrinkage ,and then break.

3. Shrink Neck State

(after d)



have no apparent yielding phenomena and :

σ 0.2 = stress in 0.2% of residue elongation

Mechanical Properties:Yielding Point σs (MPa)

- minimum value in yielding state

- plastic deformation appears.

Yielding point σ0.2

The stress of any point in the pressure vessel caused by pressurefrom medium should be below the elastic limit and cannot happen theplastic deformation.



The maximum value of stress from thebeginning of being stressed to the end of

fracture.


Ultimate Tensile Stress σb (MPa)



σb

σs

Elastic Plastic

σ

ξ

Yielding point

Normal or low temperature:

considering: yield [yield/tensile] ratio: σ s / σ b

Generally speaking, σs <σb

σs/ σb ↓ , Plasticity ↑, Deformation ↑

σs

/ σb

↑,

Plasticity↓, Deformation ↓Strength Usage ↑

Ultimate Tensile Stress σb (MPa)




Elevated temperature:

Creep Ratemm/mm*h(P con.)

Temperature(0

C)1Cr18Ni9Ti

425 475 520 550

10-6 176 91 33 6

considering: σ n and σ D as well as the previous


Creep Rate

M h i l P ti




Creep Limit σ n

The temperature in which metals creep

Creep phenomena:

When the materials is in high temperature and incertain stress, the stress increases as the time isgoing.

Carbon steel > 420

0

CAlloy steel > 4500C

Light metal and alloy > 50-1500C

Pt, Sn Normal Temperature



τ

ε

o


Creep Curve

ε

τ



Mechanical Properties:Creep limit σ n (MPa)

Definition: The ability of materials to resist theslowly plastic deformation under high temperature.

Under certain temperature, the creep speed does notexcess the stress stipulated.

Stipulated creep speed: 10-7 mm / mm . H10-6 mm / mm . H

1% straining within 105 hours1% straining within 104 hours



Definition: Rupture strength under certain temperature,the material cracks in a stress after a period of stipulated time. This stress is called creep rupture

strength. Stipulated time: 105 hours

Because the designed life time of chemical equipments is commonly 105

hours, the stress under which material cracks is said to be rupture strength.

Creep rupture strength is the ability to resist cracking under certaintemperature and load. The stronger the ability is, the longer it willendure under the same conditions.


Creep Rupture Strength σD (MPa)




Fatigue limit (Strength) σ -1(MPa)

Fatigue strength: the maximum stress, under whichthe materials do not happen fatigue destruction or failure after infinite times of alternate load action.

Fatigue phenomenon: the constructional elementsdestruct under the alternate load action.

Times of Fatigue Test: ~





Plastic Deformation

Elongation After the unit of structure is cracked by tensile

force, the ratio of the total stretched length and the

origin length is called Percentage Elongation,

described by δ%

1)Definition: the ability of plastic deformation

but not destructing under external force.

2)Commonly used Index:

Percentage Elongation

Shrinkage of Sectional Area

Cold Bending Property





Plastic Deformation

h i l i



%100%10000

0

×

∆

=×

−

= l

l

l

l l k k

δ

lk — the gauge length after

cracking, mml0 — the origin gauge length,

mm△l

k

—the absolute length after

cracking, mm




The meaning of Percentage Elongation:i) The value of reflects the degree of the

plastic deformation before the material

cracks.ii) The larger , the better the plasticity of

material.

iii) Plastic material > 5%; Low carbon steel

= 20~30%

iv) Hard brittle material < 5%; Cast iron

= 1%





SHRINKAGE SECTION

After the unit of structure is cracked, the ratioof the reduced area of the cross-section and theoriginal (cross) sectional area is called Shrinkageof Sectional Area which is described by ψ%.

Fk —the minimum As after cracking ，mm2

F0 —original sectional area As ， mm2

% F F F ψ θ

k θ 100×

−=





Cold Bending Property

Welding joint

R

The larger the , the better the plasticity

of the material.The of Low Carbon Steel is about 60%.

With R increasing, the plasticity of materials will be better and better.


M h i l P ti



i) Forming handling(process) and welding ease,such as bending and rolling 、 forging press

cold impacting 、 welding and etc.ii) Make the unit of structure to avoid cracking

for deformation after bearing load.

iii) The Pressure Vessels and their spare partsshould have the characteristic.

Mechanical Properties:The real meaning of the Plastic Index:




HardnessI. Definition: when something which is

harder than material itself is pressed on the surfaceof it, it will resist the pressure by deformation or bedamaged, such abilities are called Hardness.

I. The Hardness Index:

Brinell Hardness (HB)

Rochwell Hardness (HR)

Vickers Hardness (HV)





The test of HB:

d

D

P

)( )(

222 aMP

d D D D

p

F

p HB

−−

==

π

p ——Pressure, N

D——The diameter of

the rigid ball, mm

d ——The diameter of the indent, mm

F ——The area of the Indent, mm2




Generally, good Hardness leads to good

Strength and good resistance to wear and tear.

Experimental Value (MPa):

Low Carbon Steel HB

High Carbon Steel HB

Gray Cast Iron HB

I. Application of Hardness in Engineering

Mechanical Properties:The relationship of Hardness and Strength:




Impact toughness ak

Definition:

The ability of materials to resist the impact

load, i.e., the ability of materials that will makeplastic deformation immediately and rapidlywhen suddenly attacked by dynamic loading.



88




Impact Toughness




p

The larger is a k , the better is the ability of

materials to resist the impact load.

For Mediate and Low Pressure Vessels,a k ≥30 35J/cm2 , commonly a k 60 J/cm2.

The relationship between Toughness andPlasticity:

Generally, stronger toughness makes strongerplasticity; but strong plasticity may not make strong

toughness .

Hard Brittle Materials’ a k

Plastic Materials’ a k

PLASTIC (PERMANENT) DEFORMATION



PLASTIC (PERMANENT) DEFORMATION(at lower temperatures: T < T /3)

91

Physical Properties:



a. Modulus of elasticity (E)

(M Pa)ζ σ

=

E

Nature of E:1) It’s the index of materials’ ability to resist

elastic deformation. E↑ , ability to resist

deformation↑. E of steel is about 2.105

M Pa .

2) For the same material, T ↑ , E↓ .





b. Poisson’s Ratio

ζ

ζ µ

'=

(For steel: 0.3)

′ —— transverse stress

—— longitudinal stress





c. Thermal Expansion Coefficient ( )

•Physical Meaning of :

When T increases by 1 , the increasing℃

length per unit length is called Thermal

Expansion Coefficient.•Application of in Engineering.

）C/1( °==∆

∆∆∆

t l

l t l l α α


Chemical Properties:




Definition: It’s the chemical stability of materials in medium, i.e. , it’s the nature that

whether the materials react with medium

chemically or electro-chemically leading tocorrosion.

Two index:

• Corrosion Resistance• Resistance to Oxidation




a. Corrosion resistancethe ability of metal materials to resist the corrosioncaused by the medium (such as atmosphere, watervapor, electrolyte).

b. Oxidation resistance

1 ） Resist to high temperature oxidation;

2 ） Resist to oxide etch by other gaseousmedium, such as water vapor, CO2 , SO2 , etc.




Manufacturing Properties

A. Definition: Proterties ( mechanical, physical &chemical) are technical / processing properties of material.

B.Classification:

Casting

Forging

Welding

Machining

Heat treatment

Cold – Warm forming

M f t i P ti



Casting Property : Fluidity, Congealing Shrinkage Rate

Forging Property : Resistance to Thermal Fragment,

Resistance to Oxidation, Thermo-plasticity.

Welding Property : Fluidity of parent material and

welding flux in the melting state, Congealing,Shrinkage Rate, Thermo-plasticity.

Machining Property : Hardness, Brittleness.

Heat Treatment Property : Heat Treatment Feasibility.

Cold & Warm forming Property: Plasticity, Toughness.

Manufacturing Properties

Classification and



1. According to the content of carbon (C%):

Low Carbon Steel

Medium Carbon Steel

High Carbon Steel

2.According to the smelting methods:

Full Killed Steel

Rimmed Steel

Semi-killed Steel

3.According to the quality:

Common Steel

High Grade Steel

Super High Grade Steel

designation of the equipments

A di t th t t f b (C%)



1. Low-carbon steel (C<0.25%) : Low strength and goodplasticity, used in chemical vessels in welding andmechanical units with low loads.

2. Medium Carbon Steel (C=0.25%~0.6%) : Medium

strength and plasticity, used as the important units of shaft,

gear, top cap of high pressure equipments and so on.

3. High Carbon Steel (C>0.6%) : High strength andhardness, poor plasticity, used as string, wire line and so on.

According to the content of carbon (C%)

According to the smelting methods



According to the smelting methodsFull Killed Steel:

deoxidized with a strong deoxidizing agent(silicon or aluminum)

to reduce the oxygen content during solidification of the moltensteel in the ingot.

Rimmed Steel ( boiled steel): A low-carbon steel containing sufficient iron oxide to give acontinuous evolution of carbon monoxide while the ingot is

solidifying, resulting in a case or rim of metal virtually free of voids. Sheet and strip products made from rimmed steel ingotshave very good surface quality.

Semi-killed Steel: A commonly used grade of steel manufactured for low carbon

bars and structural. A steel is considered semi killed so that it isincompletely deoxidized and it contains sufficient dissolvedoxygen to react with the carbon to form carbon monoxide tooffset st in the ingot.





What happens during rapid cooling?

• Phase diagrams only show stable phases that are formed

during slow cooling

• If cooling is rapid, the phase diagram becomes

invalid and metastable phases may form

• In the case of steel, the formation of ferrite and cementite

requires the diffusion of carbon out of the ferrite phase. What

happens if cooling is too rapid to allow this?

The crystal lattice tries to switch from fcc

(austenite) to bcc (ferrite). Excess carbon ->distorted body-centred lattice MARTENSITE

Martensite (α’)



Martensite (α )

• Distorted bcc lattice

• Non-equilibrium carbon content

• Forms plate-like or needle-shaped

grains

Fe, C 2, Mn 0.7 (wt%)



P d i h d d t d t l



Producing quenched and tempered steels

• Critical cooling rate for martensite formation depends on

concentration of alloying elements (e.g. C, Mn, Cr, Ni). Alloying elementsdelay the formation of ferrite and pearlite -> increase chances for

martensite formation

• Critical cooling rate defines concept of HARDENABILITY (i.e. ease of

martensite formation)

• Component thickness is an important parameter

Medium carbon steels generally used in quenched and tempered

condition, high-carbon steels almost always.

Applications: chisels, hammers, drills, cutting tools, springs...

□ Quenching and tempering not possible for low carbon steels ->

microstructure = ferrite + pearlite

Applications: car panels, bridges, pipes.



Corrosion

2.3. Corrosion & Protection of Chemical



2.3. Corrosion & Protection of ChemicalEquipments

Harm of corrosion

Chemical Corrosion

Electrochemical Corrosion

Inter-crystalline corrosion

Stress corrosion

Ha m of co osion



ht F

p p 210 /mg K ⋅

−

=

ht

m2F

p1

p0

K

g

g

g/cm2·h

Time of corrosion action —

Contact Area of corrosivemedia and test piece —

WT after corrosion —

WT before corrosion —

Corrosion Rate —

1.weight changing:

Harm of corrosion

Harm of corrosion



2.corrosion degree:

K a —Thickness variation per year mm/year

—Metallic density g/cm3

hF

γ

P V and h F V =⋅= _ _

γ ⋅

∆=∆∴ F

ph

Harm of corrosion

Harm of corrosion



Harm of corrosion

3.Three Grades’ Standard of Metallic Resistanceto Corrosion:

Grade I: K a < 0.1 mm/year (corrosion resistant)

Grade II: K a = 0.1 ~ 1.0 mm/year (available)

Grade III: K a > 1.0 mm/year (unavailable)

Types of metallic corrosion



1.Uniform (General) Corrosion: i. Corrosion is over the whole metallic

surface

ii. Effect and danger are small

iii. Remaining enough corrosion allowance in

designation can still assure the strength

and expected life of equipments

Types of metallic corrosion



2.Local Corrosion:

i. Corrosion is at the local region in metals

ii. Very dangerousiii. Remaining the corrosion allowance in

designation has no effect.

2 Local Corrosion:



iv. Categories of Local Corrosion

(1)Seam Corrosion

(2)Pitting Corrosion

For example:

the pitting corrosion of Cr-Ni stainless

steel in the media containing [Cl- ]

2.Local Corrosion:

2 Local Corrosion:



(3)Stress Corrosion

(4)Inter-crystalline Corrosion

For example:the inter-crystalline corrosion of

Cr-Ni stainless steel under certain conditions

2.Local Corrosion:

Chemical Corrosion



1.Definition: The corrosion caused by chemical reactions

between metals and drying gas or non-electrolytesolution is called Chemical Corrosion.

Chemical Corrosion

Chemical Corrosion



2.Characteristics: i. Corrosion products are on the metallicsurface

ii. No electric current in the cause of corrosion

iii. The two natures of the products from

chemical reactions:

(1)Stability —— Passivation

(2)Unstability —— Activation

Chemical Corrosion

Chemical Corrosion



i. Metallic high temperature oxidation

(1)Oxidation resistance:

oxidized rapidly at high T

forming oxidation film

stopping oxidation

Chemical Corrosion

Chemical Corrosion



(2)High temperature oxidation of carbon steel and cast iron:

Stable

Unstable

Stablelayer I: Fe2O3

layer II: Fe3O4

layer III: FeO

T > 570 oxidation layer forms℃

inner layer Fe3O4 outer layer Fe2O3

T < 570 oxidation layer forms℃

T > 300 oxidation surface appears℃

Chemical Corrosion

Fe2O3



T < 570 ℃ T > 570℃

2 3

Fe3O4

FeO

Fe

Composition of ironic oxidation layer

Chemical Corrosion



(3)Solutions:

Adding some Cr Si Al to form stable

oxidation film of Cr2

O3

SiO2

Al2

O3

which

can prohibit the oxidation reaction from

proceeding.

Chemical Corrosion

Chemical Corrosion



ii. High temperature decarburization(1) T > 700 ℃

oxidation and decarburization both exist

Fe3C + O2 3Fe + CO2

Fe3C + CO2 3Fe + 2CO

Fe3C + H2O 3Fe + CO + H2

Chemical Corrosion

Chemical Corrosion



(2)Result

*Cementite Ferrite

with Strength, hardness and Fatigue

Strength all decreasing.

*Forming the air bubble which is the crack

initiation point.

(3)PreventionAdding Al or W

Chemical Corrosion

Chemical Corrosion



iii. Hydrogen corrosion (hydrogen brittleness)At relevant low temperature and pressure

(T≤200 ,℃ P ≤5MPa), H2 won’t

corrode the carbon and alloy steelsapparently.

At high T and P, the corrosion actions of

H2 to steels are obvious.

Chemical Corrosion

Chemical Corrosion



Mechanism of hydrogen corrosion:

Stage I —— “Hydrogen brittleness stage”

H disperses inward and dissolves.

Stage II —— “Hydrogen attack stage”

Chemical reaction vary the

structure of steels:

Fe3C + 2H2 3Fe + CH4

Chemical Corrosion




1.Definition: The corrosion caused by electrochemicalreactions between metals and electrolytes iscalled Chemical Corrosion.





2.Mechanism: Anode reaction —— Me Me+ + e

Electron movement —— eanode ecathode

Cathode reaction —— D + ecathode [D e]





3.Conditions of electrochemical

corrosion:•There is potential difference on the parts of metallicsurface or between different metals.

•The parts which have potential difference are connectedwith each other or the anode is connected with cathode.

•The metal with potential difference is in the electrolyteor the electrolyte where the anode and cathode areconnected with each other.





Definition

It is the phenomenon that the corrosion occurs between two crystalline surfaces and causes the

grain boundary continuously damaged. Nature

It’s a kind of local and selective corrosive damage.

Inter crystalline corrosion




Occurring in

Austenitic stainless steels

ReasonLack of Cr element in the grain boundaryAustenitic stainless steels (C<0.14%)

*At high temperature (1050ºC) C distributes completely in whole alloy.

Inter crystalline corrosion

*Between 400~850℃

C + Cr + Fe (Cr Fe) C



C + Cr + Fe (Cr . Fe)23C6

Anode

Cr 12.5%

Inter-crystallineCorrosion occurs

Separate out along the grain boundary Cr%

Cr lacking

Corrodingminicell

Cathode — Grain

— Cr lacking

region

Grain

(Cr . Fe)23C6

Cr lacking region

Grainboundary

Stress corrosion



i. Definition

The destruction is caused by both corrosive

media and the tensile stress action, this kind of damage is called Stress Corrosion.

Stress corrosion

Stress corrosion



ii. Initiation Circumstances

Carbon steel and various kinds of Alloy steel (suchas austenitic stainless steel) are in the media listed asfollowing:

(1)High concentrated chloride solution above

80℃

(2)High temperature and pressure water at

150~300 ℃(3)High temperature and concentrated caustic

solution

Stress corrosion

Stress corrosion



iii. Mechanism

Stage I: Breeding stage

The primary destruction (mechanical crack) is

formed in metallic surface under the co-actionof corrosion and tensile stress.

Stress corrosion

Stress corrosion



Stage II: Corrosion crack’s extension stage

Corrosive media dissolve the passivation film inthe cracks to form anode with the film becoming

cathode, the electrochemical corrosion thereforeoccurs.

The crack extents rapidly under the co-action of this corrosion and tensile stress.

Stress corrosion

Stress corrosion



Stage III: Breaking stage

St ess co os o

Stress corrosion



iv. Prevention measure

(1)Decrease or clear up the stress concentration

(2)Select the stress corrosion resistant materials:

Two-phase stainless steel ——

austenite + small amount (about 5%) of Ferrite

such as: 1Cr18Mn10Ni5Mo3N

0Cr17Mn13Mo2N 0Cr21Ni5Ti



Mechanism of cathodic protection:

The protected metallic devises are

polarized into cathodes by the direct current

(DC) from outer electrical power supply

taking the auxiliary electrode as the anode.

When the potential of cathode < that

of anode, the corrosion will be prohibited.



Corrosion Resistant Measures in MetallicEquipments



1.Selecting materials reasonably 2.Adding the lined protection

Equipments



Adding the lined protection

i. Metallic lining: stainless steel,

other metals(Cu Al Ti Cr Ni)ii. Nonmetallic lining: plastics,

rubbers, enamelware, etc.

+-



iii. Coating

iv. Adding corrosion

buffering agents

v. Electrochemical

protection

such as:

cathodic protectionCathodic Protection

Apparatuses

Heat Treatmentfi i i f h



1.Definition of heat treatment

Heat treatment is the technical process or treatmentsto steels in solid state according to the scheduled

requirements like heating, keeping warm and cooling,

their aims are to vary the internal structure and gain the

desired properties.

2.Basic Theories of heat treatment:

•When the basic components of steels (Fe) is heated to a

certain degree, its lattice structure of steel will vary fromone form to another as the temperature.

•Ferrite (F) and Austenite (A) are both the solid solution of

Fe, so they have the lattice structure of iron.

Heat Treatment



3.Bring forward the problem:

Find out the method and path of altering the propertiesof steels

4.Purpose of heat treatment

Eliminating some shortages of steels

Improving some properties of steels

5.Advantages of heat treatment

Intensifying the metallic materials, fully developing

the potential of materials, lightening the mass of

equipments and guaranteeing the security and expected

life of equipments.



Cooling media and way of cooling



Cooling in furnaceCooling in still airCooling in oilCooling in waterCooling in brine

Cooling CapacityCooling Speed

Heat Treating Process of steels:



Annealing

Normalizing

Quenching

Tempering



Quench



(1)Process :

Heating the steel pieces to the quenching temperature, cool them quicklyin the quenching agents after the warm-keeping treatment, then theAustenite changes into the Matensite.

(2)Quenching Temperature

*Hypo-eutectoid Steel (C<0.8%) heating above the A3 line 30~50ºC*Hyper-eutectoid Steel (C>0.8%) heating above the A1 line 30~50ºC

(3)Quenching Agent

*Mineral Oil, Water, and Brine.

*Generally speaking: Carbon Steel, cooling in water and brine.

Alloy Steel, cooling in oil.

Quench



(4)Quenching Function

developing the hardness, strength and wear (abrasion) resistance.

*The emergency cooling in quenching is apt to make flaw inthe steel pieces, so the tempering is commonly needed to clear up

the stress after quenching.

*Quenching and Tempering are always combined to thetechnical process.

iii. Tempering

(1)P



(1)Process

Heat the steel pieces which are already quenched to the certaintemperature (T<Tcritical), cool them quickly in still air after the warm-keepingtreatment.

(2)Purpose

Reduce or clear up the internal stress of workpieces after quenching,stabilize the internal structure and gain the different mechanical properties.

(3)Types of Tempering *Tempering at low temperature

after quenching, tempering between 150~250ºC.

Function——reduces the internal stress and brittleness of quenchingsteels, and at the same time keeps the high hardness and high wear

resistance.Usage ——in spares of various tools and ball bearing after carburation.





Common used materials

Common carbon steel



Vietnamese StandardCode ItemsTCVN 3600-81 Roofing steel sheet. Galvanized, acid-pickled.TCVN3601-81 Roofing steel sheetTCVN 3779-83 Thin acid-pickled sheet steelsTCVN 3780-83 Tinplate. Size, dimensions

TCVN 3781-83 Zincplate steel sheet. Technical requirementsTCVN 6525-99 Hot-dip zinc-coated carbon steel sheetTCVN 471:2004 Coated metal products, used in internal and external

construction works. Technical propertiesTCVN 470:2005 Aluminium coated and hot dip galvanised steel strip

and sheets

TCVN 1765:75 Carbon steel

Common carbon steel



- TCVN 1765-75 : 3 groups A, B, C.

Group A : according to mechanical property

Symbol : CTXX

CT : means carbon steel

XX : ultimate tensile stress σ b (N/mm2)example : CT38

Group A

Giíi h¹n bÒn (σ b = 380N/mm2

)



Symbols of different Standards



TCVN GOCT GB UNS AISI/SAE JIS AFNOR DIN BSC45 45 45 G10450 1045 S45C X45 C45 06A4540Cr 40X 40Cr G51400 5140 SCr440 42C4 42C4 530A40OL100Cr2 X15 GCr15 G52986 42100 SUJ2 100C6 100C6 535A9920Cr13 20X13 2X13 S42000 420 SUS420J1 Z20C13 X20Cr13 420S2908Cr18Ni10

08X18H90

0Cr18Ni9 S30200 304 SUS304 Z7CN18.09 X15Cr-Ni18304S31

CD100 Y10 T10 T72301 W109 SK4 Y1-90 10 -210Cr12 X12 Cr12 T30403 D3 SKD1 Z200C12 C105W1 BD380Ư18Cr4V P18 W18Cr4V T12001 T1 SKH2 Z80WCV X210C12 BT1

----------- 18-04-01 S 18-0-1 ASTM

-----------CT34 CT2 A2 - 36 SS330 F3360 Fe360 Fe360GX28-48 C130 HT300 F12803 No40 FC300 FGL300 GG30 260GC50-2 B150 QT500-7 F33800 8055-06 FCD500 FGS500-7 GGG50 B500/7

Common carbon steelThe content of the harmful elements S & P can be a little more :



(S≤0.055%, P≤0.045%)

Carbon steel StandardDesignationsFrance: AFNORXC 68Germany: DIN 1.1231Sweden: SS 1770 , SS 1778United States: AMS 5115 , AMS 5115C , ASTM A29 , ASTM A510 , ASTM A576 ,

ASTM A682 , MIL SPEC MIL-S-11713 (2) , SAE J403 , SAE J412 , SAE J414 , UNS G10700

Element Weight %

c 0.65-0.75

Mn 0.60-0.90

p 0.04 (max)

s 0.05 (max)

Rimmed Carbon Steel Suitable under the condition of P≤0.6MPa, t=0~250ºC,



S≤12mm.

a clean surface low in carbon content. known as drawing quality steel.

the steel is partially deoxidized. Carbon content is less

than 0.25% and manganese content is less than 0.6%.

do not retain any significant percentage of highlyoxidizable elements such as Aluminum, silicon or

titanium.

especially where ease of forming and surface finish are

major considerations.

ideal for rolling, large number of applications, and is

adapted to cold-bending, cold-forming and cold header

applications.

High-quality carbon steel



– Content of S & P to be (S & P≤0.04%)

– Uniform texture, good surface quality, superiorproperties than Common Steels.

– The number in designation indicates the percentage of the average content of C=0.08% & C=0.2%

– Steels that commonly contain Mn (without indicatingMn), if Mn < 0,7%

– Steels that contain Mn=0.7~1.2% (indicating Mn)

Super high-quality carbon steel



p g q y

S & P≤0.03%

Both the texture and properties of this

kind of steels’ are superior to that of

High Grade Steel.

Stainless steels



• Definition: > 11 wt% Cr. Ni, Mn may also be present

• Cr -> adherent Cr 2O3 film -> protection against corrosion

and oxidation

• Most stainless steels are austenitic (alloying elements

stabilise γ phase down to room T)

• Austenitic stainless steel is non-magnetic -> useful as

quick test

• Ferritic and martensitic stainless steels also available ->

increases range of mechanical properties available for

specific applications (Corrosion resistance not as good as

for austenitic stainless steel)

Cast Iron



1.The chemical components of

commonly used cast iron:

95% Fe + (2.5% ~ 4%) C + ( ~1%) Purities2.Structure:

Pealite + Cementite + Ladeburite + Graphite

Cast Iron



High carbon content low melting point

Cast Iron



• Cheap

• can produce complex parts quickly and easily throughsand casting

• BUT brittle Two types:

• Grey iron: Fe + C (graphite)

Formation of graphite rather than cementite promotedthrough high C and Si content, slow solidification rate

• White iron: Fe + Fe3C

Properties and Characteristics



Excellent casting property

Good machinability

Good wear resistance

Excellent property to reduce vibration

Low plasticity and brittleness

Low tensile strength and high (ultimate)

compression strength



i. Gray cast iron



(1)Properties and characteristics

*C exists in the form of plate-like graphite

*Gray fracture

*Low mechanical properties

*Excellent corrosion resistance in H2SO4

and NaOH

Grey cast iron



• Among least expensive metallic materials

• High fluidity -> can cast complex shapes

• Graphite flakes -> high damping capacity and good machineability ->

used e.g. as base structure for machines and heavy equipment

• BUT brittle due to shape of graphite flakes -> nodular iron better

Fe, C 3.52, Si 3.26, Mn 0.47 (wt%)

Spherical graphite cast iron

(1)Properties and characteristics

*C i i f f i i



*C exists in the form of spherical graphite

*Have better strength and a certainplasticity and toughness, its overall

mechanical properties are close to

that of steels.*Better corrosion resistance than that of

Gray Cast Iron except when it is in theacid solution.

Ductile / Nodular cast iron



• Addition of Mg / Ce to grey iron -> graphite forms as spheres rather than flakes -> improved toughness

• Applications: valves, pump bodies, gears, crankshafts

Fe, C 3.2, Si 2.5, Mg 0.05 (wt%)

iii. High-silicon cast iron (G)



(1)Properties and characteristics *Adding amount of Si (14.5~18%) to improve thecorrosion resistance of the cast iron.

White cast iron



• Exceptionally hard, but brittle and almost impossible tomachine used in very few applications e.g. rollers in rolling

mills

• Used as intermediary in production of malleable iron: heat

treatment at 800-900°C causes decomposition of cementite ->

graphite clusters. Resulting microstructure and properties

similar to nodular iron. Typical applications: connecting

rods, transmission gears, pipe fittings, flanges



4.Properties and Designation of

commonly used cast iron:



Gray cast iron :

Spherical graphite cast iron:

High-silicon cast iron



Common Material used inChemical Equipments

Objectives



01/09/12

Select suitable material of construction

Specify design temperature and

pressureCalculate wall thickness

Material of Construction



01/09/12

Mechanical and physical propertiesCorrosion resistance

Ease of fabrication Availability in standard sizes

Cost




01/09/12

Preliminary Selection

Selection Charts

Literature Previous experience

Advise from materials supplier

Advise from equipment manufacturer

Advise from consultants




01/09/12

Final Selection

Based on economic analysis which

would include

Material cost

Maintenance cost

Commonly Used Materials



01/09/12

Commonly Used Materials

Metals

Polymers or PlasticsCeramic Materials

Metals



01/09/12

Carbon steels

Stainless steels

Specialty alloys

Carbon Steels



01/09/12

Most common engineering material

Advantages

InexpensiveGood tensile strength and ductility

Available in a wide range of

standard forms and sizesEasily worked and welded

Carbon Steels

Li it ti



01/09/12

Limitations• Corrosion resistance not good

• External surface need painting to prevent atmosphericcorrosion

Suitable for use with:

Most organic solvents

Steam, air, cooling water, boiler feed water

Concentrated sulfuric acid and caustic alkalies

Stainless Steels



01/09/12

Most frequently used corrosion resistantmaterials in the chemical industry

High chromium or high nickel-chromium

alloys of iron chromium content must be > 12%

Nickel added to improve weldability and

corrosion resistance in non-oxidizing env.

Stainless Steels



01/09/12

Main Types of Stainless Steel

Type 304 – 18% Cr & 8% Ni

Type 304L – low carbon version to

improve welding of thick plates Type 316 – Mo added to improve

corrosion resistance in reducing

conditions and at high temperature.

Stainless Steels



01/09/12

Limitations – Intergranular corrosion or weld

decay possible in reducing

environment

– Stress cracking can be caused by a

few ppm of chloride ions

Special Alloys



01/09/12

Monel – 67% Ni, 33% Cu

Better corrosion resistance than SS No stress-corrosion cracking in chloride

solutions Temp. up to 500oC

Inconel - 76% Ni, 15% Cr, 7% Fe

High temperature acidic service Temp. up to 900oC

Plastics



01/09/12

Provide corrosion resistance at low cost.

Main advantages:

Excellent resistance to weak mineral acidsTolerate small changes in pH, minor

impurities or oxygen content

Light weight, easy to fabricate and install

Plastics



01/09/12

Major Limitations:

• Moderate tempeature and pressure

applications (T < 100oC; P < 5 atm.)• Low mechanical strength

• Only fair resistance to solvents

Plastics



01/09/12

Main Classes:

1. Thermoplastic – can be reshaped

2. Thermosetting – cannot be remouldedThermoplastic

• Polyethylenes (low cost; T < 50oC)

• Polypropylene ( T up to 120oC)• Polyvinyl chloride ( T ≤ 60oC)

Plastics



01/09/12

Thermosetting

- good mechanical properties (T 95oC)

- good chemical resistance (except strong alkalies)

Examples:

• Phenolic resins –filled with carbon, graphite, silica

• Polyester resins – reinforced with glass or carbon fibre toimprove strength



Rubber Lining

Metal surface lined with rubber to provide;



01/09/12

Metal surface lined with rubber to provide; Cost effective solution for corrosion control and

abrasion resistance e.g. acid storage, steelpickling

Why rubber?

• Able to bond strongly to various surfaces

• Good combination of elasticity andtensile strength



1.4.2 Effect of Alloy Elements to theproperties of steels



1.Alloy elements:i. Definition

The elements that are added on

purpose to develop the structure and

characteristics of steels.

ii. Main alloy elements

Cr Ni Mn Si Al MoV Ti Cu B Nb W Re



2.Alloy Steel

Definition

Alloy steels are those steels thatcontain the alloy elements which develop theproperties of steels.

Characteristics of the main alloy

elements:



elements:

i. Cr (1)Cr>13%, corrosion resistancedramatically

(2)Strength, hardness, wear resistance,oxidation resistance and hardenability all

(3)Plasticity and toughness

(4)Adds strength at high temperature

ii. Ni

(1)Enlarge the range of corrosion resistance

of stainless steel especially improve the



of stainless steel, especially improve the

resistance to base.

(2)Broad the -phase region as to be the

element that form the austenite.

(3)Develop the strength as well as keepexcellent properties of plasticity and

toughness.

(4)Improves strength at high T

iii. Mn



(1)Develop the strength and impacttoughness at low temperature.

(2)Broad the -phase region.

(3) Counteracts sulfur brittleness.

(4)Increases hardenability.

iv. Si

(1)Develops strength and fatigue



(1)Develops strength and fatigue

durability at high temperature.(2)Improve heat resistance

(3)Resistant to the corrosion of such media

as H2S and so on.(4)If amount of Si is too much,

plasticity and impact toughness both

(5)Strengthens steel

(6)Increases hardenability

v. Mo



(1)Develop the resistance of stainlesssteels to the chloride anion Cl-.

(2)Enhances H corrosion resistance.

(3)Improve the heat resistance.

(4)Raises grain-coarsening temperature.(5)Mo<0.6%, plasticity .

(6)Counteracts tendency toward temper

brittleness.

vi. Al



(1)Restricts grain growth.(2)Develops the impact toughness.

(3)Resistant to the corrosion caused by H2S.

(4)Improves the oxidation and heat resistance.(5)Cheap, common substitute for Cr among

heat-resistant steels.

vii. Ti

(1)Restricts grain growth.



(2)Develops strength and toughness.(3)Improves the oxidation and heatresistance.

(4)Stablizes C to prevent the

“inter-crystalline corrosion”.

(5)Prevents formation of austenite in high

chromium steels; prevents localized

depletion of chromium in stainless steelduring long heating.

viii. V



(1)Developes high-temperature strength.

(2)Increases hardenability.

(3)Restricts grain growth.

(4)Keeps the strength and improve theplasticity.

(5)Resists tempering

AE S P H/WR IT CR OR HR FD GR H

Cr



Ni

Mn P

Si H2S

Mo Mo<0.6% HCl

Al H2S

Ti in-c

V

Re

AE——alloy element

S ——strength

P ——plasticity



P plasticity

H/WR ——hardness and wear resistanceIT ——impact toughness

CR ——corrosion resistance

OR ——oxidation resistance

HR ——heat resistanceFD ——fatigue durability

GR ——grain refining

H ——hardability

in-c ——inter-crystalline



1.Definition:They are the steels that are formed by adding a fewalloy elements at the basis of Common Low CarbonSteel.

Common Low Alloy Steel

2.Composition:



(1)C<0.2%(2)Alloy elements

*Mn 1~1.5%

*Si Cr Ti V Nb Ni Al… 0.015 ~ 0.6%

3.Structure: Ferrite + Pearlite

4.Properties and characteristics:



4.Properties and characteristics:

i. High strength and large yield ratio

ii. Excellent welding property

iii. Good resistance to the corrosion of

atmosphere

iv. Perfect properties at low temperature

5.Designation (GB1591-88)

(New Designation GB/T1591-94)



(New Designation GB/T1591 94)

16Mn 16MnR 16Mng 15MnV15MnVR

15MnVg 09Mn2V 18MnMoNbR

The number ahead is the percentage of theC content, such as 16Mn (C = 0.16%).

Indicate the main alloy elements, thenumber thereafter is the percentage of that



number thereafter is the percentage of thatelement. If it is less than 1.5%, it can beomitted.

Content of alloy elements:1.5 ~ 2.49% Sign as “2” 2.5 ~ 3.49%

Sign as “3” 3.5 ~ 4.49% Sign as “4”



Commonly-used Designation:



i. Boiler Steel20g 22g 12Mng 16Mng 15MnVg

14MnMoVg 18MnMoNbg

ii. Vessel SteelQ235-AR 20R 16MnR 15MnVR

09MnVR 18MnMoNbR



Stainless Steel and Corrosion(Acid) Resistant Steel



Acid Resistant steels are the kind of alloysteels which are resistant to the corrosion

caused by acid or strong caustic media.

As a rule, we called them both “StainlessSteel”.

Examples:

*Chromium Stainless Steel*Chromium-nickel Stainless Steel

( )

1.Chromium Stainless Steel:



i. Component

< 0.2% C + (13 ~ 28%) Cr + Fe

ii. ConstructionFerrite or Martensite

(no Austenite even at high temperature)



iv. Commonly-used Chromium Stainless Steel



1Cr13 2Cr13 0Cr13 0Cr17 0Cr17Tiv. Designation

(1)The first number:

Average C content Average with C

amount of 1000 points0 C < 0.1% 1: C≤0.15% 2: C≈0.2%

(2)The second number:

percentage of the average content of Cr

2.Chromium-nickel Stainless



Steel: i. Component

≤ 0.14% C + ( 17~19% ) Cr + ( 8 ~11%) Ni+ Fe

Briefly called “18 — 8” Steel

Typical Designation: 1Cr18Ni9Ti

ii. Construction

Single austenite structure at normaltemperature

iii. Characteristics



iii. Characteristics

(1)High strength and good plasticity

& toughness

(2)Large range of suitable temperature

-196 ~ 800℃ ℃(3)Excellent technical properties

(4)Good corrosion resistance

ΘNon-corrosive media:

cold phosphorus acid, nitric acid, acetic acid,

hydrogen sulfide, sulfate, nitride, base liquid,



hydrogen sulfide, sulfate, nitride, base liquid,

petroleum chemicals, etc.

ΘCorrosive media:

hydrochloric acid, dilute sulfuric acid (<10%),

hot phosphorus acid, oxalic acid ,melting caustic potassium, melting caustic

alkali, Cl-, bromine (Br), iodine (I), etc.

(5)Inter-crystalline corrosion easily occurs between400~800 ℃



Θ Definition of inter-crystalline corrosion:

It is the phenomenon that the corrosion occursbetween two crystalline surfaces and causes the grainboundary continuously damaged.

ΘNature:

It’s a kind of local and selective corrosive damage.

ΘOccurring in:



Austenitic stainless steelsΘReason:

Lack of Cr element in the grain boundary

ΘAustenitic stainless steels (C<0.14%):*At high temperature (1050ºC)

C distributes completely in whole alloy.

*Between 400~800℃

C + Cr + Fe (Cr . Fe)23C6

Separate out along the grain boundary



Anode

Cr 12.5%

Inter-crystallineCorrosion occurs

p g g y

Cr%

Cr lacking

Corroding minicell

Cathode — Grain

— Cr lacking

region

Grain

(Cr . Fe)23C6

Cr lacking region

Grainboundary

ΘDamage:

To be brittle, even softly beating can makes

it break into dust. Have very low strength.



it break into dust. Have very low strength.

ΘPreventive measures:

*Solution heat treatment ——

quenching again (1100~1150ºC) to

dissolve C and Cr into the austenite.*Reduce the content of C ——

preventing C to combine with Cr, then less

Cr will be separated out.

For example: 0Cr18Ni9 (C ≤ 0.08%)00Cr18Ni9 (C ＜ 0.03%)

*C stabilization treatment ——



adding Ti or Nb to form TiC or NbC tostabilize C.

For example: 1Cr18Ni9Ti 1Cr19Ni11Nb

*Add microelement —— adding B can vary the nature of grainboundary to prevent (Cr . Fe)23C6 to be

separated out.

(6) Pitting corrosion occurs in the media

containing [Cl-]



ΘMechanism:[Cl-] intrudes into the flaw of passivation

film (Cr2 O3) and reacts with metallic ion to

form strong acidic salts ([M+

] + [Cl-

] → MCl)which can dissolve the passivation film ——

the locally corroded film becomes a “passive-

active” minicell —— with corrosion taking

place.

ΘDamage:

Fast corrosion speed easily perforates the



thin (only several mini-meter thick) stainlesssteel by corrosion.

ΘPreventive measures:

*Adding some alloy elementsThe most effective elements to improve the

pitting corrosion resistance: Cr, Mo

Secondarily effective elements: Ni, Si, N, Re

*Cr≥25%, pitting corrosion won’t occur.

2%Mo improve pitting corrosionresistance dramatically, Mo and [Cl-]



y, [ ]form the protective film (MoOCl2) which

can prevent the passivation film being

perforated.

*Materials resistant to the corrosion of [Cl-]:high Cr-Ni stainless steel containing Mo

such as: 1Cr18Ni12Mo2Ti

00Cr20Ni30Mo2Nb000Cr30Mo2

Heat-resisting Steel and Low-temperature Steel



1.Heat-resisting Steel:

i. Characteristics

(1)Excellent high-temperature oxidationresistance (excellent high-T chemical

stability)

(2)Good high-T mechanical properties

(strength at high T)



(b)Refractory steel



*mainly resistant to creep but also resistantto oxidation.

*used in the parts that are loaded at high T.

such as: heating tube, reactor, etc.

*commonly used steels’ designation:

12CrMo Cr5Mo 1Cr18Ni9Ti Cr25Ni20

2.Low-temperature Steel: i. Working temperature



< -20 Low temperature℃ -20 ~-40 Non-cryogenic temperature℃

< -40 Cryogenic temperature℃

ii. Characteristics

(1)Excellent low-temperature toughness

(2)Excellent processing workability and

weldability

iii. Requirements of structure



(1)Low content of C (0.08~0.18%) —— form homogeneous ferritic structure.

(2)Homogeneous austenitic structure is

desirable at cryogenic temperature.iv. Elements added

Mn Al Ti Nb Cu V N

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