Metal Alloys Formation 1 WEC Objective To have an understanding of Manufacturing of steels &...

Metal Alloys Formation

1WEC

Objective

To have an understanding of

• Manufacturing of steels & their products,

• Alloy designation,

• Classification,

• Properties & uses of various types …..Plain/ alloy/tool etc,

• Effects of common alloying elements

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Metal Alloys• Most engineering metallic materials are alloys.

• Elemental metals are generally very soft and not very usable.

• Metals are alloyed to enhance their properties, such asstrength,hardness or corrosion resistance,

and to create new properties, such assuperconductivity and shape memory effect.

• Engineering metal alloys can be broadly divided into

–Ferrous alloys and

–Non-ferrous alloys

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Engineering Materials

Metal

Non-ferrousFerrous

Carbon Low Alloy High Alloy

Cast ironsCast ironsSteelsSteels

Low-C

Medium-C

High-C

Tool (Mo,V,W,Cr, Ni)

Stainless (Cr, Ni)

……

High-strength low-alloy……

Grey iron

Nodular iron

White iron

Malleable iron

Alloy cast irons

Classes of Metals

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Steel

Structural framing

Roofing / Cladding

Interior products

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The Whole Spectrum of Steel Products!

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Alloy Designation

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AISI - SAE Classification System AISI XXXX

American Iron and Steel Institute (AISI)

• classifies alloys by chemistry

• 4 digit number– 1st number is the major alloying element

– 2nd number designates the subgroup alloying element OR the relative percent of primary alloying element.

– last two numbers approximate amount of carbon (expresses in 0.01%)

http://www.steelnumber.com/en/number_en10027_eu.php

• Alloy Designation Alloy Designation– AISI: American Iron and Steel Institute– SAE: Society of Automotive Engineers– ASTM: American Society for Testing and Materials– UNS: Unified Numbering System

AISI Grade X1X2X3X4

Carbon Steels and Low Alloy Steels

Older, but still widely

used

Primary alloying elements

Carbon content

10, 11, 12 plain C steel13 Mn steel2x Ni steel, x=%Ni3x Ni-Cr Steel, x=%Ni+Cr4x Mo Steel, x=%Mo5x Cr steels, x=%Cr6x Cr-V Steels, x=%Cr+V7x W-Cr Steels, x=%W+C9x Si-Mn Steels, x=%Si+Mn

X1X2

eg. 15 = 0.15%C5195 =?

1040Fe-0.4%C

2520Fe-5%Ni-0.2%C

Fe-1%Cr-0.95%C10WEC

What is a steel and alloy of?

Iron (Fe) and Carbon (C)

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Plain Carbon Steels

An alloy of Fe & C

whose properties depends

only upon the %age of

Carbon present in it.

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Metal Alloys

Non-ferrousFerrous

Carbon Low Alloy High Alloy

Cast ironsCast ironsSteelsSteels

Low-C

Medium-C

High-C

Tool (Mo,V,W,Cr, Ni)

Stainless (Cr, Ni)……

High-strength low-alloy……

Grey iron

Nodular iron

White iron

Malleable iron

Alloy cast irons

Classes of Metals

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Plain Carbon Steel vs. Alloy Steel

Lowest cost

Should be considered first in most application

Classifications

• Low Carbon Steel

• Medium Carbon Steel

• High Carbon Steel

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Plain Carbon Steels: General Properties

• Yield strength: 300MPa (mild steels) - 700MPa (high C steels)

• Tensile strength: 400-1000 MPa

• Ductility: EL% 15-30

• Young’s modulus: 210 MPa.

• Divided into

– low (<0.3%C),

– medium (0.3-0.6%C) and

– high (0.6-1.2% C) carbon levels

• Increasing C content increases strength & hardness, but decreases ductility

& toughness

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Low Carbon Steel

• Carbon < 0.3wt%• Used wherever soft,

deformable materials are needed

• E.g., structural sections, rivets, nails, wire, pipe.

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Medium Carbon Steels

• Carbon = 0.3 - 0.6wt%

• Used where higher strength is required

• E.g., gears, shafts, axles, rods, etc.

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High Carbon Steels

• Carbon = 0.6 - 1.2wt%

• used where high hardness is required

• E.g. hammers, chisels, drill, springs.

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Mild steel panels for easy shaping

Medium-carbon steel chassis for strength and toughness

high-carbon steel springs

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Low-C

Medium-C

High-C

Tool

Tool (Mo,V,W,Cr, Ni)

Stainless (Cr, Ni)

……

High-strength low-alloy……

Metal Alloys

Non-ferrousFerrous

Carbon Low Alloy High Alloy

Cast ironsCast ironsSteelsSteels

Grey iron

Nodular iron

White iron

Malleable iron

Alloy cast irons

Classes of Metals

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Alloy Steel

Alloy steel may be defined as one whose characteristics

properties are due to some elements other than Carbon.

Although all Plain-Carbon steels contain moderate

amounts of Mn & Si, but they are not considered alloy

steels because the principal function of Mn & Si is to act

as de-oxidizer during steel manufacturing process.

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Why alloying is necessary?

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Why alloying is necessary?Many purposes, some of the most important are:-

i. increase harden-ability,

ii. reduce danger of warpage,

iii. improve strength & toughness at high & low

temperatures,

iv. resist grain growth at elevated temperature,

v. improve wear, corrosion, fatigue & creep

resistance.

vi. improve machine-ability,

vii. improve magnetic properties.23WEC

Alloying Elements used in Steel

• 2% to 5%

• Increases toughness

• Increases impact resistance• 12% to 20% with low amounts of C possess great

corrosion / scaling resistance• universal grain refiner in alloy steels • unfortunately is a powerful graphitiser. • Invar

– contains 36% Ni– virtually no thermal expansion– used for sensitive measuring devices

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Alloying Elements used in Steel

• Usually < 2%

• increases hardenability and strength

• 5 % Cr steels used for making forging dies

• typically used in combination with Ni and Mo

• 10.5% < Cr < 27% = stainless steel –– used for corrosion resistance

• Improves non-scaling properties

• Causes grain growth

• Reduces toughness

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Alloying Elements used in Steel

• Usually < 0.3%

• has strong carbide stabilizing influence

• increases hardenability and strength

• Mo-carbides help increase creep resistance at elevated temps

• imparts some sluggishness to tempering influences

• improves the tensile strength & sp. heat resistance

• has favorable influence on the welding properties.

• Steel with higher contents tend to be difficult to forge

• typical application is hot working tools26WEC

Alloying Elements used in Steel

• acts as de-oxidizer during steel manufacturing • combines with sulfur (MnS) to prevent brittleness & improves

machining • forms stable Carbides• >1%

– increases hardenability• improves strength, wear resistance of steel• 11% to 14%

– increases hardness– good ductility– high strain hardening capacity– excellent wear resistance

• Ideal for impact resisting tools27WEC

Alloying Elements used in Steel

• Usually 0.03% to 0.25%

• has strong carbide-forming tendency.

• stabilities martensite and increases hardenability.

• induces resistance to softening at high temperatures once the steel is hardened

• increases hot hardness properties in High Speed & Tool steels by increasing cutting properties.

• increases strength without loss of ductility

• Like Nickel it restrains grain growth

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Alloying Elements used in Steel

• helps to form stable carbides

• renders transformations very sluggish - hence, once

hardened, a steel resists tempering influences.

• increases hot hardness

– used as cutting tool steels

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Alloying Elements used in Steel

• Imparts brittleness

– Okay if combined with Mn

• Improves machining

• Some free-machining steels contain 0.08% to

0.15% S

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Alloying Elements used in Steel

• for low carbon steels, can drastically increase

hardenability

• improves machinablity and cold forming capacity

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• deoxidizer

• 0.95% to 1.30%

• produce Al-nitrides during nitriding

Alloying Elements used in Steel

• 0.10% to 0.50%

• increases corrosion resistance

• Reduces surface quality and hot-working ability

• used in low carbon sheet steel and structural steels

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• About 2%• increases strength without loss of ductility

• enhances magnetic properties

Alloy Steel

• >Most common alloy elements:

– Chromium, nickel, molybdenum, vanadium,

tungsten, cobalt, boron, and copper.

• Added in small percents (<5%)

– increase strength and hardenability

• Added in large percents (>20%)

– improve corrosion resistance or stability at

high or low temps

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High Strength Low Alloy SteelsLow alloy = alloying elements <10%

• Yield strength : 800-1100 MPa

• Tensile strength: 950-1300MPa

• Ductility : EL% 15-20

• Young’s modulus: 200 MPa (alloying generally reduces Young’s Modulus)

Uses

• Used where high strength or hardness is needed – eg high strength bolts, connecting rods, springs, torsion bars, ball bearings.

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Low-C

Medium-C

High-C

Tool

Tool (Mo,V,W,Cr, Ni)

Stainless (Cr, Ni)

……

High-strength low-alloy……

Metal Alloys

Non-ferrousFerrous

Carbon Low Alloy High Alloy

Cast ironsCast ironsSteelsSteels

Grey iron

Nodular iron

White iron

Malleable iron

Alloy cast irons

Classes of Metals

35WEC

Tool Steels

A class of (usually) highly alloyed steels designed

for use as industrial cutting tools, dies, and molds

• To perform in these applications, they must

possess

– high strength, hardness, hot hardness, wear resistance,

and toughness under impact

• Tool steels are heat treated

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AISI Classification of Tools Steels

T, M High‑speed tool steels ‑ cutting tools in machining

H Hot‑working tool steels ‑ hot‑working dies for

forging, extrusion, and die‑casting

D Cold‑work tool steels ‑ cold working dies for

sheet metal press-working, cold extrusion, and forging

W Water‑hardening tool steels

S Shock‑resistant tool steels ‑ tools needing high toughness, as in sheet metal punching and bending

P Mold steels ‑ molds for molding plastics and rubber

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Tool Steels• Carbon tool steels: 0.8~1.2%C• High alloy tool steels are often

alloyed with Mo, V, W, Cr and/or Ni

• E.g., HSS, W-Cr-V (18-4-1)• Yield strength: 1000-1500 MPa• Tensile strength: up to 2000MPa• Ductility: EL% 5-15• Young’s modulus: 200 MPa

(alloying generally reduces Young’s Modulus)

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Tool Steels

Uses• Used where extreme

hardness is required.• Ductility/toughness usually

sacrificed• E.g. Moulds and dies, saws,

cutting tools, punches

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Stainless Steel (SS)Highly alloyed steels designed for corrosion

resistance

• Principal alloying element is chromium, usually greater than 11.5%

– Cr forms a thin impervious oxide film that protects surface from corrosion

– “Stainless-ness” comes from the formation of a self-repairing Cr2O3 thin, adherent &

impervious oxide film that protects or passivates the underlying steel.

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Stainless Steel (SS)

• Nickel (Ni) is another alloying ingredient in certain SS to increase corrosion protection

• Carbon is used to strengthen and harden SS, but high C content reduces corrosion protection since chromium carbide forms to reduce available free Cr, therefore Carbon content is kept very low - < 0.1% to avoid Cr3C2

formation

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Properties of Stainless Steels

• In addition to corrosion resistance, stainless steels

are noted for their combination of strength and

ductility

– While desirable in many applications, these

properties generally make SS difficult to work

in manufacturing

• Significantly more expensive than plain C or low

alloy steels

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Types of Stainless Steel

• Classified according to the predominant phase

present at ambient temperature:

1. Austenitic stainless ‑ typical composition

18% Cr and 8% Ni

2. Ferritic stainless ‑ about 11.5% to 27% Cr,

low C (0.25% max), and no Ni

3. Martensitic stainless ‑ as much as 18% Cr

but no Ni, higher C content (0.15-0.75%) than

ferritic stainless

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Additional Stainless Steels

• Traditional stainless steels developed in early 1900s

• Several additional high alloy steels have been developed and are also classified as stainless steels:

4. Precipitation hardening stainless ‑ typical composition = 17% Cr and 7%Ni, with additional small amounts of alloying elements such as Al, Cu, Ti, and Mo

5. Duplex stainless ‑ mixture of austenite and ferrite in roughly equal amounts

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Stainless Steels - Typical Mechanical Properties

• Yield strength : 200-1600 MPa

• Tensile strength : 300-1800MPa

• Ductility : EL% 2-20

• Young’s modulus:~170 MPa (alloying

reduces Young’s Modulus)

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Designation Scheme for Stainless Steels

• Three‑digit AISI numbering scheme

• First digit indicates general type, and last two

digits give specific grade within type

– Examples:

Type 302 – Austenitic SS18% Cr, 8% Ni, 2% Mn, 0.15% C

Type 430 – Ferritic SS 17% Cr, 0% Ni, 1% Mn, 0.12% C

Type 440 – Martensitic SS 17% Cr, 0% Ni, 1% Mn, 0.65% C

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Assignment

Alloy steels•Cr steels•Ni steels•Ni-Cr steels•Mn steels•Mo- steels•V-steels

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Thanks

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