Metal Alloys Formation 1 WEC Objective To have an understanding of Manufacturing of steels & their products, Alloy designation, Classification, Properties

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

2WEC

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



Low-C

Medium-C

High-C


Stainless (Cr, Ni)……


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


Stainless (Cr, Ni)

……


Metal Alloys

Non-ferrousFerrous



Grey iron

Nodular iron

White iron

Malleable iron

Alloy cast irons

Classes of Metals

20WEC

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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• 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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• 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


• 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


• 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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• 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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• Imparts brittleness

– Okay if combined with Mn

• Improves machining

• Some free-machining steels contain 0.08% to

0.15% S

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• 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


• 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


Stainless (Cr, Ni)

……


Metal Alloys

Non-ferrousFerrous



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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Documents

Metal Alloys Formation 1 WEC Objective To have an understanding of Manufacturing of steels & their products, Alloy designation, Classification, Properties