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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
3WEC
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
5WEC
Steel
Structural framing
Roofing / Cladding
Interior products
6WEC
The Whole Spectrum of Steel Products!
7WEC
Alloy Designation
8WEC
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)
11WEC
Plain Carbon Steels
An alloy of Fe & C
whose properties depends
only upon the %age of
Carbon present in it.
12WEC
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
13WEC
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
14WEC
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
15WEC
Low Carbon Steel
• Carbon < 0.3wt%• Used wherever soft,
deformable materials are needed
• E.g., structural sections, rivets, nails, wire, pipe.
16WEC
Medium Carbon Steels
• Carbon = 0.3 - 0.6wt%
• Used where higher strength is required
• E.g., gears, shafts, axles, rods, etc.
17WEC
High Carbon Steels
• Carbon = 0.6 - 1.2wt%
• used where high hardness is required
• E.g. hammers, chisels, drill, springs.
18WEC
Mild steel panels for easy shaping
Medium-carbon steel chassis for strength and toughness
high-carbon steel springs
19WEC
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
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.
21WEC
Why alloying is necessary?
22WEC
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
24WEC
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
25WEC
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
28WEC
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
29WEC
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
30WEC
Alloying Elements used in Steel
• for low carbon steels, can drastically increase
hardenability
• improves machinablity and cold forming capacity
31WEC
• 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
32WEC
• 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
33WEC
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.
34WEC
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
36WEC
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
37WEC
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)
38WEC
Tool Steels
Uses• Used where extreme
hardness is required.• Ductility/toughness usually
sacrificed• E.g. Moulds and dies, saws,
cutting tools, punches
39WEC
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.
40WEC
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
41WEC
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
42WEC
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
43WEC
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
44WEC
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)
45WEC
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
46WEC
Assignment
Alloy steels•Cr steels•Ni steels•Ni-Cr steels•Mn steels•Mo- steels•V-steels
47WEC
Thanks
48WEC