This document discusses different categories and types of alloy and special steels. It describes the general categories as carbon and alloy steels, stainless steel, tool and die steels, and cast steels. It then explains the effects of various alloying elements when added to steels and provides examples of how they impact properties. Various steel types are defined, such as high-strength low-alloy steels, bearing steels, and tool steels. Specific applications of different steels are also mentioned.

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MODULE – 5
ALLOY & SPECIAL STEELS
Rahul Kumar
KIIT UNIVERSITY

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General Categories of Alloy Steels
Carbon and Alloy Steels
Stainless Steel
Tool and Die Steels
Cast Steels (Crucible Steels)

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Effects of Alloying Elements in Steels
•Boron: improves hardenability without the loss of (or even with some
improvement in) machinability and formability
•Calcium: deoxidizes steels, improves toughness and improve formability
and machinability
•Carbon: improves hardenability, strength, hardness and wear resistance,
as well as reduces ductility, weldability and toughness
•Cerium: controls shape of inclusions and improves toughness in high-strength
low alloy steels, as well as deoxidizes steels

4. • Chromium: improves toughness, hardenability, wear and corrosion
resistance and high-temperature strength. It also increases depth of
hardness penetration resulting from heat treatment by promoting
carburization
• Cobalt: improves strength and hardness at elevated temperatures
• Copper: improves resistance to atmospheric corrosion and to lesser
extent increases strength with little loss in ductility, as well as also
adversely affects hot-working characteristics and surface quality
• Lead: improves machinability, as well as causes liquid-metal
embrittlement
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5. • Magnesium: has the same effects as cerium
• Manganese: improves hardenability, strength, abrasion resistance and
machinability, as well as deoxidizes molten steel, reduce shot shortness,
and decreases weldability
• Molybdenum: improves hardenability, wear resistance, toughness,
elevated-temperature strength, creep resistance and hardness, as well
as minimizes temper embrittlement
• Nickel: improves strength, toughness and corrosion resistance, as well
as improves hardenability
• Niobium (columbium): imparts fineness of grain size and improves
strength and impact toughness, as well as lowers transition temperature
and decrease hardenability
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• Phosphorus: improves strength, hardenability, corrosion resistance
and machinability, as well as severely reduces ductility and toughness
• Selenium: improves machinability
• Silicon: improves strength, hardness, corrosion resistance, and
electrical conductivity; it decreases magnetic-hysteresis loss,
machinability and cold formability
• Sulfur: improves machinability when combined with manganese, as
well as lowers impact strength and ductility and impairs surface
quality and weldability

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• Tantalum: has effects similar to those of niobium
• Tellurium: improves machinability, formability and toughness
• Titanium: improves hardenability; it deoxidizes steels
• Tungsten: has the same effects as cobalt
• Vanadium: improves strength, toughness, abrasion resistance and
hardness at elevated temperatures, as well as inhibits grain growth
during heat treatment
• Zirconium: has same effects as cerium

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1. Carbon and Alloy Steels
•carbon and alloying steels are the most commonly used metals
•structural makeup and controlled processing of these steels make them
suitable for many different functions
•basic product shapes include plate, sheet, bar, wire, tube, castings, and
forgings
•increasing % of alloying elements in steels, increases properties they
impart (different elements are added to give different properties
•elements pass on properties such as hardenability, strength, hardness,
toughness, wear resistance, etc
•some properties are beneficial while others are detrimental

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Carbon Steels
•also known as plain carbon steels
•group by % of carbon content (weight basis)
•higher the carbon content greater the hardness, strength and wear
resistance after heat treatment
•soft, tough, easily machined, welded & case hardened
•designation: e.g. 1040 steel - 0.40 wt % C
•types:
Low-carbon steel (mild steels)
Medium-carbon steel
High-carbon steel

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Low-carbon steel (mild steels)
•has less than 0.30 % carbon
•used in everyday industrial products like bolts, nuts, sheet, plate and
tubes
Medium-carbon steel
•has 0.30% to 0.60 % carbon
•used for jobs requiring higher strength such as machinery, automotive
equipment parts, and metalworking equipment
High-carbon steel
•has more than 0.60 % carbon
•used parts that require the highest strength, hardness and wear
resistance
•once manufactured they are heat treated and tempered

11. High carbon steel nails
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Low carbon steel wires
Medium carbon steel nuts

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Alloy Steels
•contain significant amounts of alloying elements
•expensive
Types of Alloy Steels
• High strength low alloy steels (HSLA)
• Microalloyed steels
• Nanoalloyed steels
• Bearing steels
• Cold forming steels
• Chained steels

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High-Strength, Low-Alloy Steels (HSLA Steels)
•developed to improve the ratio of strength to weight
•commonly used in automobile bodies and in transportation industry
(reduced weight makes for better fuel economy)
Microalloyed Steels
•provide superior properties without the use of heat treating
•when cooled carefully these steels develop enhanced and consistent
strength
Nanoalloyed Steels
•have extremely small grain size (10-100 nm)
•Since their synthesis is done at atomic level their properties can be
controlled specifically

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High strength low alloy
steel sheets
Microalloyed steel
connecting rods
Nanoalloyed steel
bicycle hub

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Bearing steel pipes
Cold forming steel
front
Chained steel chain

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2. Stainless Steels
•primarily know for their corrosion resistance, high strength, and
ductility and chromium content
•reason for name stainless is due to the fact that in presence of oxygen,
steel develops a thin, hard, adherent film of chromium
•Even if surface is scratched, protective film is rebuilt through
passivation
•for passivation to occur, there needs to be minimum chromium content
of 10 to 12 % by weight

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• tend to have lower carbon content since increased carbon content
lowers the corrosion resistance of stainless steels
• since carbon reacts with chromium, it decreases the available
chromium content which is needed for developing protective film
• using stainless steel as reinforcing bars, has become a new trend in
concrete structures such as highways buildings and bridges
• more beneficial than carbon steels because it is resistant to
corrosion from road salts and the concrete itself

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Applications Products of Stainless Steels

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3. Tool and Die Steels
•generally alloyed steels
•medium to high carbon
•up to 25% total alloying elements
•design for high strength, impact toughness and wear resistance at
normal and elevated temperatures
•used at temperatures up to 600°C
•specialty steels – very expensive
•quench and tempered
•very clean steels
•applications like dies, drills, cutting blades, hot working dies, etc

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Desirable Properties of Tool Steels
•Hardness - Resistance to Deforming & Flattening
•Toughness - Resistance to Breakage & Chipping
•Wear - Resistance to Abrasion & Erosion
•Corrosion - Resistance to Rusting and Pitting

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Alloying Elements in Tool Steels & their Effects
Carbon (C) +Strength, +Hardenability, -Toughness
Chromium (Cr) +Strength, +Hardenability, +Corrosion Resistance - Toughness
Molybdenum (Mo) +Strength, +Hardenability, +Toughness, +Hot Hardness
Vanadium (V) +Hardenability, +Toughness, +Hot Hardness, +Wear
Tungsten (W) +Strength, +Hardenability, +Hot Hardness, -Toughness
Cobalt (Co) +Hot Hardness, +Wear, -Toughness
Manganese (Mn) +Strength, +Hardenability, +Toughness
Nickel (Ni) +Hardenability, +Toughness, +Corrosion Resistance
+ increases
- decreases

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Classification of Tool Steels
Tool Steel Class of Alloys Examples (industrial names)
Cold Work W (water hardening)
O (oil hardening)
A (air hardening)
D (high C & Cr)
W1, W2, W5
O1, O2, O6, O7
A2, A4, A6, A7, A8, A9, A10, A11
D2, D3, D4, D5, D7
Shock
Resisting
S S1, S2, S4, S5, S6, S7
Hot Work H Chromium types: H10-H19
Tungsten types: H20-H39
Molybdenum types: H40-H59
High Speed MT
Molybdenum types: M1, M2, M3-1, M3-2,
M4, M6, M7, M10, M33, M34, M36, M41
Tungsten types: T1, T4, T5, T6, T8, T15
Mold P P6, P20, P21

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Classification of Tool Steels

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Cold Work Tool Steels
•used at low temperature-sharpness
•include all W, O, A & D class of alloys
•typical applications include cold working operations such as stamping
dies, draw dies, burnishing tools, coining tools and shear blades

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Shock Resisting Tool Steels
•used at low temperature-toughness & impact toughness
•include all S class alloys
•toughest tool steels
•typically applications include screw driver blades, shear blades, chisels,
knockout pins, punches, and riveting tools

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Hot Work Tool Steels
•used at high temperature-toughness, high resistance to wear & cracking
•include all H class alloys
•typical applications include dies for forging, die casting, heading,
piercing, trimming, extrusion and hot-shear and punching blades

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High Speed Tool Steels
•used at high temperature-sharpness
•Include M1 to M52, T1 to T15 class of alloys
•can be hardened to 62-67 RC and can maintain it in service temperatures
as high as 540°C, making them very useful in high-speed machinery
•typical applications include end mills, drills, lathe tools, planar tools,
punches, reamers, routers, taps, saws, broaches, chasers and hobs

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4. Cast Steels (Crucible Steels)
• term originally applied to crucible steel (sometimes used to describe
tool steels, which is misleading)
• fine variety of steel, originally made by smelting blister or cementation
steel & pouring molten steel into moulds
• manufacture is essentially a refining process, which is dependent on
pre-existing furnace products
• cannot not subjected to further forging or rolling