Alloying Elements used in Steel
Alloying Elements used in Steel
Manganese (Mn)
combines with sulfur to prevent brittleness>1%
– increases hardenability 11% to 14%
–increases hardness
–good ductility
–high strain hardening capacity
–excellent wear resistance
Ideal for impact resisting tools
Sulfur (S)
Imparts brittleness
Improves machineability
Okay if combined with Mn
Some free-machining steels contain 0.08% to 0.15% S
Examples of S alloys:–11xx – sulfurized (free-cutting)
Nickel (Ni)
Provides strength, stability and toughness, Examples of Ni alloys:
–30xx – Nickel (0.70%), chromium (0.70%)
–31xx – Nickel (1.25%), chromium (0.60%)
–32xx – Nickel (1.75%), chromium (1.00%)
–33XX – Nickel (3.50%), chromium (1.50%)
Chromium (Cr)
Usually < 2%
increase hardenability and strength
Offers corrosion resistance by forming stable oxide surface
typically used in combination with Ni and Mo
–30XX – Nickel (0.70%), chromium (0.70%)
–5xxx – chromium alloys
–6xxx – chromium-vanadium alloys
–41xxx – chromium-molybdenum alloys
Molybdenum (Mo)
Usually < 0.3%
increase hardenability and strength
Mo-carbides help increase creep resistance at elevated temps
–typical application is hot working tools
Vanadium (V)
Usually 0.03% to 0.25%
increase strength–without loss of ductility
Tungsten (W)
helps to form stable carbides
increases hot hardness –used in tool steels
Copper (Cu)
0.10% to 0.50%
increase corrosion resistance
Reduced surface quality and hot-working ability
used in low carbon sheet steel and structural steels
Silicon (Si)
About 2%
increase strength without loss of ductility
enhances magnetic properties
Boron (B)
for low carbon steels, can drastically increase hardenability
improves machinability and cold forming capacity
Aluminum (Al)
deoxidizer
0.95% to 1.30%
produce Al-nitrides during nitriding
Effects of 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 may improve formability and machinability.
- Carbon: improves hardenability, strength, hardness, and wear resistance; it reduces ductility, weldability, and toughness.
- Cerium: controls the shape of inclusions and improves toughness in high-strength low alloy steels; it deoxidizes steels.
- Chromium: improves toughness, hardenability, wear and corrosion resistance, and high-temperature strength; it increases the depth of the 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 a lesser extent, increases strength with little loss in ductility; it adversely affects the hot-working characteristics and surface quality.
- Lead: improves machinability; it causes liquid-metal embrittlement.
- Magnesium: has the same effects as cerium.
- Manganese: improves hardenability, strength, abrasion resistance, and machinability; it deoxidizes the molten steel, reduce shot shortness, and decreases weldability.
- Molybdenum: improves hardenability, wear resistance, toughness, elevated-temperature strength, creep resistance, and hardness; it minimizes temper embrittlement.
- Nickel: improves strength, toughness, and corrosion resistance; it improves hardenability.
- Niobium (columbium): imparts fineness of grain size and improves strength and impact toughness; it lowers transition temperature and may decrease hardenability.
- Phosphorus: improves strength, hardenability, corrosion resistance, and machinability; it 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; it lowers impact strength and ductility and impairs surface quality and weldability.
- 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; it inhibits grain growth during heat treatment.
- Zirconium: has the same effects as cerium
Manganese
Strength / hardness
Lowers weldability & ductility if present in high amount with high Carbon steels.
Free machining grade contains upto 1.9% (Ex. Rail steel)
Between 2 to 11 % Mn gives rise to brittleness
Between 11 to 14 % Mn – steel Called as Had-field Mn steel’- used in Jaw crusher plates-
It is basically Austenitic steel, So soft steell
During working because of crushing forces (impact abrasion
On the surface — Austenite ® Martensite
Surface hardening takes place
Surface becomes hard/wear resistant/core remains soft/tough (Best combination for impact abrasion)
Silicon
Acts as deoxidizer
Oxidation resistance
Strengthens low alloy steels.
Along with Mn, increases elastic ratio-so, used in springs
Chromium
Carbide former so Resistance to wear
Hardenability
Corrosion resistance
(Ex 1% Cr / 0.5% C ® Gears, Bolts, Cutting edge tools
2% Cr / 1% C ® Ball bearing steel (EN31 / SAE 52100)
Molybdenum
Hardenability
Makes grains finer
Toughness
Tensile strength
Creep Resistance – So high temp. (Creep resistance) parts (Boilers)
Corrosion resistance
Wear resistance – So, tool steels
Hot hardness / High strength
(Ex. Pressure vessel, Air-craft structural parts, Automobile Axles)
Nickel
Toughness / resistance to impact
Distortion in quenching ¯
Strength
Austenitic regions.
Fatigue strength
Vanadium
Makes grains finer.
Hardenability
Powerful carbide formers – so, in tool steels
Strength / toughness
Hot hardness / high temp. Strength
Fatigue strength (Ex. Leaf & coil springs, heavy duty axles, shafts, driving parts, valves)
Tungsten
Strong carbide former – so wear resistance
Hot hardness / High temp. Strength – so cutting ability so used in tools hardness
Aluminium
Acts as deoxidizer
Makes grains finer
Nitriding hardness
Boron
Hardenability – A few thousands of boron percentages causes several times
increase in hardenability and so replaces several hundred times its
weight of critical elements.
Copper
Corrosion resistance
Cobalt
Strength / hardness / fatigue strength
Hot hardness or heat resistance
Titanium
Deoxidizer
Carbide former
Makes grains finer
Sulphur
Sulphur combines with Iron to form – FeS
With Mn to form – MnS
Maximum permissible – 0.05 %
In machining grade steel – 0.075 to 0.15 %
Phosphorus
Dissolves in ferrite and increases strength and hardness.
Maximum permissible – 0.05%
Higher Phosphorus – strength
ductility
