1 July 2022

Alloying Elements used in Steel | Effects of Elements in Steels

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

  1. Boron: Improves hardenability without the loss of (or even with some improvement in) machinability and formability.
  2. Calcium: Deoxidizes steels, improves toughness, and may improve formability and machinability.
  3. Carbon: improves hardenability, strength, hardness, and wear resistance; it reduces ductility, weldability, and toughness.
  4. Cerium: controls the shape of inclusions and improves toughness in high-strength low alloy steels; it deoxidizes steels.
  5. 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.
  6. Cobalt: improves strength and hardness at elevated temperatures.
  7. 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.
  8. Lead: improves machinability; it causes liquid-metal embrittlement.
  9. Magnesium: has the same effects as cerium.
  10. Manganese: improves hardenability, strength, abrasion resistance, and machinability; it deoxidizes the molten steel, reduce shot shortness, and decreases weldability.
  11. Molybdenum: improves hardenability, wear resistance, toughness, elevated-temperature strength, creep resistance, and hardness; it minimizes temper embrittlement.
  12. Nickel: improves strength, toughness, and corrosion resistance; it improves hardenability.
  13. Niobium (columbium): imparts fineness of grain size and improves strength and impact toughness; it lowers transition temperature and may decrease hardenability.
  14. Phosphorus: improves strength, hardenability, corrosion resistance, and machinability; it severely reduces ductility and toughness.
  15. Selenium: improves machinability.
  16. Silicon: improves strength, hardness, corrosion resistance, and electrical conductivity; it decreases magnetic-hysteresis loss, machinability, and cold formability.
  17. Sulfur: Improves machinability when combined with manganese; it lowers impact strength and ductility and impairs surface quality and weldability.
  18. Tantalum: has effects similar to those of niobium.
  19. Tellurium: improves machinability, formability, and toughness.
  20. Titanium: improves hardenability; it deoxidizes steels.
  21. Tungsten: has the same effects as cobalt.
  22. Vanadium: improves strength, toughness, abrasion resistance, and hardness at elevated temperatures; it inhibits grain growth during heat treatment.
  23. 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

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