Effect of alloying elements on steel
1. Carbon : Carbon content in steel affects
- Hardness
- Machinability
- Tensile strength
- Melting point
2. Nickel :
- Increases toughness and resistance to impact
- Acts as graphitizer
- Lowers the critical temperatures of steel and widens the range of successful heat treatment
- Improves fatigue strength.
- Renders high-chromium iron alloys austenitic
3. Chromium :
- Joins with carbon to form chromium carbide, thus adds to depth hardenability with improved resistance to abrasion and wear
4. Silicon :
- Improves oxidation resistance
- Acts as a deoxidizer
- Strengthens low alloy steels
- Promotes graphitization
5. Titanium :
- Forms hard and stable carbide and raises creep strength.
- Prevents formation of austenite in high chromium steels
- Reduces martensitic hardness and hardenability in medium chromium steels.
6. Molybdenum :
- Promotes hardenability of steel
- Makes steel fine grained
- Makes steel unusually tough at various hardness levels
- Counteracts tendency towards temper brittleness
- Raises tensile and creep strength at high temperatures
- Enhances corrosion resistance in stainless steels
- Forms abrasion resisting particles.
7. Vanadium :
- Promotes fine grains in steel
- Increases hardenability (when dissolved)
- Imparts strength and toughness to heat-treated steel
- Forms carbides and nitrides
8. Tungsten :
- Increases hardness (and also red-hardness)
- Promotes fine grain
- Promotes strength at elevated temperatures.
9. Manganese :
- Contributes markedly to strength and hardness (but to a lesser degree than carbon)
- Counteracts brittleness from sulphur
- Lowers both ductility and weldability if it is present in high percentage with high carbon content in steel.
10. Copper :
- Copper causes precipitation hardening when exceeds 0.3%.
- Increases resistance to atmospheric corrosion
- Acts as a strengthening agent.
11. Boron :
- Increases hardenability or depth to which steel will harden when quenched.
12. Aluminium :
- Acts as a deoxidizer
- Produces fine austenitic grain size
- If present in an amount of about 1%, it helps in promoting nitriding.
13. Cobalt :
- Contributes to red-hardness by hardening ferrite
- Improves mechanical properties such as tensile strength, fatigue strength and hardness
- Refines the graphite and pearlite
- Retards the transformation of austenite and thus increases hardenability and freedom from cracking and distortion.
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