Effects of Alloying Elements



Effect of Carbon

Increase of Carbon increases hardness and tensile strength, reduces ductility, increases responsiveness to heat treatment (surface hardening), reduces formability in either hot or cold.

High carbon is undesirable for SS due to carbide precipitation, reduces corrosion resistance

Effect of Silicon, Sulphur and Phosphorus

Silicon

Silicon is used as deoxidizer during process of manufacture.
Silicon addition in the range of 1.5 to 2% improves hardenability. Used in some tool steel.

Sulphur

Sulphur in large quantity improves machinability.
Sulphur is detrimental to hot forming properties
Sulphur has detrimental effect on corrosion resistance and weldablity.

Phosphorus

Phosphorus addition increases yield strength and reduces ductility at low temperature. 
Believed to increase resistance to atmospheric corrosion
Phosphorus has detrimental effect on corrosion resistance and weldbility.

Effect of Manganese

Manganese is used as deoxidizer and to impart strength.
Manganese addition improves hot working properties.
Manganese like nickel is an austenite former. Has been used as substitute for Nickel in 200 series SS

Effect of Chromium, Nickel

Cr is ferrite former.
Cr increases resistance to oxidation
 Cr increase response to heat treatment.
Cr increases depth of hardness penetration.
Cr with the addition of nickel in large amount increases the resistance to oxidation and corrosion
Nickel is austenite former
Nickel increases strength and toughness both at high and low temperature

Effect of Molybdenum and Nitrogen

Molybdenum increases penetration of hardness and increases toughness.
Mo improves creep strength, resists softening at high temperature.
Mo when added to austenitic SS improves resistance to pitting and crevice corrosion especially in chloride and sulphur containing environments.
Nitrogen like Nickel is an austenite former.
Nitrogen addition improves the yield strength of SS

Effect of Copper

Copper in small amount improves resistance to atmospheric corrosion
Copper addition increases yield and ultimate strength with slight loss of ductility.
Copper addition is done to produce precipitation hardening properties
 Copper addition enhances corrosion resistance in sea water environments and sulphuric acid

Effect of Titanium, Niobium/Columbium

Titanium is added to austenitic SS as a stabilizing element to make the steel immune to harmful carbide precipitation leading to inter granular corrosion.
Niobium/columbium is added to steel in order to stabilize carbon, as such, performs in the same way as titanium.
Niobium also has the effect of strengthening steels and alloys for high temperature service.

Effect of Aluminum, Boron, Tungsten,

Aluminum is used as an active deoxidizer in producing steel. It refines the grain size.
Boron is added in small quantity to improve hardenability. Acts as an intensifier, increasing the depth of hardening during quenching
Tungsten is used as an alloying element in tool steel and tends to produce a fine, dense grain and clean cutting edge when use in small quantity. Used in large quantity to produce high speed steel which retains hardness even at high temperature developed in high speed cutting. Also used in heat resisting steel where retention of strength at high temperature is required, usually used in combination with Cr or other alloying elements.

Effect of Vanadium, Cobalt

Vanadium usually in small quantity 0.15 to 0.20% retards grain growth, even after hardening from high temperatures or after periods of extended heating. Tool steel containing vanadium resists shock better.

Cobalt becomes highly radioactive when exposed to intense radiation of nuclear reactors. SS used in nuclear service will have a Co restriction of 0.2%.nickel used in SS invariably have Co as residual element.

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