Effect of elements in Alloy steels

Manganese is used in steel to produce a clean metal. If manganese exceeds 1.65 -2.10%, the product is classed as alloy steel.

• It increase hardenability and strength.
• It also adds to the strength of the metal and helps in heat treating.
• Counteracts brittleness from sulphur
• Lower both ductility and weldability if present in high percentage with high carbon content in steel.

Some times an excess of manganese is used for hard steel as manganese is a carbide forming element.

Silicon is often used to increase the resiliency of steel for making springs. It increases the strength properties especially elastic limit without loss of ductility. Silicon is an important alloying element (0.2 - 0.7%) in certain high-yield point structural steels. If silicon exceeds 0.60-2.2%, product is classed as alloy steel. Increasing silicon increases resiliency of steel for spring applications. Spring raises the critical temperature for heat treatment. Increasing silicon content promotes susceptibility of steel to decrease. It is used for magnetic circuits in electrical equipments. It is used in spring steels which contain 2% silicon, 0.2% manganese and 0.6 % carbon. It is the principal deoxidizing used in steel making.

• Improves oxidation resistance
• Strengthens low alloy steels
• Acts as a deoxidizer

Rimmed and capped steels contains no significant amount of silicon. Semi killed steel may contain a moderate amount of silicon. Fully killed steels may contain various amounts of silicon upto 0.30% maximum. It is less effective than manganese in increasing strength and hardness. In low-carbon steels, it is usually detrimental to surface quality.

Molybdenum

• Adds toughness and higher strengths to steel.
• Promotes hardenability of steel
• Makes steel fine grained
• Makes steel usually 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.
• It increases dynamic and high temperature characteristics.
• It is resistant to tempering and maintain their strength at elevated temperature.
• They have good creep resistance.

It is used for making high speed steels. It forms stable carbides resulting in fine grain size.

Nickel

• Increases strength and toughness.
• Helps to resist corrosion.
• Improves shock resistance
• It counteracts brittleness which develops in most pearlitic steels at subnormal temperature.
• It lowers the critical temperature of steel and widen the temperature range for successful heat treatment.
• Strengthens steels
• Renders high chromium iron alloys austenitic
• Lessens distortion in quenching.

Mostly 2-5% of nickel combined with other alloying elements produce toughness.