effect of elements in alloy steels

7/28/2019 Effect of Elements in Alloy Steels

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Effect of elements in Alloy steels

Vanadium:

It gives steel a fine-grained structure and increase its toughness. It is often used in tool steels because of its increased resistance to impact.

Increases hardenability

Imparts strength and toughness to heat-treated steel

Causes marked secondary hardening

It is used with chromium to make chrome-vanadium steel from which transmission parts and gears are manufactured. This type

of steel is very strong and has excellent shock resistance. Less than 0.2% is used normally with 0.5 to 1.5% of chromium.

Chromium

It provides corrosion resistance.

Increase hardenability or the depth to which steel can be hardened Adds hardness, toughness and resistance to wear.

Gears and axles are often made of chrome-nickel steel because of its strength. Chromium less than 0.2% can be effective in

increasing hardenability.

Niobium

Greatly increases tensile strength of steel. Only 40 lb of niobium per ton of steel will increase the tensile strength by10,000 to 15000 lb/in

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Tungsten in the form of tungsten carbide

Gives steel high hardness even at red heats.

Promotes fine grains

Resists heat Promote strength at elevated temperatures

It is used with chromium, vanadium, molybdenum, or manganese to produce high speed steel used in cutting tools. Tungsten

steel is said to be "red-hard" or hard enough to cut after it becomes red-hot.

Titanium is a very strong, very lightweight metal that can be used alone or alloyed with steels. It is added to steel to give them

high strength at high temperatures. Modern jet engines used titanium steels.

It prevents localized depletion of chromium in stainless steels during long heating

Prevents formation of austenite in high chromium steels

Reduces martensitic hardness and hardenability in medium chromium steels.

Phosphorus and Lead are added to steel to increase its machinability.

Phosphorus is considered detrimental in steel but small quantities up to 0.2% in low carbon steels increases hardness,

strength and corrosion resistance. Phosphorus increases strength and hardness to approximately to the same extent as carbon

in steels which are normally used in hot-rolled conditions. In some steels, high phosphorus content is undesirable because it

decreases ductility and impact toughness. It is undesirable in high carbon steels on account of excessive loss of ductility. It

improves machinability in lower carbon steels and improves resistance to atmospheric corrosion.

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.


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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. I t 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 inincreasing 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.

Sulphuris not desirable in steel since it forms iron sulphide which cause brittleness and hot-shortness - a tendency to crack

during hot working. Sulphur in steel forms the weak and soft sulphate "Fe"s which weakens the steel and promotes hot-

shortness or brittleness at red heat. But sometimes a very small amount of sulphur is left in the steel to aid machinability.

Manganese either present naturally or in small quantities added to the steel combines with small amount of sulphur that is

usually present to form manganese sulphide which does not have much effect if not in large quantities and is well dispersed. If

manganese sulphide is present in large quantities and in the proper form, it imparts desirable mechanical properties to steel.

Therefore, certain free-machining steels which are to be machined automatically and are used for parts that will not be


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subjected to impact have 0.08 to 0.15% sulphur added. It is beneficial to machinability and the higher sulphur content of some

steels reflect this useful property. It is detrimental to surface quality in low-carbon and low manganese steel. It decreases

ductility and impact resistance. Weldability also decreases with increasing sulphur content.

Copper

It is used in percentage of 0.1 - 0.4 to produce resistance to atmospheric corrosion.

Acts as a strengthening agent.

Although copper is corrosion-resistant, it is not used in steel for this purpose. Copper is nowadays, used extensively in low-

carbon sheets especially thin gauges and other structural steels. It has minor effect on mechanical properties. It is beneficial to

corrosion resistance if amount present exceeds 0.20%. When present in appreciable amounts, it is detrimental to hot working

operations. It effects forge welding and is detrimental to surface quality. It does not effect arc or acetylene welding.

Cobalt

Improves mechanical properties such as tensile strengths, fatigue strength and hardness.

Refines the graphite and pearlite It is a mild stabilizer of carbides Improves heat resistance Retards the transformation of austenite and thus increases hardenability and freedom from cracking and distortion. Contributes to red-hardness by hardening ferrite

Boron

It is a very powerful hardenability agent and increases hardenability or depth to which steel will harden whenquenched.

It is being 250-750 times as effective as nickel, 75- 125 times more effective than molybdenum and about 100 times as

powerful as chromium. It is expensive but used in minute quantities.

Aluminum:

It is used to deoxidize steel Produces fine grain size. It is used to obtain non-aging characteristics alone or in the presence of other elements

Prevents recurrence of strains in sheets and strip.

REFERENCE:

http://www.steeltalk.com (18/12/2012)
http://www.steeltalk.com/http://www.steeltalk.com/http://www.steeltalk.com/

effect of elements in alloy steels

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