Effect of alloying element in Steel

                                          Effect of alloying Element in Steel

Steel is an alloy of iron and carbon, but other elements are also added to enhance the property of material. Every element added to this alloy serve  the special function and enhance the mechanical properties (when added to appropriate proportion).

Some of these alloying elements are discussed bellow:

1) Carbon- This is the principal alloying element which transform Iron into steel (when added up to                        2.1%).

        Its presence in the steel effects the property discussed bellow:

       a)     Due to carbon, the ultimate tensile strength and  yield strength of the steel increases at the                            expense  of ductility.

     b)     The toughness of material decreases as the carbon content increases, hence the metal becomes                      brittle. (High carbon steel is highly brittle due to high carbon content).

     c)     Due to susceptibility to martensitic transformation with higher carbon content, it increase the                     hardenability of the material. For this reason it is being used in heat processes such as case                     hardening, carburizing etc.

     d)    In low alloy steel (especially Cr-Mo and C-Mo) the increase in carbon increases the creep                           strength.

Carbon Ø  Symbol- C Ø  Atomic No.- 6 Ø  Atomic mass- 12.011u Ø  Atomic wt.(CIAAW)-12.0096 Ø  Ionization energy-11.260 kJ/mol (1st gr.) Ø  Electronic configuration- [He]2s2 2p2 Ø  Oxidation states- +4, +2, -4 Ø  Group- 14 , Period- 2  , Block- P

v  Carbon naturally found in Solid form.

2) Manganese (Mn) - The second most common element in steel is manganese. It can be present in                         various proportion ( up to 1.5% in carbon steel). 

      The manganese content affects the following properties:

      a)     It improves the UTS and yield strength.

      b)     It improves toughness of the material.

      c)      It also prevents hot creaking via formation of MnS (T melting = 1610°C) instead of FeS (T                     melting = 769°C).

      d)      Mn also improves hardenability but not same extent as carbon.

Manganese Ø  Symbol- Mn Ø  Atomic No.- 25 Ø  Atomic mass- 46u to 72u Ø  Atomic wt.(CIAAW)-54.938  ± 0.001 Ø  Ionization energy-717.3 kJ/mol (1st gr.) Ø  Electronic configuration- [Ar]3d5 4s2 Ø  Oxidation states- -3, -1, 0, +1, +2, +3, +5, +6,+7 (depending upon oxidation state, an acidic, basic or amphoteric oxide)

v  Manganese naturally found in Solid form.

3)  Silicon(Si) - The range of Silicon in steel is 0.15%-0.8%. It comes from the deoxidizing material                     used during steel making ( or from flux used in process like SAW, ESW etc.). Silicon effects                   the properties as described bellow:

      a)      It refines the grain structure.

      b)     It also increase the UTS and yield strength at the expense of ductility.

      c)     Excess of silicon increases the brittleness of the steel.

Silicon Ø  Symbol- Si Ø  Atomic No.- 14 Ø  Atomic mass- 28.0855u Ø  Ionization energy-786.5 kJ/mol (1st gr.) Ø  Electronic configuration- [Ne]3s5 3p2 Ø  Oxidation states--4, -3,-2, -1, 0, +1, +2, +3, +4 ( amphoteric oxide).

v  Silicon naturally found in Solid form.

4)  Tungsten (W) - Tungsten is rare material found naturally on earth as compared with other                                elements.  Its melting point is 3422°C. Atomic No. is 74 .Atomic mass 183.84 u. Tungsten                      effects the properties of steel as follows:

      a)     It increase strength, wear resistance and hardness of the steel.

      b)     Tungsten steel have superior hot-work and greater cutting efficiency at elevated temperature.

      c)     It also forms carbide named Tungsten carbide which is the hardest carbide in carbide group.

Tungsten Ø  Symbol- W Ø  Atomic No.- 74                                  Ø  Atomic wt.- 183.84 Ø  Ionization energy- 770 kJ/mol (1st gr.) Ø  Electronic configuration- [Xe] 4f14 5d4 6s2 Ø  Group- 6 Ø  Period- 6 Ø  Block- D

v  Tungsten naturally found in Solid form at standard temp. and pressure.

5)  Chromium (Cr) - Chromium content range depends upon types of steel. In low alloy steel,                             chromium is present up to 10% whereas in stainless steel (or high alloy steel), chromium can                   as high as 30%. Its effect on different types of steels are as follows:

5.1) Low alloy steel: 

     a)   It increases UTS, yield strength and hardness of the steel.

     b)  It reduces ductility and toughness of the steel.

     c)  It increases creep strength and high temperature tensile strength.

5.2)   Stainless steel (or high alloy steel):

    a)  It improves corrosion resistance property in steel.

   b)   It is strong ferrite phase stabilizer.

   c)   It increase the strength of stainless steel.

Chromium Ø  Symbol- Cr Ø  Atomic No.- 24 Ø  Atomic wt.- 51.996 Ø  Ionization energy- 652.9 kJ/mol (1st gr.) Ø  Electronic configuration- [Ar] 3d5 4s1 Ø  Group- 6, Block- D Ø  Period- 4 Ø  Density- 7.15 g/cm3

Chromium naturally found in Solid form at standard temp. and pressure.

6) Nickel (Ni) - Nickel effects the properties of stainless steel as follows:

    a)  It improves the ultimate tensile strength without any loss in ductility of the steel.

   b)   It improves the notch toughness at cryogenic temperature.

   c)   It is an austenitic stabilizer.

   d)  In low alloy, the addition of nickel increase the hardenability.

Nickel Ø  Symbol- Ni Ø  Atomic No.- 28 Ø  Atomic mass- 58.6934 u Ø  Ionization energy- 652.9 kJ/mol (1st gr.) Ø  Electronic configuration- [Ar] 3d8 4s2 Ø  Group- 10, Block- D Ø  Period- 4 Ø  Density- 8.908 g/cm3

Solid at standard Temp. & Pressure

7)  Molybdenum (Mo) - 

   a)   It increase the high temperature strength and creep property in low alloy steel and maximum                   amount of Mo in low alloy is restricted to 2.1%.

   b)  In high alloy it can be added to higher percentage to enhance the corrosion resistance property.

Molybdenum Ø  Symbol- Mo Ø  Atomic No.- 42 Ø  Atomic mass- 95.95 u Ø  Ionization energy- 684.3 kJ/mol (1st gr.) Ø  Electronic configuration- [Kr] 4d5 5s1 Ø  Group- 6,   Block- D Ø  Period- 5 Ø  Density- 10.28 g/cm3

Solid at standard Temp. & Pressure

8)  Vanadium (V) - 

   a) Vanadium content is restricted up to 0.5% and it increases the high temperature strength and creep         properties.

  b)  It may lead to carbide formation and consistently results in embrittlement.

  c)   It retards grain growth, permitting higher quenching temperature.

  d)   It also enhances the red- hardness properties of high-speed metal cutting tools.

Vanadium Ø  Symbol- V Ø  Atomic No.- 23 Ø  Atomic Wt.- 50.9415 u Ø  Ionization energy- 650.9 kJ/mol (1st gr.) Ø  Electronic configuration- [Ar] 3d3 4s2 Ø  Group- 5, Block- D Ø  Period- 4 Ø  Density- 6.11 g/cm3

Solid at standard Temp. & Pressure

9) Phosphorus (P)- This element is present in the steel as an impurities and had very adverse effects             on  properties such as:

  a)   Creaking of metal.

  b)   Brittleness at room temperature.

       Due to this reason it's amount in the steel must be restricted up to 0.03% max.

Phosphorus Ø  Symbol- P Ø  Atomic No.- 15 Ø  Atomic mass- 30.973762  u Ø  Ionization energy- 1011.8 kJ/mol (1st gr.) Ø  Electronic configuration- [Ne] 3s2 3p3 Ø  Group- 15, Block- P Ø  Period- 3 Ø  Density- 1.823 g/cm3

Solid at standard Temp. & Pressure

10) Sulphur (S) - Same like phosphorus, it is also present in the steel as an impurities. It also had                  adverse effect on the property of steel are as follows:

   a)   It leads to the hot creaking in the material due to the formation of FeS.

   b)   It decrease weldability, impact toughness and ductility of the steel.

   c)   It enhance machinability of the steel.

      Due to this reason it's amount in steel is restricted up to 0.03% max. 

Sulphur Ø  Symbol- S Ø  Atomic No.- 16 Ø  Atomic mass- 32.065 u Ø  Ionization energy- 999.6 kJ/mol (1st gr.) Ø  Electronic configuration- [Ne] 3s2 3p4 Ø  Group- 16, Block- P Ø  Period- 3 Ø  Density- 2.07 g/cm3

Solid at standard Temp. & Pressure

11) Copper (Cu) - 

      In significant amounts is detrimental to hot-working steel. Copper negatively affects forge welding,        but does not seriously affects arc or oxyacetylene welding.

   a)   It improves atmospheric corrosion resistance in the steel.

   b)   Weathering steels are sold having greater than 0.20% copper.

Copper Ø  Symbol- Cu Ø  Atomic No.- 29 Ø  Atomic mass- 63.546 u Ø  Ionization energy- 745.5 kJ/mol (1st gr.) Ø  Electronic configuration- [Ar] 3d10 4s1 Ø  Group- 11, Block- D Ø  Period- 4 Ø  Density- 8.96 g/cm3

Solid at standard Temp. & Pressure

12) Cobalt (Co) -

  a)   It increases the heat resistance of steel.

  b)   It provides strength at high temperature in the steel.

  c)   It is preferred in tool steel.

Cobalt Ø  Symbol- Co Ø  Atomic No.- 27 Ø  Atomic mass- 58.933 u Ø  Ionization energy- 760.4 kJ/mol (1st gr.) Ø  Electronic configuration- [Ar] 3d7 4s2 Ø  Group- 9, Block- D Ø  Period- 4 Ø  Density- 8.90 g/cm3

Solid at standard Temp. & Pressure

13) Aluminum (Al) -

  a)   It is used as a deoxidizer in the steel.

  b)   It has grain refinement feature, therefore it prevents the growth of austenite grains.

  c)   It increases aging resistance.

Aluminum Ø  Symbol- Al Ø  Atomic No.- 13 Ø  Atomic mass- 26.982 u Ø  Ionization energy- 577.5 kJ/mol (1st gr.) Ø  Electronic configuration- [Ne] 3s2 3p1 Ø  Group- 13, Block- P Ø  Period- 3 Ø  Density- 2.70 g/cm3

Solid at standard Temp. & Pressure

Classification of Metals (carbon and alloying elements)

 Classification of Metals

1.0  What is Metal ?

        Metal is a class of substance characterized by high electrical and thermal conductivity as well as            by malleability, ductility and high reflectivity if light.

1.1 Classification of metal

      Metals are classified as follows- 

     A) Ferrous metal- Ferrous metals are those whose primary constituent element is iron. It may be in                  Divalant (Fe2+) or Trivalant (Fe3+) form. Example- Steel, Cast iron etc.

    

      B)Non-ferrous metal- Non-Ferrous metals are those which don't have Iron its primary constituent                   element. Example- Nickel and its alloys, Aluminum and its alloys etc.

1.2 Ferrous metals and its alloys

      Depending upon the percentage of Iron, carbon and other alloying element ferrous metals are                   classified as follows:

      

       A) Steel- Steel s an Iron-Carbon alloy containing carbon up to 2.1% max.

      B) Cast-Iron- Cast Iron is also Iron carbon alloy that contain carbon more than 2.1%.

A.1)  Based on Carbon and alloying element percentage steels are classified as follows-

      

     A 1.1)  Carbon steel- Carbon steel are those in which main alloying element is carbon. It also                            contains other alloying elements like Mn (<1.6%), Si (<0.6%), Cu (<0.6%). Based on carbon                  percentage of carbon steels are classified as follows

  A1.1.1) Low carbon Steel- This types steel contains carbon petcentage up to 0.3%. If carbon                                percentage lies between 0.15% - 0.3% it is called as Mild Steel.

A1.1.2)  Medium Carbon Steel- This type Steel contains carbon percentage from 0.3% to 0.5%.

A1.1.3)  High carbon Steel- If the carbon percentage is more than 0.8% then that steel is known as                        high  carbon steel.

A.2)    Alloy Steel- Steel is called alloy steel if Mn >1.65%, Si > 0.6% and Cu >0.6%. It is further                             classified into two types.

A.2.1)  Low alloy steel- If the total alloy content is less than 8% then it is classified as low alloy steel.

A.2.2) High alloy steel- If the total alloy content is more than 8% then steel is classified as high alloy                     steel.

A 3)  Stainless Steel-  Stainless steel is high alloy steel contain major alloying elements as chromium                 and Nickel. The percentage of chromium and nickel present in the metal determine phase to be               formed and based on these stainless steels are classified as follows:

 

          a)  Austenitic steel

          b)  Ferritic steel

          c)  Martensitc steel

          d)  Duplex steel

          e)  Precipitation hardening steel

Family	Weldability	Ductility	High temperature resistance	Common Grade
Austenitic steel	High	High	High	304,310,316
Ferritic Steel	Low	Medium	High	430
Martensitic	Low	Low	Low	410,420
Duplex	High	Medium	Low	2205
Precipitation hardening	Low	Medium	Low	630

A.4)   Tool Steel- Tool steel contains various amounts of tungsten, molybdenum, cobalt, and vanadium              to increase the heat resistance and durability of the metal. Tools steel is divided into six group.

   a)     Water-hardening

   b)     Cold-work

   c)     Shock-resisting

   d)     High-speed

   e)     Hot-work

   f)     Special purpose

B)   Cast Iron- Cast iron, an alloy of iron that contains more than 2.1% C, along with varying amounts of silicon and manganese and traces of  impurities such as sulfur and phosphorus. It is made by reducing iron ore in a blast furnace.

       

           

Type	Nature of Graphite	Ductility
White cast iron	Not present	Negligible
Grey Cast iron	Flake	Negligible
Malleable C.I.	Flake to nodular	Present
Nodular C.I.	Nodular	Present
Compact graphite C.I.	Worm like	Present

                                                           Non-Ferrous Metal 

Non-ferrous metals are alloys or metals that do not contain any appreciable amount of iron. All pure metals are non-ferrous elements, except for iron(Fe). Non-ferrous metals are mainly used due to the properties as given below:

a) Easy to fabricate (including machinability, casting and welding)

b) High corrosion resistance

c) Good thermal and electrical conductivity.

There is a great verity of non-ferrous alloys available in the market, but the most commonly used non-ferrous metals are Nickel, copper and aluminum and their alloys.