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Mechanical Engineering

01-BIS Symbol-Logo

BIS Indian standards for Designation of steels | Designation of steel alloys

BIS Indian Standards for Designation of Steels

Bureau of Indian Standard shortly BIS uses the following designation. Symbolic Letters and Numbers to designate the steel grade (e.g. Mechanical, Physical, and Chemical). The standard IS No. is 7598:1990.

Classification of Steel names

For the purpose of the designation, steels are classified into two types. They are:

  • Group 1
  • Group 2

Group 1 – According to their application and Mechanical or Physical properties

Group 2 – According to their Chemical composition


Principal symbols:

G – Steel casting

P – Steel for pressure purposes

D – Flat products for cold forming

R – Rails

nnn – specified minimum yield strength for the smallest thickness range

Cnn – Cold rolled

Dnn – Hot rolled for direct cold forming

Xnn – Product where rolled conditions are not specified


Additional Symbols:

B – Gas bottles

M – Thermo-mechanically rolled

N – Normalized rolled

Q – Quenched / Tempered

S – Simple pressure vessels

T – Tubes

G – Other

H – High Temperature

L – Low Temperature

R – Room Temperature

X – High and Low temperature


Designation of Plain carbon steels

These are denoted as x, C, y

Where,

x – Number 100 times the average percent of carbon

y – Number 100 times the average percent of Manganese

Example:

30C8

Where,

30 = 100 times the average % of Manganese

8 = 100 times average % of Carbon

Average % of Carbon = 30/100 = 0.3%

Average % of Manganese = 8/100 = 0.08%

Actual means, the actual carbon % is not 0.3, but varies between 0.2 – 0.4%, so that the average becomes (0.2 + 0.4)/2 = 0.3%, and

Manganese from say 0.07 – 0.09%, so that the average (0.07+0.09)/2 = 0.08%


Designation of Alloy Steels

Alloy steels are denoted by arranging the alloying elements in the descending order of their proportion, and the average % of each element is shown with its chemical symbol before that number. The letter C is omitted here, and just the number is written to denote carbon percentage. When an alloying element is less than 1% that element is denoted by an underline after writing up to two decimal places.

Example:

Alloy steel of the following composition is to be designated

Carbon = 0.13 to 0.17%; Silicon = 0.1 to 0.4%; Chromium = 0.5 – 0.8%; Manganese = 0.4 – 0.5%

Here,

Carbon varies from 0.13 to 0.17

Therefore average % of C = (0.13 + 0.17)/ 2  = 0.15

Among the other alloying elements, Chromium is the largest in composition with the average % being 0.5 to 0.8%

Therefore average % of Cr = (0.5 + 0.8) / 2 = 0.65

Therefore the above example’s designation will be 15 Cr 65

Note: since it is less than 1% it is shown by an underline

01-Material Selection – steel based alloys some apllications

Selection of Materials based on Mechanical Properties | How to do a Material Selection


Selection of Materials based on Mechanical Properties

Selection of Materials based on mechanical properties for a design has a very important component in Machine design. When put into service, different machine elements face different working conditions, which hey have to survive. This, in turn depends on the material by which they are made. Hence we say that a correct choice of material determines the working of any machine component.

Typical Mechanical Properties and applications are:

1. Strength:

Steel with Alloying elements such as

  1. Nickel steel – Turbine Blades. Nuts, Screws
  2. Nickel Chromium Steel or Stainless Steels – Aircraft component, Gear with Heavy loads
  3. Chromium Molybdenum Steels – Gear box shafts, Gears
  4. Silicon – Manganese Steel – Axles, Shafts

 2. Hardness:

  1. Alloy steel – Gears, Chain sprockets Bearings, Bushes cutting tools, Grade 400 – 500 cutting tools
  2. Stellite – Cutting tools for Surgeons
  3. Ceramics – Cutting tools, Refracting Linings

3. Ductility:

  1. Steel – Thin wires, Rods
  2. Copper – Thin wires, Rods
  3. Aluminium – Thin Wires, Rods
  4. Silver – Thin Wires, Rods

4. Malleability:

  1. Aluminium – Sheets
  2. Galvanized Iron – Sheets

5. Toughness:

  1. Titanium – Aircraft parts, Machine tools, Connecting rod valves

6. Machinability:

  1. Cast iron – Bed-ways of Machine tools, Frames, Piston Rings, Brake Drums, Flywheels, gears

ALLOYS

Often, a material cannot possess all the required qualities. Some materials are added together in certain proportions to achieve the collective goodness of them. The resulting composition is called as Alloys.

Some important alloys and their typical uses are given below:

1. Steel based Alloys:

01-Selection of Materials based on Mechanical Properties-Design of Machine elements material selection for engineering materials - Steel components and its applications

  1. Nickel steel – Turbine Blades. Nuts, Screws
  2. Nickel Chromium Steel or Stainless Steels – Aircraft component, Gear with Heavy loads
  3. Chromium Molybdenum Steels – Gear box shafts, Gears
  4. Silicon – Manganese Steel – Axles, Shafts

2. Aluminium based Alloys:

01-selection of material - Aluminium based alloy and its application

  1. Duralumin – Precision tools, Air crafts, Automobile Body Panels
  2. Alumel – Thermocouples
  3. Silumin – Humid Environment parts

3. Nickel based Alloys:

  1. German silver – Cutlery, Silverware
  2. Chromel – Thermocouples
  3. Monel – Oil drilling industries, Magnetic field measuring instruments
  4. Ni-chrome – Heating elements, Explosives, Firework Industries

4. Copper based Alloys:

01-Mechanical Material selection - Copper based alloys and its applications

  1. Brass – Utensils, Decorative items
  2. Bronze – Turbines, Blades, Springs, Coins, Bushings, Bearings