Types of Steel

Table of Contents

• Steel making
• Elements in Steel
• Types of Steel
• Types of High Alloy Steels

One of our most important manufactured products used in all industries has many applications & uses. Steel can be molded, pressed, machined, welded & woven to suit different purposes.

Steel making:  It’s a three-step process.

1. Iron Making: Iron ore, coke & a flux (limestone) are combined in a blast furnace to produce molten iron containing about 4% carbon.
2. Steel Making: Excess carbon is removed in a basic oxygen steel making vessel and the required alloy is added. The molten steel is then cast into billets, blooms, or slabs.
3. Shaping: Steel is rolled to various sizes and shapes in a rolling mill.

Steels are basically a wide range of iron-based alloys with carbon up to 1 .7 %.

• In plain carbon steels other elements are silicon (up to 0.6%), manganese(up to 1.65%), sulphur (up to 0.35%) & phosphorous (up to 0.13%).

      1. Elements in Steel: 

• Carbon 

• • Up to 1.7 %
  • Promotes formation of carbides (cementite, pearlite & martensite)
• Manganese
  • Deoxidizes the metal and facilitates hot working
  • Neutralizes sulfur by forming manganese sulfide which increases strength
  • Provides work-hardening property
• Silicon
  • Deoxidizes steel
  • Increases resistance to scaling
• Phosphorous
  • An impurity
  • Decreases ductility and toughness
• Sulfur
  • An impurity
  • Decreases strength and impact resistance
  • Improves machinability

     2. Types of Steel :

• Low Carbon Steels
  • Carbon up to 0.3 %
  • Good ductility & weldability
  • Comparatively low strength & not easily heat treatable

Welding: Have very good weldability.

No special precautions required

• Medium Carbon steels
  • Carbon 0.3 to 0.6 %
  • Better strength & hardness than low carbon steel

Welding: Slight preheat around 200-250 deg. C and slow cooling.

 Use a low hydrogen type electrode

• High Carbon Steels
  • Carbon : 0.6 % to 1.71 %
  • Easily heat treatable to high hardness

Welding: Poor weldability.

                                      Tendency to crack

                                       High preheat around 300 deg. C and very slow cooling

                                       Maintain high interpass temperature-300 deg. C

                       Post weld heat treatment and stresses relieving desirable

• Alloy Steels

Contain alloying elements other than silicon, manganese, sulfur & phosphorous

• High Alloy Steels

Alloying elements more than 10 % ( Ni, Mn, Cr)

Welding: High carbon equivalent hence form martensite.

                 Preheat around 300 deg. C and maintain interpass

                 Cool slowly

• Low Alloy Steels

Alloying elements less than 10 %

           Welding:  Preheat requirements minimum.

Types of High Alloy Steels :

• Austenitic Manganese steels: 

More than 10 % manganese & high carbon

• • Known as Hadfield Steels
  • Work harden in service

Welding: Forms hard Carbides at temperatures above 175 deg. C.

                 No, preheat and fast cooling

• Stainless Steels :

• • Chromium minimum 11.5 %
  • Excellent corrosion resistance
  • The addition of nickel gives good toughness & strength at sub-zero and elevated temperatures

Welding: Loose corrosion resistance on exposure over 500 deg. C

                                      No, preheat and fast cooling

                                      Low current & stringer beads

• Tool Steels:

• • Used as Cutting Tools, Shear Blades, Dies, etc. 
  • Contain high carbon
  • Have a high amount of tungsten, molybdenum, chromium, cobalt, etc., and withstand temperatures up to 550 deg.

Welding: Difficult to weld.

                  High preheat around 350 deg. C & cool slowly

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