Properties & Applications of Steel Types: Mild, Medium, High Carbon & High Speed, Lecture notes of Materials science

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Module - 4

Alloys & It’s Property

(Part-1)

Ferrous Alloy

Steel

• (^) Steel is an alloy of iron, carbon, and several other elements like manganese, silicon

is an important constituent because of its ability to increase the hardness and

strength of the steel.

• (^) It contains carbon upto 2 %.
• (^) Carbon is most important element and hence steels are classified according to

carbon content.

 Low carbon steel (mild steel ) less then 0.30 % C

 Medium carbon steel 0.30 to 0.70 % C

 High carbon steel 0.70 to 2.0 C

 When elements like Nickel, chromium, tungsten are present in sufficient quantity,

the steel is called “alloy steel”.

Mild steel

Properties

• (^) Bright fibrous structure.
• (^) Can be readily forged and welded
• (^) Can be permanently magnetized
• (^) Rusts rapidly
• (^) Can be harden and tempered but not easily.

Application of mild steel

• (^) Mild steel or low carbon steel are used for wire, structural shapes

screw machine parts such as screws, nuts and bolts, storage tanks,

automobile frames, sheet.

• (^) The sheet made up of mild steels are soft, very ductile, easily

machined, since the carbon content is low so heat treatment process

is ineffective.

Composition of HCS

Carbon 0.7%-2.0%

Silicon 0.2%- 0.6%

Manganese 0.2%-0.8%

Phosphorus 0.05% - 0.15%

Chromium 0.12% - 0.2%

Sulphur 0.005% – 0.05%

Uses of High carbon steel

• (^) High carbon steels are widely used in cutting tools such as knives,

drills, taps, hand tools, reamers and for abrasion-resisting properties.

• (^) Using heat treatment process properties of these steels are improved,

so these are used to make products having high strength and

hardness.

This steel is also used for making product having edges, shear blades

and also for spring wire, wire rope.

High speed steel (HSS)

• (^) HSS contains on its alloying elements in addition to carbon additional

alloying elements such as tungsten, molybdenum, chromium and

vanadium.

• (^) The alloying elements form carbides with the carbon present in steel.
• (^) Proper heat treatment gives high hardness and strength which is

necessary for the tool.

• (^) Tungsten and molybdenum form hard complex carbides with carbon

and iron in steel which gives secondary hardening.