Steel

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Constituents

The term ‘steel’ usually refers to plain carbon steel, defined as alloys of iron and carbon that do not contain more than 2% carbon and are malleable in block and or ingot form.

Steel will have chemical composition containing:

Carbon: 0.16-0.25%
Manganese: 1.5-16%
Silicon: 0.1-0.5%

Structural Steel Chemical Composition (BS 4360:1990)

Grade	C %	Si %	Mn max %	P max %	S max %	Nb max %	V max %	Normal supply condition
40	0.16	0.10/0.50	1.50	0.04	0.03	–	–	Normalised
43	0.16	0.10/0.50	1.50	0.04	0.03	–	–	Normalised
50	0.18	0.10/0.50	1.50	0.04	0.03	0.10	0.10	Normalised
55	0.22	0.10/0.50	1.60	0.04	0.03	0.10	0.20	Normalised

Mechanical Properties Of Steel

Grade	Tensile strength N/mm²	Minimum Yield strength for thickness shown N/mm²		Minimum elongation, %	Minimum charpy V-notch, impact
Grade	Tensile strength N/mm²	<10mm	>100mm	Minimum elongation, %	Temp/ ⁰C	Energy/ J
40	340/500	260	205	25	-50	27
43	430/580	275	225	22	-50	27
50	490/640	355	305	20	-50	27
55	550/700	450	400	19	-50	27

Sources from Construction Materials, Their Nature and Behaviour

Classification

Both cast and wrought carbon steel have been generally classified into approximate grades based on the carbon content:

Ingot Iron	Lowest possible content of carbon and other alloying elements, made in basic open-heart furnaces, corrosion resistant, used largely for sheet.
Extra soft or Dead soft steel	0.08-0.18% carbon, this type of steel is characterized by ductility, toughness, weldability, and is used where cold-workability is desirable; generally it is used where strength or stiffness is not important.
Mild, structural steel	0.15-0.29% carbon; characterized by strength combined with easy machinability, used for buildings, bridges, bolts, boilers, railroad rolling stock.
Medium grade	0.25-0.35% carbon; harder and stronger than mild structural grade yet can be hot-forged; used for shipbuilding and machinery.
Medium hard grade	0.35-0.65% carbon
Spring grades	0.85-1.05% carbon
High carbon tool steel	1.05-1.20% carbon

Finishes

Hot dipping, electro galvanizing, spraying and sherardizing are all processes whereby a protective coat of zinc is applied to steel and iron to seal them against corrosion.