Normalising Assignment Help

Heat Treatment Of Steel - Normalising

Normalising

It is utilized as a finishing treatment for carbon steels providing higher strength than annealing. There is also no actual loss of ductility. In such process the soaking and heating is same as in full annealing other than part is permitted to cool in air hence cooling are much faster. The finer grains are generated since there is lesser time available for them to grow. The finer grain structure raises the yield and ultimate hardness, strengths and impact strength. However, the ductility is, slightly reduced.

The effect of minute grain size is more noticeable in impact strength after thar in tensile strength at low carbon content, like 0.2%. The tensile strength enhances only via 5% while impact strength might enhances by as much as 20% via normalizing than with annealing. At higher carbon content, like 0.4% C this is only the impact strength other than also the tensile strength that enhances marked via about 15%.

Normalizing often applied to forgings and castings is stress relieving process. This increases strength of medium carbon steel to several extents. While applied to low carbon steel it improves machine-ability.

Alloy steels whether the austenite is suitably stable can be normalized to produce hard martensitic structure. Cooling in air generates high rate of cooling that can decompose the austenitic structures in that type of steels and martensite is generated. This increases the hardness to a great extent. Table no.7 explains the hardness obtainable in several normalized steels. Table no.8 explains variation of annealing and normalizing temperature and resulting hardness for various carbon contents of plain carbon steels.

                                                  Table no.7: Hardness of Annealed and Normalized Carbon Steels

Conditions

Hardness BHN

Commercial

Iron

Structural Steel

Total Steel

Low C

Medium C

High C

Annealed

80 - 100

125

160

185

220

Normalised

90 - 100

140

190

230

270


 Table no. : Variation of Annealing and Normalizing Temperature and Resulting Hardness for various Carbon Contents

Sl. No.

C %

Annealing Temperature oC

Normalising Temperature oC

Hardness after Annealing (BHN)

Hardness after Normalising (BHN)

1

0.18 - 0.22

860 - 900

900 - 925

110 - 149

120 - 160

 

2

0.23 - 0.28

850 - 890

890 - 910

130 - 180

140 - 190

3

0.29 - 0.38

840 - 880

880 - 900

140 - 206

150 - 220

4

0.39 - 0.55

820 - 870

840 - 870

150 - 217

180 - 230

5

0.56 - 0.80

790 - 840

810 - 840

160 - 230

210 - 270

6

0.81 - 0.99

790 - 830

810 - 840

170 - 230

260 - 300


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