TABLE OF CONTENTS A very high proportion of the steels used in industry has a ferrite-pearlite structure. These include a wide range of plain carbon steels where alloying additions are primarily made for steel-making purposes, although they do have a strengthening role as well. For example, manganese is added to combine with sulphur, but it is also a strengthener, while manganese and silicon are deoxidizers and aluminium is used as a deoxidizer and as a grain refiner, and therefore a strengthener. Many low and medium alloy steels, e.g. those with nickel, give ferrite-pearlite structures, but here only essentially plain carbon steels will be dealt with.
Most plain carbon steels are not subject to heat treatment in the sense of quenching followed by tempering, but they are cooled at different rates to obtain a range of structures. Two important treatments are normalizing and annealing which have special, but not very precise, meanings when applied to steels.
Normalizing In the process of normalizing the steel is reheated about 100 C above the A c 3 temperature to form austenite, followed by air cooling through the phase transformation. This has as its object the refinement of the austenite and ferrite grain sizes, and the achievement of a relatively fine pearlite. It is often used after hot rolling, where a high finishing temperature can lead to a coarse microstructure.
The rate of cooling during normalizing is dependent on the dimensions of the steel, but some control can be exerted by using...
