In the case of steel (see IRON AND STEEL) the solid solution is very hard, while the pearlite complex is much softer.
This alloy, if allowed to solidify completely before chilling, turns into a uniform solid solution, and at still lower temperatures the solid solution breaks up into a pearlite complex.
The pearlite when highly magnified somewhat resembles the lead-tin eutectic of fig.
When cooled slowly below 670 degrees, martensite yields a heterogeneous mixture of pearlite and ferrite (or cementite, if the original mixture contained between 0.
Subsequent cooling gives a coarse texture, or an arrangement of ferrite, cementite and pearlite grains which is greatly coarsened, reflecting the condition of the austenite crystals from which they were born.
Any of these operations not only allows the transformations from austenite to pearlite to proceed, but also relieves internal stresses in the steel.
As soon as a little carbon enters the alloy and a soft steel is formed, small angular areas of pearlite appear at the boundaries of the ferrite crystals (Fig.
Tiny white granules of pure iron (ferrite) have small accumulations of dark-etching pearlite interspersed between them.
Pearlite is a definite conglomerate of ferrite and cementite containing about six parts of the former to one of the latter.
At that moment, in fact, the ferrite, cementite or pearlite which previously existed has lost its identity by everything going into the solid solution called austenite.
Pure iron, having no carbon, naturally would show no pearlite when examined under a microscope; only abutting granules of iron are delicately traced.
For annealing the simpler types of low-carbon steels the following temperatures have been found to produce uniform machining conditions on account of producing uniform fine-grain pearlite structure: 0.
With increasing carbon in the steel the volume of iron crystals becomes less and less, and the relative amount of pearlite increases, until arriving at 0.
Both the primary and eutectic austenite have changed in cooling into a mixture of pearlite and pro-eutectoid cementite, too fine to be distinguished here.
Here the black bat-like patches are the masses ofpearlite plus pro-eutectoid cementite resulting from the splitting up of the primary austenite.
Physical properties and assumed microscopic constitution of the pearlite series, graphiteless steel slowly cooled and white cast iron.
Turning from these cases in which the steel is used in the slowly cooled state, so that it is a mixture of pearlite with ferrite or cementite, i.
The percentage of pearliteand of free ferrite or cementite in these products is shown in fig.
By "total ferrite" is meant both that which forms part of the pearlite and that which is in excess of the pearlite, taken jointly.
The triangular structure characteristic of cast steel showing ferrite and pearlite (enlarged 50 times)] [Illustration: Courtesy of E.
We see, therefore, that when martensite is allowed to cool slowly, it yields a heterogeneous mixture either of ferrite andpearlite (when the original mixture contained up to 0.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "pearlite" in a variety of sentences. We hope that you will now be able to make sentences using this word.
