Steel Worked In Austenitic State

: The Working Of Steel

As a general rule steel should

be worked when it is in the austenitic state. (See page 108.) It

is then soft and ductile.

As the steel is heated above the critical temperature the size of

the austenite crystals tends to grow rapidly. When forging starts,

however, these grains are broken up. The growth is continually

destroyed by the hammering, which should consequently be continued

down to th
upper critical temperature when the austenite crystals

break up into ferrite and cementite. The size of the final grains

will be much smaller and hence a more uniform structure will result

if the mother austenite was also fine grained. A final steel

will be composed of pearlite; ferrite and pearlite; or cementite

and pearlite, according to the carbon content.

The ultimate object is to secure a fine, uniform grain throughout

the piece and this can be secured by uniform heating and by thoroughly

rolling it or working it at a temperature just down to its critical

point. If this is correctly done the fracture will be fine and

silky. Steel which has been overheated slightly and the forging

stopped at too high a temperature will show a granular fracture.

A badly overheated or burned steel will have iridescent colors

on a fresh fracture, it will be brittle both hot and cold, and

absolutely ruined.