Is there a difference between Billet and Bar?

The difference is subtle but extremely important!

Billet vs Bar

Billet is a semifinished round which has been partially worked, but will be further worked to final size.  Bar is finished material that has been completely rolled to size.

This distinction is important.  Most specifications have minimum required mechanical properties, which almost always include hardness, yield strength, tensile strength, and ductility.  As applications get more demanding, such as low temperature oil and gas applications and aerospace, additional testing is required which could include toughness, hot stress rupture, hot tensile, and grain size to name a few.  Furthermore, these more stringent specifications will actually specify a minimum reduction of area requirement for forging or rolling. 

All of these materials start out as cast material, and mechanical hot working is done in order to completely break up the cast ingot structure and set up the kind of grain structure required to meet the mechanical properties in the specifications.    Bar will have enough reduction to meet all properties.  The less expensive billet may not always have enough reduction and may not meet all specification requirements.

So when you have a demanding specification for bar, it is imperative to be sure that you are receiving bar, and not semifinished billet.