It often is used as a direct replacement for plain carbon steel and can offer dramatic cost reductions for parts that require a lot of machining. The machinability rating of ductile iron bar stock will be similar to free machining carbon steel grades, such as 12L14, 11L17, 86L20, 1141 and 1144, and achievable machining speeds will be significantly higher.

Ductile iron contains graphite in the form of very small, round nodules that give the material free machining properties without the addition of lead, bismuth, sulfur or phosphorus.

The continuous casting process eliminates typical foundry defects, such as gas holes, hard spots, slag inclusions and inconsistent properties, that result from different molding methods. Bars are cast through a water-cooled graphite die mounted on the bottom of a large bar machine crucible. The ferrostatic head pressure created by the molten metal in the bar machine crucible forces iron into the die, producing a very fine-grained microstructure. The outer “rim” is the only part of the bar that is solid when it exits the die. The core is molten iron. Heat from the molten iron core reheats the rapidly chilled outer skin, producing a homogenized microstructure that is cooled to room temperature in still air.

Ductile iron bar stock consists of a microstructure that is made up of graphite nodules in a solid metal matrix. The solid metal matrix will be similar to the matrix structure in carbon steel bars, and the amount of combined carbon determines the mechanical and physical properties of each grade.

The 60-40-18 ductile iron grade has a ferritic matrix obtained by annealing (heat treating). The mechanical properties will be less than low carbon steels, and this grade is not recommended for sliding wear applications. All grades of ductile iron bar stock respond very well to conventional heat-treating methods.

Composition: Typical chemical composition and ranges, actual values depend on cross section size.

Information provided by Dura-Bar