Chapter 16

2. Chapter 16 Cast Irons Cast Irons

3. A section through the iron-carbon-silicon phase diagram at 2.5% Si illustrates the microstructure obtained on cooling a typical gray iron.

4. Gray iron is designated by its grade number, which indicates its minimum tensile strength in ksi.

5. Gray iron is the most widely used cast iron. White iron derives its name from its fracture appearance, which is white and crystalline.

6. A fracture through a flanged gray iron specimen with a chilled (white) iron area shows the boundary region between the two kinds of microstructure as mottled iron.

7. The microstructure of ferritic malleable iron consists of temper carbon nodules in a ferrite matrix.

8. Malleable iron has greater ductility than gray iron.

9. Ductile iron exhibits considerable elongation compared with equivalent strength grades of gray iron.

10. The microstructure of ductile iron consists of spheroidal graphite in a matrix of ferrite, pearlite, or martensite.

11. The morphology of the graphite in compacted graphite iron is more blunted than the graphite in gray iron.

12. Alloy elements in alloy irons are either graphitizers or carbide stabilizers.

13. Difficulties in welding cast irons are caused chiefly by their high carbon content and low ductility.

14. Matching and nonmatching welding filler metals may be used to weld cast irons.

15. The preheat temperature selected for welding cast irons depends on the restraint in the joint, the welding process, the type of welding filler metal, the cast iron microstructure, and whether or not post-weld heat treatment is to be performed.