Induction Hardening of Gray Cast Iron?

[scnh]

Looking for help on determining parameters for induction hardening and quenching of gray cast iron threaded components to a depth of 0.030-0.050" (50 HRC). So far, have experienced problems with inconsistent hardness profile surface into core (drops down below 50 HRC at approx. 0.015" and then back up over 50 HRC at 0.020". Trying set up some design of experiments, but would welcome expert advice for this endeavor as I am new to this technology.

Thank you.

 

[metengr]

scnh;
Some information to consider

Induction Hardening
Gray iron castings can be surface hardened by the induction method when the number of castings to be processed is large enough to warrant the relatively high equipment cost and the need for special induction coils. Considerable variation in the hardness of the cast irons may be expected because of a variation in the combined carbon content. A minimum combined carbon content of 0.40 to 0.50% C (as pearlite) is recommended for cast iron to be hardened by induction, with the short heating cycles that are characteristic of this process. Heating castings with lower combined carbon content to high hardening temperatures for relatively long periods of time may dissolve some free graphite, but such a procedure is likely to coarsen the grain structure at the surface and will result in undesirably large amounts of retained austenite in the surface layers. The recommended minimum induction hardening temperature for gray iron is 870 to 925 °C (1600 to 1700 °F).

Ref; ASM Handbook, Volume 4, Heat Treating
Heat Treating of Gray Irons