Nickel alloy scrap: Inconel, Hastelloy, Monel and the chips they leave behind

Most nickel alloy scrap is superalloy: metal built to work hot. USGS Circular 1196-Z (revised 2009) says superalloys keep most of their strength even after long exposure above 650 C (1,200 F), and names three major classes, based on nickel, iron or cobalt.

USGS gives these figures for the alloys shops name on their bins:

• Inconel 718: nickel-base, about 5 percent niobium; USGS (Circular 1196-I, 2004) calls it the most important niobium-bearing superalloy.
• Waspaloy: roughly 58 percent nickel, 20 percent chromium, 14 percent cobalt and 4 percent molybdenum, for turbine engine parts.
• Hastelloy X: roughly 47 percent nickel and 22 percent chromium, for furnace rolls and trays and jet engine tailpipes.
• Monel: nickel-copper alloys with 65 to 70 percent nickel that can be hardened by cold working, used largely in marine work because they corrode slowly in flowing seawater.

Those are approximate table values. The names are trademarks of their owners, used here only as common alloy names.

Sources: USGS Circular 1196-Z (rev. 2009); USGS Circular 1196-A-M (2004).

Most superalloy scrap goes back into the alloy it came from. USGS (Circular 1196-I, 2004) found that about 70 percent of the superalloy scrap processed worldwide in 1996 was recycled into the same alloy. That needs a known alloy, so give each one its own labeled bag or drum.

Weight will not sort these for you. NASA's 1972 handbook lists alloy 718 at 8.19 g/cm3 and NIST's table uses 8.900 for cobalt, so a 718 offcut weighs only about 8 percent less than a same-size piece of cobalt. USGS says scrap sorters start with shape, recognizable objects, color and weight, then check with a magnet, the spark pattern on a grinding wheel, or chemical analysis.

The easiest label is the shop's own paperwork. If the job traveler or mill cert says 718, write 718 on the bag. If nobody knows, bag the pieces alone and mark them unknown.

Sources: USGS Circular 1196-A-M (2004); NASA materials data handbook, alloy 718 (1972); NIST X-ray mass attenuation tables, Table 1.

ISO 513:2012 gives these alloys their own machining group: S, colour brown, for heat-resistant special alloys based on iron, nickel and cobalt, plus titanium. Worn carbide inserts and end mills from that work are the main thing we buy. Keep them in their own pail; our pages on carbide inserts and end mills and drills show how to sort them, and they can ride in the same shipment or pickup.

Sources: ISO 513:2012 (sample pages).