GGG-NiCr20.2 is an austenitic ductile iron from the "Ni-Resist" family, alloyed with roughly 18–22% nickel and 1.75–2.75% chromium. The nickel content is what shifts the iron matrix into a fully austenitic, non-magnetic structure — the same fundamental change seen across every Ni-Resist grade — while the chromium addition is what sets this grade apart from chromium-free variants like GGG-Ni22. That chromium forms a thin, stable oxide layer at elevated temperature and adds a measure of carbide-forming hardness to the matrix, giving GGG-NiCr20.2 better resistance to oxidation and scaling in hot, corrosive service than a nickel-only austenitic iron would offer.

The trade-off for that added heat and oxidation resistance is a slightly harder, more abrasive matrix than the chromium-free grades. In practice, GGG-NiCr20.2 is a common choice for exhaust manifolds, turbocharger housings, and other components that see both thermal cycling and corrosive combustion byproducts, as well as pump and valve components in mildly oxidizing chemical service where straight nickel grades would be marginal.

GGG-NiCr20.2 machines like a tougher relative of the chromium-free Ni-Resist grades. The austenitic matrix still brings the characteristic gumminess and work-hardening tendency of that structure, but the added chromium forms fine carbides that increase abrasive wear on the cutting edge beyond what straight nickel austenitic iron produces. Expect noticeably higher cutting forces and faster edge wear than on GGG-Ni22 or GGG-Ni35 at comparable speeds.

As with other austenitic ductile irons, maintaining a steady, adequate feed rate is critical — any dwelling or rubbing lets the surface work-harden and makes the next pass considerably tougher to machine cleanly. A sharp, positive cutting edge that shears rather than pushes through the material reduces both the heat buildup and the work-hardening that chromium-bearing austenitic irons are prone to.

Because this grade combines austenitic toughness with carbide-forming abrasiveness, it calls for carbide grades with both good toughness and solid wear resistance, run at reduced speeds relative to standard ferritic ductile iron and well below what the chromium-free Ni-Resist grades can tolerate. Rigid setups and coolant help manage the heat this matrix generates at the cutting edge.