GG20 is the mid-strength grade in the DIN 1691 gray iron series, guaranteeing a minimum tensile strength of 200 N/mm². It sits at a practical crossover point: still cast with enough carbon and silicon to keep a well-developed flake graphite structure and good machinability, but with a finer graphite network and a somewhat higher pearlite fraction in the matrix than GG10 or GG15, which is what pushes the strength and wear resistance up a notch.

That balance makes GG20 one of the most commonly specified general engineering gray irons. It shows up in engine blocks, gearbox housings, machine tool bases, brake components, and pipe fittings — applications where moderate strength, good wear resistance against sliding contact, and gray iron's characteristic vibration damping all matter more than ductility or shock resistance. As with the rest of the GG family, GG20 has essentially no useful elongation and is unsuitable for parts subject to impact loading or significant tensile stress.

GG20's cutting behavior still follows the same rules as the softer grades in the family: free graphite flakes break up the matrix and cause the chip to fracture into short, manageable fragments rather than curling into a continuous ribbon. But GG20's finer graphite network and increased pearlite content raise the matrix strength noticeably compared with GG10 or GG15, which translates into higher cutting forces, more heat generation at the tool-chip interface, and faster progressive flank wear over a production run.

Pearlite itself is harder and more abrasive than the ferrite that dominates the softer grades, so as pearlite content climbs through the GG series, abrasive wear becomes a bigger factor relative to the mechanical damage from graphite alone. Combined with the usual hard, sand-embedded skin on as-cast surfaces, this makes edge wear resistance the primary selection criterion for tooling on GG20 — more so than on GG10 or GG15, where raw machinability alone was often enough.

Chip control remains a non-issue thanks to the discontinuous fracture mode common to all gray irons, so the practical focus for GG20 is choosing a carbide grade with enough hot hardness and abrasion resistance to hold up against the harder pearlitic matrix without sacrificing edge sharpness on lighter finishing passes.