GG30 is a high-strength grade in the DIN 1691 gray iron series, guaranteeing a minimum tensile strength of 300 N/mm². Reaching that strength requires a finer, more restrained graphite flake structure and a matrix that's almost fully pearlitic, a significant shift from the ferrite-dominant low grades. The finer graphite also improves fatigue strength and wear resistance, which is why GG30 is specified where gray iron needs to work harder than a general-purpose casting.

Typical applications include heavy machine tool beds and columns, diesel engine blocks and cylinder liners, brake drums and rotors under higher thermal load, and hydraulic components where both pressure tightness and wear resistance at sliding interfaces matter. GG30's finer structure also gives it noticeably better surface finish potential than the coarser low grades, which is valuable on precision-ground surfaces like machine tool ways. As with every grade in the series, it remains brittle with essentially no ductility, so it's chosen for compressive and wear-resistant duty rather than tension or impact service.

GG30's fine graphite structure and near-fully pearlitic matrix make it one of the harder-cutting grades in the DIN 1691 series. The chip-breaking mechanism is unchanged — graphite flakes still fracture the chip into short segments — but there's noticeably less free graphite to interrupt the matrix, and the pearlite itself carries hard iron carbide lamellae that resist deformation far more than ferrite does. The net effect is higher cutting forces, more heat generated at the edge, and faster abrasive wear than the softer grades.

At this hardness level, GG30 starts to behave more like a moderately hard steel in terms of tool loading, even though its chip formation still stays discontinuous and free-cutting compared with an actual steel of similar hardness. Abrasive wear from the carbide lamellae and residual silicate inclusions is the dominant failure mode on inserts run at this grade, and it accelerates quickly if edge geometry is too aggressive or if speeds push cutting temperatures too high.

Coated carbide with strong hot hardness is essentially required for consistent tool life on GG30 in production settings. Chip evacuation itself is still a non-issue, but achieving good surface finish on the finer-grained casting requires more attention to edge sharpness and wear state than the coarser low grades demand.