GTS-65-02 is a blackheart malleable cast iron from the German DIN 1692 system, equivalent to EN-GJMB-650-2 under the current EN 1562. As with every malleable iron grade, the casting is poured as a fully carbidic "white" iron with no free graphite, then transformed into a usable engineering material by a long post-casting anneal. The blackheart process holds the casting at temperature in a neutral or protective atmosphere rather than an oxidizing one, so the carbon isn't removed from the surface — it precipitates in place as small, rounded "temper carbon" particles distributed through the full section, giving a consistent structure from the outside in regardless of wall thickness.

GTS-65-02 sits well up the strength ladder within that blackheart family. Reaching a 650 N/mm² minimum tensile strength with only a 2% minimum elongation means the anneal cycle is tuned to preserve a largely pearlitic matrix rather than graphitizing it toward ferrite — the opposite trade-off made for the softer, more ductile blackheart grades. That pearlitic structure delivers the hardness and wear resistance needed for higher-load components such as suspension links, gear housings, and heavy-duty pipe fittings, at the cost of the shock resistance and elongation that make the lower-numbered grades so forgiving. It's the malleable iron equivalent of choosing a higher-carbon steel: more strength and wear life, less give before failure.

At roughly 230 HB, GTS-65-02 is one of the harder malleable iron grades you'll encounter, and it machines noticeably differently from the ferritic and low-pearlite grades in the same family. The predominantly pearlitic matrix increases cutting forces and generates more heat at the tool-chip interface, so tool life becomes the limiting factor rather than surface finish — a reversal from the softer grades, where finish and built-up edge are the bigger concerns. Chips still break reasonably well thanks to the temper-carbon particles distributed through the matrix, but expect shorter tool life and more attention to coating selection than on GTS-45-06 or GTS-55-04.

Because the matrix is uniform through the section, machining behavior doesn't shift with depth of cut the way whiteheart grades can — what changes is simply the abrasion load on the edge as hardness climbs. A coated carbide grade with good hot hardness handles the elevated cutting temperatures from this pearlitic structure far better than an uncoated grade, and a slightly heavier edge preparation helps resist the higher mechanical loading without sacrificing too much of the shearing action this material still rewards.

Stable, rigid setups matter more here than on the softer grades — the combination of higher cutting forces and reduced ductility makes GTS-65-02 less tolerant of chatter or deflection, and a marginal edge will wear quickly rather than gracefully.