GTS-70-02 is the top of the standard blackheart malleable cast iron series under the German DIN 1692 system, equivalent to EN-GJMB-700-2 in current EN 1562 terms. Every malleable iron begins as a fully carbidic "white" iron casting with no free graphite, and only becomes usable through a long, controlled post-casting anneal. Blackheart processing holds the casting in a neutral or protective atmosphere rather than an oxidizing one, so no carbon is removed from the surface — it precipitates in place as small, rounded temper-carbon particles distributed evenly through the whole section, which is why blackheart malleable iron can be produced successfully in thicker sections than the whiteheart route allows.

At a 700 N/mm² minimum tensile strength with only a 2% minimum elongation, GTS-70-02 sits at the strength ceiling of the malleable iron family — the anneal cycle here is tuned to hold onto a largely pearlitic matrix rather than converting it toward softer, more ductile ferrite. That trade favors hardness and wear resistance over the shock-absorbing toughness that makes lower-numbered malleable grades so useful, which is exactly why GTS-70-02 turns up in demanding applications such as suspension ring links and other components that see sustained loading rather than impact. It's roughly comparable in service role to a higher-carbon, heat-treated steel, just delivered through cast iron's easier near-net-shape production route.

GTS-70-02 is the hardest and most demanding grade in the malleable iron family to machine, typically running in the 240-270 HB range with a heavily pearlitic matrix. Cutting forces and tool-tip temperatures run noticeably higher than on any of the softer GTS grades, and tool life — not surface finish — is the practical limiting factor in production. The temper-carbon particles distributed through the matrix still help break chips, but they can't offset the abrasive effect of a matrix that's mostly pearlite rather than ferrite.

Because the structure is uniform through the section, the challenge doesn't change with depth of cut the way it does on whiteheart grades — what changes is simply how aggressively the edge wears as hardness and pearlite content increase. A coated carbide grade with strong hot hardness and abrasion resistance is essentially mandatory here; uncoated grades that might work fine on ferritic malleable iron wear unacceptably fast on GTS-70-02.

Rigidity and vibration control matter more on this grade than on any other in the malleable iron series — the combination of high cutting forces and low ductility leaves very little margin for chatter, and a marginal edge will chip or wear out well before it would on a softer grade. Slightly heavier edge preparation than used on the lower-strength grades helps the insert survive the higher mechanical loading involved.