C90700 is a cast copper-tin bronze often called "90-10 bronze" for its nominal composition: roughly 88-90% copper alloyed with 10-12% tin, with essentially no zinc, aluminum, or lead in the mix. That high tin content is what sets true tin bronzes apart from the more common leaded and unleaded bronze castings — tin in solid solution raises strength and hardness substantially over pure copper while also improving resistance to corrosion and wear, particularly against other metal surfaces under sliding contact. Sand-cast C90700 reaches roughly 44 ksi typical tensile strength with 20% elongation and a Brinell hardness around 80, giving it a useful balance of strength and ductility for a bearing-grade bronze.

Those properties make C90700 a longstanding choice for gears, worm gears and worm wheels, gearbox components, and bearings operating under heavy loads at relatively low speeds — conditions where the alloy's low coefficient of friction and good wear resistance really pay off. It also sees use in pressure-tight applications like valve bodies and restaurant equipment, since tin bronze castings resist porosity and hold pressure well up to moderate service temperatures.

C90700's machining behavior is defined by its tin content rather than by hardness or strength alone. Tin in solid solution produces a somewhat harder, more abrasive matrix than a plain copper-zinc brass, and the alloy also contains hard, tin-rich delta-phase constituents in the as-cast microstructure that increase flank wear compared with softer copper alloys. With no lead added for free-machining performance, C90700 relies on the natural characteristics of the cast structure rather than a chip-breaking additive to control cutting behavior.

Chip formation is generally favorable — the alloy tends to produce well-broken, manageable chips rather than the long stringy chips typical of ductile, low-tin copper alloys, since the cast, somewhat coarser-grained structure of a tin bronze fractures more readily under the tool. That's good news for chip evacuation on turning and grooving operations, but it also means the cutting edge is exposed to more abrasive wear than on the softer brasses in this reference library.

Because C90700 is a casting rather than a wrought bar product, surface porosity, sand inclusions, or a hard scale layer on unmachined surfaces can accelerate edge wear on the first pass. Starting with a light cleanup cut, using PVD-coated grades for wear resistance, and keeping speeds in the moderate range typical of bearing bronzes all help get consistent tool life out of this alloy.