Maraging C350 sits at the top of the standard 18% nickel cobalt-bearing maraging steel family, delivering the highest strength of the common C-series grades through the same martensite-plus-aging mechanism that defines every alloy in this group. Cooling from solution-annealing temperature forms a soft, low-carbon nickel-cobalt-molybdenum-titanium martensite. Raising the cobalt and titanium content well above the C200/C250/C300 grades below it, and then aging at moderate temperature to precipitate fine intermetallic compounds through that martensite, is what pushes C350 to its exceptional strength level.

The "350" designation reflects the alloy's approximate minimum yield strength once fully aged — roughly 350,000 psi, or about 2,415 MPa — making it one of the highest-strength commercially available maraging grades. That strength comes with a narrower toughness margin than the lower-numbered grades, so C350 tends to get reserved for applications where the extra strength-to-weight ratio is worth the tighter design and process controls: high-performance rocket motor cases, specialized aerospace fasteners and fittings, and precision tooling that has to hold an edge or a profile under extreme loading.

No independently verifiable standard cross-reference numbers were available for this specific grade in the source data (the UNS/AMS numbers found were duplicates of the C300 grade's references and could not be confirmed as correct for C350). Confirm designation cross-references against mill certification for critical applications.

C350 follows the same two-condition machinability pattern as the rest of the maraging family, but with the widest gap between annealed and aged states of any standard grade. In the solution-annealed (unaged) condition — typically around 34-36 HRC — the low-carbon martensite still machines reasonably predictably with standard carbide tooling, though cutting forces run a bit higher than on the lower-strength C200/C250 grades due to the increased cobalt and titanium content. Nearly all rough and semi-finish machining is done at this stage, ahead of final aging.

Once aged, C350 reaches roughly 57-60 HRC — the hardest of the standard maraging grades, and firmly into tool-steel territory. At that hardness, conventional turning and milling become impractical for anything beyond very light finishing; grinding and EDM are the normal methods for shaping aged C350. The cutting speeds below apply strictly to the solution-annealed, pre-aging condition, which is how this material should be roughed out before its final heat treatment.