Maraging Steel 1.2709 (18Ni-300)

Maraging steel 1.2709 (X3NiCoMoTi18-9-5) corresponds to the grade known in US designations as 18Ni-300 (maraging 300). It contains about 18% nickel, 9% cobalt, 5% molybdenum and less than 1% titanium, with almost no carbon (≤ 0.03%). On cooling it forms a soft, tough martensite and gains its strength in a single low-temperature aging step that precipitates intermetallic particles. The low carbon content makes it one of the most reliable steels for laser powder bed fusion; in some material lists it appears as MS1.

Choose it for injection mold inserts, cores and slides with conformal cooling channels, and for high-strength functional parts with complex geometry. After aging at about 480–500 °C it reaches roughly 50–54 HRC with only a small, uniform contraction, so most machining can be done before hardening and only critical faces are finished afterward. It is not stainless, it is less wear-resistant than cold-work tool steels at 57–62 HRC, and printed inserts cost more than conventionally machined ones, so printing pays off where cooling or geometry justifies it. It is offered through Uretyco's manufacturing partners as a DMLS material; feasibility and lead time are confirmed in quote review.

Mechanical and physical properties

Printing maraging steel by DMLS and SLM

Maraging steel prints reliably, without the cracking tendency of carbon-rich tool steels such as H13. The usual laser powder bed fusion rules still apply: supports anchor overhangs, every cavity needs a powder exit, and accuracy depends on orientation and part size. For tooling, the design of the cooling channels matters as much as the steel:

• Conformal cooling channels: channels follow the molding surface at a roughly constant distance instead of being drilled in straight lines. Channel size, pitch and distance to the surface come from the mold designer's thermal or mold-flow simulation; leave enough steel between channel and cavity for injection pressure and later polishing.
• Self-supporting channels: round channels up to about 6–8 mm print without internal supports. Larger ones use a teardrop or diamond profile, because supports inside a channel cannot be removed.
• Powder removal and flushing: channels need open inlets and outlets with no dead ends, so that powder can be removed and the channel flushed. Ask for a flow or pressure test if channel function is critical.
• Supports and machining stock: supports are removed by wire EDM, sawing or machining. Leave stock on parting faces, shut-offs, fits and ejector pin holes, which are finished after aging.
• Hybrid builds: a complex upper section can be printed onto a pre-machined steel base, so only the part that needs conformal cooling is printed. Ask for it in the quote notes; feasibility depends on the partner.
• Walls and details: walls down to about 0.5 mm can be printed, but tooling features such as thin ribs and core pins need enough section to withstand injection pressure; check them in the mold simulation.

Aging and heat treatment

Maraging steel is hardened by aging, not by quenching: the part is held at about 480–500 °C for several hours and cooled in air. Without a quench, distortion is minimal and the size change is a small, predictable contraction. A typical sequence is printing, optional solution annealing, rough machining in the soft condition, aging, then finish machining, grinding, EDM and polishing.

Tolerances and surface

As-built surfaces are matte, around Ra 5–10 µm, and printed dimensions typically hold about ±0.1–0.2 mm on small features, with larger deviations on big inserts; final values are confirmed in the quote and order review. Molding surfaces, shut-offs, parting faces and fits are machined, ground or EDM-finished after aging, and machined features follow Uretyco's default of ISO 2768-mK unless the drawing states otherwise. State whether dimensions apply before or after aging, and give the required polish level or Ra for molding surfaces.

Finishing options

Printed tooling is almost always finished after aging. The steps below are agreed in the quote and should be marked on the drawing.

Cost and lead-time drivers

Printed inserts compete with conventionally machined inserts with drilled cooling, so the decision rests on cycle time, part quality and geometry rather than on the insert price alone. The main cost levers:

• Printed volume and build height: solid inserts are slow and expensive to print. Print only the section that needs conformal cooling, ideally as a hybrid build on a machined base.
• Supports and their removal: steel supports are removed by wire EDM or machining, which adds labor and time.
• Heat treatment: aging, plus any solution annealing or nitriding, adds furnace steps to the lead time.
• Finishing after aging: hard machining, grinding, EDM and polishing can make up a large share of the total cost.
• Inspection and documents: hardness tests, flow tests, measurement reports and material certificates are opt-in; request them at quote time. Feasibility and lead time are confirmed in the quote and order review.

Maraging steel vs. common alternatives

For simple inserts that drilled channels can cool, a machined tool steel is usually cheaper and faster. A2 is harder and better against cold-work wear, H13 is the established choice for hot work such as aluminum die casting, and 17-4 PH trades hardness for corrosion resistance. Maraging steel is the right choice when the geometry or the cooling layout can only be printed.

When not to choose maraging steel

Typical applications

• Injection mold inserts, cores and slides with conformal cooling channels.
• Core pins, lifters and other slender tooling parts with internal cooling.
• Prototype and bridge tooling for short production runs.
• Tooling inserts for other molding processes where cooling limits the cycle time.
• High-strength functional parts with complex geometry in motorsport and mechanical engineering.
• Jigs, gauges and fixtures that need hardness and complex shapes.

Specifying maraging steel on Uretyco

1. 1
   Upload the insert model and a drawing

   STEP plus a PDF drawing that marks molding surfaces, shut-offs, parting faces, ejector holes, threads and the faces to be machined after printing.

2. 2
   Choose DMLS and maraging steel 1.2709

   The material may also be listed as MS1 or 18Ni-300. Select the layer thickness setting if offered, and mention a hybrid build if only part of the insert should be printed.

3. 3
   State the heat treatment and hardness

   For example aged to 50–54 HRC with the test location, plus solution annealing or nitriding if required.

4. 4
   Define the cooling channels

   Give inlets and outlets, connection threads and any flow or pressure test, and make sure every channel can be emptied of powder.

5. 5
   Specify finishing and documents

   State machining allowances and the polish level or Ra of molding surfaces, and request hardness, measurement or material documents at quote time.

6. 6
   Review the quote

   Feasibility, build strategy, heat treatment and lead time are confirmed in the quote and order review before production starts.

FAQ

What hardness does printed maraging steel reach?

About 33–37 HRC as built and about 50–54 HRC after aging at about 480–500 °C. It does not reach the 57–62 HRC of cold-work tool steels such as A2. State the required range and the test location on the drawing.

Are 1.2709, 18Ni-300 and MS1 the same material?

They describe the same alloy family. 1.2709 (X3NiCoMoTi18-9-5) is the European material number, 18Ni-300 is the US-style grade name, and MS1 is a powder supplier's trade name that appears in some material lists. Powder compositions and heat-treatment recommendations differ slightly between suppliers, so specify the material number and the required hardness rather than a trade name.

When does conformal cooling pay off?

When cooling limits the cycle time or causes warpage: deep cores, thin and slender features, and hot spots that drilled channels cannot reach. The benefit depends on the part, the plastic and the mold design, so evaluate it with mold-flow or thermal simulation before ordering. On long production runs, shorter cycles and less scrap can repay the higher insert price.

Do maraging steel inserts rust?

Yes. 1.2709 is not a stainless steel, and conformal channels are hard to inspect once rust has started. Use treated cooling water or a corrosion inhibitor, dry and oil the channels before storage, and choose a printable stainless grade when the water quality cannot be controlled.

Related resources

• Tool Steel A2Machined cold-work tool steel at 57–62 HRC.
• Stainless Steel 17-4 PHCorrosion-resistant precipitation-hardening steel.
• AlSi10Mg (Printed Aluminum)Lightweight printed alloy for complex parts.
• Injection MoldingThe process where printed inserts are used.
• Injection Molding DFMWall thickness, draft, gates and tooling.
• 3D PrintingWhen metal printing is justified.