UNS K93540 Forgings, Maraging 350 (C350) Rings, Discs, Shafts and Bars

Open-die forged and seamless rolled UNS K93540 to AMS 6515 and MIL-S-46850, made to drawing by Jiangyin Jiangnan Metal Co., Ltd. in Jiangyin, Jiangsu, China.

• UNS K93540
• Maraging 350
• C350
• 18Ni(350)
• W.Nr. 1.6355
• AMS 6515
• MIL-S-46850
• EN 10204 3.1 / 3.2

Published 18 May 2016. Last updated 28 August 2026. Compiled and reviewed by the metallurgical engineering team at Jiangyin Jiangnan Metal Co., Ltd.

UNS K93540 summary data

What is UNS K93540 (Maraging 350)?

Maraging steel takes its name from martensite and ageing. The alloy holds almost no carbon, under 0.03% in UNS K93540, so cooling from the annealing temperature produces a soft iron and nickel martensite instead of a hard, brittle one. Hardness comes later, from an ageing treatment near 480 C that precipitates fine intermetallic particles, mainly Ni₃(Ti,Mo) and Fe₂Mo, through the martensite.

Cobalt and titanium set the strength level inside the 18% nickel family. UNS K93540 carries the highest additions of both, around 12% cobalt and 1.4% titanium, which is why it ages to roughly 350 ksi where Maraging 300 reaches 300 ksi and Maraging 250 reaches 250 ksi. Cobalt does not form the precipitate itself. It lowers the solubility of molybdenum in the matrix so more molybdenum-bearing precipitate can form during ageing.

For a forging, that behaviour has three practical results.

• Solution annealed material sits at 30-35 HRC, so rough and finish machining are both done before hardening.
• Ageing contracts the part by roughly 0.05% and the change is uniform in all directions. There is no quench and no scale, which is why large die blocks are machined complete and then aged.
• Carbon below 0.03% removes the hydrogen cracking mechanism, so the grade welds in the annealed condition and the weld can be re-aged with the parent metal.

Toughness is the limitation. At 350 ksi both fracture toughness and elongation fall below Maraging 300 and Maraging 250, so section size, notch geometry and NDT class need more attention. Where a design is limited by toughness rather than by strength, Maraging 300 is usually the better forging.

Chemical composition of UNS K93540

The table below is the range we forge to. Every heat carries a ladle analysis on the mill certificate. Product analysis taken from the forging itself can be added when the order calls for it.

Composition range compiled by Jiangyin Jiangnan Metal Co., Ltd. against AMS 6515 and MIL-S-46850. Residual elements are controlled tightly because titanium and molybdenum are the strengthening additions. Carbon in particular is suppressed, since it ties up titanium as TiC and cuts the volume of strengthening precipitate available during ageing.

Mechanical properties of UNS K93540 forgings

UNS K93540 leaves the works in one of two conditions and the properties are not comparable between them. Figures below are room temperature results from test pieces cut from forging prolongations.

Source: Jiangyin Jiangnan Metal Co., Ltd. UNS K93540 forging specification. Annealed values are typical and are not normally an acceptance requirement. Maraged values are the room temperature figures we certify, and the AMS 6515 acceptance minima including 56 HRC are met and reported on the EN 10204 certificate. Results on a given forging depend on section size, forging reduction and test piece location, all of which should be agreed at order.

Physical properties

Values are nominal for the alloy and are given for design guidance, not as acceptance criteria.

Heat treatment of UNS K93540

Heat treatment runs in two stages. The forging stays soft while it is being cut and is hardened afterwards at a temperature low enough that nothing moves.

1. Solution anneal, 815-830 C (1500-1525 F), about 1 hour per 25 mm of ruling section, air cool. This dissolves the ageing precipitates and returns the forging to soft iron and nickel martensite at 30-35 HRC. The alloy carries no carbon to speak of, so no protective atmosphere is needed, although a clean furnace is preferred to keep the surface free of contamination.
2. Rough and finish machine. Nearly all machining is done at this stage.
3. Age, 480 C (900 F) for 3 to 6 hours, air cool. Intermetallic precipitates form and strength rises to about 2,413 MPa (350 ksi) at 56 HRC minimum. Heavier sections are held longer at temperature, and the alloy tolerates small variations in soak time without trouble.

Die casting dies and hot-work tooling often call for a modified cycle instead. Anneal at 815-830 C for one hour per 25 mm after rough machining, then age at 527-538 C (980-1000 F) for 6 hours after finish machining. That over-ages the alloy slightly and gives up peak hardness in exchange for better thermal fatigue resistance and longer die life.

UNS K93540 forged shapes and size capability

We forge UNS K93540 to customer drawings. The table lists the shapes we make in this grade together with the works size envelope. UNS K93540 is a vacuum melted specialty alloy, so the practical maximum on any order is set by the ingot available at the time and sizes are confirmed at enquiry.

Works size envelope of Jiangyin Jiangnan Metal Co., Ltd. The sizes above are our general capability across grades. Confirm UNS K93540 availability for your dimensions when you enquire.

How we manufacture UNS K93540 forgings

Melting and raw material

UNS K93540 is a vacuum melted alloy. For AMS 6515 and MIL-S-46850 work the accepted route is vacuum induction melting followed by vacuum arc remelting, VIM plus VAR, which holds oxygen, nitrogen and inclusion content low enough to support 350 ksi properties. We buy certified VIM plus VAR ingot and billet from qualified mills and supply the melt certificate with the forging. Electroslag remelted material can be offered where the customer specification permits it. Tell us which melting route your specification calls for at enquiry, since it affects both price and lead time.

Forging

The works runs 1 tonne, 3 tonne, 5 tonne and 9 tonne open-die forging hammers, hydraulic presses up to 5,000 tonnes and seamless ring rolling mills up to 6 m. Maraging steel is forged in a narrower temperature window than carbon or low-alloy steel and is finish forged under controlled reduction to develop uniform structure through the section. Forging and cooling records go into the job file and are available with 3.2 certification.

Heat treatment and machining

Solution annealing and ageing are done in house on calibrated furnaces with recorded charts. Forgings can be delivered black, rough machined to an allowance, proof machined, or finish machined to your drawing.

Testing, inspection and certification

Maraging 250 vs Maraging 300 vs UNS K93540 (Maraging 350)

The three commercial 18% nickel maraging grades share one base chemistry and differ mainly in cobalt and titanium. Choosing between them is almost always a strength against toughness decision.

Comparison table compiled by Jiangyin Jiangnan Metal Co., Ltd. from published alloy specifications. All three grades can be forged to drawing on request.

Applications for UNS K93540 forgings

UNS K93540 is chosen when a component has to carry the highest possible load inside a limited envelope and the design can live with modest toughness and poor corrosion resistance. Open-die forged applications include the following.

• Tooling and die casting. Die blocks, die inserts, extrusion tooling and cold forming punches, where the near-zero distortion on ageing lets a large die be finish machined before hardening.
• Power transmission. High-torque shafts, spindles, gear blanks and coupling components in gearboxes, turbines and compressors.
• Aerospace structural hardware. Landing gear components, actuator bodies, high-strength fasteners and shafting.
• Motorsport and high-performance machinery. Crankshafts, connecting components and drivetrain parts where weight matters.
• Oil, gas and heavy industry. High-load rings, sleeves, bushings and valve components in equipment where 350 ksi capability justifies the alloy cost.
• Ordnance and defence structural components, supplied only against documented end use. See the compliance note below.

UNS K93540 holds essentially no chromium, so it corrodes like a plain low-alloy steel. Parts going into wet or marine service are nitrided, plated or coated. Where corrosion resistance is a design requirement in its own right, a precipitation hardening stainless such as 17-4PH (UNS S17400) or PH13-8Mo is usually the right substitution, at a much lower strength level.

Equivalent designations and cross reference

Cross reference compiled by Jiangyin Jiangnan Metal Co., Ltd. Equivalences are approximate. Where a purchase order calls up a specific specification, that specification governs.

Frequently asked questions about UNS K93540

About the manufacturer

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China, operating since 2008 under an ISO 9001:2015 quality system. The works employs around 460 people, including 9 senior engineers and 32 intermediate engineers, and produces open-die forgings and seamless rolled rings in carbon steel, alloy steel, tool steel, stainless steel, nickel alloys and maraging steels including UNS K93540.

Raw material control, forging, heat treatment, machining, testing and inspection all sit inside one facility, so a UNS K93540 forging stays traceable from melt certificate through to the final dimensional report. Forgings ship worldwide with EN 10204 3.1 or 3.2 certification.

Compliance and trademark notices

Related grades we forge

• Waspaloy forgings, nickel superalloy for hot-section turbine hardware
• MP159 forgings, multiphase cobalt and nickel alloy, high strength with corrosion resistance
• MP35N forgings, cobalt, nickel, chromium and molybdenum alloy for corrosive high-load service
• Multimet N155 forgings, iron-base heat resisting alloy
• 17-4PH (UNS S17400) forgings, PH stainless where corrosion resistance is required
• PH13-8Mo forgings, high-toughness PH stainless
• Seamless rolled rings, forged shafts and forged discs