What is 1.6355 steel?

1.6355 is the EN material number for Maraging 350, sold also as C350 and 18Ni(350). It is an iron-based steel containing 17 to 19 percent nickel and 12 to 13.5 percent cobalt with molybdenum and titanium, and under 0.03 percent carbon. Strength comes from Ni3Ti and Ni3Mo precipitates formed during a low-temperature ageing treatment rather than from carbon or carbides.

What is the chemical composition of 1.6355?

Nickel 17.0 to 19.0 percent, cobalt 12.0 to 13.5 percent, molybdenum 4.6 to 5.2 percent, titanium 0.3 to 0.6 percent, aluminium 0.05 to 0.15 percent, carbon 0.03 percent maximum, balance iron. There is no chromium in the composition, so 1.6355 has no corrosion resistance.

What is 1.6355 used for?

Aerospace structures and landing gear parts, rocket motor cases, gun and cannon barrels, die casting and extrusion tooling, high-performance transmission shafts and couplings, precision tooling that must hold size through hardening, and powder feedstock for additive manufacturing. It is not used for pressure vessels, tanks, silos or heat exchangers, where cheaper grades perform better and code approval exists.

How is 1.6355 heat treated?

Solution anneal at 815 to 830 degrees Celsius for about one hour per 25 mm of section, then air cool. Machine the part in this condition. Age at 480 to 490 degrees Celsius for 3 to 6 hours and air cool. Ageing shrinks the part about 0.05 percent in length, uniformly enough that finish machining before ageing is normal practice.

How does 1.6355 differ from 1.2709 Maraging 300?

1.6355 carries 12 to 13.5 percent cobalt against roughly 8.5 to 9.5 percent in 1.2709. The extra cobalt raises aged yield strength from about 1,900 MPa to about 2,400 MPa, and costs fracture toughness and money. Specify 1.2709 unless the calculation fails at 1,900 MPa.

EN 1.6355 · X2NiCoMo18-12-4 · AMS 6515

1.6355 Maraging Steel Forgings — Maraging 350 / C350

1.6355 is the EN material number for Maraging 350, sold also as C350 and 18Ni(350). It is a steel: the balance is iron, with 17–19% nickel, 12–13.5% cobalt, molybdenum, titanium and under 0.03% carbon. Ageing at 480–490 °C precipitates Ni₃Ti and Ni₃Mo and takes yield strength to roughly 2,400 MPa. There is no chromium in it, so it does not resist corrosion. Jiangyin Jiangnan Metal forges 1.6355 into rings, shafts, bars, discs and blocks, supplied solution annealed or aged, with an EN 10204 3.1 certificate.

Send a drawing with the condition you need, solution annealed for your own machining or aged to hardness, and a priced offer comes back within one working day.

Email a drawing for quote Call +86 189 2135 9659

1.6355 at a glance, aged condition

Yield strength: 2,400MPa
Tensile strength: 2,500MPa
Hardness: 54–58HRC
Nickel: 17–19%
Cobalt: 12–13.5%
Carbon: ≤0.03%

Definition

What is 1.6355 maraging steel?

Maraging is a contraction of martensite and ageing. A conventional hardened steel takes its strength from carbon locked into a distorted martensite lattice, which is why it comes out hard and brittle together. Maraging steel does the opposite. Carbon is held under 0.03%, and the nickel content produces a soft, tough martensite on cooling from the solution anneal. Strength is added afterwards at low temperature, by precipitating Ni₃Ti and Ni₃Mo particles a few nanometres across through that martensite.

Three things follow, and all three change how the part gets made. The material sits at 30–35 HRC before ageing, so machining comes first and hardening last. Ageing needs no quench, so distortion is small; the part shrinks about 0.05% in length, repeatably enough that finish machining beforehand is normal practice. And with almost no carbon there is no brittle heat affected zone, so it welds without preheat.

Why 1.6355 sits under nickel alloys, and why it is still a steel

Nickel is the main alloying element at 17–19%, which is why 1.6355 is listed in this section beside the nickel-based alloys Jiangyin Jiangnan Metal forges. What separates the two families is the balance element. In 1.6355 the balance is iron. In Inconel 625, Monel 400 and Hastelloy C-276 the balance is nickel.

The difference shows up in selection. Nickel-based alloys are bought for corrosion resistance and for strength at 600–1,000 °C. 1.6355 is bought for strength at room temperature. It softens above roughly 400 °C, and with no chromium in the composition it rusts. Neither family substitutes for the other.

Table 1 — 1.6355 set against a nickel-based alloy
Criterion	1.6355 / Maraging 350	Inconel 625, for contrast
Balance element	Iron, so it is a steel	Nickel, so it is a nickel alloy
Nickel content	17–19%	58% min
Chromium	None	20–23%
Bought for	Room-temperature strength	Corrosion and heat resistance
Yield strength	~2,400 MPa aged	~450 MPa
Service temperature	up to ~400 °C	up to ~980 °C
Corrosion resistance	None, needs plating or coating	Excellent

If the part has to survive a wet or hot environment, 1.6355 is the wrong grade whatever its strength. If the part is strength-limited at room temperature and weight matters, no nickel-based alloy comes near it.

Composition

Chemical composition of 1.6355

Table 2 — 1.6355 / Maraging 350 composition, % by weight
Element	Min	Max	What it does
Nickel (Ni)	17.0	19.0	Forms the soft carbon-free martensite, and supplies Ni₃Ti and Ni₃Mo
Cobalt (Co)	12.0	13.5	Drops molybdenum solubility and drives precipitation, the main strengthener in cobalt-type maraging grades
Molybdenum (Mo)	4.6	5.2	Forms Ni₃Mo and Fe₂Mo
Titanium (Ti)	0.3	0.6	Forms Ni₃Ti, the single biggest lever on aged strength
Aluminium (Al)	0.05	0.15	Deoxidiser, contributes NiAl
Carbon (C)	—	0.03	Held low because carbon takes titanium out of solution as TiC
Manganese (Mn)	—	0.10	Residual, restricted
Silicon (Si)	—	0.10	Residual, restricted
Phosphorus (P)	—	0.010	Embrittles grain boundaries
Sulfur (S)	—	0.010	Embrittles grain boundaries
Iron (Fe)	Balance		Base element

There is no chromium in 1.6355. Any corrosion requirement has to be met by plating, nitriding or coating, or by picking a different grade.

Properties

Mechanical properties of 1.6355

1.6355 ships in one of two conditions and they behave nothing alike. State which one you need on the order. It decides the price, and whether you can put a tool to the part.

Table 3 — Typical room-temperature properties by condition
Property	Solution annealed	Aged 480–490 °C
0.2% yield strength	~830 MPa	~2,400 MPa
Tensile strength	~1,000 MPa	~2,500 MPa
Elongation in 50 mm	15–18%	6–8%
Reduction of area	65–75%	30–40%
Hardness	30–35 HRC	54–58 HRC
Machinability	Good, machine here	Grinding or EDM only
Density	~8.08 g/cm³
Modulus of elasticity	~186 GPa

A quenched and tempered 4340 shaft runs around 1,000 MPa yield. Aged 1.6355 gives about 2.4 times that in the same section, which is the whole reason anyone pays for it.

Heat treatment

Heat treatment of 1.6355

Table 4 — Standard heat treatment sequence
Stage	Temperature	Time	Cooling	Result
Forging	1,150–1,200 °C	—	Air	Finish above 900 °C, do not work below 800 °C
Solution anneal	815–830 °C	1 h per 25 mm	Air	Soft nickel martensite, 30–35 HRC
Machining	—	—	—	All cutting done here
Ageing	480–490 °C	3–6 h	Air	Ni₃Ti and Ni₃Mo precipitation, 54–58 HRC

Ageing shrinks the part about 0.05% in length, and it does so uniformly. Machine to final size first and work the allowance out from part length. That predictability is why maraging steel displaces through-hardening tool steels on precision tooling.

Equivalents

1.6355 equivalent designations

Table 5 — 1.6355 across standards
System	Designation
EN material number	1.6355
EN designation	X2NiCoMo18-12-4
Trade names	Maraging 350, C350, 18Ni(350)
Aerospace specification	AMS 6515
Military specification	MIL-S-46850
Nearest lower grade	1.2709 / X3NiCoMoTi18-9-5 / Maraging 300

Export control. Maraging steel above defined strength thresholds is a controlled item on the Nuclear Suppliers Group and Wassenaar Arrangement lists in most jurisdictions. Confirm licence requirements for your destination before ordering. Jiangyin Jiangnan Metal asks for an end-use statement on 1.6355 enquiries.

Product forms

1.6355 forged product forms

Table 6 — 1.6355 forgings supplied
Form	Size range	Weight	Usual condition
Seamless rolled rings	Ø200–1,500 mm	20 kg–3 t	Solution annealed
Forged bars and shafts	Ø60–500 mm	30 kg–2 t	Solution annealed
Forged discs and blanks	Ø150–1,000 mm	25 kg–1.5 t	Solution annealed or aged
Forged blocks	up to 600 × 400 × 1,500 mm	40 kg–2 t	Solution annealed
Forged sleeves and bushings	Ø100–800 mm	15 kg–1 t	Solution annealed

Parts go out as forged, rough machined with allowance, or finish machined and aged to hardness. Say which you want in the enquiry.

Applications

What 1.6355 is used for

1.6355 costs several times what alloy steel costs per kilogram and gives nothing back in corrosion resistance. It gets specified where strength-to-weight, or holding size through hardening, is worth paying for.

Table 7 — Established applications for Maraging 350
Sector	Typical parts	Reason for the grade
Aerospace	Landing gear components, structural fittings, rocket motor cases	Strength-to-weight, with usable toughness at 2,400 MPa
Defence	Gun and cannon barrels, ordnance components	Holds strength through repeated thermal and pressure cycling
Tooling	Die casting dies, extrusion tooling, punches, mandrels	Cut soft, aged with 0.05% dimensional change
Motorsport and high-performance drivetrain	Transmission shafts, gears, couplings	Torque capacity in minimum diameter
Precision equipment	High-speed rotors, springs, flexures	Dimensional stability and fatigue strength
Additive manufacturing	Powder feedstock for LPBF and WAAM	Weldability and response to post-build ageing

Where 1.6355 is the wrong grade. Pressure vessels, tanks, silos, heat exchangers, columns and towers, cement and sugar mill equipment, pulp and paper plant, pharmaceutical process equipment. Those duties need corrosion resistance, code approval or low cost, and 1.6355 offers none of the three. Jiangyin Jiangnan Metal forges carbon steel, alloy steel and stainless steel grades for that work.

Selection

1.6355 or 1.2709? Maraging 350 against Maraging 300

These two grades cover most maraging steel demand. Buyers often ask for 1.6355 where 1.2709 would have done the job at lower cost and better toughness.

Table 8 — 1.6355 compared with 1.2709
Criterion	1.6355 / Maraging 350	1.2709 / Maraging 300
Cobalt	12.0–13.5%	8.5–9.5%
Titanium	0.3–0.6%	0.6–0.8%
Aged yield strength	~2,400 MPa	~1,900 MPa
Aged hardness	54–58 HRC	50–54 HRC
Fracture toughness	Lower	Higher
Relative cost	Higher	Baseline
Availability	Limited, longer lead time	Widely stocked, including AM powder
Specify when	Design is strength-limited and weight-critical	Almost everything else, most tooling included

Start from 1.2709. Move up to 1.6355 when the calculation fails at 1,900 MPa yield and the part cannot be made any bigger.

Quality

Melting route, testing and certification

Maraging steel lives or dies on cleanliness. Titanium and aluminium are reactive, and at 2,400 MPa yield an oxide inclusion is a fatigue crack waiting to start. AMS 6515 calls for double vacuum melting, vacuum induction melting followed by vacuum arc remelting. Melting route is confirmed on enquiry against the specification the part is built to.

Table 9 — Testing available on 1.6355 forgings
Test	Standard	Scope
Chemical analysis	ASTM A751	Every heat, standard
Tensile and elongation	ASTM A370 / ISO 6892-1	Every heat lot, standard
Hardness	ASTM E18 (HRC)	Every piece, standard
Ultrasonic testing	ASTM A388 / EN 10228-3 / SEP 1921	On request
Magnetic particle	ASTM E709 / EN 10228-1	On request
Inclusion rating	ASTM E45	Recommended for aerospace work
Certificate	EN 10204 3.1	Standard, 3.2 third party on request

Questions

1.6355 frequently asked questions

Is 1.6355 a nickel alloy?

No. Nickel is the main alloying element at 17–19%, but the balance is iron, which makes 1.6355 a steel. Nickel-based alloys such as Inconel 625, Monel 400 and Hastelloy C-276 have nickel as the balance element and are used for corrosion resistance and service above 600 °C. 1.6355 is used for room-temperature strength and rusts in humid air.

What strength does 1.6355 reach after ageing?

Around 2,400 MPa yield and 2,500 MPa tensile at 54–58 HRC, with 6–8% elongation. Before ageing it is about 1,000 MPa tensile at 30–35 HRC, and that is the condition to machine it in.

Why is the carbon held so low?

Carbon combines with titanium to form titanium carbide, taking titanium out of solution and starving the Ni₃Ti reaction that provides the strength. It would also bring back the brittleness maraging steel exists to avoid.

How much does 1.6355 move during ageing?

About 0.05% shrinkage in length, uniform and repeatable, with no quench and very little distortion. Finish machining before ageing is normal, with the allowance worked out from part length. This is why maraging steel is chosen over through-hardening tool steels for precision tooling.

Can 1.6355 be welded?

Yes, and more easily than most high-strength steels. Carbon under 0.03% means no hard heat affected zone to crack, so preheat is not normally needed. Weld in the solution annealed condition, then age the weldment to bring the joint to full strength.

Does 1.6355 resist corrosion?

No. There is no chromium in it and it rusts in humid air. Parts are normally plated, nitrided or coated in service. Where corrosion resistance is the requirement, look at 17-4PH or 15-5PH, which are precipitation-hardening stainless steels at lower strength.

What is the minimum order quantity?

One piece. Open-die forging uses flat universal dies rather than a part-specific cavity, so there is no tooling to amortise and a single prototype or spare is economical.

How do I get a quotation?

Email a drawing in PDF, DWG or STEP with the condition you need, solution annealed or aged, plus quantity and test level, to sales@steelforgepieces.com, or call +86 189 2135 9659. Offers come back within 24 working hours.

Related grades

Grades often compared with 1.6355

Each grade page carries its own composition, properties and heat treatment data. If you are still choosing between grades, send the load case rather than a grade name and the engineering team will propose the cheapest material that meets it.

Contact

Request a quotation for 1.6355 forgings

Jiangyin Jiangnan Metal Co., Ltd.
Open-Die Forging Factory
No.1 Chengxiqiao Road, Zhouzhuang Town
Jiangyin City, Jiangsu Province 214423, China
Tel / WhatsApp / WeChat: +86 189 2135 9659
Email: sales@steelforgepieces.com
Hours: Mon–Sat 08:00–17:30 (GMT+8)

Email a drawing for quote Contact us

Composition and property figures are compiled from AMS 6515 and published Maraging 350 datasheets and are typical values. Check them against the mill certificate for the heat supplied. Page last updated 7 August 2026.