1.4418 (X4CrNiMo16-5-1) Forgings

What is 1.4418, and what does "soft martensitic" mean?

Every martensitic stainless steel gets its strength the same way: heat it above the transformation point, cool it fast, and the structure shears into martensite. How hard and how brittle that martensite turns out is set almost entirely by carbon. In 1.4021 (X20Cr13) the carbon is 0.16 to 0.25 %, and the result is hard, strong and notch sensitive. In 1.4418 the carbon ceiling is 0.06 %.

What is lost in carbon is put back as nickel. Four to six per cent nickel keeps the structure fully martensitic on cooling despite the low carbon, and 0.80 to 1.50 % molybdenum lifts pitting resistance. The steel that comes out is what the trade calls a soft martensitic stainless: strong, but not hard and not brittle.

In the quenched and tempered condition the structure is not martensite alone. Valbruna publishes roughly 80 % martensite, 10 % austenite and 10 % ferrite for 1.4418 in +QT900, and the exact split moves with where the heat sits inside the chemistry band. The austenite reverted during tempering is what carries the toughness: it is ductile at temperatures where the martensite on its own would not be, and it is the reason both specified tempering conditions sit above 550 °C and not at the hardness peak lower down.

That combination is what every application of the grade is built on:

• Strength with toughness. 700 MPa proof strength at 80 J impact energy is a combination the 13 % chromium grades cannot reach.
• Weldability. Low carbon means the heat-affected zone forms soft martensite. A welded joint in 1.4418 keeps most of its properties, which is why it is used for fabricated turbine runners.
• Corrosion resistance close to 1.4301. Normally the strength of a martensitic steel is bought at the cost of corrosion resistance. Here the chromium, nickel and molybdenum together put it close to austenitic 1.4301 in most media, and it is insensitive to intergranular corrosion.

1.4418 chemical composition

Cast analysis limits in per cent by mass from EN 10088-3. Jiangyin Jiangnan Metal melts its own steel, so these are the limits the heat is aimed at, not limits checked on a purchased billet.

Why one datasheet says sulphur 0.030 % and another says 0.015 %

Both are right, for different product forms. EN 10088-3, which covers semi-finished products, bars, rods, wire, sections and bright products, sets sulphur at 0.030 % maximum. EN 10088-2, which covers sheet, plate and strip, sets 0.015 % maximum. A forging is normally bought against Part 3.

EN 10088-3 also carries a footnote against the sulphur limit for this grade: a controlled sulphur content of 0.015 % to 0.030 % is recommended and permitted where machinability matters. That is a permission, not a default, and it points the wrong way for a shaft.

It matters because sulphur is the element a customer is most likely to restrict below the standard. Sulphides improve machinability and damage transverse toughness and pitting resistance, and on a turbine or propeller shaft the transverse properties are the ones that are being paid for. A restricted sulphur limit is set at the furnace and cannot be corrected afterwards, so it belongs on the enquiry rather than on the purchase order.

Pitting resistance equivalent

PREN, calculated as %Cr + 3.3 × %Mo + 16 × %N, runs from 17.9 at the bottom of the composition band to 22.3 at the top. That is a wide spread for one grade, and where a heat lands inside it is an engineering variable, not a rounding error. Where the part is going into brackish or intermittently wetted service, ask for the PREN to be aimed at the upper half of the band and have it stated on the certificate.

1.4418 mechanical properties

EN 10088-3 specifies one annealed condition and two quenched and tempered conditions. The number after QT is the minimum tensile strength in MPa, not a temperature.

Proof strength at elevated temperature

The grade loses little strength across its working range: +QT900 still holds 580 MPa at 300 °C, which is 83 % of its room-temperature minimum. The service ceiling comes from the tempering temperature, not from strength, which is covered under service limits.

Bright bar and small sections

Bright bar up to 10 mm in +QT900 is specified separately and runs higher, at 750 MPa minimum proof strength and 900 to 1150 MPa tensile, with elongation dropping to 10 %. Those values belong to drawn and ground bar, not to forgings, and they are listed here only because a purchaser comparing a forging certificate against a bar datasheet will otherwise see a mismatch and query it.

Physical properties of 1.4418

Which datasheet edition. The values above are from the Deutsche Edelstahlwerke Acidur 4418 datasheet. The current Swiss Steel edition of the same datasheet gives 0.70 Ω·mm²/m for electrical resistivity and 10.8 ×10^-6/K for 20 to 100 °C expansion instead. Neither is wrong; they are different revisions. If your specification names one, say which at enquiry.

Thermal conductivity of 15 W/(m·K) is low, about half that of a 13 % chromium steel. On a heavy section that shows up twice: the soak before forging takes longer per millimetre of section than a carbon steel of the same size, and the quench produces a steeper thermal gradient through the wall. Both are planned for at the quotation stage.

Heat treatment and forging windows

Four temperature bands govern the grade, and one band is avoided entirely. Jiangyin Jiangnan Metal instruments all of them, and the furnace charts are issued with the order on request.

Which datasheet edition. The temperatures above are from the Deutsche Edelstahlwerke Acidur 4418 datasheet. The current Swiss Steel edition of the same sheet narrows two of them: soft annealing at about 600 °C and not above 625 °C, and hardening from 1000 to 1050 °C. We work to whichever the order names.

Why nothing is tempered between 450 and 550 °C

Both conditions EN 10088-3 specifies temper at 550 °C or above, and that is deliberate. On the mill tempering diagram for this grade, hardness and tensile strength peak at around 450 °C while impact energy is at its lowest, and the useful combination of strength with toughness only appears once the reverted austenite has formed higher up. A forging tempered at 480 °C would look strong on a hardness tester and fail a Charpy test.

A part that will run warm in service is tempered above the band rather than into it, so that service does not finish the tempering. And where a forging is tempered at the bottom of the +QT900 range, near 550 °C, the cool from tempering is controlled, not left to drift down through the range below.

Some supplier datasheets describe 450 to 550 °C as a temper embrittlement range for this grade. We have not been able to source that wording to EN 10088-3 or to the mill datasheet, so it is stated here as the range that is not used for tempering, not as a standard requirement. The practical instruction is the same either way.

Forging practice

1.4418 is rated as moderately forgeable, which is fair: harder work than a plain carbon steel, easier than a free-machining grade with its narrow window. Getting a 1.4418 forging right comes down to the heating curve, the finishing temperature and the cool afterwards.

• The heating curve, not just the temperature. Low thermal conductivity and a martensitic structure at room temperature mean a fast charge into a hot furnace puts the surface into tension against a cold core. The piece goes in slowly to above 800 °C, then up quickly to 1150 to 1180 °C.
• Finishing above 950 °C. Deformation below that leaves the steel stiff and the reduction goes into surface tearing instead of into the section. Heavy work is planned around reheats.
• Controlled cooling after the last blow. This grade air hardens. A heavy section left to cool in the yard becomes untempered martensite and can crack before it reaches the heat-treatment shop. The piece goes to the furnace or into dry ash.

Because the grade air hardens, the forging is annealed at 600 to 650 °C before rough machining and then hardened and tempered to the ordered condition. On heavy sections we rough machine before the final heat treatment, so the quench reaches the true wall thickness and the tensile test coupon represents the part and not an oversize block.

Welding 1.4418

Weldability is the practical argument for this grade over 1.4021 or 1.4057, and it is the reason fabricated hydro turbine runners are built from it. The 0.06 % carbon ceiling means the heat-affected zone transforms to soft martensite, which does not crack the way a high-carbon martensitic heat-affected zone does. The steel is welded with all the common processes.

• Preheat 100 to 200 °C, held through the joint. The range is deliberately below the martensite start temperature.
• No hydrogen or nitrogen in the shielding gas. Argon or argon with a small helium addition. Hydrogen-bearing mixtures are excluded outright.
• Filler 1.4430, the austenitic 316L type, where the weld does not have to match the parent strength. Where it must match, a matching soft martensitic consumable is used and the assembly is heat treated afterwards.
• Anneal or temper after welding. Without it, the mechanical values in the weld metal and heat-affected zone can differ substantially from the parent metal, whatever the filler.

A note on sequence that saves arguments later: if the forging is supplied in +QT900 and then welded without a post-weld cycle, the heat-affected zone is no longer in the certified condition, and the certificate covers the forging as delivered, not the fabrication. State the welding plan at enquiry and the tempering temperature can be set above the post-weld cycle you intend to run.

Corrosion resistance and service limits

1.4418 is more corrosion resistant than any plain martensitic stainless steel and is broadly comparable with austenitic 1.4301 in most media. The molybdenum addition makes limited marine use possible. It resists weak acids and alkalis, oxidising acids such as nitric acid, and weakly chloride-bearing media, and it is insensitive to intergranular corrosion.

On stress corrosion cracking, the mill wording needs care. The datasheet describes 1.4418 as resistant to fatigue corrosion and stress corrosion cracking, and against austenitic grades in hot chlorides that holds. It is not a blanket immunity. This is a martensitic steel running at 700 to 1100 MPa, and soft martensitic grades are susceptible to sulphide stress cracking in wet H₂S and to hydrogen embrittlement under cathodic protection or after plating. If the duty involves H₂S, cathodic protection or electroplating, treat the hardness ceiling and the environment as design constraints and state them at enquiry.

The seawater line gets misquoted in both directions. A PREN of 17.9 to 22.3 is not a seawater alloy: permanent stagnant immersion will pit it. It is also not a freshwater-only alloy: propeller shafting, rudder stocks and pump shafts in flowing or intermittently wetted seawater are among the grade's largest applications, because flow and the absence of crevices keep pits from initiating. Where the duty is permanent immersion, or where crevices under bearings and couplings cannot be designed out, the correct step up is a duplex grade such as 1.4462.

Service temperature

The Deutsche Edelstahlwerke datasheet gives minus 30 to plus 300 °C. Other mill sheets for the same grade quote higher upper limits, around 550 °C and in one case 600 °C, so the figure is not settled across the industry. The physical constraint is clear enough: the upper limit is set by the tempering temperature, because running a part near its own tempering range over-tempers it and the strength loss is permanent. Take 300 °C as the conservative working figure and confirm anything above it against the datasheet edition your specification names.

EN 10088-3 specifies no sub-zero impact values for 1.4418. The reverted austenite does help at low temperature, and some databases quote toughness far below zero, but the lowest test result we can point to on a published mill sheet is minus 40 °C. If the part has to be qualified below minus 30 °C, the test temperature and the acceptance energy are agreed at enquiry and tested on a coupon from the same heat, not taken from a datasheet.

Machining 1.4418

Machinability is rated as moderate and behaves like a structural steel of the same hardness. The hardness is the variable that matters, not the fact that the steel is stainless.

Machinability can be improved by a small sulphur addition up to 0.030 %, which is within the EN 10088-3 limit. It is not free: the same sulphides cut corrosion resistance and transverse mechanical properties. On a screw-machine part that trade is usually worth making; on a turbine or propeller shaft it is not, and the sulphur is restricted instead. Because the melting is on site, the aim is set before the heat rather than measured after it.

1.4418 can also be nitrided, and it takes a polish, which matters for the sealing surfaces on pump and centrifuge components.

1.4418 compared with the grades it competes against

The question is rarely what 1.4418 is. It is whether a cheaper grade will do, or whether the duty needs more corrosion resistance than 1.4418 has.

Read the nickel and carbon columns together. 1.4057 has the same chromium as 1.4418 and a quarter of the nickel, which is why it costs less and why it welds badly and runs short on toughness. 17-4 PH reaches higher strength and is tunable through the aging condition, but its PREN is lower and it is the wrong answer where water is the problem. A182 F6NM is the grade ASTM-written projects actually specify, and it is a different chemistry, not a translation of 1.4418: at 790 MPa minimum tensile it sits between +QT760 and +QT900, on 13 % chromium against 16 %. 1.4462 is the step up when the duty is chloride corrosion and not strength.

1.4418 equivalent designations

What we forge in 1.4418

Jiangyin Jiangnan Metal Co., Ltd. produces the following product families in 1.4418. Every item is forged from a single piece of steel melted on site, with no welding, no casting and no purchased billet of unknown origin.

Delivery condition is +QT900 as standard unless the order says otherwise, supplied as forged with an agreed allowance, rough machined for volumetric inspection, or finish machined to drawing. Anti-rust coating and seaworthy packing are included for export.

How a 1.4418 order runs through the works

Melting, forging, heat treatment, machining and testing are all on one site, so every piece traces back to its melt number rather than to a billet supplier's certificate.

1. Melting and ladle refining. Steel is melted in the electric arc furnace, refined in the ladle furnace and decarburised under vacuum. VOD is the step that matters on this grade: it takes carbon to the 0.06 % ceiling while holding chromium, and it allows nitrogen to be set at or above the 0.020 % minimum instead of hoped for. Maximum heat size is 60 t.
2. Chemistry verified at the furnace. Cast analysis by optical emission spectrometry to ASTM E415 and infrared carbon and sulphur analysis to ASTM E1019. On 1.4418 the carbon, nitrogen and sulphur readings decide whether the heat is released.
3. Forging. Pre-heat slowly to above 800 °C, soak at 1150 to 1180 °C, work on the 6,300 t, 4,000 t or 2,000 t press finishing above 950 °C. Rings are punched and expanded over a saddle mandrel or rolled on the 6 m, 3 m or 1 m mill. The piece is then cooled in the furnace or in dry ash.
4. Annealing. 600 to 650 °C in the heat-treatment shop, which holds 14 furnaces, before rough machining.
5. Rough machining. Heavy sections are rough machined before final heat treatment so the quench reaches the true wall thickness and the test coupon represents the part.
6. Hardening and tempering. 950 to 1050 °C, quenched in polymer, oil or air; tempered at 550 to 620 °C for +QT900 or 590 to 620 °C for +QT760. Long shafts are quenched vertically in one of the two 15 m well furnaces to control distortion. Furnace charts are issued with the certificate.
7. Testing. Tensile testing to ISO 6892 and ASTM A370 on 600 kN and 300 kN machines, Charpy V-notch impact with a low-temperature bath to minus 60 °C, Brinell hardness, and metallography where the order calls for it.
8. Non-destructive examination and certification. Ultrasonic examination to EN 10228-3 or ASTM A388, magnetic particle examination to ASTM E709, then an EN 10204 3.1 inspection certificate, or 3.2 witnessed by BV, DNV, LR, SGS, TUV or the customer's own inspector.

Standards referenced

EN 10088-3 does not cover forgings. Its scope is semi-finished products, hot or cold formed bars, rods, wire, sections and bright products, and it states that it does not apply to components manufactured by further processing of those forms. It defines the grade, the chemistry and the property levels, and a forging is certified against those levels in practice, but the product standard for an open-die stainless forging is EN 10250-4. Tell us which one the drawing calls for, because the acceptance requirements are not the same.

What to send with a 1.4418 enquiry

We quote from a drawing or a written specification. A complete enquiry usually gets a price, a weight and a lead time back within two working days.

Minimum order is 10 kg with no minimum piece count. Lead time normally runs 20 to 60 days. 1.4418 needs no remelting step for general engineering work, so it sits at the lower end of that range unless an aerospace melt route or third-party inspection has to be scheduled.

1.4418 questions and answers

Glossary

Soft martensitic stainless steel

A martensitic stainless steel with carbon held very low, typically 0.06 % or less, and nickel added to keep the structure martensitic. The martensite that forms is tough and weldable, not hard and brittle. 1.4418 and F6NM are the two grades most often meant by the term.

+A, annealed

Heat treatment condition symbol of EN 10088-3. For 1.4418 it means 600 to 650 °C with a furnace or air cool, giving 320 HBW maximum.

+QT760 and +QT900

Quenched and tempered to a minimum tensile strength of 760 MPa or 900 MPa. The number is the bottom of the tensile band, not a temperature. Both conditions also carry an upper tensile limit.

Rp0.2, Rm, A and KV

0.2 % proof strength, tensile strength, elongation after fracture and Charpy V-notch absorbed energy. Longitudinal values are measured along the grain flow, transverse values across it.

Stabilised austenite

Finely dispersed austenite that precipitates during tempering above about 500 °C and reaches a maximum near 610 °C. It is the reason a soft martensitic steel keeps its toughness at low temperature.

Temper embrittlement

Loss of toughness caused by tempering in, or slow cooling through, a particular temperature band. For 1.4418 that band is 450 to 550 °C.

PREN

Pitting resistance equivalent number, %Cr + 3.3 × %Mo + 16 × %N. A screening index for chloride pitting resistance, not a service prediction.

Cast analysis and product analysis

Cast analysis is taken from the liquid steel and is what the EN 10088-3 limits apply to. Product analysis is taken from the finished product and may deviate by the tolerances given in the standard.

Ruling section

The governing thickness or diameter of the piece, which decides which row of the property table applies and whether the acceptance values are longitudinal or transverse.

EN 10204 3.1 and 3.2

A 3.1 inspection certificate is issued by the manufacturer's inspection department, independent of production. A 3.2 certificate is also validated by the purchaser's inspector or an inspection body named in the order.

Summary of supply

Data sources and reuse

This page is published by Jiangyin Jiangnan Metal Co., Ltd. and reviewed by its metallurgy department. The technical data on it may be reused under CC BY 4.0 with attribution.

• EN 10088-3, chemical composition and mechanical property tables for X4CrNiMo16-5-1, including the elevated-temperature proof strength values.
• EN 10088-1 and EN 10088-2, grade list, physical property values and the sheet, plate and strip sulphur limit.
• Deutsche Edelstahlwerke material datasheet Acidur 4418 for 1.4418 / X4CrNiMo16-5-1, document 2015-0028: physical properties, heat treatment and hot-forming temperatures, forging practice, welding practice, corrosion data and cutting conditions. Where the current Swiss Steel edition of the same sheet differs, the difference is noted in the text.
• EN 4627, EN 4630 and EN 4721, aerospace acceptance regimes for X4CrNiMo16-5-1 forgings and bar.
• Valbruna Nordic datasheet for 1.4418 in +QT900: phase balance of the quenched and tempered structure.
• Works records of Jiangyin Jiangnan Metal Co., Ltd. for plant capability, production route and inspection scope.

Jiangyin Jiangnan Metal Co., Ltd. (2026). "1.4418 (X4CrNiMo16-5-1) Forgings."
Jiangyin, Jiangsu, China.
https://www.steelforgepieces.com/Stainless-Steel/1.4418.html
Last reviewed 22 September 2026.

Values on this page are for reference. They do not replace the current edition of the applicable standard or the agreed purchase order, and should be confirmed against the governing specification before design use.