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EN 1.4418, designated X4CrNiMo16-5-1 under EN 10088-3, is a low-carbon martensitic-austenitic stainless steel developed for applications where standard martensitic grades fall short. Its dual-phase microstructure — predominantly martensite with retained austenite and a minor ferrite fraction — delivers a balance of tensile strength, impact toughness, and corrosion resistance that is difficult to match within a single alloy class. Supplied in the quenched and tempered condition (QT 900), it meets a guaranteed minimum tensile strength of 900 MPa while retaining meaningful ductility and weldability.
Chemical Composition
All values conform to EN 10088-3 requirements for 1.4418.
| Element | Standard Limit | Typical Value |
|---|---|---|
| Carbon (C) | ≤ 0.06 % | 0.03 % |
| Chromium (Cr) | 15.0 – 17.0 % | 16.0 % |
| Nickel (Ni) | 4.0 – 6.0 % | 5.0 % |
| Molybdenum (Mo) | 0.80 – 1.50 % | 1.0 % |
| Silicon (Si) | ≤ 0.70 % | ≤ 0.70 % |
| Manganese (Mn) | ≤ 1.50 % | ≤ 1.50 % |
| Phosphorus (P) | ≤ 0.040 % | ≤ 0.040 % |
| Sulfur (S) | ≤ 0.015 % | ≤ 0.015 % |
The low carbon content (≤0.06%) minimises carbide precipitation at grain boundaries, which is a key reason 1.4418 maintains better post-weld properties than older high-carbon martensitic grades such as 1.4021 or 1.4034. Chromium at 16% builds the passive film that underpins corrosion resistance; molybdenum at 0.80–1.50% extends that resistance into chloride-containing media; nickel at 4.0–6.0% stabilises the austenite phase and contributes substantially to low-temperature toughness.
Standard: EN 10088-3 : 1.4418, condition QT 900 Melting route: EAF + AOD refining
Mechanical Properties — QT 900 Condition, Room Temperature
Values guaranteed per EN 10088-3.
| Property | Requirement | Notes |
|---|---|---|
| Tensile Strength R_m | 900 – 1050 MPa | Minimum 900 MPa guaranteed |
| 0.2% Proof Strength R_p0.2 | ≥ 700 MPa | — |
| Elongation A | ≥ 12 % | 50 mm gauge length |
| Reduction of Area Z | ≥ 45 % | — |
| Hardness | 28 – 34 HRC | Typical QT range |
| Charpy V-Notch Impact Energy KV | ≥ 40 J | Room temperature |
The QT 900 designation denotes the lower bound of the tensile strength range; actual production material typically sits in the 950–1000 MPa range while still comfortably meeting elongation and toughness minima.
Physical Properties
| Property | 20 °C | 100 °C | 200 °C | 300 °C | 400 °C |
|---|---|---|---|---|---|
| Density (kg/dm³) | 7.7 | — | — | — | — |
| Modulus of Elasticity (GPa) | 200 | 195 | 185 | 175 | 170 |
| Thermal Expansion Coefficient (×10⁻⁶ K⁻¹) | — | 10.3 | 10.8 | 11.2 | 11.6 |
| Thermal Conductivity (W/m·K) | 24.0 | 25.5 | 27.0 | 28.5 | 30.0 |
| Electrical Resistivity (μΩ·cm) | 78 | 82 | 86 | 90 | 94 |
| Magnetic Behaviour | Magnetic across all listed temperatures |
Thermal conductivity is notably higher than austenitic grades (typically 15–16 W/m·K at 20 °C), which can be relevant in heat-transfer applications and affects welding heat input calculations.
Heat Treatment Specifications
Solution treatment: 950 – 980 °C, hold 30 – 60 min, air cool.
Quenching: Air-quench from solution temperature.
Tempering (QT 900): 580 – 620 °C, hold 2 – 4 h, air cool.
Post-weld stress relief (optional): 200 – 250 °C; keeps residual stress low without degrading hardness.
Tempering in the 580 – 620 °C window avoids the temper-embrittlement range that affects some martensitic grades, which is one reason 1.4418 retains its Charpy impact values after welding and PWHT when procedures are followed correctly.
Performance Characteristics
Strength and ductility in balance. The QT 900 condition achieves high tensile strength without the brittleness typical of plain martensitic grades at similar hardness levels. Elongation ≥12% and reduction of area ≥45% indicate meaningful plastic deformation capacity before fracture — important in fatigue-loaded and shock-loaded components.
Impact toughness at low temperatures. Retained austenite in the microstructure absorbs energy during crack propagation. ≥40 J Charpy at room temperature, with usable toughness maintained at moderately sub-zero temperatures, makes 1.4418 suitable for offshore and cold-climate service where 410/420 grades are not viable.
Weldability. Low carbon content and controlled Cr-Ni balance keep martensite start temperature (Ms) high enough that the HAZ re-austenitises predictably. With correct pre-heat (typically 100–150 °C for section thickness > 10 mm) and PWHT at 580 – 620 °C, weld joints recover mechanical properties close to the parent material. This is a significant improvement over high-carbon martensitic alternatives.
Fatigue and wear resistance. The hardness range (28 – 34 HRC) combined with surface compressive stress achievable through controlled machining translates to good fatigue life under cyclic and alternating loads, as well as moderate abrasion resistance.
Corrosion Resistance
| Environment | Performance |
|---|---|
| Fresh water, neutral atmosphere | Excellent; passive film stable |
| Weak acids and dilute alkalis | Good resistance |
| Low-chloride seawater / brackish water | Better than 410/420; pitting and crevice resistance improved by Mo content |
| Mild chloride + tensile stress | Acceptable SCC resistance |
| Air, up to 550 °C | Oxidation resistance stable |
1.4418 outperforms conventional 410 and 420 martensitic grades in chloride environments, primarily because of the molybdenum addition and lower carbon content. It is not, however, equivalent to duplex or super-austenitic grades in highly aggressive seawater service; PRE (Pitting Resistance Equivalent) ≈ 18 – 20, which positions it as a moderate-chloride-environment grade.
Typical Applications
The grade is routinely specified where other stainless steels offer either the strength or the corrosion resistance, but not both at the required combination.
Marine engineering: Offshore platform structural fittings, seawater pump shafts, marine valve bodies and trim, propeller shafts.
Oil & gas / petrochemical: Pipeline connectors, pressure fittings, hydraulic valve components, wellhead parts.
Water treatment: High-pressure pump internals, impellers, mechanical seals, water supply system components.
Power generation: Hydraulic turbine runners and guide vanes, transmission shafts, power equipment drive components.
General mechanical engineering: High-strength shafts, fasteners, precision-machined structural parts requiring both strength and corrosion resistance.
Why C&N
At C&N (Hongcheng Pipe Fittings Limited), we’ve spent years focusing on one thing: supplying the right material, in the right form, to projects that can’t afford specification errors. Our 1.4418 stock is produced to EN 10088-3 and supplied with full mill test reports traceable to heat number. We work with fabricators, engineering contractors, and procurement teams across the marine, oil & gas, and industrial sectors — and we’re straightforward about what a material can and can’t do.
If you’re working on a project where EN 1.4418 might be the right call — or if you’re not sure and want a second opinion — contact us. We’ll respond with specifics, not a sales pitch.
