Also known asEN 1.4594X5CrNiMoCuNb14-5FV520BUNS S45000AMS5773EXM-25
● Complete Material Guide · Updated 2025
What Is 1.4594 (X5CrNiMoCuNb14-5) Steel? A Complete Material Guide
By: Jiangsu Liangyi Engineering Team
Published June 2025~2,100 words · 9-min read
✓ 25+ Years Forging Experience✓ ISO 9001:2015 Certified✓ Exported to 50+ Countries
1.4594 (X5CrNiMoCuNb14-5) is a precipitation-hardening martensitic stainless steel that combines yield strength ≥720 MPa, tensile strength ≥930 MPa, hardness up to ~40 HRC, and outstanding weldability — properties unmatched simultaneously by any other common PH stainless steel grade, making it the material of choice in oil & gas, power generation, marine, and aerospace industries worldwide.
Quick Answer
1.4594 steel (EN designation X5CrNiMoCuNb14-5, also known as FV520B or UNS S45000) is a martensitic precipitation-hardening stainless steel containing 13–15% Cr, 5–6.5% Ni, 1.2–2% Mo, 1.2–2% Cu, and 0.15–0.6% Nb. After solution annealing (1,020–1,070 °C) and aging (480–620 °C), it achieves yield strength ≥720 MPa, tensile strength ≥930 MPa, elongation ≥15%, and hardness up to ~40 HRC. It is standardized in EN 10088-3 and AMS5773E, and widely used in open die forgings, seamless rolled rings, and machined components for oil & gas, turbines, marine, and chemical processing applications.
Section 01
Overview: Why Engineers Choose 1.4594
Definition: 1.4594 (X5CrNiMoCuNb14-5) is a European Standard (EN 10088-3) martensitic precipitation-hardening stainless steel that achieves very high strength and hardness through a controlled aging heat treatment, rather than conventional quench hardening. It is also commercially known as FV520B (UK trade name) and UNS S45000 (USA).
In the crowded landscape of stainless steels, 1.4594 occupies a uniquely valuable engineering position. It is not the toughest alloy available, nor the most corrosion-resistant in isolation. What it delivers is a precisely balanced combination of properties — strength, hardness, weldability, machinability, and corrosion resistance — that is extremely difficult to achieve simultaneously in any single material grade.
The addition of niobium (Nb) and copper (Cu) to the base Cr-Ni-Mo matrix is the defining metallurgical signature of 1.4594. Copper drives the precipitation-hardening response during aging; niobium stabilizes carbides and suppresses sensitization, dramatically improving weld quality without requiring post-weld annealing in most applications. All mechanical data and composition ranges presented in this guide are derived from EN 10088-3:2005, AMS5773E, and verified industry technical references.
⚠
Key metallurgical identity
1.4594 hardens by aging (precipitation), not by quenching — making it far easier to machine before final heat treatment than conventional hardened martensitic grades such as 420 or 440C. This is its primary manufacturing advantage.
Section 02
Chemical Composition per EN 10088-3
Definition: The chemical composition of 1.4594 (X5CrNiMoCuNb14-5) per EN 10088-3:2005 specifies a Cr-Ni-Mo martensitic stainless matrix uniquely modified with copper (Cu: 1.2–2.0%) and niobium (Nb: 0.15–0.60%) to enable precipitation hardening and improved weldability.
Table 1 — Chemical Composition of 1.4594 (X5CrNiMoCuNb14-5), wt% per EN 10088-3:2005
Element
Symbol
Specification (wt%)
Metallurgical Role
Carbon
C
≤ 0.07
Low C suppresses sensitization; maintains toughness and weldability
Silicon
Si
≤ 0.70
Deoxidation; minor solid-solution strengthening
Manganese
Mn
≤ 1.00
Austenite stabilizer; deoxidation during melting
Chromium
Cr
13.0 – 15.0
Primary corrosion resistance via stable Cr₂O₃ passive layer
The Cr-Ni-Mo triad establishes the corrosion-resistant austenitic matrix that transforms to martensite on cooling from the solution annealing temperature. The narrow carbon ceiling (≤0.07 wt%) is critical — it keeps chromium carbides from precipitating at grain boundaries during welding or slow cooling, avoiding the sensitization that plagues higher-carbon martensitic grades like 420 stainless. The Cu+Nb additions are the grade's unique contribution, fundamentally differentiating 1.4594 from simpler martensitic stainless steels.
Section 03
Mechanical Properties of 1.4594 Steel
Key property summary: In the aged condition per EN 10088-3, 1.4594 achieves minimum yield strength 720 MPa, tensile strength 930 MPa, elongation 15%, and hardness up to ~40 HRC — combining very high strength with the ductility levels typical of austenitic stainless steels.
≥720
MPa
Yield Strength Rp0.2
≥930
MPa
Tensile Strength Rm
≥15%
A5
Elongation at break
≤366
HBW
Hardness annealed max
~40
HRC
Peak hardness aged 480°C
7.8
g/cm³
Density
ⓘ
Strength–toughness balance: why it matters
A tensile strength above 930 MPa combined with ≥15% elongation is exceptional for any stainless steel. Conventional martensitic grades achieving this strength level typically sacrifice ductility to below 10% elongation. The Cu–Nb microstructure of 1.4594 enables both simultaneously.
Effect of Aging Temperature on Mechanical Properties
By selecting different aging temperatures, engineers can tune the mechanical properties of 1.4594 forgings across a broad range. This flexibility is a major manufacturing advantage over conventional hardened steels:
Table 2 — Mechanical Properties of 1.4594 vs. Aging Temperature
Aging Temp.
Tensile Str. (Rm)
Yield Str. (Rp0.2)
Elongation (A5)
Hardness
Recommended for
480 °C / 4–6h
≥1,200 MPa
≥1,050 MPa
10–12%
38–40 HRC
Static high-load, wear resistance
540 °C / 4–6h
~1,050 MPa
~900 MPa
12–14%
~35 HRC
Balanced structural parts
580 °C / 4–6h
~950 MPa
~800 MPa
15–18%
~30 HRC
Dynamic load, impact service
620 °C / 6–8h
~870 MPa
~720 MPa
18–22%
~28 HRC
Max toughness, fatigue, sour service
← Swipe to scroll →
Source: Mechanical property ranges derived from EN 10088-3:2005, AMS5773E, and industry technical data sheets. Values shown are typical/indicative; specify to your applicable standard for guaranteed minimum values. See also: SteelNumber.com — 1.4594 data.
Engineers specifying 1.4594 for a project can request material test reports, dimensional tolerances, and EN10204 3.1 certification directly — see the custom 1.4594 forgings to your specification page for full product details and available forms.
Section 04
Heat Treatment Process for 1.4594 Forgings
Definition: The heat treatment of 1.4594 consists of two steps: (1) solution annealing to dissolve all precipitates and form a homogeneous martensitic structure, and (2) aging at a controlled temperature to precipitate copper-rich intermetallic phases that strengthen the matrix. No quenching is required after aging — simple air cooling is sufficient.
01
Solution Annealing (Austenitizing)
1,020 – 1,070 °C → Water / Oil Quench or Forced Air Cool
The forging is heated to fully dissolve all precipitates and homogenize the alloy into single-phase austenite. Rapid cooling locks this supersaturated state as martensite. In this condition, the steel is at its softest and most machinable — all complex machining and tight-tolerance work is performed here.
02
Inspection & Machining (Optional)
Room Temperature
After solution annealing, components are straightened, dimensionally inspected, and non-destructively tested (UT/MT). Final machining to tight tolerances is performed at this stage before the aging hardens the material. This is a significant advantage over conventional quench-hardened steels.
03
Aging (Precipitation Hardening)
480 – 620 °C × 4–8 hours → Air Cool
Controlled heating drives diffusion and precipitation of nanoscale copper-rich intermetallic phases within the martensitic matrix. These precipitates dramatically impede dislocation movement, increasing hardness and strength. The specific temperature selects the strength/toughness trade-off. Air cooling is sufficient — no quench needed.
✓
Key manufacturing advantage
Because 1.4594 is machined in the soft solution-annealed condition, then aged to final hardness, complex geometries and tight tolerances are achievable without the distortion risk of conventional quench-hardened steels. Dimensional change during aging is minimal — typically <0.05% linear.
Section 05
1.4594 vs. 17-4PH vs. 15-5PH: Complete Comparison
Engineers frequently evaluate 1.4594 against the two most widely specified precipitation-hardening stainless grades. The following comparison highlights where 1.4594 offers clear engineering advantages:
Table 3 — Comparative Properties: 1.4594 (FV520B) vs. 17-4PH (1.4542) vs. 15-5PH (1.4545)
Property
1.4594 / FV520B / UNS S45000
17-4PH / 1.4542
15-5PH / 1.4545
Mo Content
1.2–2.0% Highest
<0.5%
<0.5%
Pitting / Crevice Corrosion Resistance
Very High Best
Moderate
Moderate
Weldability
Excellent — Nb stabilized, no sensitization Best
Good — post-weld HT required for best corrosion resistance
Good
Toughness at High Hardness
Excellent Best
Moderate
Moderate–Good
Peak Hardness
~40 HRC (aged 480 °C) Similar
~44 HRC (H900)
~42 HRC
Machinability (solution-annealed)
Very Good
Very Good
Very Good
Primary Standards
EN 10088-3, AMS5773E, API 6A
ASTM A693, AMS5643
ASTM A693, AMS5862
Typical Industries
Oil & gas, marine, turbines, chemical processing
Aerospace, nuclear, general engineering
Aerospace, defense
← Swipe to scroll →
1.4594 is the only common PH stainless steel that simultaneously delivers superior Mo-driven pitting resistance, Nb-enabled weldability without post-weld annealing, and excellent toughness at high hardness levels — making it uniquely suited to demanding corrosive environments.
Section 06
Forgeability, Machinability and Weldability
Hot Forging of 1.4594
1.4594 is readily hot-forged across a broad temperature window. For open die forging and seamless ring rolling, the workpiece is soaked at 1,150–1,200 °C to ensure full plasticity. The alloy tolerates the high deformation ratios required for large forged rings (up to 6,000 mm diameter) and heavy bars without cracking. Forging is completed above 900 °C to avoid working in the two-phase region, which can introduce microstructural heterogeneity. After forging, solution annealing is applied prior to aging.
At Jiangsu Liangyi, 1.4594 open die forgings and seamless rolled rings are produced in single-piece weights from 30 kg to 30,000 kg, with EN10204 3.1 material certification as standard and 3.2 available via third-party inspection on request.
Machinability
In the solution-annealed condition, 1.4594 machines comparably to other 13–15% Cr martensitic stainless grades and is significantly more productive than austenitic grades (316L, 304). The recommended machining sequence is: forge → solution anneal → rough machine → age → finish machine. Light finishing cuts after aging are straightforward because dimensional change during aging is minimal.
Weldability
The niobium content of 1.4594 is specifically designed to improve weld quality. Nb preferentially combines with carbon to form stable NbC carbides during welding, preventing the formation of chromium carbides at grain boundaries. This eliminates sensitization — the primary cause of intergranular corrosion failure in welded martensitic stainless steels. For most applications, post-weld annealing is not required. A matching-composition (1.4594 / FV520B) filler material should be used when optimum weld metal corrosion resistance is critical.
ⓘ
Weldability vs. conventional martensitic grades
Conventional martensitic stainless steels (e.g., 420, 431) require preheating to ≥200 °C and post-weld heat treatment to avoid cold cracking and sensitization. 1.4594 typically requires neither in moderate service — a significant time and cost saving in fabrication.
Section 07
Industrial Applications of 1.4594 Forgings
The unique combination of high strength, hardness, and corrosion resistance makes 1.4594 / FV520B forgings the specified material across eight major industries:
⚙
Rotating Pump Components
Impellers, shaft sleeves, and wear rings for chemical and marine pumps requiring simultaneous hardness and corrosion resistance.
⛤
Oil & Gas Downhole Tools
Drill collars, mandrels, and valve bodies exposed to H₂S, CO₂, and chloride-bearing brines — compliant with API 6A.
⚡
Power Generation Turbines
Steam turbine blades, impellers, and compressor discs requiring fatigue strength and steam-side corrosion resistance.
🔧
High-Strength Fasteners
Bolts, studs, and nuts for subsea, chemical plant, and marine environments (ASTM A453 compatible).
🏭
Chemical Processing Equipment
Reactor shafts, agitator blades, and vessel internals exposed to acids, chlorides, or oxidizing media.
⚓
Marine & Offshore Structures
Seawater pump shafts, propeller hubs, and structural connectors for offshore platforms and naval vessels.
✈
Aerospace Structural Parts
Forged fittings, brackets, and actuator components — AMS5773E certified for aerospace applications.
🔨
Food & Medical Equipment
High-hardness shafts and wear parts for food processing machinery where corrosion resistance and cleanability are mandated.
Across all of these industries, Jiangsu Liangyi supplies the full range of 1.4594 forged product forms — open die forgings, seamless rolled rings, forged bars, discs, flanges, shafts, and custom-machined components — to 50+ countries worldwide.
Section 08
Applicable Standards and Certifications
Table 4 — International Standards for 1.4594 (X5CrNiMoCuNb14-5) Forgings
Wellhead and Christmas tree equipment material requirements
USA / Oil & Gas
EN10204 3.1
Material test report — manufacturer authorized inspection certificate
Europe / Global
EN10204 3.2
Material test report — countersigned by independent third-party inspector
Critical applications
ASTM A 388
Ultrasonic examination of heavy steel forgings
USA / NDT
EN 10228-3
Ultrasonic testing of steel forgings
Europe / NDT
← Swipe to scroll →
Quality control for 1.4594 forgings produced at Jiangsu Liangyi includes: full raw material traceability (EAF/AOD/ESR melt records), chemical composition verification by OES or ICP, complete mechanical property testing (tensile, hardness, impact as applicable), and non-destructive examination (UT per ASTM A388 or EN 10228-3, MT/PT) per the applicable standard. UT inspection is available for all forged rings on request. EN10204 3.2 certificates can be arranged via independent third-party inspection agencies. For full certification options and ordering information, see the 1.4594 forging products from Jiangsu Liangyi.
Section 09
Frequently Asked Questions about 1.4594 Steel
1.4594 (X5CrNiMoCuNb14-5) is a martensitic precipitation-hardening stainless steel standardized in EN 10088-3. It contains 13–15% Cr, 5–6.5% Ni, 1.2–2% Mo, 1.2–2% Cu, and 0.15–0.6% Nb. After aging heat treatment, it achieves minimum yield strength of 720 MPa, tensile strength 930 MPa, and hardness up to approximately 40 HRC. It is also known as FV520B (UK trade name), UNS S45000, and XM-25.
Yes. FV520B is the British commercial trade name (originally Firth Vickers); UNS S45000 is the Unified Numbering System designation; XM-25 is the ASTM designation; and 1.4594 / X5CrNiMoCuNb14-5 is the European Standard (EN) designation. All refer to nominally the same precipitation-hardening martensitic stainless steel alloy.
Per EN 10088-3, the minimum tensile strength (Rm) of 1.4594 in the aged condition is 930 MPa, with minimum yield strength (Rp0.2) of 720 MPa and minimum elongation (A5) of 15%. At a lower aging temperature of approximately 480 °C, tensile strength can exceed 1,200 MPa with yield strength above 1,050 MPa.
The heat treatment cycle for 1.4594 is: (1) Solution anneal at 1,020–1,070 °C followed by rapid cooling (water, oil, or forced air) to produce a soft martensitic structure. (2) Age at 480–620 °C for 4–8 hours, then air cool. Lower aging temperatures maximize hardness and strength; higher temperatures optimize toughness and ductility. No quench after aging is required.
Yes. 1.4594 can be qualified for sour service per NACE MR0175 / ISO 15156 when aged to produce hardness at or below 36 HRC (typically achieved by aging at 580–620 °C). The material must be heat-treated to the hardness limit specified by the applicable sour service standard for the operating environment.
1.4594 forgings are covered by EN 10088-3 (Europe), AMS5773E (USA aerospace), ASTM A693 (USA general), ASME SA-705 (pressure vessels), and API 6A (oil & gas). Material certificates are issued per EN10204 3.1 (manufacturer) or 3.2 (third-party countersigned). UT inspection follows ASTM A388 or EN 10228-3.
Jiangsu Liangyi Co., Limited produces 1.4594 open die forgings and seamless rolled rings from a minimum of 30 kg to a maximum of 30,000 kg per single piece, with ring diameters up to 6,000 mm. EN10204 3.1 material certificates are standard; 3.2 is available via third-party inspection on request. Contact us at sales@jnmtforgedparts.com with your drawing and quantity for a detailed quotation.
Source Custom 1.4594 Forgings from a Certified Manufacturer
Jiangsu Liangyi Co., Limited (Liangyi Forging) — established 1997 — is an ISO 9001:2015 certified manufacturer of 1.4594 / X5CrNiMoCuNb14-5 open die forgings, seamless rolled rings, forged bars, and custom-machined components, exported to 50+ countries across Europe, North America, the Middle East, and Southeast Asia.
Single-piece weight: 30 kg – 30,000 kg
Ring diameters: up to 6,000 mm
Products comply with AMS5773E, EN10088-3, ASTM, API 6A & ASME
Material certs: EN10204 3.1 standard; 3.2 available via third-party inspection on request