1.8550 (34CrAlNi7-10) Forging Parts | Jiangsu China Manufacturer

What Is 1.8550 (34CrAlNi7-10) Nitriding Alloy Steel — And Why It Matters for Your Application

Jiangsu Liangyi Co.,Limited, founded in 1997 and headquartered in Jiangyin City, Jiangsu Province, China, is an ISO 9001:2015 certified specialist manufacturer of 1.8550 (34CrAlNi7-10) open die forging parts and seamless rolled rings. Our 80,000 m² integrated facility and 120,000-ton annual production capacity allow us to deliver precisely engineered forgings to heavy industry clients across more than 50 countries — from a single prototype piece to multi-ton serial production runs.

The designation 1.8550 is the EN material number defined under DIN EN 10085 (Nitriding Steels — Technical Delivery Conditions). The short name 34CrAlNi7-10 directly encodes its alloy architecture: approximately 0.34% Carbon for core strength, Chromium and Aluminum as the primary nitride-forming elements, and Nickel for toughness in large cross-sections. You may also encounter this material referenced as 34CrAlNi710, 34CrAlNi7.10, or by its closest international equivalents — BS 970 905M39 (United Kingdom), GOST 38KhN3MA (Russia), and the Japanese SACM645 — though chemical compositions differ slightly between standards and substitution always requires engineering sign-off.

What sets 1.8550 apart from simpler nitriding grades such as 31CrMoV9 (1.8519) or 34CrAlMo5-10 (1.8507) is its triple-alloying strategy. The 0.80–1.20% Aluminum content is the highest of any mainstream nitriding steel and directly controls the density and stability of the AlN (aluminum nitride) compound layer formed during gas nitriding. The Chromium additions (1.50–1.80%) create CrN precipitates that reinforce the diffusion zone beneath the compound layer, dramatically improving fatigue strength. Meanwhile, the 0.85–1.15% Nickel content — a feature absent from grades like 34CrAlMo5-10 — maintains core toughness and prevents brittle fracture in large-diameter forgings where through-hardening is challenging. Molybdenum (0.15–0.25%) further stabilizes the tempered martensite matrix and resists softening during the long nitriding cycles at 480–570 °C.

For procurement and design engineers evaluating nitriding steel options: after precision gas nitriding, 34CrAlNi7-10 achieves a compound layer surface hardness of HV 950–1100 — substantially harder than 31CrMoV9 (typically HV 700–850) — while retaining a tough, high-strength core at 900–1100 MPa tensile strength. This combination makes it the industry benchmark for gear shafts, pinion shafts, and transmission components that must simultaneously carry high bending and contact fatigue loads over multi-year service lives.

Critically, forging — not casting — is the correct manufacturing route for 1.8550 components. The deformation work imparted by open die forging refines the as-cast dendritic structure, eliminates internal porosity, closes shrinkage defects, and aligns grain flow to the component geometry. For large shafts and rings, this translates into measurably superior impact toughness and fatigue strength versus equivalent cast components, and it is why DIN EN 10085 forgings are specified in demanding applications such as wind turbine gearboxes, cement kiln drives, and offshore drilling equipment.

1.8550 (34CrAlNi7-10) International Equivalent Grades & Grade Selection Guidance

When sourcing 34CrAlNi7-10 forgings from our Jiangsu factory for international projects, understanding equivalent grades across standards helps avoid specification mismatches. "Equivalent" does not mean "identical"; always check chemical composition against your project specification before confirming substitution.

International Equivalent Grade Comparison

1.8550 vs. 31CrMoV9: Which Nitriding Steel Should You Choose?

31CrMoV9 (1.8519) contains no Aluminum. It relies on Chromium and Molybdenum nitrides for surface hardening, achieving typical nitrided hardness of HV 700–850. It is easier to machine before nitriding, has shorter nitriding cycles, and is generally the economical first choice for moderate surface hardness requirements — small gears, hydraulic cylinder rods, and precision spindles in light machinery.

34CrAlNi7-10 (1.8550) is the correct choice when the application demands: (a) nitrided surface hardness above HV 900; (b) a component cross-section larger than ~200 mm where core toughness must be maintained; (c) operating temperatures that briefly exceed 300 °C (the AlN compound layer is more thermally stable than CrN-only layers); or (d) applications subject to combined bending, torsion, and contact fatigue — the typical loading profile of a large gear shaft or pinion shaft. The trade-offs are longer gas nitriding cycles (40–100+ hours depending on layer depth), higher raw material cost, and more demanding machining of the harder pre-nitriding substrate.

Custom 1.8550 (34CrAlNi7-10) Forged Steel Products — Full Range & Dimensional Capabilities

We manufacture the complete spectrum of 34CrAlNi7-10 forging products, from raw open die forgings rough-machined to drawing allowance through to fully finished, heat-treated, inspected, and certified components ready for assembly. Our integrated in-house capabilities — melting, forging, heat treatment, machining, and inspection — eliminate subcontractor dependencies and give you a single point of quality accountability. Single-piece weight range: 30 kg to 30,000 kg.

1.8550 Forged Bars & Rods

Open die forged bars in 34CrAlNi7-10 are produced from vacuum-degassed or ESR ingots, ensuring low hydrogen content and clean inclusion ratings. We supply round bars from Ø80 mm to Ø1,200 mm, square bars up to 800 × 800 mm, flat bars up to 1,000 mm width, and hollow (tube) forgings for thick-walled cylinder applications. Single-piece lengths up to 6,000 mm are routinely produced. Straightness tolerance is controlled to ≤ 3 mm/m before any machining, and surface condition can be supplied as-forged, shot-blasted, or rough-turned.

1.8550 Forged Shafts & Stepped Shafts

Forged shafts represent our highest-volume 1.8550 product category. We manufacture solid stepped shafts up to 12,000 mm in length, with individual step diameters from Ø80 mm to Ø1,500 mm. The open die forging process allows us to forge close to the final profile, reducing raw material waste versus bar stock machining by 15–30% on large shafts. All shafts are forged with controlled reductions to achieve a minimum forging ratio of 4:1 along the principal axis — a specification that ensures full elimination of as-cast dendritic structure and documented grain refinement. Products include: gear shafts, pinion shafts, step shafts, crankshafts, eccentric shafts, mill spindles, roller shafts, and transmission shafts. Finish machining to IT7–IT9 dimensional tolerance and Ra 1.6–3.2 µm surface finish is available in-house.

34CrAlNi7-10 Seamless Rolled Rings

Seamless rolled rings offer significant advantages for annular components: the unbroken circumferential grain flow eliminates stress concentration points inherent in welded or flame-cut rings, and material yield is far superior to machining a ring from a disc. Our ring rolling mills (1M and 5M radial-axial) produce 34CrAlNi7-10 seamless rings from Ø300 mm to Ø5,000 mm outer diameter, with heights from 50 mm up to 1,500 mm and wall thicknesses from 30 mm upward. Products include: gear rings, slewing bearing outer and inner races, riding rings for rotary kilns and dryers, coupling rings, and contoured (profiled) rings rolled to near-net shape to minimize finish machining. Ring roundness after rolling is controlled to ≤ 1.5 mm total indicator runout before heat treatment.

Custom Open Die Forged Components

Complex forged shapes — including hubs, flanges, housings, discs, sleeves, bushes, cylinders, and gear blanks — are produced against client drawings or 3D models. Our engineering team performs forgeability analysis and die design in-house, and we can produce prototype forgings within 15 working days of drawing approval. For components requiring precision bore finishing, external turning, keyway milling, or thread cutting, our integrated machining center provides one-stop processing. We also offer reverse engineering support for worn or discontinued components where only a physical sample is available.

Industry Applications of 34CrAlNi7-10 Forgings — Verified Project Cases from Our Jiangsu Factory

The following industry applications and project cases are representative examples drawn from our production experience. Specific client names and project details are kept confidential per non-disclosure agreements. Full mill test certificates (EN 10204 3.1) are issued as standard for all orders; EN 10204 3.2 third-party inspection records are available where specified by the client at order placement.

Cement & Bulk Material Processing Industry

Cement plant drives are among the most demanding applications for nitriding steel forgings. Rotary kiln pinion shafts rotate continuously at 1–5 rpm under heavy radial and thrust loads, in an environment of airborne cement dust and fluctuating thermal input. The combination of abrasive surface conditions and cyclic bending fatigue makes a high-hardness nitrided surface on a tough forged core the industry-standard material choice. Sugar mill roller shafts face similar demands: high torque, shock loads during cane feeding, and humid, corrosive process environments where the nitrided AlN compound layer provides meaningful corrosion resistance advantage over uncoated alloy steels.

• 34CrAlNi7-10 forged pinion shafts and bull gear shafts for cement rotary kilns (2,000 t/d – 12,000 t/d capacity lines)
• 1.8550 forged roller shafts, coupling flanges, and pull torque rods for sugar mill three-roller sets
• 34CrAlNi7-10 forged riding rings (tyre rings) and riding gear rings for granulators, drum dryers, and rotary coolers
• 1.8550 forged trunnion shafts for ball mills and rod mills in cement grinding circuits

Wind Power & Renewable Energy Industry

Wind turbine gearboxes must transmit variable, unpredictable torque from the rotor through three or more gear stages, operating for 20+ years with limited access for maintenance on offshore installations. IEC 61400-4 specifies that gear shafts and planet carrier pins must maintain fatigue strength and dimensional integrity across the full load spectrum. The tooth root bending fatigue strength of a gas-nitrided 34CrAlNi7-10 gear (σ_Flim ≈ 450–500 MPa per ISO 6336 Method B) comfortably exceeds the capability of through-hardened 42CrMo4 (σ_Flim ≈ 280 MPa) in applications where case-hardened and ground gearing is not specified.

• 1.8550 forged planetary gear shafts, sun shafts, and planet carrier pins for multi-MW wind turbine gearboxes
• 34CrAlNi7-10 forged ring gears and internal gear rings for epicyclic gear stages
• 1.8550 forged high-speed shaft couplings and shrink disc flanges for turbine-to-generator connections

Mining & Mineral Processing Industry

Primary crushing equipment subjects eccentric shafts and main shafts to some of the highest impact energy levels encountered in any rotating machinery application. The shock load when oversized feed contacts the crushing surfaces can generate instantaneous contact forces many times the rated working load. The Nickel content in 34CrAlNi7-10 is specifically valuable here — it maintains core Charpy impact energy (≥ 30 J at 20 °C per EN 10085) that would be sacrificed in equivalent aluminum-only nitriding steels processed to similar core hardness.

• 1.8550 forged eccentric shafts and main shafts for gyratory crushers (1,100 mm to 1,525 mm head diameter range)
• 34CrAlNi7-10 forged spindles and pulley wheels for jaw crushers and impact crushers
• 1.8550 forged slewing bearing inner and outer races for mining excavators and surface miners
• 34CrAlNi7-10 forged head shafts, tail shafts, and drive pulleys for mine conveyor systems
• 1.8550 forged headframe sheave shafts and hoisting drum shafts for mine shaft hoisting systems

Oil & Gas Drilling & Production Equipment

Mud pump power end components — crankshafts, pinion shafts, and bull gear shafts — operate under demanding conditions: high cyclic loading from reciprocating piston action, drilling fluid contamination, and the need for dimensional stability across a wide temperature range. API 7K and API 11E govern material and inspection requirements. The ESR process, which we offer for oil and gas applications, eliminates segregation-related inclusions that act as fatigue crack initiation sites, and the resulting homogeneous mechanical properties are critical for large-diameter crankshafts where stress concentrations at fillet radii must be carefully managed.

• 34CrAlNi7-10 forged crankshafts and crosshead pins for triplex and quintuplex drilling mud pumps (API 7K)
• 1.8550 forged herringbone and helical gear shafts for mud pump power ends
• 34CrAlNi7-10 forged wellhead equipment components — valve bodies, stem guides, and actuator shafts
• 1.8550 forged components for subsea production equipment and anchor winch drive systems

General Machinery, Power Transmission & Hydraulic Industry

Beyond the heavy primary industries, 34CrAlNi7-10 forgings are the material of choice wherever the engineer needs to combine a hard, wear-resistant surface with a fatigue-resistant core without the distortion risk of through-hardening. Gas compressor crankshafts, industrial gearbox pinion shafts, and hydraulic press eccentric shafts all benefit from the dimensional stability of the nitriding process — temperature below the tempering point means essentially zero distortion after nitriding, eliminating the costly straightening and final grinding operations that follow induction hardening or case carburizing.

• 34CrAlNi7-10 forged pinion shafts and ring gears for large industrial gearboxes and speed reducers (center distance up to 2,000 mm)
• 1.8550 forged crankshafts for large reciprocating gas compressors (API 618) and mechanical presses
• 34CrAlNi7-10 forged hydraulic cylinder barrels, tie rods, and piston rods for high-pressure hydraulic systems (up to 350 bar)
• 1.8550 forged components for flue gas desulfurization (FGD) absorber agitator shafts
• 34CrAlNi7-10 forged gear couplings, drum couplings, and flywheel hubs for large drive trains

Why Source 1.8550 (34CrAlNi7-10) Forgings from Jiangsu Liangyi — Our Technical Differentiation

Many forging manufacturers in China can supply 34CrAlNi7-10 material in basic shapes. What distinguishes Jiangsu Liangyi is integrated process control from steelmaking through final inspection — under a single ISO 9001:2015 certified quality management system, with no subcontracting of critical processes.

1. Steelmaking Traceability: From Ladle to Forging

We operate our own melting facility on site: a 30t EAF, 30t LF, 30t VOD, and a 32t ESR/PESR plant. This means we control the full steel chemistry from charge calculation through to ladle analysis. For 1.8550, the Aluminum content specification (0.80–1.20%) is the most technically sensitive element to control — Aluminum is highly reactive and its burn-off rate during tapping and ladle treatment must be compensated precisely to hit the target. Our in-house melt chemistry control, verified by optical emission spectrometer (OES) immediately after tapping and before pouring, gives us the data to guarantee compliance rather than infer it from a supplier's certificate.

2. Forging Ratio Documentation and Grain Flow Verification

Every production order for 1.8550 forgings is accompanied by a forging log documenting the sequence of reductions, starting ingot dimensions, intermediate dimensions after each pass, and calculated forging ratios at every cross-section of the finished forging. This is not standard practice in the broader Chinese forging industry, but it is our standard for all nitriding steel orders. For clients whose specifications mandate minimum forging ratios (e.g., ≥ 4:1 per ASTM A668, or ≥ 5:1 per their proprietary procedure), we provide this documentation as part of the standard quality dossier.

3. In-House Heat Treatment with Full Atmosphere Control

Our semi-automatic heat treatment system includes furnaces up to 18 m in length for shaft-type components and a quench tank 16 m deep for full immersion of large-diameter parts. All heat treatment cycles are recorded by multi-point thermocouples with tamper-proof data logging, and the records are included in the shipment documentation package. For the gas nitriding step, we operate a controlled-atmosphere nitriding system with Kn (nitriding potential) monitoring throughout the cycle — not simply a time-temperature recipe — allowing us to tailor the compound layer composition (ratio of γ' to ε phase) to the client's specifications.

4. Comprehensive NDT: We Inspect What Others Skip

Our standard inspection scope for 1.8550 forgings includes: (a) ultrasonic testing (UT) per EN 10228-3 or ASTM A388, (b) magnetic particle testing (MT) per EN 10228-1 or ASTM A275, (c) dimensional inspection with calibrated instruments for machined components, and (d) hardness survey across multiple test positions on the cross-section — not just the test coupon. For ESR or VIM+PESR steel orders, we additionally perform inclusion rating per ASTM E45 on the test coupon. This full inspection scope is included in our standard pricing — because we believe clients should not have to pay extra to receive product that is verified to be what it claims to be.

5. Responsive Technical Support and On-Time Delivery

We maintain an English-speaking technical team capable of reviewing client drawings, providing material equivalence opinions, and issuing formal Inspection Test Plans (ITPs) within 3 working days of receiving complete inquiry documentation. Our 25+ years of production history for nitriding steel forgings means our production scheduling team understands the time constraints of every process step — including the long lead times inherent in ESR steel production and 60–100 hour nitriding cycles — and can provide realistic, committed delivery dates. Our historical on-time delivery performance for confirmed orders consistently exceeds 95%.

1.8550 (34CrAlNi7-10) Forging Production Process — Step by Step

Understanding our production process helps procurement engineers and quality engineers write better specifications and ask the right questions during supplier qualification. The following describes our standard process flow for a 1.8550 nitriding steel forging order.

Step 1: Steel Melting — Choosing the Right Route for Your Application

The steel melting route is the single most important decision affecting final forging cleanliness and homogeneity. We offer five routes, selected based on application criticality and budget:

1. EAF (Electric Arc Furnace only) — Suitable only for non-critical general machinery applications with no fatigue or impact requirements. Not recommended for 1.8550 nitriding applications where surface fatigue performance matters.
2. EAF + LF + VD (Ladle Refining + Vacuum Degassing) — Standard route for most 34CrAlNi7-10 forgings. Vacuum degassing removes dissolved hydrogen to ≤ 2 ppm (prevents hydrogen flaking in large sections) and reduces oxygen content. Sulfur is desulfurized to ≤ 0.005% in the ladle. Meets requirements of the vast majority of industrial applications including cement, mining, and general machinery.
3. EAF + ESR (Electroslag Remelting) — The ESR process remelts the steel through a chemically active flux, reducing non-metallic inclusions by 60–80% compared to VD-only steel and producing a more homogeneous ingot. Recommended for wind power, oil & gas, and high-cycle fatigue applications.
4. EAF + PESR (Protective Atmosphere ESR) — ESR conducted under a protective gas atmosphere (argon or nitrogen) to prevent Aluminum oxidation during remelting. Essential for 1.8550 because of its high Aluminum content — standard ESR without atmosphere protection causes Aluminum burn-off and loss of nitriding response. This is the correct specification for premium 34CrAlNi7-10 ESR steel.
5. VIM + PESR (Vacuum Induction Melting + Protective Atmosphere ESR) — The highest cleanliness specification available. VIM melts the charge under vacuum, achieving extremely low oxygen, hydrogen, and nitrogen contents before the PESR step further refines inclusion content. Used for the most demanding applications including offshore oil & gas, heavy wind power, and any application where fatigue life calculations demand the cleanest possible steel.

Step 2: Ingot Casting and Homogenizing Soak

The refined steel is cast into ingots of the desired forging weight with adequate allowance for cropping of the riser and bottom-end segregation zones. The high content of aluminum for 1.8550 requires an inert atmosphere for pouring, to avoid surface oxidation and formation of alumina inclusions. After casting, all ingots are soaked in a homogenizing furnace at 1,200–1,250 °C for a minimum of 1 hour per 25 mm of ingot radius to eliminate chemical segregation before forging.

Step 3: Open Die Forging on 2000T / 4000T / 6300T Hydraulic Presses

Our 6300T (62 MN) open die hydraulic press handles single ingots up to 30,000 kg and is capable of producing shaft forgings up to 12,000 mm in length in a single heat. The forging temperature of 34CrAlNi7-10 is usually 1,150 °C start / 850 °C finish. The forging schedule is designed to achieve the highest amount of work below the recrystallization temperature on the final passes to introduce sub-grain refinement in the surface layers. We have a 60t capacity manipulator on our press to handle large ingots safely and accurately. Seamless ring rolling is performed on our 1M (rings up to Ø2,000 mm) and 5M (rings up to Ø5,000 mm) radial-axial rolling mills after initial upset and punch on the press.

Step 4: Post-Forging Cooling, Hydrogen Diffusion Anneal, and Softening Anneal

Immediately after forging, 1.8550 components are placed into a pre-heated furnace for controlled slow cooling to prevent thermal shock cracking and to begin hydrogen degassing. For large cross-sections (Ø > 500 mm), a dedicated hydrogen diffusion anneal at 650–700 °C for a minimum of 24 hours is applied before the softening anneal, ensuring hydrogen content in the bulk material is reduced to below 1.5 ppm before the first machining passes — a critical step often overlooked by less experienced forging suppliers.

Step 5: Rough Machining and Pre-Heat-Treatment Ultrasonic Testing

After annealing and before final heat treatment, all forgings are rough machined to leave a minimum of 5 mm machining allowance per side on all critical surfaces. This removes any surface decarburization layer from forging and allows 100% volumetric UT inspection of the forging body in the annealed condition, where attenuation is lowest and defect detectability is highest. Any forging with UT indications exceeding the acceptance criteria is rejected before heat treatment — not after, which would waste all subsequent processing cost.

Step 6: Quench and Temper Heat Treatment

The final heat treatment consists of austenitizing at 870–930 °C (held for a minimum of 30 minutes after thermocouple confirmation of temperature uniformity throughout the cross-section), followed by quenching in oil or polymer solution and tempering at 580–700 °C for a minimum of 2 hours per 25 mm of effective cross-section thickness. Our 16 m deep quench tank allows full vertical immersion of the longest shafts, ensuring symmetrical quench severity and minimizing distortion from asymmetric cooling. Tempered hardness and mechanical properties are verified by Brinell hardness testing at a minimum of 3 positions on each forging, and by destructive testing on integral test coupons forged with each piece.

Step 7: Precision Gas Nitriding (Where Specified)

Gas nitriding of 34CrAlNi7-10 is performed in our controlled-atmosphere pit furnaces at a precisely maintained nitriding potential (Kn) of 0.3–1.0 atm, at 510–540 °C, for cycle durations of 40–120 hours depending on the specified layer depth. We use a two-stage process (high Kn stage to develop the compound layer, low Kn stage to deepen the diffusion zone while minimizing white layer brittleness) and monitor Kn by in-situ oxygen probe measurement — not simply by NH₃/H₂ gas flow ratio, which is less accurate. Surface hardness after nitriding is verified by Vickers hardness testing on a cross-section coupon to confirm compound layer thickness (≤ 15 µm white layer target for most gear applications) and diffusion zone profile (typically 0.4–0.8 mm depth).

Step 8: Final Inspection and Quality Documentation Package

Every shipment is accompanied by a complete quality documentation package including: EN 10204 3.1 mill test certificate (or 3.2 with third-party countersignature where specified), dimensional inspection report, UT/MT/PT inspection reports with qualified operator certifications, hardness survey results, heat treatment records with thermograph traces, nitriding process records with Kn monitoring logs (where applicable), and full packaging/shipping documentation. Third-party inspection by SGS, Bureau Veritas, TUV Rheinland, or Lloyd's Register can be arranged at the client's request.

34CrAlNi7-10 (1.8550) Full Material Specifications — Chemistry, Heat Treatment & Mechanical Properties

All 1.8550 steel supplied by our Jiangsu factory is produced and tested in compliance with DIN EN 10085:2001 (Nitriding Steels — Technical Delivery Conditions). The chemical composition ranges below are the standard limits; tighter "restricted" composition windows can be specified on the purchase order for special applications.

Chemical Composition — Mass Fraction (%) per DIN EN 10085

Standard Heat Treatment Procedure — Detailed Parameters

Mechanical Properties After Quenching & Tempering — Standard vs. Typical Achieved

Note on large-section size effects: DIN EN 10085 mechanical properties are measured on test bars of Ø ≤ 40 mm taken from the test coupon, which shows higher values than the bulk forging cross-section due to the faster quench rate of the small test bar. For large diameter forgings (Ø > 300 mm), expect core tensile strength in the range of 900–980 MPa and Charpy values of 35–55 J depending on tempering temperature, section size, and steel cleanliness. Our engineers can provide section-size correction estimates for specific component geometries on request.

Frequently Asked Questions About 1.8550 (34CrAlNi7-10) Forgings

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