Chemical composition, mechanical properties, heat treatment, nitriding process, international equivalents (38CrMoAl / SACM 645 / 905M39), and industrial forging applications — all in one reference.
34CrAlMo5-10 (EN material number 1.8507) is a chromium-aluminum-molybdenum nitriding alloy steel standardized under DIN EN 10085:2001. It contains 0.30–0.37% carbon, 1.30–1.60% chromium, 0.70–1.10% aluminum, and 0.15–0.25% molybdenum. The aluminum content reacts with nitrogen during gas nitriding at 500–520 °C to form a dense aluminum nitride (AlN) compound layer, delivering surface hardness values exceeding 900 HV while the quenched-and-tempered core retains tensile strength of 900–1100 MPa and Charpy impact energy of at least 35 J. International equivalents include 38CrMoAl (China), SACM 645 (Japan), and 905M39 (UK).
34CrAlMo5-10, material number 1.8507 under the European EN system, is a chromium-aluminum-molybdenum nitriding alloy steel standardized in DIN EN 10085:2001 (Nitriding Steels — Technical Delivery Conditions). It is one of the most widely specified nitriding grades in heavy industrial engineering: selected for components that must carry a high-hardness, wear-resistant surface while maintaining a tough, load-bearing core.
The defining characteristic of 1.8507 is its aluminum content (0.70–1.10%). During gas nitriding, aluminum reacts with diffusing nitrogen to form a dense aluminum nitride (AlN) compound layer at the steel surface. This layer, combined with chromium nitride (CrN) precipitates in the diffusion zone beneath, delivers surface hardness values that routinely exceed 900 HV — without the dimensional distortion risk associated with conventional case hardening, because nitriding takes place below the steel's transformation temperature.
Nitriding with 1.8507 is performed after final machining at 500–520 °C. Because no quenching step follows nitriding, components experience minimal distortion — making this the preferred route for precision shafts, spindles, and gear components where tight tolerances must be maintained to the finished state.
In forged form, 34CrAlMo5-10 combines the fiber-flow integrity and freedom from internal porosity that only solid-state hot working can deliver. Jiangsu Liangyi Co., Limited supplies custom 1.8507 open-die forgings and seamless rolled rings, from 30 kg prototype pieces to 30,000 kg production components, with full EN 10204 3.1 material certification as standard.
The European EN steel naming system encodes alloy chemistry directly into the grade designation. Understanding each token lets engineers read a material specification without referring to a lookup table.
| Token | Meaning | Value in 1.8507 |
|---|---|---|
| 34 | Carbon content × 100 (nominal wt%) | ~0.30–0.37% C |
| Cr | Chromium — primary nitride-forming element | 1.30–1.60% Cr |
| Al | Aluminum — controls AlN compound layer density and hardness | 0.70–1.10% Al |
| Mo | Molybdenum — matrix stabilizer, prevents softening during nitriding | 0.15–0.25% Mo |
| 5 | Cr content × 4 (encodes the Cr band) | ~1.25–1.60% Cr |
| 10 | Mo content × 10 (encodes the Mo band) | ~0.15–0.25% Mo |
The material number 1.8507: prefix 1. = steel; 8 = nitriding steel class; 507 = sequential identifier. In international sourcing you may encounter this written as 34CrAlMo510, 34CrAlMo5.10, or referenced under a national standard equivalent (see Section 7).
All values are weight percentages (wt%). For large cross-section forgings, premium heats are produced to tighter internal limits than the standard requires, with reduced sulfur, phosphorus, and total oxygen content achieved through vacuum degassing (VD).
| Element | Min (%) | Max (%) | Primary Role in Steel |
|---|---|---|---|
| C — Carbon | 0.30 | 0.37 | Core martensite strength after quench and temper |
| Si — Silicon | 0.10 | 0.40 | Deoxidizer; mild solid-solution strengthener |
| Mn — Manganese | 0.40 | 0.70 | Hardenability; grain refinement after forging |
| P — Phosphorus | — | 0.025 max | Impurity; grain boundary embrittlement risk if elevated |
| S — Sulfur | — | 0.015 max | Impurity; toughness vs. machinability trade-off |
| Cr — Chromium | 1.30 | 1.60 | CrN precipitates in diffusion zone; hardenability |
| Al — Aluminum | 0.70 | 1.10 | AlN compound layer — the primary surface hardening mechanism |
| Mo — Molybdenum | 0.15 | 0.25 | Temper resistance; prevents softening during 500 °C nitriding cycles |
Aluminum above 1.10% increases core brittleness and creates forging difficulties by lowering the solidus temperature. Below 0.70%, the AlN compound layer becomes insufficiently dense and surface hardness targets may not be achieved. Always verify Al content in the incoming mill certificate before production commences.
Mechanical properties are specified and tested in the quenched and tempered (Q+T) condition prior to nitriding. After nitriding, core properties remain essentially unchanged because the nitriding temperature (500–520 °C) is below the tempering temperature used to establish them.
| Property | Condition | Typical Value | Test Standard |
|---|---|---|---|
| Tensile Strength (Rm) | Q+T before nitriding | 900–1100 MPa | ISO 6892-1 |
| Yield Strength (Rp0.2) | Q+T | ≥ 750 MPa | ISO 6892-1 |
| Elongation (A5) | Q+T | ≥ 12% | ISO 6892-1 |
| Reduction of Area (Z) | Q+T | ≥ 45% | ISO 6892-1 |
| Charpy Impact (KV) | Q+T, room temp. | ≥ 35 J | ISO 148-1 |
| Core Hardness | Q+T | 26–34 HRC (255–320 HB) | ISO 6506 |
| Surface Hardness | After gas nitriding | ≥ 900 HV0.3 | ISO 6507 |
| Compound Layer Depth | After gas nitriding | 5–20 μm (white layer) | Metallographic section |
| Total Case Depth | After gas nitriding | 0.10–0.60 mm | Hardness traverse |
Hot-work at 1050–1200 °C with controlled cooling. Forging ratio ≥ 3:1 ensures complete breakdown of the cast dendritic structure and closure of internal voids throughout the cross-section.
Hold at 710–750 °C, furnace-cool at < 30 °C/h to achieve hardness ≤ 229 HB. Improves machinability for rough stock removal and relieves forging stresses.
Austenitize at 870–920 °C with full soak time. Oil or polymer quench to produce a martensitic microstructure and maximum hardness as the baseline for tempering.
Temper at 600–650 °C for a minimum of 2 hours per 25 mm of cross-section. The tempering temperature must always exceed the nitriding temperature by at least 30–50 °C — a constraint unique to aluminum-bearing nitriding steels.
Machine to near-final dimensions, leaving 0.1–0.3 mm stock per surface for post-nitriding correction if required.
Nitride at 500–520 °C in a controlled ammonia atmosphere for 20–100 hours. Dimensional change is typically < 0.05 mm per surface.
Standard practice: temper at 600–650 °C; nitride at 500–520 °C. If this margin is violated, the core softens during the nitriding cycle and Q+T mechanical properties will not be present in the finished component.
Nitriding is a thermochemical surface-hardening process in which atomic nitrogen diffuses into steel from a nitrogen-rich atmosphere at sub-transformation temperatures. For 34CrAlMo5-10, the dual reaction of nitrogen with aluminum (forming AlN) and with chromium (forming CrN) produces surface hardness values unachievable with non-Al-bearing grades at the same process temperature.
Components are placed in a sealed furnace and exposed to a dissociated ammonia (NH₃) atmosphere at 500–520 °C for 20–100 hours. Ammonia decomposes at the steel surface, releasing atomic nitrogen which diffuses inward. The resulting compound layer (white layer, 5–20 μm) consists of ε-phase (Fe₂₋₃N) and γ'-phase (Fe₄N) iron nitrides reinforced by AlN precipitates. The diffusion zone beneath (up to 0.6 mm) contains coherent CrN precipitates that contribute additional fatigue strength improvement of 20–30% versus un-nitrided material.
| Parameter | Typical Range for 34CrAlMo5-10 | Notes |
|---|---|---|
| Process Temperature | 500–520 °C | Must be ≥ 30 °C below prior tempering temperature |
| Atmosphere | NH₃ / N₂ or NH₃ cracked | Nitriding potential (Kn) controlled throughout cycle |
| Cycle Duration | 20–100 hours | Longer cycle for greater case depth |
| Compound Layer | 5–20 μm (white layer) | ε + γ' phases; often removed by honing for sealing surfaces |
| Total Case Depth | 0.10–0.60 mm | Measured by hardness traverse to 550 HV cutoff |
| Surface Hardness | 900–1100 HV0.3 | Highest of standard EN nitriding grades (excl. 1.8550) |
| Dimensional Change | < 0.05 mm per surface | Predictable; compensated in machining allowance |
Plasma nitriding uses a glow-discharge plasma at approximately 470–500 °C — slightly lower than gas nitriding. This offers tighter compound layer control, easier masking of non-nitrided areas, and cycle time reduction of 25–40%. It is better suited to moderate-sized precision components in batch quantities than to large open-die forgings.
Salt bath nitrocarburizing operates at 560–590 °C, which can approach or exceed the tempering temperature for standard Q+T 34CrAlMo5-10 material, risking core softening. For precision components where Q+T core properties are part of the design basis, gas or plasma nitriding is the engineering-correct choice.
34CrAlMo5-10 (1.8507) is recognized under multiple national standards with slightly varying composition limits. Always verify composition against the applicable project standard — no two grades are chemically identical.
| Standard | Country / Region | Designation | Key Difference vs. 1.8507 |
|---|---|---|---|
| DIN EN 10085 | Europe (EN) | 34CrAlMo5-10 / 1.8507 | Reference grade |
| GB/T 3077 | China | 38CrMoAl / 38CrMoAlA | Slightly higher C (0.35–0.42%); broader Al range; widely used in Chinese industry |
| JIS G4052 | Japan | SACM 645 | Very close composition; standard for Japanese automotive and precision machinery |
| BS 970 Part 3 | United Kingdom | 905M39 | C 0.35–0.43%; still referenced in older UK specifications |
| GOST 4543 | Russia / CIS | 38Kh2MUA / 38Х2МЮА | Higher Cr (1.35–1.65%); slightly different Al window |
| AFNOR | France | 40CAD6-12 | French legacy grade; used in French aerospace and defense specifications |
| UNI | Italy | 40CrAlMo6-12 | Legacy Italian designation; composition essentially equivalent |
| SS 14 | Sweden | SS 2940 | Similar composition range |
| CSN | Czech / Slovak | CSN 15340 | Widely used in legacy Central European industrial equipment |
Three EN nitriding grades dominate industrial forging applications. Understanding their differences prevents over-specification or under-specification.
For components under approximately 150–200 mm, 34CrAlMo5-10 delivers adequate core toughness at lower material cost. For cross-sections above 300 mm, evaluate 34CrAlNi7-10 (1.8550) to ensure adequate Charpy impact energy at the center of the section.
The combination of a wear-resistant nitrided surface and a tough, load-bearing core makes 34CrAlMo5-10 the correct material for components where surface-dominated failure modes — pitting, scuffing, abrasive wear — coexist with bulk stress-carrying requirements.
Nitrided 34CrAlMo5-10 gear shafts satisfy ISO 6336-5 quality class MQ for industrial gearboxes in wind energy, mining conveyors, cement mills, and marine propulsion. Gear geometry is preserved to within 0.01–0.05 mm of the pre-nitriding form.
Screw barrels for plastic extrusion and injection molding are one of the highest-volume global applications. The nitrided bore resists abrasion from glass-fiber-filled polymer melts, significantly extending service intervals versus un-nitrided alloy steel.
CNC machining center spindles and lead screws require dimensional stability and long wear life at bearing seats. The low-distortion character of gas nitriding below 520 °C allows components to be nitrided after grinding with minimal post-nitriding correction.
Forged 34CrAlMo5-10 cylinder rods benefit from the nitrided surface's resistance to fretting wear against seals, and from compressive residual stress introduced by nitriding, which improves fatigue life under cyclic bending loads.
Gas-nitrided 1.8507 crankshafts in heavy-duty diesel engines deliver wear-resistant journal surfaces with fatigue strength improvements of 20–30% versus un-nitrided equivalents, compatible with full crankshaft geometry including fillet radii.
Aerospace structural components in 34CrAlMo5-10 (or its equivalent SACM 645 / 905M39) include actuator shafts, hinge pins, and precision bushings where wear resistance and fatigue performance under cyclic aerodynamic loading are primary design criteria.
In cone crusher main shafts and ball mill trunnion spindles, a tough forged core combined with a hard nitrided surface provides resistance to both bulk bending loads and abrasive wear from mineral particles at bearing interfaces.
34CrAlMo5-10 forgings are used in valve stems and centrifugal pump shafts where wear from sand-laden fluids reduces component life. Note: confirm hardness complies with NACE MR0175 limits before specifying in H₂S sour service environments.
34CrAlMo5-10 is produced by open-die forging and seamless ring rolling within standard practice for medium-alloy engineering steels. Its aluminum content requires attention to heating and post-forging cooling to avoid defects that can compromise nitriding response or ultrasonic test acceptance.
Work within the recommended hot-working range, finishing above 950 °C to avoid the two-phase (ferrite + austenite) region. Billets should be charged below 600 °C and heated at a controlled rate — especially for cross-sections above 300 mm — to avoid thermal gradients that can initiate cracking. Soaking time at forging temperature must ensure full temperature equalization throughout the section.
Apply the minimum reduction ratio across the full cross-section to ensure complete breakdown of the cast ingot structure, closure of any central porosity, and development of a wrought fiber-flow pattern. This is the key metallurgical reason why open-die forged 34CrAlMo5-10 components outperform bar-stock machined alternatives in fatigue and toughness tests.
For forgings above 5,000 kg, the starting material should be vacuum-degassed (VD) to achieve total oxygen below 20 ppm and dissolved hydrogen below 2 ppm. Hydrogen-induced flaking — invisible on the surface but detectable by ultrasonic testing — is a real risk in heavy Al-bearing nitriding steel heats without proper VD treatment and controlled post-forging cooling.
Jiangsu Liangyi Co., Limited is an ISO 9001:2015 certified open-die forging manufacturer established in 1997, located in Jiangyin, Jiangsu, China. We produce 34CrAlMo5-10 forgings with full EN 10204 3.1 material test certificates as standard. Third-party inspection (EN 10204 3.2) can be arranged through internationally recognized inspection bodies at the client's request and specification. For available shapes, weight range (30 kg to 30,000 kg), lead times, and to request a quote, visit the 34CrAlMo5-10 (1.8507) forging product page.
| Standard | Scope |
|---|---|
| DIN EN 10085:2001 | Chemical composition and mechanical properties of nitriding steels |
| EN 10250-3 | Open steel die forgings for general engineering — alloy special steels |
| EN 10228-3 | Ultrasonic testing of ferritic/martensitic steel forgings |
| EN 10204 | Material test reports (Type 3.1 mill certificate; Type 3.2 third-party inspection) |
| ISO 6507 | Vickers hardness test — compound layer and case depth measurement |
| ISO 6892-1 | Tensile testing at room temperature |
| ISO 148-1 | Charpy pendulum impact test |
Jiangsu Liangyi Co., Limited — ISO 9001:2015 certified open-die forging manufacturer established in 1997 — supplies 1.8507 components from 30 kg to 30,000 kg to industrial clients in 50+ countries. EN 10204 3.1 material certificates as standard; 24-hour quote response.