17NiCrMoS6-4 (DIN 1.6569) is a low-alloy, nickel-chromium-molybdenum case-hardening steel per EN 10084, featuring added sulfur (0.020–0.040%) for superior machinability. After carburizing and hardening, it achieves a surface hardness of 58–62 HRC and a core tensile strength of 1000–1300 MPa. It is the industry-standard material for transmission gears, camshafts, drive shafts, and high-load mechanical components requiring a hard wear-resistant surface combined with a tough, impact-resistant core.
Understanding 17NiCrMoS6-4 at a Glance
17NiCrMoS6-4 — Werkstoff number 1.6569 — is a low-alloy, nickel-chromium-molybdenum case-hardening steel standardized under EN 10084 (Technical delivery conditions for case-hardening steels). It is the free-cutting variant of 17NiCrMo6-4 (1.6566), distinguished by deliberately added sulfur (S: 0.020–0.040%) that forms manganese sulfide (MnS) inclusions — natural chip-breakers that dramatically improve machinability without compromising core toughness. Jiangsu Liangyi manufactures the full range of 17NiCrMoS6-4 open die forgings and seamless rolled rings, supplied to EU and global industrial markets from 1 tonne MOQ.
Engineers specify 17NiCrMoS6-4 when a component must combine a hard, wear-resistant surface with a tough, impact-absorbing core — a dual performance profile that through-hardening alone cannot deliver. The carburized case acts as armor; the quenched-and-tempered core acts as a shock absorber. Together, they enable 1.6569 to outperform simpler grades in high-contact, high-shock applications.
Engineering rule of thumb: If your component faces abrasive sliding contact on its surface while absorbing shock or bending loads in its core — a transmission gear tooth is the textbook example — 17NiCrMoS6-4 belongs on your material shortlist. The "S" suffix tells you: superior machinability is engineered into the grade, not added later through coatings or surface treatments.
According to EN 10084, the specified application profile for this grade includes parts requiring a core tensile strength of 1000–1300 N/mm² combined with good wear resistance, such as gearbox internals, piston bolts, spindles, camshafts, and steering components.
Chemical Composition per EN 10084
Each alloying element in 17NiCrMoS6-4 serves a defined mechanical function. The table below shows the specified heat analysis ranges (ladle analysis) per EN 10084 — the values your EN 10204/3.1 mill certificate must confirm.
| Element | Symbol | Range (%) | Engineering Function |
|---|---|---|---|
| Carbon | C | 0.14 – 0.20 | Controls core hardenability; kept low to maintain ductile, impact-resistant core |
| Silicon | Si | 0.15 – 0.40 | Deoxidizer during steelmaking; minor solid-solution strengthening |
| Manganese | Mn | 0.60 – 0.90 | Hardenability booster; combines with sulfur to form MnS chip-breaker inclusions |
| Phosphorus | P | ≤ 0.025 | Controlled impurity — excess causes grain-boundary embrittlement and reduced toughness |
| Sulfur | S | 0.020 – 0.040 | MnS inclusions → chip breaking → higher machining speed, reduced tool wear |
| Chromium | Cr | 0.80 – 1.10 | Uniform case depth across section; oxidation and wear resistance |
| Molybdenum | Mo | 0.15 – 0.25 | Prevents temper embrittlement; deepens hardenability in large sections |
| Nickel | Ni | 1.20 – 1.60 | Core toughness and low-temperature impact resistance (key differentiator) |
| Copper | Cu | ≤ 0.40 | Residual element limit; minor atmospheric corrosion benefit |
| Aluminium | Al | 0.020 – 0.050 | Grain refiner — controls austenite grain coarsening during high-temperature carburizing |
Why the Ni–Cr–Mo Combination Is Uniquely Synergistic
The three principal alloying elements work in concert, not independently. Nickel (1.20–1.60%) raises the toughness of the martensite formed during quenching, giving the core its critical impact resistance — a property that Cr-only or Mn-Cr grades cannot match at the same alloy cost. Chromium (0.80–1.10%) promotes uniform carbon diffusion during carburizing, ensuring case depth is consistent across complex gear geometries with variable cross-sections. Molybdenum (0.15–0.25%) closes the temper embrittlement window that appears in plain Ni-Cr steels when tempered in the 350–500°C range, making the final part far more reliable under prolonged shock service in industrial gearboxes.
Specification note: Always request heat analysis (ladle composition), not product analysis (which allows wider tolerances). Confirm sulfur is within 0.020–0.040% — values outside this range indicate either a non-sulfurized grade (too low) or uncontrolled sulfur (too high, risking transverse property degradation).
Mechanical Properties After Case Hardening
The values below reflect 17NiCrMoS6-4 in the carburized, quenched, and tempered (Q+T) condition for reference diameter ≤ 30 mm, per EN 10084 treatment category E. All properties are minimum guaranteed values unless stated otherwise.
Section-size effect: EN 10084 certifies properties for specific diameter ranges (categories A–E). For sections above 63 mm, hardenability drop-off means tensile strength may fall to the lower bound. Always specify the treatment category explicitly in your purchase order. For parts with bore diameters above 100 mm, evaluate upgrading to 18CrNiMo7-6 (1.6587).
Heat Treatment Sequence for 17NiCrMoS6-4
Achieving 58–62 HRC surface hardness while preserving core toughness requires a disciplined six-stage thermal cycle. Deviating even ±20°C from the specified temperatures can cause excessive retained austenite, insufficient case depth, or a brittle core. The standard carburizing route is as follows:
Hot Forging
Heat billet uniformly to 900–1150°C. Complete all forging reductions above 900°C to ensure full recrystallization and prevent surface cracking. Slow-cool forgings after completion.
900 – 1150 °CSoft Annealing (Recommended Before Heavy Machining)
Heat to 680–720°C, hold to achieve thermal equilibrium, then slow furnace-cool at ≤20°C/hour. Produces a soft, spheroidized carbide microstructure ideal for heavy roughing cuts. Target hardness: ≤ 217 HB.
680 – 720 °CCarburizing
Expose the finished-machined part to a controlled carbon-rich atmosphere (carbon potential 0.75–0.85%C). Duration calculated to achieve target effective case depth (ECD) of 0.5–1.5 mm. Precise atmosphere control is critical — over-carburizing creates a brittle carbide network that fails in contact fatigue.
880 – 980 °CCore Quench
Direct oil- or polymer-quench from the carburizing temperature. Hardens the core and dissolves any coarse carbides. The nickel and molybdenum in 1.6569 ensure reliable martensitic transformation in the core even at larger cross-sections.
Quench from 880 – 980 °C in oilCase Quench (Double Quench Process)
Reheat to 780–820°C (above case Ac₁, below core Ac₃) and oil-quench again. This second quench refines the carburized case grain structure, maximizes surface hardness, and minimizes dimensional distortion in precision gear blanks.
780 – 820 °CLow-Temperature Tempering
Temper for 1–2 hours to relieve quench residual stresses and reduce the risk of grinding cracks during final surface finishing — without meaningfully reducing surface hardness. Final HRC target: 58–62.
150 – 200 °CAfter heat treatment, final grinding and inspection for effective case depth (by micro-hardness traverse per ISO 2639), surface hardness (Rockwell C), and core properties (tensile coupon or Brinell) complete the process before shipment.
Industrial Applications of 17NiCrMoS6-4
EN 10084 explicitly defines the intended applications for 17NiCrMoS6-4 as components requiring a core tensile strength of 1000–1300 N/mm² combined with good wear resistance. In practice, this covers a wide range of high-stress mechanical components across multiple industries:
Automotive Driveline
The highest-volume application is automotive and commercial vehicle gearing. A typical manual gearbox contains 8–14 individual gear sets, and multiple Tier 1 OEM suppliers specify 17NiCrMoS6-4 forgings for the higher-load positions in the gear stack. The grade's improved machinability over non-sulfurized 17NiCrMo6-4 directly reduces cycle time on CNC gear-hobbing and gear-grinding equipment, lowering cost-per-part in high-volume transmission lines running continuous shifts.
Heavy-Duty Industrial Gearboxes
In cement mills, wind turbine pitch and yaw drives, mining conveyors, and marine reduction gearboxes, gear face widths are wide and operating loads are near-continuous. 17NiCrMoS6-4 forged gear blanks combine the structural consistency of a quality forge with predictable case depth uniformity — making them the default blank material for gear manufacturers designing above 100 kW continuous power. The grade is commonly ordered as custom 1.6569 forged blanks, gear shaft forgings, and seamless rolled rings for finish machining by the gear manufacturer.
Agricultural and Off-Highway Equipment
Tractor PTO shafts, combine harvester gearheads, and wheel loader axle components face high shock loads combined with contamination by abrasive soil particles. The tough Ni-rich core of 1.6569 absorbs shock without fracturing, while the 58–62 HRC case resists the micro-scratching and pitting contact fatigue that rapidly degrades case-hardened parts with insufficient hardness depth.
17NiCrMoS6-4 vs. Similar Case-Hardening Grades
Selecting the wrong grade means over-engineering (unnecessary cost) or under-engineering (premature failure). The four grades most frequently evaluated alongside 1.6569 are compared below:
17NiCrMoS6-4 — 1.6569
- Free-cutting S-addition — fastest machining
- Tough Ni-rich core resists shock & bending
- Cr ensures uniform case depth in complex shapes
- Mo eliminates temper embrittlement risk
- EN 10204/3.1 certification as standard
17NiCrMo6-4 — 1.6566
- No sulfur — slightly better transverse fatigue
- Preferred for weldable or safety-critical parts
- Identical heat treatment cycle to 1.6569
- Slower machining, higher tool cost
20MnCr5 — 1.7147
- Lower alloy cost — no Ni, lower Mo
- Adequate for lighter-duty gears (bore <80 mm)
- Less core toughness at larger sections
- Common in passenger car differential gears
18CrNiMo7-6 — 1.6587
- Higher alloy — for large deep-hardening parts
- Used in wind turbine ring gears (>200 mm bore)
- Deeper effective case depth achievable
- Premium cost — specify only when section demands
How to Order 17NiCrMoS6-4 Forged Parts
Sourcing forged 1.6569 blanks — round bar forgings, discs, shafts, or near-net shapes — requires precise technical communication to your supplier. The following parameters must appear in your purchase specification or RFQ to avoid material, heat treatment, or certification non-conformances:
Material Designation
State: 17NiCrMoS6-4 per EN 10084, Werkstoff Nr. 1.6569. Request heat (ladle) analysis and confirm sulfur is within S: 0.020–0.040%. If you receive a product analysis, ask for the heat analysis separately.
Melting Route
Specify per your quality requirements: EAF (standard); EAF+LF+VD (improved cleanliness, recommended for gears); ESR (electroslag remelting — for aerospace or critical fatigue applications). Cleanliness directly impacts fatigue life by up to 40%.
Delivery Condition
Choose: hot-forged black, rough-turned (RT), peeled, or soft-annealed (SA ≤ 217 HB). Soft-annealed is preferred if your machine shop will perform heavy roughing cuts before carburizing.
Inspection & Certification
Request an EN 10204/3.1 Material Test Certificate (MTC) — we can provide this covering: chemical composition, heat number, mechanical test results (tensile, impact), and ultrasonic inspection per SEP 1921 or EN 10228-3. For critical first-article qualification, EN 10204/3.2 (third-party counter-signatory) can be arranged on request.
For custom-forged 17NiCrMoS6-4 components with EN 10204/3.1 MTC available on request, visit 17NiCrMoS6-4 forged parts from Jiangsu Liangyi — ISO 9001:2015 certified manufacturer supplying bars, discs, shafts, and near-net shapes from 1 tonne MOQ.