The Three-Tier Material Framework for Helical Gears
All steel materials used for spiralformade kugghjul fall into one of three performance tiers, determined by the achievable tooth flank surface hardness and the heat treatment required to reach it. The tier selection drives all other material choices — it is the first decision, before specific grade, heat treatment depth, or accuracy class are specified:
Gear is cut after heat treatment (QT or normalise). Final surface hardness limited to HB 350. No post-cut hardening that distorts profile. DIN Class 7–9 by hobbing. Lowest cost and shortest lead time. Examples: 45#, 40Cr, 35CrMo. Applications: general industrial gearboxes, cranes, conveyors, moderate-duty pump drives at speed below 15 m/s.
Induction hardened surface with QT core. Post-hardening grinding restores accuracy. Contact fatigue life significantly higher than Tier 1. Examples: 42CrMo induction HRC 50–55. Applications: rolling mill roughing stand pinions, crusher drives, medium-duty mining drives where shock resistance must be balanced with surface hardness.
Carburized (or gas nitrided) with tooth grinding to DIN Class 4–6. Maximum contact fatigue strength and service life. Examples: 20CrMnTi, 20CrNiMo, 17CrNiMo6. Applications: automotive, EV, CNC, marine, aerospace, high-cycle industrial — any application where fatigue life, noise, and speed range are critical.
Complete Material Grade Reference
Hård tandad flank karburerad spiralväxel — the combination of HRC 58–62 surface hardness, controlled case depth, and tough QT core is achievable with 20CrMnTi (standard grade) or 17CrNiMo6 (premium marine and offshore grade)
| Grade | DIN Equivalent | HT Method | Ythårdhet | σ_H lim (MPa) | Charpy at −20°C | Relativ kostnad | Primary Application |
|---|---|---|---|---|---|---|---|
| 45# | C45 / Ck45 | QT (HB 220–280) | HB 220–280 | 490–560 | 20–30 J | 1.0× (baseline) | Soft flank industrial: cranes, conveyors, low-speed pump drives |
| 40Cr | 41Cr4 | QT (HB 260–320) | HB 260–320 | 530–600 | 25–35 J | 1,1× | Improved soft flank: moderate industrial, shaft-mounted drives |
| 42CrMo | 42CrMo4 | QT (HB 280–320) or induction HRC 50–55 | HB 280–320 or HRC 50–55 | 590–680 (QT); 820–950 (induction) | 35–50 J (QT); 25–40 J (induction) | 1.2–1.5× | Rolling mills, crusher pinions, mine hoists, offshore winches |
| 20CrMnTi | 20MnCr5 (approx) | Carburize + Q + T; HRC 58–62 | HRC 58–62; case depth 0.8–1.5 mm | 1500–1650 | 30–50 J (core) | 1.8–2.2× | Standard automotive, EV reducer, CNC machine tools, industrial precision gearboxes |
| 20CrNiMo | 21NiCrMo2 | Carburize + Q + T; HRC 58–62 | HRC 58–62; case depth 0.8–1.8 mm | 1500–1700 | 40–60 J (core) | 2.2–2.6× | High-cycle industrial, heavy automotive, where better core toughness than 20CrMnTi needed |
| 17CrNiMo6 | 17CrNiMo6 (DIN same) | Carburize + Q + T; HRC 58–62 | HRC 58–62; case depth 1.0–2.5 mm | 1600–1800 | 55–80 J at −40°C | 2.8–3.5× | Marine (DNV certified), offshore, Arctic service, naval, mine hoists requiring −40°C Charpy |
| 38CrMoAl | 41CrAlMo7 | Gas nitrided; HV 700+ (HRC 62+) | HV 700–900; case depth 0.1–0.5 mm | 1200–1450 | 25–35 J | 2.5–3.0× | Machine tool gearboxes needing dimensional stability after hardening |
| SS316L | 1.4404 | Solution annealed + optional gas nitriding | HB 160–200 (annealed); HV 800+ (nitrided) | 520–650 | Excellent | 3.5–5.0× | Food processing direct contact zone, pharmaceutical, marine auxiliary pumps |
When to Upgrade from 20CrMnTi to 17CrNiMo6
Both 20CrMnTi and 17CrNiMo6 are carburized to HRC 58–62 and deliver similar contact fatigue strength (σ_H lim). The decision to upgrade to 17CrNiMo6 — at 1.5–2× the material cost — is justified by three specific requirements that 20CrMnTi cannot reliably meet:
- Sub-zero temperature Charpy requirement: 17CrNiMo6 delivers 55–80 J Charpy at −40°C, meeting DNV GL, Lloyd’s Register, and KR class society ice-class certification requirements. 20CrMnTi typically delivers only 20–40 J at −40°C — below the 27 J certification limit for Arctic and polar service vessels. When Charpy at −40°C is specified, 17CrNiMo6 is mandatory.
- Very large section size: 20CrMnTi has limited hardenability — in sections above approximately 80–100 mm diameter, the centre does not fully transform to martensite during quenching, reducing core hardness and impact toughness. 17CrNiMo6’s higher nickel and chromium content provides adequate hardenability through sections up to 400–500 mm diameter. For large-module spiralväxel blanks (M20+, OD 400+ mm) where core properties are critical, 17CrNiMo6 is required.
- High shock loading at low temperature: Mine hoist spiralformade kugghjul and offshore crane pinions operating in cold climates require both high surface hardness (for contact fatigue life) and tough cores at low temperature (for shock absorption). This combination is achievable only with 17CrNiMo6 — it is the unique intersection of these requirements that makes it the premium marine and offshore grade.
Material Grade Selection Matrix by Application
Soft tooth flank spiralväxel — 45# or 40Cr QT, DIN Class 7–8 by precision hobbing. The correct material choice for the majority of general industrial gearboxes below 15 m/s pitch-line velocity where fatigue life with H1 service factor meets the design requirement
| Ansökan | Recommended Grade | HT Option | DIN-klass | Justification |
|---|---|---|---|---|
| General industrial (crane, conveyor, pump) <15 m/s | 45# or 40Cr | QT HB 220–320 | 7–9 | Cost-optimised; adequate fatigue life at moderate load and speed |
| Industrial gearbox >15 m/s, precision required | 20CrMnTi | Carburize + grind | 5–6 | Ground surface needed for noise and EHL film at high speed |
| Automotive transmission / EV reducer | 20CrMnTi | Carburize + grind DIN 4–5 | 4–6 | Maximum fatigue life + NVH at 35–100 m/s pitch-line velocity |
| Crusher, rolling mill roughing stand | 42CrMo | Induktions HRC 50–55 | 7–8 | Shock resistance from QT core; case-core boundary toughness |
| Marine main propulsion / offshore | 17CrNiMo6 | Carburize + grind | 5–7 | Charpy −40°C certification; large section hardenability |
| Mine hoist, Arctic service | 17CrNiMo6 | Carburize + grind | 5–7 | 27 J at −40°C regulatory requirement; shock + cold combined |
| Machine tool gearbox (dimensional stability) | 38CrMoAl | Gas nitride | 6–7 | Minimal distortion from nitriding preserves pre-nitriding accuracy |
| Food processing direct contact zone | SS316L | Annealed or nitrided | 7–9 | EU 1935/2004, FDA 21 CFR compliance; CIP corrosion resistance |
International Grade Equivalents
Korea Ever-Power purchases material with mill certificates confirming compliance with the specified grade. For customers specifying spiralformade kugghjul using grades from DIN, ASTM, or JIS standards, the approximate equivalents to the most common Korean grades are:
| Korean / Generic Grade | DIN (Germany) | ASTM / SAE (USA) | JIS (Japan) | BS (UK) |
|---|---|---|---|---|
| 45# | C45 / Ck45 | AISI 1045 | S45C | 080M46 |
| 40Cr | 41Cr4 | AISI 5140 | SCr440 | 530A40 |
| 42CrMo | 42CrMo4 | AISI 4140 | SCM440 | 708M40 |
| 20CrMnTi | 20MnCr5 (approx.) | SAE 8620 (approx.) | — | — |
| 17CrNiMo6 | 17CrNiMo6 | SAE 9310 (approx.) | SNCM815 (approx.) | — |
| 38CrMoAl | 41CrAlMo7 | AISI 7140 (Nitralloy) | SACM645 | 905M39 |
| SS316L | 1.4404 (X2CrNiMo17-12-2) | AISI 316L | SUS316L | 316S11 |
Korea Ever-Power — Full Material Grade Range In-House
Korea Ever-Power’s in-house manufacturing covers all material grades described in this guide — from 45# soft tooth flank industrial gears through 17CrNiMo6 carburized marine gears — with OES spectrometer material verification at incoming inspection and full material certification included with every order
Korea Ever-Power tillverkar spiralformade kugghjul across all material grades described in this guide, with material verified by OES spectrometer at incoming inspection and mill certificate supplied with every order. All grades from 45# through 17CrNiMo6 are available as standard materials; SS316L and SS304 for food contact applications; 38CrMoAl for nitrided machine tool gears. As a direct tillverkare av spiralväxlar, Korea Ever-Power provides the engineering consultation needed to select the correct grade for a specific application — confirming that the selected material provides adequate σ_H lim for the design contact stress, appropriate Charpy values for the operating temperature, and compatible heat treatment with the required DIN accuracy class. Browse the full produktsortiment för spiralväxlar or contact the engineering team for a material recommendation.
Vanliga frågor
20CrMnTi was developed in Korea and Japan specifically for the gear and bearing industry as a reliable, cost-effective carburizing steel. Its well-characterised and well-controlled carburizing behaviour (consistent carbon uptake, predictable case depth, minimal distortion compared with some higher-alloy grades) makes it easier to produce consistently across different furnace batches — critical for automotive PPAP SPC control requirements. 20CrNiMo has slightly better core toughness and is preferred when the shock loading requirement is higher, but costs approximately 15–25% more than 20CrMnTi and has slightly more variable carburizing behaviour. For standard automotive and industrial spiralväxel applications, 20CrMnTi’s lower cost and more predictable processing make it the default choice.
Gas nitriding at 490–530°C is a low-temperature process compared with carburizing (880–940°C). The lower temperature means the gear’s dimensional distortion during nitriding is typically only 0.01–0.03 mm — far less than the 0.05–0.15 mm distortion from carburizing and quenching. A spiralväxel precision-hobbed to DIN Class 6 before nitriding typically maintains DIN Class 6–7 after nitriding without any further tooth grinding. This dimensional stability is the specific advantage that makes 38CrMoAl the preferred material for CNC machine tool gearboxes where the gear is precision-machined within a completed assembly that cannot be easily disassembled for post-hardening grinding. The trade-off is shallower case depth (0.1–0.5 mm maximum vs 0.8–2.5 mm for carburizing) and somewhat lower contact fatigue strength than carburized grades.
σ_H lim is the allowable contact stress (Hertz pressure) at the tooth flank under the pulsating load cycle of gear meshing, expressed in MPa per ISO 6336-5. It represents the material’s contact fatigue strength in the surface-hardened condition — not its tensile strength or yield strength. The dramatic range from 490 MPa (45# QT) to 1800 MPa (17CrNiMo6 carburized) reflects the enormous difference in surface hardness: the Hertz contact stress limit scales approximately with the surface hardness to the power of 1.5–2. Doubling the surface hardness from HB 280 to HRC 60 increases σ_H lim by a factor of approximately 3. This is why the investment in carburizing and grinding for a spiralväxel translates directly to a 3× increase in allowable contact stress — meaning a 3× smaller gear for the same load capacity, or 3× longer service life in the same gear size.
Yes, with the understanding that SS316L is a Tier 1 (soft tooth flank) material — its σ_H lim of 520–650 MPa is similar to 45# QT. A SS316L spiralväxel carries moderate loads well but cannot match the contact fatigue strength of carburized alloy steel. Gas nitriding SS316L raises the surface hardness to HV 800–1000 and improves σ_H lim to approximately 1000–1200 MPa — approaching the performance of induction-hardened 42CrMo while retaining full corrosion resistance. For food processing applications requiring moderate-to-high load capacity in a corrosion-resistant spiralväxel, SS316L gas nitrided is the correct specification. Korea Ever-Power offers gas nitrided SS316L spiralformade kugghjul in M2–M12 for food and pharmaceutical drive applications where both load capacity and food contact compliance are required simultaneously.
Need Material Grade Confirmation for Your Helical Gear?
Korea Ever-Power’s engineering team reviews your application type, operating temperature, shock loading level, and any certification requirements — then confirms the correct material grade with justification before any production cost is committed. Submit enquiry with application description.
45# through 17CrNiMo6 · SS316L · 38CrMoAl nitrided · OES verification · Material certification standard
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