When specifying open die forgings for structural machinery, gearboxes, shafts, or gear rings, engineers frequently narrow the material shortlist to two DIN/EN manganese steels: 20Mn5 (1.1133) and 20MnCr5 (1.7147). Their names look almost identical and nominal carbon content is the same — yet they are engineered for fundamentally different service demands. Choosing the wrong grade increases total component cost through unnecessary alloy spend or premature surface wear in service.
This guide is based on 25+ years of production experience at Jiangsu Liangyi Co., Limited, an ISO 9001:2015 certified open die forging manufacturer supplying both grades to industrial clients in 50+ countries from our 80,000 m² facility in Jiangyin, Jiangsu Province, China.
Grade Overview at a Glance
Both grades share approximately 0.17–0.23% carbon — the sweet spot for balancing core toughness with hardenability. The critical difference is the addition of chromium in 20MnCr5 (1.00–1.30%) versus ≤0.30% residual in 20Mn5. That single alloying choice changes carburizing behavior, case depth profile, core properties after heat treatment, and cost — making the two steels suited to distinctly different engineering problems.
Chemical Composition: 20Mn5 vs 20MnCr5 Compared
The table below shows ladle (cast) analysis limits per their respective EN standards. Small differences in alloying create large differences in service capability.
| Element | 20Mn5 (1.1133) — EN 10250-2 | 20MnCr5 (1.7147) — EN 10084 | Engineering Significance |
|---|---|---|---|
| Carbon (C) % | 0.17 – 0.23 | 0.17 – 0.22 | Near-identical carbon keeps core toughness comparable in both grades. |
| Manganese (Mn) % | 1.10 – 1.40 | 1.10 – 1.40 | Identical Mn range — primary hardenability booster in both grades. |
| Chromium (Cr) % | ≤ 0.30 (residual) | 1.00 – 1.30 | Key differentiator. Cr in 20MnCr5 drives deeper, more uniform carburized case depth and higher hardenability in thick sections. This is the fundamental reason for the grade difference. |
| Silicon (Si) % | 0.15 – 0.40 | 0.15 – 0.40 | Standard deoxidation range — no functional difference between grades. |
| Phosphorus (P) % | ≤ 0.030 | ≤ 0.025 | Tighter P limit in 20MnCr5 improves toughness at the case-core boundary after carburizing. |
| Sulfur (S) % | ≤ 0.035 | ≤ 0.035 | Standard limit — no meaningful difference between grades. |
| Aluminum (Al) % | ≥ 0.020 (Al-killed) | ≥ 0.020 | Grain refinement and nitrogen fixing in both grades. |
Microstructure and Heat Treatment Comparison
Understanding how each grade responds to heat treatment — and the resulting microstructure — is essential for specifying the correct delivery condition on your purchase order and drawing.
- Typical delivery conditionNormalized or Q&T
- Normalizing temperature890–940 °C
- Normalized microstructureFerrite + pearlite
- Q&T microstructureTempered martensite
- Carburizing suitabilityNot recommended
- Induction hardeningFeasible on journals
- Hardness (normalized)140–200 HB
- Hardness (Q&T)200–280 HB
- Typical delivery conditionSoft-annealed (pre-carburize)
- Soft annealing temperature680–720 °C
- Carburizing temperature880–950 °C
- Case depth (CHD)0.5 – 2.5 mm
- Surface hardness (carburized)58 – 62 HRC
- Core hardness (carburized)30 – 42 HRC
- Surface microstructureMartensite + carbides
- Core microstructureTempered bainite / low-C martensite
Mechanical Properties: Side-by-Side Data Table
All values assume standard longitudinal test specimen orientation and standard heat treatment conditions per EN requirements. Data is representative of production forgings — confirm specific requirements on drawing or purchase order.
| Property | 20Mn5 — Normalized (≤100 mm section) | 20Mn5 — Q&T (100–250 mm section) | 20MnCr5 — Carburized (surface / core) |
|---|---|---|---|
| Tensile strength Rm | 500–700 MPa | 600–800 MPa | Core: 800–1,100 MPa |
| Yield strength Re / Rp0.2 | ≥ 295 MPa | ≥ 390 MPa | Core: ≥ 590 MPa |
| Elongation A5 | ≥ 22% | ≥ 18% | Core: ≥ 9% |
| Reduction of area Z | ≥ 50% | ≥ 40% | Core: ≥ 35% |
| Charpy impact KV (room temp) | ≥ 27 J | ≥ 35 J | Core: ≥ 25 J |
| Surface hardness | 140–200 HB | 200–280 HB | 58–62 HRC (surface) |
| Core hardness | Same as surface | Same as surface | 30–42 HRC |
| Fatigue limit — rotating bending | ~220 MPa | ~300 MPa | 500–650 MPa (carburized surface) |
| Wear resistance | Moderate | Moderate – Good | Excellent (carburized case) |
| Impact at −40 °C | ≥ 20 J (Q&T) | ≥ 27 J (Q&T) | Not primary design criterion |
Application Fit — Where Each Grade Belongs
- Large flanges and forged discs (>200 mm section)
- Structural shafts (non-case-hardened)
- Seamless rolled rings for slewing equipment
- Pressure vessel and boiler forgings
- Mining and construction machinery hubs
- Hydraulic cylinder forgings
- Heavy gear blanks (pre-carburizing stage)
- Forged step shafts for industrial drives
- Offshore structural components (Q&T + H₂ control)
- Gear shafts and pinion shafts
- Gearbox ring gears (carburized)
- Differential bevel gears
- High-speed transmission components
- Carburized bearing inner rings
- Worm gear forgings
- Agricultural and off-highway gearboxes
- Planetary gear carriers and sun gears
- Wind turbine gearbox shafts
Machinability and Weldability Comparison
| Attribute | 20Mn5 (1.1133) | 20MnCr5 (1.7147) |
|---|---|---|
| Machinability (pre-heat treat) | Good — clean chip break, low tool wear | Good in soft-annealed condition pre-carburizing |
| Machinability (post-heat treat) | Good (Q&T ≤ 280 HB) | Post-carburize: precision grinding only (58–62 HRC) |
| Tool life (relative index) | Higher | Lower — Cr carbides increase cutting tool abrasion |
| Grinding allowance for carburized surfaces | N/A | 0.1–0.3 mm to be left on bearing and sealing surfaces before carburizing |
| Carbon equivalent CE (IIW formula) | ~0.40 – 0.45 | ~0.55 – 0.65 |
| Weldability | Good — preheat ≥ 100 °C for section > 25 mm | Moderate — preheat 150–200 °C required |
| Post-weld heat treatment | Stress relief 580–620 °C recommended | Required after welding; not feasible on carburized surfaces |
| Production flow complexity | Lower — typically one machining setup post-HT | Higher — machine → carburize → grind sequence required |
20MnCr5 components must be machined to near-net shape before carburizing, with only 0.1–0.3 mm grinding stock left on bearing and sealing surfaces. This means the machining workflow must be sequenced with the heat treatment schedule — an important consideration when evaluating supplier lead times and total delivery time.
20Mn5 forgings in Q&T condition can typically be machined in a single setup after heat treatment, simplifying production flow and reducing total cycle time for large structural components. This contributes directly to the lower total cost of 20Mn5 forgings in structural applications.
Cost and Lead Time: 20Mn5 vs 20MnCr5
20MnCr5 commands a cost premium on three levels: the Cr-alloyed steel billet costs more than 20Mn5; the carburizing + hardening + tempering cycle is more time- and energy-intensive than normalizing; and post-carburize precision grinding adds a machining step that 20Mn5 does not require. For a complete machined gear shaft, the total cost premium of 20MnCr5 over 20Mn5 typically ranges 30–60%, depending on geometry, section size, and batch quantity.
That premium is only justified if you actually need what 20MnCr5 delivers. Specifying 20MnCr5 for a large structural forging where surface hardness is irrelevant to the application adds 30–60% cost with zero engineering benefit. The reverse is equally true: using 20Mn5 in a carburized gear application results in inadequate surface hardness and shortened fatigue life — with replacement cost that far exceeds the original material saving.
Decision Framework: How to Choose Between 20Mn5 and 20MnCr5
Work through these seven questions in order. The first question that returns a clear YES gives you your grade.
Frequently Asked Questions about 20Mn5 and 20MnCr5 Forgings
Conclusion: Choosing the Right Manganese Steel Forging Grade
The choice between 20Mn5 (1.1133) open die forging manufacturer page and 20MnCr5 (1.7147) is not about which grade is "better" — it is about which engineering problem each grade was designed to solve.
Choose 20Mn5 (1.1133) when your component is a large structural forging — shaft, ring, flange, disc — where through-section toughness, normalizing simplicity, weldability, and total component cost are the dominant considerations. It is the correct and most cost-efficient grade for the vast majority of open die forgings in the 100–500 mm section range, delivered normalized (≤100 mm) or Q&T (>100 mm).
Choose 20MnCr5 (1.7147) when your component is a precision gear shaft, pinion, gear ring, or wear-critical part that will undergo carburizing to achieve a hard surface layer over a tough core. The 1.00–1.30% chromium content is not a luxury addition — it is the metallurgical mechanism that makes uniform deep case depth achievable, and it is what separates 20MnCr5 from simple manganese steels in gear applications.
At Jiangsu Liangyi, we manufacture both grades entirely within our 80,000 m² facility in Jiangyin, Jiangsu Province, with full in-house forging, heat treatment, NDT, and machining — no subcontracting at any stage. Our ISO 9001:2015 quality system covers the complete process from raw steel melting through final inspection. If you are uncertain which grade fits your application, send us your engineering drawing and service conditions — our team provides a direct technical recommendation within 24 hours.
for 20Mn5 or 20MnCr5 Forgings