EN 10305-1 42CrMo4 Precision Seamless Steel Tube Cold Drawn Steel Tube BK Condition
EN 10305-1 is the European standard for seamless cold-drawn precision steel tubes. It specifies technical delivery conditions for tubes used in applications requiring close dimensional tolerances, smooth surface finish, and consistent mechanical properties.
The standard covers tubes manufactured from various steel grades, with 42CrMo4 being the most popular choice for high-strength, high-pressure components.
42CrMo4 (also known as 1.7225 or AISI 4140) is a chromium-molybdenum alloy steel known for:
- High tensile strength
- Excellent toughness
- Good fatigue resistance
- Superior hardenability
When supplied under EN 10305-1, 42CrMo4 tubes are delivered in the cold-drawn and stress-relieved (BK) condition – ready for precision machining and demanding applications.
| Quick Facts | Value |
|---|---|
| Standard | EN 10305-1 |
| Material | 42CrMo4 (1.7225 / AISI 4140 equivalent) |
| Manufacturing Process | Seamless + Cold Drawn |
| Delivery Condition | BK (cold-drawn + stress-relieved) |
| Key Features | Tight tolerances, smooth surface, high strength |
The manufacturing process for EN 10305-1 42CrMo4 precision tubes follows strict quality controls to ensure consistency and reliability.
Step 1 – Mother Tube Production
A solid, round billet of 42CrMo4 steel is heated and pierced to create a hollow seamless shell – the "mother tube."
Step 2 – Pickling & Phosphating
The mother tube is chemically treated to remove scale and apply a lubricant coating. This prepares the surface for cold drawing.
Step 3 – Cold Drawing
The tube is pulled through a die and over a mandrel to achieve precise dimensions. Multiple drawing passes may be used. Cold drawing improves dimensional accuracy, increases strength through work hardening, and produces a smooth surface finish.
Step 4 – Stress Relieving (BK Condition)
After cold drawing, the tube is heat-treated at a controlled temperature (typically 450–600°C) to remove residual stresses from drawing while maintaining improved mechanical properties. Unlike full annealing, stress relieving avoids complete softening.
Under EN 10305-1, tubes can be supplied in several delivery conditions. For 42CrMo4, BK is the most common.
| Condition Code | Description | Typical Application |
|---|---|---|
| BK | Cold-drawn + stress-relieved | Hydraulic cylinders, machining |
| BKW | Cold-drawn + light annealing | Further cold forming |
| BKS | Cold-drawn + softening annealing | Extensive cold forming |
| GBK | As-cold-drawn (no heat treatment) | Limited applications |
BK condition provides:
- Dimensional accuracy to ISO 8448 (or better)
- Surface roughness typically ≤ 0.8 µm Ra
- Residual stresses reduced by 80–90%
- Good machinability without full softening
EN 10305-1 references the material specifications from EN 10297-1 for 42CrMo4. The chemical composition is tightly controlled to ensure consistent hardenability and mechanical properties.
| Element | Content (%) | Function |
|---|---|---|
| Carbon (C) | 0.38 – 0.45 | Provides strength and hardenability |
| Silicon (Si) | ≤ 0.40 | Deoxidizer: strengthens ferrite |
| Manganese (Mn) | 0.60 – 0.90 | Improves strength and hardenability |
| Phosphorus (P) | ≤ 0.025 | Low for toughness (controlled) |
| Sulfur (S) | ≤ 0.025 | Low for cleanliness |
| Chromium (Cr) | 0.90 – 1.20 | Increases hardenability and wear resistance |
| Molybdenum (Mo) | 0.15 – 0.30 | Prevents temper embrittlement; boosts high-temp strength |
Note: EN 10305-1 does not specify a free-cutting version. For precision tubes, sulfur is kept low to ensure clean material suitable for non-destructive testing and high-pressure service.
| Grade | C | Cr | Mo | Key Difference |
|---|---|---|---|---|
| 42CrMo4 | 0.38–0.45 | 0.90–1.20 | 0.15–0.30 | Highest strength |
| 41Cr4 | 0.38–0.45 | 0.90–1.20 | — | No molybdenum |
| 25CrMo4 | 0.22–0.29 | 0.90–1.20 | 0.15–0.30 | Lower carbon, more weldable |
| E355 (St 52) | ≤ 0.22 | — | — | Carbon steel, lower strength |
Why 42CrMo4? The combination of chromium and molybdenum gives this grade superior hardenability and strength compared to plain carbon or simple chromium steels.
The mechanical properties of EN 10305-1 42CrMo4 tubes depend on the delivery condition (BK) and the wall thickness. Below are the minimum guaranteed values per the standard.
| Wall Thickness (mm) | Yield Strength Rp0.2 (MPa) | Tensile Strength Rm (MPa) | Elongation A (%) |
|---|---|---|---|
| ≤ 8 mm | ≥ 600 | 700 – 880 | ≥ 10 |
| 8 – 20 mm | ≥ 550 | 650 – 850 | ≥ 10 |
| > 20 mm | ≥ 500 | 620 – 820 | ≥ 10 |
*Values are minimum requirements per EN 10305-1. Actual values can be higher depending on cold drawing reduction and stress relieving parameters.*
| Property | Typical Value |
|---|---|
| Hardness (HB) | 210 – 260 HB (BK condition) |
| Condition | Yield Strength (MPa) | Tensile Strength (MPa) | Application |
|---|---|---|---|
| BK (as-supplied) | 500–600 | 650–880 | Machining into components |
| Quenched + Tempered | 800–1000+ | 1000–1200+ | Final high-strength parts |
Important: The BK condition is designed for machinability, not final service strength. After machining the tube into a cylinder barrel or component, most customers perform a final quench and temper heat treatment to achieve the full strength potential of 42CrMo4.
| Parameter | Tolerance (typical) |
|---|---|
| Outside diameter (OD) | ISO 8448 – class H9 / H10 |
| Inside diameter (ID) | ISO 8448 – class H8 / H9 |
| Wall thickness | ± 5–10% depending on size |
| Straightness | ≤ 1.0 mm per meter |
| Surface roughness (ID) | Ra ≤ 0.8 µm (typical) |
Actual tolerances vary by diameter and wall thickness. Please consult our technical team for your specific size requirements.
Primary Use: Hydraulic cylinder barrels
Other Applications:
- Mechanical engineering components
- Heavy-duty vehicle parts
- Oil & gas equipment
- General high-strength mechanical parts
Quick Pick:
| Need | Choose |
|---|---|
| High-pressure cylinder barrel | 42CrMo4 |
| Medium-pressure cylinder | E355 (St 52) |
| Piston rod | 42CrMo4 + QT |
We take quality seriously. Every EN 10305-1 42CrMo4 tube we supply is backed by comprehensive testing and traceability.
| Test | Standard / Method | Purpose |
|---|---|---|
| Chemical analysis | Optical emission spectrometry (OES) | Verify composition per EN 10297-1 |
| Tensile test | EN ISO 6892-1 | Confirm yield, tensile, and elongation |
| Hardness test | EN ISO 6506-1 (Brinell) | Verify consistency |
| Flattening test | EN ISO 8492 | Check ductility |
| Drift expanding test | EN ISO 8493 | Check ID surface integrity |
| Non-destructive testing (NDT) | EN 10246-3 (eddy current) or EN 10246-7 (ultrasonic) | Detect surface and subsurface defects |
| Dimensional inspection | Micrometers, bore gauges, CMM | Verify OD, ID, wall thickness, and straightness |
| Surface roughness | Profilometer | Ra measurement (typically ≤ 0.8 µm ID) |
We supply all tubes with:
- EN 10204 Type 3.1 – Mill test certificate (chemical and mechanical results)
- EN 10204 Type 3.2 – Available upon request (third-party verified)
- Full traceability – Heat number stamped on each tube
EN 10305-1 requires that tubes be free of laminations, cracks, scale (rust), and significant surface defects. For hydraulic cylinder applications, we pay special attention to ID surface finish – typically achieving Ra ≤ 0.8 µm to ensure long seal life.
Ready to order or have technical questions? Our team is here to help.
Please provide the following information for a fast and accurate quote:
- Quantity (pieces or meters)
- Dimensions (OD × wall thickness × length)
- Grade (42CrMo4)
- Standard (EN 10305-1)
- Delivery condition (BK – standard)
- Certification required (3.1 or 3.2)
- Delivery location
| Advantage | Detail |
|---|---|
| Stock availability | Common sizes available for immediate shipment |
| Custom cutting | Precision saw cutting to your exact lengths |
| Competitive pricing | Direct mill partnerships |
| Technical support | In-house metallurgists and engineers |
| Global shipping | Packaged for export; door-to-door delivery available |
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