GB 40Cr Alloy Steel Round Bar
GB 40Cr is a chromium alloy steel round bar per GB/T 3077, equivalent to AISI 5140 / EN 41Cr4 / SCr440. Offers higher strength than carbon steel, reliable hardenability, and excellent induction hardening response. Diameter 10mm-500mm, ideal for shafts, gears, bolts, and medium-duty mechanical components.
| Material | Alloy Steel (Chromium) |
|---|---|
| Grade / Standard | GB 40Cr |
| Diameter | 10mm - 500mm |
| Length | 3m / 6m / 12m (or cut to length) |
| Delivery Condition | hot_rolled / normalized / quenched_tempered / annealed |
| Surface Treatment | bare / polished / coated |
| MOQ | 1 Ton |
| Delivery Time | 10-25 Days / In Stock (Common Sizes) |
| Loading Port | Tianjin / Shanghai / Qingdao |
Overview of GB 40Cr Alloy Steel Round Bar
GB 40Cr is a widely used chromium alloy structural steel round bar specified under the Chinese national standard GB/T 3077 (Alloy Structure Steels). With carbon content of 0.37-0.44% and chromium content of 0.80-1.10%, GB 40Cr delivers a balanced combination of higher strength and hardness than carbon steels (such as GB 45#), while retaining good ductility, moderate toughness, and reliable hardenability. It is the most popular mid-range alloy steel grade in China, serving as the backbone material for shafts, gears, bolts, and structural components in machinery, automotive, construction, and general engineering sectors.
Shandong Tanglu Metal Material Co., Ltd. supplies premium GB 40Cr alloy steel round bar produced by leading Chinese special steel mills through advanced EAF + LF + VD steelmaking technology. Internationally recognized as equivalent to AISI 5140, EN 41Cr4 (1.7035), and JIS SCr440, GB 40Cr offers a cost-effective alloy steel solution with proven mechanical performance, excellent machinability in the normalized or annealed condition, and dependable heat treatment response. Whether for quenched & tempered transmission shafts, induction-hardened gear teeth, or carburized pinion gears, GB 40Cr delivers consistent quality at a competitive price point for mass-production industrial applications.
Key Features and Technical Advantages
The primary advantage of GB 40Cr alloy steel is its chromium-enhanced hardenability — the 0.80-1.10% Cr content enables through-hardening in sections up to 40-50mm (1.5-2 inches) diameter with oil quenching, significantly exceeding the capability of carbon steel grades like GB 45#. This ensures more uniform mechanical properties from surface to core, making 40Cr the ideal upgrade from carbon steel when higher strength or better hardenability is required.
GB 40Cr round bar is manufactured through hot rolling, forging, cold drawing, and peeling/turning processes. In the normalized condition, it delivers tensile strength ≥980 MPa with good ductility. After quenching & tempering (Q&T), tensile strength ranges from 785 MPa to 980 MPa depending on tempering temperature, with reliable impact toughness maintained. The grade also responds well to induction hardening (surface HRC 50-55) for selective wear surfaces on shaft journals and gear teeth, and to carburizing (surface HRC 58-62) for pinion gears and camshafts requiring a hard case over a tough core.
Our 40Cr bars are available in diameter range from 10mm to 500mm, with standard lengths of 3m, 6m, and 12m. Surface conditions include hot rolled (black), forged & rough turned, cold drawn (bright), peeled, and precision ground. All bars undergo ultrasonic testing for internal soundness, and each heat is verified for chemical composition, mechanical properties, and microstructure per GB/T 3077 requirements.
Main Applications of GB 40Cr Round Bar
GB 40Cr alloy steel round bar is the standard material for medium-duty transmission shafts, drive shafts, motor shafts, pump shafts, spindle shafts, and gear box shafts in the machinery and equipment manufacturing industry. Its excellent induction hardening response makes it the preferred choice for gear teeth, spline shafts, and shaft journals requiring selective surface hardness (HRC 50-55) over a tough ductile core.
In the automotive industry, GB 40Cr is used for half-shaft shafts, steering knuckle pins, transmission gears, axle shafts, and connecting rod bolts. After carburizing, it serves as a cost-effective alternative to more expensive alloy grades for intermediate-duty pinion gears and camshaft lobes. The construction and infrastructure sectors rely on GB 40Cr for high-strength structural bolts and studs (equivalent to ASTM A325 / ISO 898 Class 8.8/10.9), foundation anchor bolts, crane shaft pins, and hydraulic cylinder piston rods.
Other key applications include agricultural equipment drive shafts and tillage tool shanks, mining equipment conveyor roller shafts and crusher eccentric shafts, forging press crankshafts and connecting rods, machine tool lead screws and ball screw shafts, and general mechanical engineering components requiring a balance of strength, hardness, and moderate cost that exceeds carbon steel capability.
Why Choose Us for GB 40Cr Alloy Steel Round Bar
Shandong Tanglu Metal Material Co., Ltd. sources GB 40Cr alloy steel round bar from Tier-1 Chinese special steel mills holding ISO 9001 and major classification society certifications. We maintain strict chemistry control per GB/T 3077 specification with consistent chromium content (0.80-1.10%), controlled residual elements (Cu ≤ 0.30%, Ni ≤ 0.30%), and clean steel practice ensuring reliable fatigue performance and heat treatment consistency.
We offer comprehensive heat treatment services including normalizing, annealing, quenching & tempering, stress relieving, induction hardening, and carburizing. Bars can be supplied in hot rolled, cold drawn, forged & rough turned, peeled, or precision ground condition per customer specification. With monthly supply capacity of 8,000 tons of alloy and carbon steel bars and extensive export experience to over 50 countries, we provide the quality consistency, competitive pricing, and reliable lead times required for both high-volume production and project-based orders. Each shipment includes original mill test certificate (MTC) per EN 10204 3.1 standard, with EN 10204 3.2 and third-party inspection (SGS, BV, DNV, LR) available upon request.
📐 Dimension & Size Table
| Diameter (mm) | Length (m) | Weight (kg/m) | Tolerance (Hot Rolled) |
|---|---|---|---|
| 10 | 6 / 12 | 0.617 | ± 0.30mm |
| 12 | 6 / 12 | 0.888 | ± 0.40mm |
| 16 | 6 / 12 | 1.578 | ± 0.40mm |
| 20 | 6 / 12 | 2.466 | ± 0.40mm |
| 25 | 6 / 12 | 3.853 | ± 0.50mm |
| 30 | 6 / 12 | 5.549 | ± 0.50mm |
| 35 | 6 / 12 | 7.553 | ± 0.50mm |
| 40 | 6 / 12 | 9.864 | ± 0.60mm |
| 45 | 6 / 12 | 12.485 | ± 0.60mm |
| 50 | 6 / 12 | 15.413 | ± 0.80mm |
| 55 | 6 / 12 | 18.650 | ± 0.80mm |
| 60 | 6 / 12 | 22.195 | ± 0.80mm |
| 70 | 6 / 12 | 30.210 | ± 1.00mm |
| 80 | 6 / 12 | 39.458 | ± 1.10mm |
| 90 | 6 / 12 | 49.940 | ± 1.20mm |
| 100 | 6 / 12 | 61.654 | ± 1.30mm |
| 120 | 6 / 12 | 88.780 | ± 1.50mm |
| 150 | 3 / 6 | 138.722 | ± 1.80mm |
| 180 | 3 / 6 | 199.759 | ± 2.20mm |
| 200 | 3 / 6 | 246.617 | ± 2.50mm |
| 250 | 3 / 6 | 385.339 | ± 3.50mm |
| 300 | 3 / 6 | 554.888 | ± 4.50mm |
| 400 | 3 | 986.467 | ± 6.00mm |
| 500 | 3 | 1541.354 | ± 8.00mm |
* Custom sizes available upon request. Tolerances per relevant international standards.
🔬 Chemical Composition
| Element | Min | Max | Display Value | Note |
|---|---|---|---|---|
| C | 0.37 | 0.44 | 0.37-0.44 | Per GB/T 3077 specification |
| Cr | 0.80 | 1.10 | 0.80-1.10 | Primary alloy element — hardenability |
| Mn | 0.50 | 0.80 | 0.50-0.80 | |
| Si | 0.17 | 0.37 | 0.17-0.37 | |
| P | - | 0.030 | ≤0.030 | |
| S | - | 0.030 | ≤0.030 | 0.020% max for improved toughness |
| Ni | - | 0.30 | ≤0.30 | Residual element |
| Cu | - | 0.30 | ≤0.30 | Residual element |
| Mo | - | 0.10 | ≤0.10 | Residual element |
* Chemical composition may vary by heat, thickness and specification. Please refer to the actual mill test certificate.
⚙️ Mechanical Properties
| Property | Value | Unit | Test Condition |
|---|---|---|---|
| Tensile Strength (Normalized) | ≥980 | MPa | GB/T 3077 specification |
| Yield Strength (Normalized) | ≥785 | MPa | GB/T 3077 specification |
| Tensile Strength (Q&T) | 785-980 | MPa | Quenched & tempered 500-600°C |
| Yield Strength (Q&T) | ≥635 | MPa | Q&T condition, ≤50mm section |
| Elongation | ≥12 | % | Gauge length 50mm, Q&T |
| Reduction of Area | ≥45 | % | Q&T condition |
| Impact Energy (Charpy V) | ≥31 | J | At 20°C, Q&T condition |
| Brinell Hardness (Annealed) | ≤207 | HBW | Maximum annealed hardness |
| Brinell Hardness (Q&T) | 240-290 | HBW | Typical Q&T range |
| Surface Hardness (Induction) | 50-55 | HRC | After induction hardening |
| Surface Hardness (Carburizing) | 58-62 | HRC | After carburizing & hardening |
| Surface Hardness (Nitriding) | 55-60 | HRC | After nitriding treatment |
| Fatigue Endurance Limit | ≥400 | MPa | 10⁷ cycles, Q&T condition |
| Modulus of Elasticity | 205-215 | GPa | Room temperature |
* Values shown are minimum requirements unless otherwise stated.
📦 Commercial Information
| Packaging | Standard seaworthy export packing. Alloy steel round bars bundled in hexagonal bundles with 3-5 high-strength steel strapping bands per bundle, weight typically 2-5 tons per bundle. Plastic end caps for bars over 40mm diameter. Each bundle clearly tagged with heat number, grade (GB 40Cr), diameter, length, and heat treatment condition. Anti-rust oil coating applied to all exposed surfaces. Custom packaging including wooden crates for premium or air shipment orders. |
|---|---|
| Payment Terms | T/T (Telegraphic Transfer),L/C (Letter of Credit),D/P (Documents against Payment),Western Union,PayPal |
| Price Term | FOB,CFR,CIF,EXW |
| Supply Capacity | 8,000 Tons/Month (Alloy & Carbon Steel Bars) |
| Loading Port | Tianjin / Shanghai / Qingdao |
Why Choose Our GB 40Cr Alloy Steel Round Bar?
Chromium-Enhanced Hardenability
Chromium content (0.80-1.10%) enables through-hardening in sections up to 40-50mm with oil quenching — significantly exceeding carbon steel capability — ensuring more uniform strength and hardness from surface to core for shaft and gear applications.
Comprehensive Size Range & Conditions
Diameter from 10mm precision bars to 500mm heavy forged bars with lengths 3m-12m. Available in hot rolled, cold drawn, normalized, annealed, Q&T, forged, rough turned, peeled, and precision ground conditions.
Best Cost-Performance Alloy Steel
GB 40Cr offers the optimal balance between carbon steel pricing and alloy steel performance. Approximately 15-25% lower cost than GB 42CrMo while providing substantially better hardenability and strength than GB 45# carbon steel.
Excellent Induction Hardening Response
Responds reliably to induction hardening (HRC 50-55) and flame hardening for selective surface wear resistance on shaft journals, gear teeth, and spline profiles — the most popular grade for induction-hardened shaft and gear components in China.
Universal International Equivalence
GB 40Cr is globally recognized as equivalent to AISI 5140, EN 41Cr4, DIN 41Cr4, JIS SCr440, and BS 530M40 — enabling seamless material substitution across international projects. Mill certified per EN 10204 3.1/3.2.
🏭 Applications of GB 40Cr Alloy Steel Round Bar
GB 40Cr alloy steel round bar is the standard choice for medium-duty mechanical components requiring a strength level beyond carbon steel capability. In the machinery industry, it is used for transmission shafts, drive shafts, gear box shafts, pump shafts, and spindle shafts. Its outstanding induction hardening response makes it ideal for gear teeth, spline shafts, and shaft journals requiring selective surface hardness. The automotive sector uses GB 40Cr for half-shaft shafts, steering knuckle pins, transmission gears, and connecting rod bolts. After carburizing, it serves as a cost-effective material for intermediate-duty pinion gears and camshafts. The construction industry relies on GB 40Cr for high-strength structural bolts (equivalent to ASTM A325 / ISO 898 Class 8.8), anchor bolts, and crane shaft pins. Other applications include agricultural equipment drive shafts, mining conveyor roller shafts, machine tool lead screws, and general mechanical engineering components requiring medium strength, good hardenability, and competitive cost.
📋 Quality & Certification
Our Certifications
- ✅ ISO 9001:2015
- ✅ CE Marking
- ✅ ABS
- ✅ DNV GL
- ✅ Lloyd's Register (LR)
- ✅ Bureau Veritas (BV)
- ✅ SGS Certified
- ✅ NK
- ✅ RINA
Mill Certificate Type
- 📋 EN 10204 3.1
- 📋 EN 10204 3.2
- 📋 Original Mill Certificate
- 📋 Third Party Inspection Available
- 📋 Certificate of Origin
❓ Frequently Asked Questions
What is GB 40Cr alloy steel round bar?
GB 40Cr is a chromium alloy structural steel round bar specified under Chinese national standard GB/T 3077 with carbon content 0.37-0.44% and chromium 0.80-1.10%. It is the most widely used mid-range alloy steel grade in China, offering a balanced combination of higher strength than carbon steel (tensile ≥785 MPa in Q&T), reliable hardenability (through-hardens in sections up to 40-50mm), good machinability, and excellent induction hardening response. It is internationally recognized as equivalent to AISI 5140, EN 41Cr4, and JIS SCr440.
What are the equivalent grades of GB 40Cr?
GB 40Cr has direct equivalents in major international standards: AISI 5140 / SAE 5140 (US), EN 41Cr4 / 1.7035 (European EN 10083), DIN 41Cr4 (German), JIS SCr440 (Japanese JIS G4104), and BS 530M40 (British). These grades share the same Cr alloy design with very similar chemistry and mechanical properties. For most general engineering applications, they are considered fully interchangeable. Exact verification against the specific project standard is recommended for critical applications.
What is the difference between GB 40Cr and GB 42CrMo?
The key difference is the molybdenum content: GB 42CrMo contains 0.15-0.25% Mo while GB 40Cr has no intentional molybdenum. This gives GB 42CrMo: 1) Greater hardenability — through-hardens in 75-100mm vs 40-50mm for GB 40Cr. 2) Higher temper resistance — better retention of hardness at high tempering temperatures. 3) Superior high-temperature strength. 4) Better fatigue resistance at high strength levels. However, GB 42CrMo is 20-30% more expensive. GB 40Cr is the better choice for medium-duty applications where 40-50mm through-hardening is sufficient and cost optimization is important. GB 42CrMo is specified when heavy sections (>50mm), high-temperature service, or maximum hardenability is required.
What is the difference between GB 40Cr and GB 45# carbon steel?
GB 40Cr contains 0.80-1.10% chromium while GB 45# has no intentional alloying elements. This gives GB 40Cr: 1) Better hardenability — through-hardens in 40-50mm sections vs only 15-25mm for GB 45#. 2) Higher normalized strength — ≥980 MPa vs ≥600 MPa. 3) Superior induction hardening response — more uniform case depth and hardness. 4) Better wear resistance in the hardened condition. 5) More consistent Q&T mechanical properties in heavier sections. However, GB 40Cr is 20-30% more expensive. GB 45# is preferred for simple, thin-section, non-critical applications; GB 40Cr is specified when higher strength, better hardenability, or induction/carburizing treatment is needed.
What heat treatments are available for GB 40Cr?
GB 40Cr responds well to: 1) Normalizing (840-870°C, air cool) — uniformizes grain, establishes baseline properties (tensile ≥980 MPa). 2) Annealing (820-840°C, furnace cool) — softens for maximum machinability (HBW ≤207). 3) Quenching (oil quench 830-860°C) & Tempering (450-650°C) — achieves tensile 785-980 MPa with controlled toughness. 4) Stress relieving (550-650°C) — reduces residual stresses. 5) Induction hardening — selective surface hardening (HRC 50-55) for shaft journals and gear teeth. 6) Carburizing (900-930°C) — achieves surface HRC 58-62 with 0.5-1.5mm case depth. 7) Carbonitriding — similar to carburizing but lower temperature, thinner case. 8) Flame hardening — manual or machine-operated selective hardening.
Can GB 40Cr be welded?
GB 40Cr can be welded with proper precautions. Preheating to 150-250°C is recommended due to its chromium content and hardenability. Low-hydrogen welding consumables (E7018 or ER70S-2) should be used. Post-weld heat treatment (PWHT) at 550-650°C is advisable for critical applications to temper the martensitic HAZ and relieve residual stresses. For non-critical structural welds with thin sections (≤20mm), welding without preheat may be acceptable but is not recommended. For pressure-containing welded structures, formal WPS/PQR qualification is required.
What surface hardening methods are suitable for GB 40Cr?
GB 40Cr responds exceptionally to: 1) Induction hardening — the most popular method, achieves HRC 50-55 with 1-3mm case depth, ideal for shaft journals, gear teeth, and spline profiles. Fast cycle time, selective hardening, minimal distortion. 2) Flame hardening — similar results to induction but with manual or semi-automatic operation, suitable for large or irregular shapes. 3) Carburizing (900-930°C) — achieves HRC 58-62 with 0.5-1.5mm case depth, used for pinion gears and camshafts. 4) Carbonitriding (820-860°C) — thinner case (0.2-0.8mm) with lower distortion than carburizing. 5) Nitriding (500-530°C) — achieves HRC 55-60 with minimal distortion, but lower surface hardness than 42CrMo due to lower Mo content. Induction hardening is by far the most common treatment for GB 40Cr.
What sizes and lengths are available for GB 40Cr round bar?
GB 40Cr alloy steel round bar is available in diameter range from 10mm to 500mm. Standard lengths include 3 meters, 6 meters, and 12 meters, with custom cut-to-length service supported. Cold drawn bars are available in diameters 10-80mm with tolerance h9/h11. Hot rolled bars are available in diameters 10-250mm from stock. For diameters 250-500mm, bars are typically forged and rough-turned with delivery 25-40 days. Precision ground bars are available in diameters 10-200mm with tolerance h6/h7. Tolerance per ISO 286 or DIN 1013 depending on condition.
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