GB 42CrMo Alloy Steel Round Bar
GB 42CrMo is a chromium-molybdenum alloy steel round bar per GB/T 3077, equivalent to AISI 4140 / EN 42CrMo4 / SCM440. Offers high strength, excellent hardenability, superior toughness, and good fatigue resistance. Diameter 16mm-600mm, available in hot rolled, Q&T, and nitrided conditions for oil & gas, wind power, and heavy machinery.
| Material | Alloy Steel (Cr-Mo) |
|---|---|
| Grade / Standard | GB 42CrMo |
| Diameter | 16mm - 600mm |
| 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 | 15-30 Days / In Stock (Common Sizes) |
| Loading Port | Tianjin / Shanghai / Qingdao |
Overview of GB 42CrMo Alloy Steel Round Bar
GB 42CrMo is one of the most widely used and trusted alloy steel round bar grades in China and global markets, specified under the Chinese national standard GB/T 3077 (Alloy Structure Steels). Classified as a chromium-molybdenum (Cr-Mo) alloy steel with carbon content typically 0.38-0.45%, chromium 0.90-1.20%, and molybdenum 0.15-0.25%, this grade delivers an outstanding combination of high strength, excellent hardenability, superior toughness, and good fatigue resistance. GB 42CrMo is internationally recognized as the equivalent of AISI 4140, EN 42CrMo4 (1.7225), and JIS SCM440, making it a truly universal alloy steel grade with seamless cross-border acceptance.
Shandong Tanglu Metal Material Co., Ltd. supplies premium GB 42CrMo alloy steel round bar produced by leading Chinese special steel mills utilizing advanced EAF (Electric Arc Furnace) + LF (Ladle Furnace) + VD (Vacuum Degassing) steelmaking technology. Our 42CrMo bars offer consistent fine-grain microstructure, ultra-low gas content (O₂ ≤ 20ppm, H₂ ≤ 2ppm), and reliable mechanical properties from surface to core, ensuring dependable performance in the most demanding oil & gas, automotive, machinery, wind power, and heavy forging applications. Whether for quenched & tempered high-strength shafts, nitrided wear-resistant components, or induction-hardened precision gears, GB 42CrMo delivers the proven metallurgical quality that engineering professionals trust.
Key Features and Technical Advantages
The core advantage of GB 42CrMo alloy steel lies in its outstanding hardenability — the synergistic effect of chromium (0.90-1.20%) and molybdenum (0.15-0.25%) enables through-hardening in sections up to 75-100mm (3-4 inches) diameter with oil quenching. This ensures uniform mechanical properties from surface to core, far exceeding the capability of carbon steel grades like GB 45# or low-alloy grades like GB 40Cr.
GB 42CrMo round bar is manufactured through hot rolling, forging, cold drawing, and peeling/turning processes. In the normalized condition, it delivers tensile strength ≥1080 MPa — nearly double that of GB 45# carbon steel. After quenching & tempering (Q&T), tensile strength ranges from 900 MPa to 1080 MPa depending on tempering temperature and section size, with excellent impact toughness maintained even at low temperatures. The grade also responds exceptionally to nitriding (surface hardness HRC 60-65), induction hardening (selective surface hardening), and carburizing for applications requiring a hard wear-resistant surface over a tough ductile core.
Our 42CrMo bars are available in diameter range from 16mm to 600mm, with standard lengths of 3m, 6m, and 12m. Surface conditions include hot rolled (black), forged & rough turned, peeled, and precision ground (h6/h7/h9). All bars undergo ultrasonic testing for internal soundness, and each heat is verified for chemical composition, mechanical properties, microstructure, and grain size per GB/T 3077 requirements.
Main Applications of GB 42CrMo Round Bar
GB 42CrMo alloy steel round bar is the workhorse material for the oil & gas drilling industry, used extensively for drill collars, heavy-weight drill pipe, stabilizer blades, mud motor shafts, downhole tools, and wellhead equipment. Its combination of high strength, toughness, and fatigue resistance makes it ideal for the extreme cyclic loading, impact, and corrosion conditions encountered in deep well drilling operations.
In the wind power industry, 42CrMo is the standard material for main shaft forgings, gearbox intermediate shafts and gears, yaw and pitch system bearings, and tower bolt connections. The automotive and heavy machinery sectors rely on 42CrMo for crankshafts, axle shafts, connecting rods, hydraulic cylinder piston rods, press ram shafts, and heavy-duty gear blanks. After nitriding, 42CrMo provides exceptional surface wear resistance for extruder screws, injection molding machine tie bars, press brake tooling, and precision hydraulic valve spools.
Other critical applications include high-strength structural bolts and studs (equivalent to ASTM A193 B7), forged flanges and fittings (equivalent to ASTM A182 F11/F12), mining equipment drill rods and crusher shafts, railway locomotive axle forgings, forging die inserts, and general heavy machinery transmission shafts operating under high torque and shock loading conditions.
Why Choose Us for GB 42CrMo Alloy Steel Round Bar
Shandong Tanglu Metal Material Co., Ltd. sources GB 42CrMo alloy steel round bar from Tier-1 Chinese special steel mills holding ISO 9001, ISO 14001, PED (Pressure Equipment Directive), and major classification society certifications (DNV, BV, LR, ABS). We maintain strict chemistry control per GB/T 3077 specification with particular attention to residual element limits (Cu ≤ 0.30%, Sn ≤ 0.030%) and ultra-low gas content (O₂ ≤ 20ppm, H₂ ≤ 2ppm, N₂ ≤ 80ppm) to ensure optimal toughness and fatigue performance.
We offer comprehensive heat treatment services including normalizing, annealing, quenching & tempering, stress relieving, nitriding, and induction hardening. Bars can be supplied in hot rolled, forged & rough turned, peeled, or precision ground condition per customer specification. With monthly supply capacity of 5,000 tons of alloy steel bars and extensive export experience to over 60 countries across Asia, Middle East, Europe, Africa, and South America, we provide the quality consistency, technical transparency, and competitive lead times required for large-scale industrial projects. 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, TÜV, ABS, DNV, LR) available upon request.
📐 Dimension & Size Table
| Diameter (mm) | Length (m) | Weight (kg/m) | Tolerance (Hot Rolled) |
|---|---|---|---|
| 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 |
| 130 | 6 / 12 | 103.963 | ± 1.60mm |
| 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 |
| 350 | 3 | 755.269 | ± 5.50mm |
| 400 | 3 | 986.467 | ± 6.00mm |
| 500 | 3 | 1541.354 | ± 8.00mm |
| 600 | 3 | 2219.549 | ± 10.0mm |
* Custom sizes available upon request. Tolerances per relevant international standards.
🔬 Chemical Composition
| Element | Min | Max | Display Value | Note |
|---|---|---|---|---|
| C | 0.38 | 0.45 | 0.38-0.45 | Per GB/T 3077 specification |
| Cr | 0.90 | 1.20 | 0.90-1.20 | Hardenability element |
| Mo | 0.15 | 0.25 | 0.15-0.25 | Hardenability & temper resistance |
| 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 |
* 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) | ≥1080 | MPa | GB/T 3077 specification |
| Yield Strength (Normalized) | ≥930 | MPa | GB/T 3077 specification |
| Tensile Strength (Q&T) | 900-1080 | MPa | Quenched & tempered 540-650°C |
| Yield Strength (Q&T) | ≥750 | MPa | Q&T condition, ≤75mm 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) | ≤217 | HBW | Maximum annealed hardness |
| Brinell Hardness (Q&T) | 260-320 | HBW | Typical Q&T range |
| Surface Hardness (Nitriding) | 60-65 | HRC | After gas/plasma nitriding |
| Surface Hardness (Induction) | 52-58 | HRC | After induction hardening |
| Fatigue Endurance Limit | ≥480 | 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 4-6 high-strength steel strapping bands per bundle, weight typically 2-5 tons per bundle. Plastic or wooden end caps for bars over 50mm diameter. Each bundle clearly tagged with heat number, grade (GB 42CrMo), diameter, length, and heat treatment condition. Anti-rust oil coating applied to all exposed surfaces. VCI wrapping available for precision ground bars. 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 |
| Price Term | FOB,CFR,CIF,EXW |
| Supply Capacity | 5,000 Tons/Month (Alloy Steel Bars) |
| Loading Port | Tianjin / Shanghai / Qingdao |
Why Choose Our GB 42CrMo Alloy Steel Round Bar?
Proven Cr-Mo Alloy Hardenability
Chromium-molybdenum alloy system (Cr 0.90-1.20%, Mo 0.15-0.25%) enables through-hardening in sections up to 75-100mm with oil quenching, ensuring uniform mechanical properties from surface to core for heavy-duty shaft and gear applications.
Comprehensive Size Range & Conditions
Diameter from 16mm precision bars to 600mm heavy forged bars with lengths 3m-12m. Available in hot rolled, normalized, annealed, Q&T, forged, rough turned, peeled, and precision ground conditions for every manufacturing stage.
Universal International Equivalence
GB 42CrMo is globally recognized as equivalent to AISI 4140, EN 42CrMo4, DIN 42CrMo4, JIS SCM440, and BS 708M40 — enabling seamless material substitution across international projects and simplifying multi-standard procurement.
Excellent Nitriding & Surface Hardening
Responds exceptionally to gas nitriding, plasma nitriding (surface HRC 60-65), and induction hardening (surface HRC 52-58), providing wear-resistant surfaces ideal for extruder screws, hydraulic rods, and precision gears.
Mill Certified & Fully Traceable
EN 10204 3.1/3.2 certification with UT testing, complete chemistry, mechanical properties, microstructure, and grain size verification. Third-party inspection per SGS, BV, DNV, LR, ABS available for critical project applications.
🏭 Applications of GB 42CrMo Alloy Steel Round Bar
GB 42CrMo alloy steel round bar is the definitive material for high-strength, high-reliability applications across multiple industries. In oil & gas, it is used for drill collars, stabilizers, mud motor shafts, downhole tools, and wellhead components. The wind power industry relies on 42CrMo for main shaft forgings, gearbox gears and shafts, and yaw/pitch system components. The automotive and heavy machinery sectors use 42CrMo for crankshafts, axle shafts, connecting rods, hydraulic cylinder rods, and transmission shafts. After nitriding, 42CrMo provides exceptional surface wear resistance for extruder screws, injection molding tie bars, press brake tooling, and precision valve spools. The grade is also the primary raw material for high-strength fasteners (equivalent to ASTM A193 B7) and forged flanges (equivalent to ASTM A182 F11/F12) used in pressure vessel and piping systems worldwide.
📋 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 42CrMo alloy steel round bar?
GB 42CrMo is a chromium-molybdenum alloy steel round bar specified under Chinese national standard GB/T 3077 (Alloy Structure Steels) with carbon content 0.38-0.45%, chromium 0.90-1.20%, and molybdenum 0.15-0.25%. It is one of the most widely used and trusted alloy steel grades in China and globally, offering an excellent combination of high strength (tensile ≥900 MPa in Q&T), superior hardenability (through-hardens in sections up to 75-100mm), good toughness, and reliable fatigue resistance. It is internationally recognized as the direct equivalent of AISI 4140, EN 42CrMo4, and JIS SCM440.
What are the equivalent grades of GB 42CrMo?
GB 42CrMo has direct equivalents in all major international standards: AISI 4140 / SAE 4140 (US), ASTM A829 4140 (US), EN 42CrMo4 / 1.7225 (European EN 10083), DIN 42CrMo4 (German), JIS SCM440 (Japanese JIS G4105), and BS 708M40 (British). These grades share the same Cr-Mo alloy design with nearly identical chemistry and mechanical properties, and are generally considered fully interchangeable for most engineering applications. For specific projects, exact verification against the applicable standard is recommended.
What is the difference between GB 42CrMo and GB 40Cr?
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 sections vs 40-50mm for GB 40Cr. 2) Higher temper resistance — better retention of hardness after tempering at high temperatures (500-650°C). 3) Better high-temperature strength — suitable for elevated temperature service. 4) Superior fatigue resistance at high strength levels. 5) Improved impact toughness in Q&T condition. However, GB 42CrMo is more expensive (~20-30% premium). GB 40Cr is preferred for general medium-strength applications; GB 42CrMo is specified when higher hardenability, temper resistance, or heavy-section through-hardening is required.
What heat treatments are available for GB 42CrMo?
GB 42CrMo responds well to: 1) Normalizing (850-880°C, air cool) — uniformizes grain structure, establishes baseline properties. 2) Annealing (800-850°C, furnace cool) — softens for maximum machinability (HBW ≤217). 3) Quenching (oil quench 830-860°C) & Tempering (400-700°C) — achieves tensile 900-1080 MPa with controlled toughness. 4) Stress relieving (600-650°C) — reduces residual stresses after machining or welding. 5) Nitriding (500-530°C, 20-100 hours) — achieves surface HRC 60-65 with minimal distortion. 6) Induction hardening — selective surface hardening (HRC 52-58) for shaft journals and gear teeth. 7) Carburizing (850-950°C) — achieves HRC 58-62 surface with 0.5-2.0mm case depth. 8) Austempering — produces bainitic structure for superior toughness.
Can GB 42CrMo be welded?
GB 42CrMo can be welded, but requires careful procedures due to its alloy content and hardenability. Preheating to 200-300°C is essential, and interpass temperature should be maintained. Low-hydrogen welding consumables (such as E10018-D2 or ER80S-D2) are recommended. Post-weld heat treatment (PWHT) at 580-650°C is strongly advised to temper the martensitic HAZ and restore toughness. Without proper preheat and PWHT, the heat-affected zone will form hard brittle martensite, leading to cracking risk. For critical welded structures such as pressure vessels, a formal WPS/PQR qualification per ASME Section IX or equivalent is required.
What surface hardening methods work best for GB 42CrMo?
GB 42CrMo responds exceptionally to: 1) Gas nitriding (500-530°C) — achieves HRC 60-65 surface with 0.2-0.5mm case depth, minimal distortion, ideal for precision hydraulic rods and extruder screws. 2) Plasma/ion nitriding (380-550°C) — faster cycle, precise control, environmentally friendly. 3) Induction hardening — selective surface hardening (HRC 52-58) for shaft journals, bearing seats, and gear teeth. 4) Carburizing (850-950°C) — achieves HRC 58-62 with deeper case but higher distortion risk. Nitriding is generally preferred for 42CrMo as it provides the hardest surface with the least dimensional change.
What is the difference between GB 42CrMo and AISI 4340?
The key difference is the presence of 1.65-2.00% nickel in AISI 4340 (GB 42CrMo has no intentional nickel). This gives AISI 4340: 1) Greater hardenability — through-hardens in 100-150mm sections vs 75-100mm for 42CrMo. 2) Higher maximum tensile strength — up to 1800 MPa in ultra-high-strength Q&T vs 1080 MPa for 42CrMo. 3) Superior low-temperature toughness — better Charpy impact at sub-zero temperatures. 4) Better fatigue endurance at very high strength levels. However, AISI 4340 is significantly more expensive (~40-60% premium). GB 42CrMo is the better choice for most general high-strength applications; AISI 4340 is reserved for extreme performance, aerospace, and ultra-safety-critical applications.
What sizes and lengths are available for GB 42CrMo round bar?
GB 42CrMo alloy steel round bar is available in diameter range from 16mm to 600mm. Standard lengths include 3 meters, 6 meters, and 12 meters, with custom cut-to-length service supported. For diameters up to 250mm, standard hot rolled bars are available from stock. For diameters 250-600mm, bars are typically forged and rough-turned with delivery 30-45 days. Precision ground bars are available in diameters 16-300mm with tolerance h6/h7/h9. Tolerance per ISO 286 (ground) or DIN 1013 (hot rolled). Special lengths up to 18 meters available for selected sizes upon project request.
Request Quote for
GB 42CrMo Alloy Steel Round Bar
Submit your requirements and receive a competitive price quote within 24 hours.
- ✓ Fast response within 24 hours
- ✓ Competitive factory-direct pricing
- ✓ Free technical consultation
- ✓ Mill test certificate provided
- ✓ Flexible payment terms available
⏱ Technical & commercial response within 24 hours
Send Your Inquiry
All fields marked with * are required