T: +86-0731-85185770
E: enquiry@qilumetal.com
E: enquiry@qilumetal.com
No. 18 Xiangfu Middle Road,Yuhua District, Changsha City
 |
Grade: AISI 4145
Equivalent Steel: GB 40CrMnMo, JIS SCM445
ASTM 4145 is a chromium-molybdenum alloy steel with a precisely controlled chemical composition of 0.43–0.48% carbon, 0.80–1.10% chromium, 0.15–0.25% molybdenum, 0.75–1.00% manganese, and 0.15–0.35% silicon. This carefully balanced formulation delivers exceptional hardenability, high strength, uniform hardness penetration, and good creep resistance, making it the material of choice for demanding applications such as drill collars, tool joints, pump shafts, and large-section heavy machinery components requiring consistent through-section properties.
| Quantity: | |
|---|---|
4145
Qilu
AISI 4145 (UNS G41450) is a low-alloy chromium-molybdenum alloy steel widely known as chromoly steel, engineered to outperform standard AISI 4140 for large-section, heavy cyclic load components. Its elevated carbon content (0.43–0.48%) delivers superior through-hardenability, eliminating core softness issues common in thick 4140 steel workpieces.
Unlike generic low-alloy steel, 4145 maintains consistent mechanical properties from surface to core after quenching & tempering, resisting torsion, fatigue fracture and abrasive wear under long-term heavy operation. It complies with ASTM A29/A29M industrial standards and API oilfield material specifications, making it the top choice for high-stress downhole and mechanical transmission parts where 4140 fails to meet load limits
Country | USA | China | Japan |
Standard | ASTM A29 | GB/T3077 | JIS G4105 |
Grade | 4145 | 40CrMnMo | SCM445 |
Grade | C | Si | Mn | P | S | Cr | Mo |
4145 | 0.43-0.48 | 0.15-0.35 | 0.75-1.00 | 0.035Max | 0.040Max | 0.80-1.10 | 0.15-0.25 |
40CrMnMo | 0.37-0.45 | 0.17-0.37 | 0.90-1.20 | 0.030Max | 0.030Max | 0.90-1.20 | 0.20-0.30 |
SCM445 | 0.43-0.48 | 0.15-0.35 | 0.60-0.85 | 0.030Max | 0.030Max | 0.90-1.20 | 0.15-0.30 |
Ultimate Tensile Strength: 896–1130 MPa
0.2% Offset Yield Strength: 758–965 MPa
Elongation: ≥15%
Reduction of Area: ≥35%
Typical Hardness Range: HRC 28–36
Low-Temperature Impact Toughness: Stable impact resistance down to -46°C
| Mechanical Property Index | Minimum Value |
| Tensile Strength | 980Mpa |
| Lower Yield Strength | 785Mpa |
| Elongation after Fracture | 10% |
| Reduction of Area | 45% |
| Impact Absorbed Energy | 63J |
| Brinell Hardness (Delivery Condition) | 217Max HBW |
Note: All mechanical property indicators are the test requirements after the sample has undergone standard heat treatment (850℃ oil quenching + 600℃ water/oil tempering), and the hardness is the upper limit of the delivery state after annealing/high temperature tempering.
Initial Forging Temperature: 1180 ~ 1220 ℃
Final Forging Temperature: 850 ~ 900 ℃
Slow heating is required for large-size ingots or billets to avoid internal thermal cracking caused by uneven temperature distribution.
Stop forging once the workpiece temperature drops below 850 ℃ to prevent coarse internal grain structure and reduced toughness.
After forging, slow cooling in sand or furnace cooling is recommended to release forging internal stress and avoid surface cracks.
Heating Temperature: 850 ℃
Holding Time: Calculate based on workpiece thickness (1.5–2 min per mm of cross-section)
Cooling Medium: Oil
Tempering Heating Temperature: 600 ℃
Holding Time: Sufficient holding to guarantee uniform internal temperature
Cooling Medium: Water or oil
Annealing Temperature: 840 ~ 860 ℃, furnace slow cooling to below 300 ℃ then air cool
High-temperature Tempering Temperature: 650 ~ 680 ℃, air cooling after heat preservation
Target Delivery Hardness: HBW ≤ 217, suitable for subsequent machining
Product type | Size range | Length |
Cold drawn bar | Φ3-Φ80mm | 6000-9000mm |
Hot rolled bar | Φ16-Φ310mm | 6000-9000mm |
Hot forged bar | Φ100-Φ1200mm | 3000-5800mm |
Hot rolled plate/sheet | T:3-200mm; W:1500-2500mm | 2000-5800mm |
Hot Forged block | T: 80-800mm; W: 100-2500mm | 2000-5800mm |
Surface Finish | Turned | Milled | Grinding(Best) | Polished(Best) | Peeled(Best) | Black Forged | Black Rolled |
Tolerance | +0/+3mm | +0/+3mm | +0/+0.05mm | +0/+0.05mm | +0/+0.1mm | +0/+5mm | +0/+1mm |
Straighness | 1mm/1000mm max. | 3mm/1000mm max. | |||||
We maintain over 10,000 tons of in-stock 4145 steel monthly for fast delivery. Stock changes daily; contact our sales team for real-time inventory.
AISI 4145 chromoly steel features medium-high carbon content, resulting in poor inherent weldability. Its heat-affected zone is prone to hard martensite formation, leading to cold delayed cracks and reduced impact toughness without standardized welding procedures. Preheat materials to 260–370°C and sustain consistent interpass temperature during multi-pass welding, use fully baked low-hydrogen electrodes, and implement post-weld stress-relief tempering at 590–650°C followed by slow furnace cooling. Welded joints are not ideal for heavy cyclic torsion and impact components; mechanical assembly is recommended for high-load service parts.
API standard drill collars, drill pipe connectors, borehole stabilizers, directional drilling tools, fishing retrieval tools, casing hangers, valve stems for high-pressure wellheads
Crusher main shafts, rock drill tool bodies, heavy-duty transmission gears, hydraulic press spindles, oversized high-strength bolt forgings
Large load drive axles, heavy truck gear shafts, bearing housings, high-torque coupling parts, mold holders for heavy forming equipment
Paper mill rolls, pump heavy shafts, wind turbine auxiliary transmission components, hydraulic cylinder rods for high-pressure systems
| Comparison Item | AISI 4145 | AISI 4140 | Suitable Scenario |
| Carbon Content | 0.43–0.48% | 0.38–0.43% | Higher carbon = stronger 4145 |
| Through-Hardenability | Excellent (large cross-section uniform hardness) | Good (core soft on diameter >100mm) | Large diameter forgings select 4145 |
| Tensile & Wear Performance | 10–15% higher strength & abrasion resistance | Balanced strength & toughness | Long-term heavy torsion load use 4145 |
| Low-Temp Impact Toughness | Slightly lower at same hardness | Better ductility under cold impact | Ultra-low temp parts select 4140 |
| Main Cost Position | Slightly higher raw material cost | More cost-efficient for small light-load parts | Light-duty small shafts use 4140 |
A1: AISI 4145 has higher carbon content than 4140, delivering better through-hardenability, tensile strength and wear resistance for large-section forgings. However, 4140 offers superior low-temperature impact toughness and better weldability, making it more suitable for low-temperature dynamic parts.
A2: In short, select standard 4145 for general machinery, 4145H for regular oilfield forgings, and 4145MOD for high-spec large-section downhole drilling components.
AISI 4145: Standard base chromoly steel with a wide allowable hardenability band, general-purpose for small & medium-sized heavy machinery parts, no strict hardenability tolerance control.
AISI 4145H: H stands for Hardenability-controlled steel, with tighter restricted alloy element ranges and fixed end-quench hardenability bandwidth. It ensures consistent core hardness for large-diameter forgings, compliant with API oilfield basic requirements.
AISI 4145MOD (Modified 4145H): Upgraded variant of 4145H with optimized Mn, Cr and Mo content to further boost deep through-hardenability. It meets stricter API 7-1 standards for ultra-large drill collars and downhole tools, delivering uniform mechanical properties across extra-thick cross-sections where standard 4145/4145H cannot reach required core strength.
A3: AISI 4145 raw bars supplied under annealed or normalized state have a maximum Brinell hardness of HBW 235, which guarantees smooth machining performance.
A4: No. AISI 4145 has high quenching tendency, direct welding without preheating will produce cold delayed cracks in the heat-affected zone. Preheating to 260–370°C and post-weld stress relief tempering are mandatory.
If you need high-performance AISI 4145 chromoly alloy steel round bars, plates, hollow drill collars or custom forgings for oil gas, mining and heavy machinery manufacturing, send your drawing, size and hardness requirements for free technical quotation and material datasheet.
