4145 SCM445 alloy structural steel
4145 alloy structural steel offers excellent strength, deep hardenability, and high fatigue resistance. With good toughness and wear resistance, ideal for heavy-duty shafts, drill collars, and other high-stress oilfield and machinery components.
- Standard: AISI 4145, JIS SCM445
- Technique: EAF + LF + VD, forged or hot-rolled, multi-directional forging ratio ≥4, quenched and tempered as required
- Shape: Round, Flat, Plates, Blocks
- Heat treatment: Supplied in quenched and tempered (QT) condition with hardness 28–34 HRC typical; annealed or normalized condition available on request
- Surface Treatment: Turned, milled / ground, sawn ends. Black (hot-rolled / forged surface) available for large sections
- Tolerance: flat bars & plates thickness: +0.5/-0.0 mm (turned); forged blocks: ±0.2 mm
- MOQ: 1 Ton
We supply AISI 4145 in various custom sizes
plate
flat
block
round size range
- Diameter: φ10-1200 mm
Chemical Composition (%)
Grade | C | Si | Mn | P (≤) | S (≤) | Cr | Mo |
4145 | 0.43–0.48 | 0.15–0.35 | 0.75–1.00 | 0.035 | 0.035 | 0.80–1.10 | 0.15–0.25 |
SCM445 | 0.43–0.48 | 0.15–0.35 | 0.60–0.85 | 0.030 | 0.030 | 0.90–1.20 | 0.15–0.30 |
Main characteristics of 4145 alloy steel
- High tensile strength – withstands extreme mechanical loads
- Deep hardenability – ensures uniform properties in large sections
- Excellent fatigue resistance – durable under cyclic stress
- Good toughness – resists impact and shock loading
4145 | SCM445 alloy steel applications
4145 steel for Oil Field Drill Collar & Tool Joint
High carbon content grants 4145 superior strength and wear resistance, reliably withstanding extreme downhole torsion and abrasive conditions for extended service life.
4145 steel for Heavy-Duty Transmission Shaft
Excellent hardenability and fatigue resistance ensure stable power delivery and long-term durability under sustained heavy loads and cyclic stresses.
4145 steel for High-Strength Fastener & Stud
Balanced toughness and high tensile strength make 4145 ideal for critical bolting applications in pressure vessels and heavy machinery, resisting deformation and fracture.
Our Production Technology For 4145 (SCM445) Engineering Alloy Steel
- EAF
- LF
- VD
- ESR
- Forged or Hot Rolled
- Annealed / Normalized / Quenched and Tempered (as specified)
- Machined surface / Peeled / Black finish
- Ultrasonic testing (UT) 100% as per ASTM A388 or SEP 1921 (upon request)
- Micro Cleanliness as per ASTM E45 (upon agreement)
- Grain size ≥ 5 per ASTM E112 for critical applications
- Hardenability must be carefully considered when designing and selecting equipment for larger sections
- Delivery condition options:Annealed (+A): hardness ≤ 250 HBQuenched and tempered (+QT): 28–36 HRC (typical oilfield delivery condition)Higher strength variant: 30–36 HRC
- Mechanical properties as per ASTM A29 / ASTM A322 or API specifications
mechanical properties & heat treatment of 4145 steel
| Heat temperature | Start forging temperature | Finish forging temperature | Cooling method |
| 1150 – 1205 °C | 1150 – 1200 °C | ≥ 850 °C | Pit, sand, or furnace cooling |
Annealing
- Annealing temperature: 790 – 845°C (alternative range: 800–850°C)
- Hold at temperature for sufficient time (minimum 30 minutes per 25mm of section thickness; for larger sections, 8–14 hours may be required)
- Cool slowly in the furnace to approximately 480°C
- Then air cool to room temperature
- Hardness after annealing: ≤ 250 HB
- Annealing in a protective atmosphere is recommended to reduce decarburization and surface scaling
Hardening
- 4145 alloy steel is typically oil quenched to achieve the required hardness. Proper preheating and austenitizing are critical to achieve the desired hardness without cracking. The hardenability limitations of this grade must always be taken into account when designing and selecting equipment
- Pre-heating (recommended): Preheat to 600 – 650°C to reduce thermal shock during austenitizing
- Austenitizing temperature: 815 – 875°C.Lower range (815–845°C): for thinner sectionsUpper range (840–875°C): for heavier sectionsAlternative range: 830–880°C for first quench, with a second stage at 880°C
- Holding time: At least 30 minutes per 25mm of section thickness (typically 2–4 hours for larger sections)
- Quenching media:Oil (preferred for most sections) — provides good hardness with moderate distortionWater or polymer — for larger sections or when faster cooling is required (water cooling can improve hardness uniformity)For induction hardening: 880°C with subsequent quenching
- Hardness after quenching: 380 – 400 HB (approx. 40–44 HRC).
Stress relieving
- Perform after rough machining, heavy stock removal, or other cold working operations to reduce residual stresses
- Heat carefully to 600 – 650°C
- Hold at temperature for 1 hour per 25mm of section thickness (minimum 2 hours)
- Air cool after holding
- This operation reduces the risk of distortion during final hardening and improves dimensional stability
Tempering
- Temper immediately after the workpiece cools to hand-warm temperature (approx. 50–70°C). Delayed tempering may cause cracking
- Number of tempers: Minimum 1 time for standard applications; 2 times recommended for critical components requiring maximum toughness and property stability
- Holding time: 1 hour per 25mm of section thickness (minimum 2 hours; for larger sections, 2–3 hours)
- Cooling method: Air cool or water cool after each tempering cycle
- Tempering temperature ranges:550 – 700°C: Standard tempering range for 4145560°C: For hardness ~300 HB (typical for oilfield applications)620 – 650°C: For 28–34 HRC (balanced properties)670°C: For lower hardness requirements200°C: Low-temperature tempering for maximum hardness (52–54 HRC)
Why Choose NSPM as Your 4145 alloy steel Supplier
Source Direct
Direct mill cooperation ensures stable supply, competitive pricing, and consistent quality. Global resource integration and strong supply chain management guarantee reliable material sourcing and long-term availability.
Stock Ready
50,000+ tons inventory across 11 warehouses enables fast delivery. Flexible cutting, short lead times, and ready stock support urgent demands and improve customers’ production efficiency.
Expert Team
600+ professionals, including R&D specialists and technical engineers, provide application-driven support. Fast response and deep tooling knowledge ensure accurate solutions for diverse industrial needs.
Fully Inspected
Strict quality control system with full traceability, UT testing, and heat treatment records. Certified standards (ISO, CE) ensure every material meets high-performance and reliability requirements.
Full-Chain Machining
From steel supply to precision machining, heat treatment, and equipment manufacturing, NSPM offers integrated solutions that enhance accuracy, efficiency, and overall tooling performance.
