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4145H Alloy Steel: High‑Strength Hardenable Cr‑Mo Bar 🛠️
4145H Alloy Steel: High‑Strength Hardenable Cr‑Mo Bar 🛠️
4145H Alloy Steel is a chromium‑molybdenum (Cr‑Mo) alloy designed for high-strength, high‑toughness applications—especially oil drilling, drill collars, and heavy industrial shafts. With enhanced hardenability, it outperforms many 41xx family steels (e.g. 4140) when large bar sizes require deep quenchability.
What Is 4145H Alloy Steel?
Chemical composition (typical):
C 0.42–0.49%, Mn 0.65–1.10%, Cr 0.75–1.20%, Mo 0.15–0.25%
Also known as AISI 4145H, UNS G41450, or 4145H Cr‑Mo bar.
4145H is a low‑alloy steel developed for oilfield down‑hole tools—specifically drill collar steel—as well as shafts, gears, bolts, and rock-drilling parts.
| Property (Tempered, Oil Quenched) | Value |
|---|---|
| Tensile strength (Rm) | 965–1 103 MPa (140–160 ksi) |
| Yield strength (0.2% Rₚ₀.₂) | ≥758 MPa (110 ksi) or ≥862 MPa (125 ksi) |
| Elongation | ≥14 % |
| Hardness | 30–36 HRC (~285–341 HB) |
| Modulus of elasticity | 190–210 GPa |
Compared to 4140, 4145H offers higher tensile/yield and improved hardenability, especially in larger cross-sections.
4145H’s chemistry and heat treatment deliver the strength, toughness, and impact resistance essential for oil drilling tools:
Used to manufacture drill collars, heavy weight drill pipes, subs, pup-joints, and fishing tools
The drill collar version often has tighter inclusion controls to enhance impact toughness HRC and low-temperature resilience
As drilling moves to deeper, harsher wells, 4145H’s hydrogen-sulfide resistance and wear life become even more crucial
4145H heat treatment typically includes:
Austenitize at 820–870 °C (1 510–1 600 °F).
Oil quenching to achieve deep hardening.
Tempering (430–700 °C) to balance strength and toughness.
Annealing or stress relieving as needed.
Hardenability:
Tailored to produce 110 ksi, 120 ksi, or 125 ksi yield conditions even in large bars (up to 20 in)
The “H” denotes a restricted hardenability range on Jominy testing
Impact strength metrics show 4145H is resilient even at low temperature:
Charpy V-notch @ 23 °C: ≥54 J; @ −32 °C: ≥27 J
Drilling‑collar grades show Izod–Charpy min >54 J at room temp
Research highlights grain refinement during quench‑temper cycles as key to improved toughness
At low temp (<0 °C), dynamic fracture toughness drops, so low‑temperature performance matters in cold wells
Being a low Cr (0.8–1.2%) and Mo (0.15–0.25%) steel, 4145H does not provide stainless-level corrosion resistance—but offers:
Better fatigue resistance versus plain carbon steel, ideal for cyclic loads in drill strings.
Some H₂S resistance, important in sour service; acceptable in standard oilfield use.
For harsh corrosion, additional coatings or corrosion-resistant alloys may be required.
4145H is often compared to the popular 4140:
4140: C 0.38–0.43%, Cr & Mo similar; good, but limited hardenability at large diameters.
4145H: More carbon and controlled Jominy profile → deeper core hardness, higher yield/tensile, and toughness for big parts.
Compared to 4340, 4145H has slightly lower toughness/strength but is more cost-effective for oil-drilling use.
Primary 4145H alloy steel oil drilling applications include:
Drill collars, pup-joints, fatigue collars
Subs, stabilizers, reamers
Heavy industrial shafts, gears, bolts, anchor bolts
Certifications reference ASTM A29/A304, SAE J1268, AMS 2750, and standards for 110/120/125 ksi bar grades
Chemistry: 0.42–0.49 C, 0.75–1.20 Cr, 0.15–0.25 Mo
Strength: Rm ~965–1 103 MPa, Ry ~758–862 MPa
Hardness: 30–36 HRC (285–341 HB)
Toughness: ≥54 J Charpy @ RT; ≥27 J @ −32 °C
Modulus: ~200 GPa; Density ~7.8 g/cm³
FAQ
1. What are the mechanical properties of AISI 4145H?
Tensile strength ~965–1 103 MPa, yield ~758–862 MPa, elongation ≥14%, hardness 30–36 HRC
2. How is 4145H heat treated?
Austenitize at 820–870 °C, oil quench, temper 430–700 °C; annealing/stress‑relief optional
3. How does 4145H compare to 4140?
4145H has higher carbon and controlled hardenability (“H”), resulting in deeper core strength and toughness in large bars.
4. What is the Charpy impact toughness of 4145H?
Typically ≥54J at 23 °C and ≥27J at −32 °C—suitable for cold drilling operations
5. Is 4145H corrosion‑resistant?
It offers modest resistance aided by Cr‑Mo content; best suited for oilfield environments, but not equal to stainless steels.
If your operation demands a high-strength, high-toughness Cr‑Mo bar for demanding oil drilling or heavy industry applications, Super‑Ingenuity specializes in precision 4145H alloy steel solutions. With expert heat-treatment credentials, strict adherence to ASTM/SAE/AMS norms, and full metallurgical traceability, we ensure components that meet your exact tensile, hardness, and Charpy toughness specs.
🛠️ Contact us today to discuss your RFQ and let our engineering team support your design validation—from material selection to finished bar delivery.
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