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4145
Qilu
Product Description
Hot forged and rolled 4145 round bar supplied annealed or QT to API drill-collar specs, 50 mm to 600 mm diameter, with heat treatment, ultrasonic testing and rough machining done in-house.
Equivalent to: AISI / SAE 4145 · DIN 42CrMo4 (close) · JIS SCM445 · GB 45CrMo · 1.7223
AISI 4145 Forged Alloy Steel in Stock
Supply form — Round bar, including heavy-wall drill-collar stock
Process — Hot forged / hot rolled
Condition — Annealed, or QT to 285–341 HB / 30–40 HRC
Diameter range — 50–600 mm
Standard — ASTM A29 / API 7-1 for drill collars
Certificate — EN 10204 3.1 standard, 3.2 on request
Lead time — 20–35 days depending on size
4145 is the higher-carbon brother of 4140 within ASTM A29. The 0.43–0.48 % carbon with 0.8–1.1 % chromium and 0.15–0.25 % molybdenum pushes tensile strength above 1000 MPa in the QT condition, which is why API 7-1 calls up a modified 4145 (often 4145H mod) for drill collars. The molybdenum keeps toughness up at the strength level required for downhole service.
| Grade | C | Mn | Si | P | S | Cr | Mo |
| 4145 | 0.43-0.48 | 0.75-1.00 | 0.15-0.30 | 0.035Max | 0.040Max | 0.80-1.10 | 0.15-0.25 |
Typical values for the QT condition. For drill-collar stock we quench and temper to API 7-1 and verify Charpy impact at the section size you will actually machine.
| Property | Annealed | QT |
| Tensile strength, Rm (MPa) | ≤ 615 | 965–1100 |
| Yield strength, Re (MPa) | ≤ 360 | ≥ 760 |
| Elongation, A5 (%) | ≥ 18 | ≥ 13 |
| Impact, KV (J) | ≥ 40 | ≥ 35 (API at 20 °C) |
| Hardness (HB) | ≤ 192 | 285–341 |
| Standard | Grade |
| ASTM / SAE (USA) | 4145 / 4145H (mod) |
| DIN (Germany) | ~42CrMo4 / 1.7223 |
| JIS (Japan) | SCM445 |
| GB (China) | 45CrMo |
| API | 7-1 drill collar stock (modified 4145) |
Oil & gas drilling — drill collars, heavy-weight drill pipe, subs and tool joints
Heavy shafting — high-tensile pinions, gear shafts, marine shafts
Mining — hammer shafts, drill rods
Fasteners — high-strength bolts and studs for structural service
4145 is oil-quenched from 840–870 °C and tempered between 550–650 °C. For drill-collar service the cycle is tuned to deliver minimum yield of 760 MPa with Charpy toughness at the actual collar OD — the through-thickness response of large sections is the critical variable, and we map hardness across the section to verify it. Tell us the OD and the spec you are buying to.
Most suppliers in this business are traders who subcontract everything. We run our own processes, which means shorter cycles and one point of accountability when something needs fixing.
Heat treatment shop — quenching and tempering to your target hardness, with furnace charts recorded per batch
Machining shop — rough turning, peeling and cutting to length, so your bar arrives ready for finish machining
Testing — ultrasonic per ASTM A388 / EN 10228-3, hardness mapping across the section, tensile and impact testing
Certification — EN 10204 3.1 as standard, 3.2 available with third-party witness (ABS, BV, CCS, GL)
Export packing — bundled, end-capped and rust-protected for sea freight
A1: API 7-1 specifies a modified 4145 (often 4145H mod) because the Cr-Mo combination delivers high yield strength (>760 MPa) with enough toughness to survive downhole shock loading at large section sizes. The chemistry also responds cleanly to quench-and-temper across thick walls.
A2: Yes. We heat treat in our own shop, ultrasonically test to ASTM A388 / EN 10228-3, and rough-turn the OD. Furnace charts and UT maps come with the mill certificate.
A3: Carbon content: 4145 is 0.43–0.48 % C versus 0.38–0.43 % for 4140, giving higher strength. 4140 is the more general-purpose grade; 4145 is chosen when you need the extra strength for heavy-wall or downhole service. See our 4140 alloy steel page for a full comparison.
Send us your diameter, length, quantity, required hardness and destination port. You will get a quotation with the full technical proposal within 24 hours.
