AISI/SAE 4145H is a chromium-molybdenum (Cr-Mo) low-alloy, medium-carbon structural steel with controlled hardenability. The "H" suffix denotes a guaranteed Jominy end-quench hardenability band, so every heat reaches uniform strength and hardness across large sections. METAL supplies 4145H as forged, quenched-and-tempered (Q+T) hollow bars, produced by boring solid forged rounds, for the oil & gas, mining, power-generation and heavy-engineering industries. With a slightly higher carbon level (0.43–0.48 %) than 4140 and a verified hardenability band, 4145H gives deeper, more stable core strength and good fatigue resistance in big forgings operated several kilometres downhole. METAL chooses clean EAF+LF+VD-refined heats and tightens the carbon and chromium ranges so that even 800 mm diameter hollow bars hold a consistent 285–341 HB through the full wall thickness.
Because the hardenability band is guaranteed, METAL can predict the as-quenched hardness of a 1200 mm forged round as reliably as a small bar, which removes the need for costly section-by-section re-qualification. The steel machines well in the annealed state, welds with preheat and post-weld stress relief, and resists temper embrittlement, so it stays tough even after high-temperature tempering. These traits explain why 4145H, rather than 4140 or 4340, is specified for the most demanding rotating and downhole members of a drill string.
METAL stocks and cross-checks the equivalents below and can issue dual-certified material test reports on request.
| Standard | Designation / Grade | Region | Note |
|---|
| AISI / SAE | 4145H | Base grade, H-band controlled |
| UNS | G41450 | UNS number for 4145 family |
| ASTM | A304 / A322 / A29 / A255 / A519 | H-steel, alloy bars, mechanical tubing |
| AMS | 6395 | 4145 aerospace bars, forgings, tubing |
| API | Spec 7-1 | Drill stem elements specification |
| EN | 42CrMo4 / 1.7225 | EU | EN 10083-3, close match |
| DIN | 42CrMo4 / 1.7225 | German equivalent grade |
| GOST | 38KhM / 40KhM | 38XM / 40XM alloy steel |
| JIS | SCM445 / SCM445H | G4053; SCM440 matches 4140 |
| GB | 42CrMo / 45CrMo | GB/T 3077 structural alloy steel |
METAL forges, bores and machines 4145H into the specific parts listed below, aligning grain flow to the load path for maximum service life.
Oil & Gas: drill collars, heavy-weight drill pipe (HWDP), tool joints, crossover subs, pup joints, stabilizers, reamers, fishing tools, blowout-preventer (BOP) rams and bodies, wellhead flanges, valves, pump rods and mandrels.
Mining: crusher main shafts, drag-bit bodies, mine hoist pins, thickener rake arms and mine car axles.
Power Generation: turbine rotor shafts, coupling spindles, high-pressure valve bodies and pressure-part bolting.
General & Heavy Engineering: large gears, connecting rods, anchor bolts, hydraulic press columns and mill rolls exposed to heavy wear.
METAL reviews each component drawing for stress concentration and selects the forging ratio, bore method and heat-treatment profile that give the best strength-to-weight and fatigue performance for that specific service.
METAL offers 4145H in a wide size range to suit both stock and custom forgings
| Product Form | Size Range |
|---|
| Hot-rolled round bar | Diameter 20–500 mm |
| Forged round bar | Diameter 150–1200 mm |
| Hollow / bored bar (BTA & trepanned) | OD 70–800 mm, ID 20–600 mm, length up to 9450 mm (31 ft) |
| Rolled flat bar | Thickness 10–200 mm, width 50–600 mm |
| Strip / flat coil | Thickness 2–20 mm, width 20–400 mm |
Delivery condition: Quenched and Tempered (Q+T) to 285–341 HB / 30–36 HRC as standard; annealed or normalized conditions available on request.
Surface condition: black (as-forged / as-rolled), rough turned, peeled, ground or polished; outer surface machined or rough peeled, bore trepanned and drifted to close tolerance.
METAL keeps common sizes in ready stock (minimum order 1 piece, about 7-day dispatch) and produces custom forgings from 3 tonnes with roughly 30-day lead time. Every hollow bar is given 100 % ultrasonic testing before shipment.
METAL controls straightness to 1.6 mm per 1000 mm, checks OD and wall tolerance against ASTM A519 and API 7-1, and applies rust-preventive oil plus seaworthy packing for export. Threaded or plain ends, hardbanding and custom bores are supplied to customer specification.
| Element | C | Mn | Si | Cr | Mo | Ni | Cu | P max | S max |
|---|
| % by weight | 0.43–0.48 | 0.75–1.05 | 0.15–0.35 | 0.80–1.10 | 0.15–0.25 | 0.25 max | 0.30 max | 0.025 | 0.035 |
METAL verifies the chemistry of every heat by optical emission spectrometry before pouring, fine-tunes the analysis to customer mechanical targets and controls phosphorus and sulphur tightly for sour-service suitability. All material is shipped under an ISO 9001 quality system with full traceability.
Chromium builds hardenability and wear resistance, molybdenum adds high-temperature strength and slows hydrogen embrittlement, while manganese and silicon strengthen the ferrite and deoxidise the melt; tight P and S keep the steel clean for sour and high-pressure wells.
Typical heat treatment: forge or normalize, austenitize at 840–870 °C and oil quench, then temper at 540–650 °C and air cool. Properties per API Spec 7-1 drill-collar grades by outside diameter
| Drill Collar OD | Yield Rp0.2 min | Tensile Rm min | Elong. min |
|---|
| 70–98.4 mm (2-3/4"–3-7/8") | 827 MPa (120 ksi) | 896 MPa (130 ksi) | 13 % |
| 101.6–174.6 mm (4"–6-7/8") | 758 MPa (110 ksi) | 827 MPa (120 ksi) | 13 % |
| 177.8–279.4 mm (7"–11") | 689 MPa (100 ksi) | 758 MPa (110 ksi) | 13 % |
Across all sizes 4145H typically shows reduction of area ≥ 40 %, hardness 285–341 HB (28.5–36 HRC), Charpy-V impact ≥ 54 J at room temperature and ≥ 27 J at -20 °C. Physical data: density 7.85 g/cm³, modulus of elasticity about 210 GPa.
Tempering between 250 and 375 °C is avoided because it lowers impact values. Compared with 4140, 4145H gives higher and more uniform strength in large sections; compared with 4340 it is more cost-effective for drilling use while still meeting API minimums. METAL heat-treats in calibrated furnaces, tests tensile, impact and hardness per heat, and ships with an EN 10204 3.1 mill test certificate under its ISO 9001 management system.
