Chromium-molybdenum alloy steel forged into drill collars, seamless rolled rings, shafts, flanges and discs at our factory in Jiangyin, Jiangsu, China. Melted EAF + LF + VD, quenched and tempered, supplied with EN 10204 3.1 or 3.2 certification.
Quotation within 24 hours. Drawings, DXF, STEP and sketches all accepted.
Summary
AISI 4145 (UNS G41450) is a medium-carbon chromium-molybdenum alloy steel containing 0.43–0.48% carbon, 0.80–1.10% chromium and 0.15–0.25% molybdenum. Quenched and tempered to 30–36 HRc it reaches a minimum tensile strength of 965 MPa (140 ksi) and a minimum yield of 827 MPa (120 ksi). The extra carbon over AISI 4140 buys deeper hardenability in heavy sections. AISI 4145H and 4145H MOD are the usual materials for API Spec 7-1 drill collars, stabilizers, subs and crossovers.
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, producing AISI 4145 and 4145H forgings from 20 kg to 30,000 kg per piece: seamless rolled rings to 4,000 mm outside diameter, forged bars, shafts, discs, flanges, blocks, sleeves and drill-string components. Enquiries: sales@steelforgepieces.com or +86 189 2135 9659.
What AISI 4145 steel is
AISI 4145 sits in the 41xx family of chromium-molybdenum low-alloy steels, between AISI 4140 and AISI 4150 on the carbon scale. It is covered by ASTM A29 for hot-wrought bars and by ASTM A322 for alloy bars intended for heat treatment, and it carries the UNS number G41450.
The roughly 0.05% extra carbon over AISI 4140 raises both attainable hardness and hardenability. Hardenability is the part that decides forgings. A 250 mm section of 4145 holds a more even hardness from surface to core after quenching than the same section in 4140. Chromium adds hardenability and tempering resistance. Molybdenum suppresses temper embrittlement and holds strength at elevated temperature.
The trade-off is weldability. Carbon equivalent runs near 0.85, so 4145 is not a grade to weld casually. It is normally specified for parts machined from a solid forging and heat treated in one piece.
4145, 4145H and 4145H MOD
AISI 4145. The base grade, with composition limits per ASTM A29.
AISI 4145H. The hardenability-guaranteed version, UNS H41450. Composition limits are wider, but the mill guarantees the Jominy end-quench band. Drill-collar specifications call for this one.
AISI 4145H MOD. A modified chemistry, usually with raised manganese, chromium and molybdenum, for sections too large for standard 4145H to through-harden. Standard 4145H holds 30–36 HRc through-section up to roughly 160 mm (6¼ in) diameter with a water or polymer quench. Above that, MOD chemistry is usually needed.
Section size decides the chemistry
Ask for plain 4145 on a 400 mm diameter forging with 30–36 HRc at mid-radius and standard chemistry will not get there. Send the section size and the hardness location, and we will propose the chemistry. The heat analysis we actually run goes on the EN 10204 3.1 certificate.
Chemical composition of AISI 4145
All values are percentage by weight, remainder iron. Our AISI 4145 is melted by electric arc furnace, refined in a ladle furnace and vacuum degassed (EAF + LF + VD) to control hydrogen, oxygen and non-metallic inclusions.
Table 1. Chemical composition, AISI 4145 vs 4145H vs typical 4145H MOD (% by weight)
Element
AISI 4145 (ASTM A29)
AISI 4145H
4145H MOD (typical)
Carbon (C)
0.43–0.48
0.42–0.49
0.42–0.49
Manganese (Mn)
0.75–1.00
0.65–1.10
0.90–1.20
Silicon (Si)
0.15–0.35
0.15–0.35
0.15–0.35
Chromium (Cr)
0.80–1.10
0.75–1.20
0.90–1.20
Molybdenum (Mo)
0.15–0.25
0.15–0.25
0.20–0.35
Phosphorus (P)
0.035 max
0.035 max
0.020 max
Sulphur (S)
0.040 max
0.040 max
0.015 max
Nickel (Ni)
0.25 max (residual)
0.25 max (residual)
0.25 max
Iron (Fe)
Balance
Balance
Balance
Base and H-band limits per ASTM A29 / ASTM A304. MOD column is a representative mill practice for heavy sections; exact limits vary by producer and are stated on the heat certificate.
Calculated carbon equivalent, IIW formula CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15, is approximately 0.85 at mid-range chemistry.
Mechanical properties of AISI 4145
Properties below are for material quenched and tempered to the 30–36 HRc range, tested at room temperature. Actual values depend on section size, quench medium and tempering temperature, and are reported per heat and per lot on the certificate.
Table 2. Typical mechanical properties, AISI 4145 quenched and tempered to 30–36 HRc
Property
Minimum
Maximum
Metric
Tensile strength
140 ksi
—
965 MPa
Yield strength, 0.2% proof
120 ksi
—
827 MPa
Elongation in 50 mm
14%
—
14%
Reduction of area
40%
—
40%
Hardness, Rockwell C
30 HRc
36 HRc
30–36 HRc
Hardness, Brinell
285 HBW
341 HBW
285–341 HBW
Charpy V-notch, room temp.
40 ft·lb
—
54 J
Charpy value is the API Spec 7-1 drill-collar acceptance level, measured 25 mm (1 in) below the outside surface. Other product forms are tested to the customer specification.
Annealed condition
Supplied annealed for customer machining and subsequent heat treatment, AISI 4145 runs approximately 197–235 HBW with a tensile strength near 655–760 MPa. This is the normal delivery condition for gear blanks and rings that the buyer will harden after cutting.
Physical properties
Table 3. Physical properties of AISI 4145 chromium-molybdenum steel
Property
Value
Condition
Density
7.85 g/cm³ (0.284 lb/in³)
20 °C
Modulus of elasticity
205–210 GPa (29–30 × 10⁶ psi)
20 °C
Poisson's ratio
0.29
20 °C
Thermal conductivity
42.7 W/m·K
100 °C
Specific heat capacity
473 J/kg·K
50–100 °C
Coefficient of thermal expansion
12.3 µm/m·K
20–100 °C
Electrical resistivity
0.22 µΩ·m
20 °C
Melting range
1416–1432 °C
—
Typical values for low-alloy Cr-Mo steel. Use for design estimation only; request certified data for code calculations.
AISI 4145 equivalent grades
There is no exact one-to-one European equivalent for AISI 4145. It sits between 42CrMo4 (1.7225) and 50CrMo4 (1.7228) on carbon content, so substitution should always be checked against the actual heat analysis rather than the grade name.
Table 4. AISI 4145 international equivalent and comparable grades
The four grades differ mainly in carbon. Higher carbon means higher attainable hardness and deeper hardening, at the cost of weldability and quench-crack resistance.
Table 5. Comparison of the common 41xx chromium-molybdenum forging grades
Choosing between 4140 and 4145: below roughly 150 mm section, 4140 usually reaches the same hardness and machines and welds more easily. Above that, or when 30 HRc is needed at mid-radius, use 4145 or 4145H MOD.
Heat treatment of AISI 4145 forgings
Table 6. Heat treatment parameters for AISI 4145 open-die forgings
Operation
Temperature
Cooling
Result
Forging
1200–1230 °C
Finish above 900 °C, then slow cool in sand or furnace
Prevents cracking from residual stress
Annealing
800–850 °C
Furnace cool 15–20 °C/h to 500 °C, then air
197–235 HBW, machinable
Normalizing
870–900 °C
Still air
Refines grain before hardening
Austenitizing
840–870 °C
Hold 1 h per 25 mm section
Full solution of carbides
Quenching
from 840–870 °C
Oil, polymer or agitated water by section size
Martensitic structure
Tempering
540–650 °C
Air cool; 580–620 °C gives 30–36 HRc
Final strength and toughness
Stress relief
550–620 °C
Slow cool, below tempering temperature
After rough machining or welding
Avoid the embrittlement window
Do not temper AISI 4145 between 250 °C and 400 °C. Tempered martensite embrittlement in this range collapses impact toughness. For service above 400 °C, also avoid slow cooling through 600–450 °C to limit classical temper embrittlement.
Weldability and machinability
Welding
AISI 4145 is classified as difficult to weld. If welding is unavoidable, the accepted procedure is:
Preheat to 300–350 °C and hold interpass temperature above preheat.
Use low-hydrogen consumables, baked and held in a quiver.
Post-weld heat treat at 600–650 °C, below the original tempering temperature, then slow cool.
Qualify the procedure to ASME IX or ISO 15614 and hardness-survey the heat-affected zone.
For sour service, cap the heat-affected zone hardness at 22 HRC per NACE MR0175 / ISO 15156. AISI 4145 at 30–36 HRc does not meet that limit, so sour-service parts are normally redesigned in a lower-carbon grade such as AISI 4130.
Machining
Machinability is roughly 55–60% of AISI 1212 free-cutting steel when annealed to 197–235 HBW. We normally supply rings and discs rough-machined in the annealed condition, heat treat, then finish-machine, which keeps distortion out of the finished dimensions.
How we forge AISI 4145
Every AISI 4145 forging we ship follows the same route. Each step is recorded against the heat number, so the certificate traces back to the original ingot.
MeltingEAF melt, ladle furnace refining, vacuum degassing. Hydrogen controlled to limit flaking in heavy sections.
Ingot / billetAluminium-killed fine-grain practice. Ingot size selected to meet the required forging reduction ratio.
HeatingSoak to 1200–1230 °C in a recorded-temperature furnace.
Open-die forgingUpset and draw on hydraulic press, or ring-rolled. Reduction ratio 4:1 minimum for rings, 5:1 for bars.
Pre heat treatmentNormalize and anneal to refine grain and bring hardness down for machining.
Rough machiningTurn, bore and face to leave a controlled heat-treat allowance.
Quench and temperAustenitize, quench, temper to the specified hardness band. Charts retained.
Testing and releaseUT, MT, hardness, tensile and impact. EN 10204 3.1 or 3.2 certificate issued.
Seamless rolled ring envelope for AISI 4145 at Jiangyin Jiangnan Metal. Rings outside this envelope are produced as forged and bored blanks.
Factory capability for AISI 4145
Table 7. Open-die forging capability, Jiangyin Jiangnan Metal Co., Ltd.
Item
Range
Forging method
Open-die (free) forging and seamless ring rolling
Single piece weight
20 kg – 30,000 kg
Forged round bar
Ø80 – Ø1,200 mm, length to 12,000 mm
Seamless rolled ring
OD 200 – 4,000 mm, height to 1,000 mm, wall from 30 mm
Forged disc / blank
Ø200 – Ø2,500 mm
Forged shaft / spindle
length to 12,000 mm
Hollow bar / sleeve
OD to 1,500 mm, bored or trepanned
Forging reduction ratio
≥ 4:1 rings, ≥ 5:1 bars
Melting route
EAF + LF + VD, aluminium-killed fine grain
Heat treatment
Annealing, normalizing, quench and temper, stress relief, with recorded charts
Machining
Rough, semi-finish and finish turning, boring, drilling, milling
Delivery condition
As forged, annealed, normalized, normalized and tempered, or quenched and tempered
Ranges apply to AISI 4145 and 4145H. Confirm the exact envelope for your part when you send the drawing.
AISI 4145 forged products we make
Drill collars and drill-string parts
AISI 4145H drill collars to API Spec 7-1, 3⅛″ to 11″ OD in 30 and 31 ft lengths, slick or spiral. Stabilizer bodies, subs, crossovers, pup joints, fishing tools and tool-joint blanks.
Seamless rolled rings
Ring-rolled AISI 4145 from 200 to 4,000 mm outside diameter for bearings, slew rings, gear blanks, tyres and retaining rings.
Forged flanges
Weld neck, blind, slip-on, long weld neck and non-standard flanges forged from AISI 4145, supplied rough or finish machined.
Shafts and spindles
Forged shafts, eccentric shafts, crankshafts, pinion shafts and spindles to 12,000 mm, straightened and UT inspected.
Discs, blocks and sleeves
Forged discs, blanks, bushings, sleeves, hollow bars and rectangular blocks for machining into tooling and pressure parts.
Gear blanks
Forged gear and pinion blanks in AISI 4145, delivered annealed for cutting or quenched and tempered to a hardness band.
Valve components
Valve bodies, blocks, bonnets, seat rings and stems for ball, gate, globe, check and plug valves.
Pressure-vessel parts
Forged tube sheets, nozzles, hubs, shell courses and closure rings for vessels, heat exchangers and air receivers.
Where AISI 4145 forgings are used
Oil and gas drilling. Drill collars, stabilizers, subs, crossovers, kellys, fishing tools, downhole motor housings.
Wellhead and subsea. Wellhead components, Christmas tree bodies, manifold blocks, deepwater production hardware.
Marine and heavy machinery. Shipbuilding shafts, forged wheels, rolls, manifolds, paper and pulp machinery.
Testing, inspection and certificates
Table 8. Standard inspection scope for AISI 4145 forgings
Test
Standard
Notes
Ultrasonic testing
EN 10228-3, SEP 1921, ASTM A388
Acceptance class agreed before production
Magnetic particle
ASTM E709, EN 10228-1
Machined surfaces
Chemical analysis
ASTM A29, ASTM E415
Ladle and product analysis
Tensile test
ASTM A370, ISO 6892-1
Location per specification
Impact test
ASTM A370, ISO 148-1
Charpy V-notch, temperature on request
Hardness
ASTM E10, ASTM E18
Brinell or Rockwell, mapped positions
Grain size
ASTM E112
Normally 5 or finer
Inclusion rating
ASTM E45, DIN 50602
On request
Dimensional
Customer drawing
Full report with the shipment
Certificate
EN 10204 3.1 / 3.2
3.2 witnessed by BV, SGS, TUV, LR, ABS, DNV or your inspector
How to order AISI 4145 forgings
Send a drawing, a sketch or just the finished dimensions. The faster we can quote, the fewer of these we have to ask about later:
Grade and specification. AISI 4145, 4145H or 4145H MOD, plus any customer or API specification that applies.
Shape and dimensions. Finished size, plus the state you want it delivered in: as-forged with allowance, rough machined or finish machined.
Delivery condition. Annealed, normalized, or quenched and tempered to a hardness band.
Mechanical requirements. Hardness range and test location, tensile, impact temperature and energy.
NDT requirement. UT standard and acceptance class, MT, and any special examination.
Certificate. EN 10204 3.1, or 3.2 with the third party you want to witness.
Quantity and destination port. For weight-based pricing and freight.
Quotations are issued within 24 hours of a complete enquiry. Typical lead time is 25 to 45 days depending on section size and heat-treatment cycle. Packing is seaworthy: wooden case, steel pallet or bundled with edge protection, marked with heat number and purchase-order number.
AISI 4145 is a medium-carbon chromium-molybdenum low-alloy steel, UNS G41450, covered by ASTM A29 and ASTM A322. It contains 0.43–0.48% carbon, 0.80–1.10% chromium and 0.15–0.25% molybdenum, and is almost always used in the quenched and tempered condition. Its main use is oilfield drilling components, where deep hardenability in heavy sections is required.
What is the difference between AISI 4145 and AISI 4145H?
AISI 4145 is controlled by chemical composition alone. AISI 4145H, UNS H41450, is the hardenability-guaranteed version: composition limits are slightly wider, but the mill guarantees hardness at specified distances on a Jominy end-quench test. Drill collar and downhole tool specifications call for the H grade because the Jominy guarantee predicts through-hardening in a thick section more reliably than a composition range does.
Is AISI 4145 the same as AISI 4140?
No. AISI 4145 carries about 0.05% more carbon (0.43–0.48% against 0.38–0.43%). That gives 4145 higher hardenability and higher attainable strength, at the cost of weldability. Below roughly 150 mm section the two grades often perform the same and 4140 is the easier choice; in heavy sections, or when 30 HRc is needed at mid-radius, 4145 is correct.
What hardness can AISI 4145 reach?
The normal delivery band for oilfield forgings is 30–36 HRc, equal to 285–341 HBW, achieved by quenching from 840–870 °C and tempering at 580–620 °C. As-quenched hardness can exceed 55 HRc but is never used in service. Annealed material for machining runs 197–235 HBW.
What is AISI 4145 used for?
Drill collars, stabilizers, subs, crossovers, pup joints and fishing tools for oil and gas drilling; wellhead and Christmas tree components; forged shafts, spindles and gear blanks for power transmission; valve bodies and seat rings; forged rings, flanges, tube sheets and nozzles for pressure vessels and heat exchangers; and rolls and shafts for mining, cement and paper machinery.
Can AISI 4145 be welded?
It can, but it is classified as difficult. The carbon equivalent is around 0.85, so welding requires preheat of 300–350 °C, low-hydrogen consumables, controlled interpass temperature and post-weld heat treatment at 600–650 °C. For sour service under NACE MR0175 / ISO 15156, the 22 HRC heat-affected-zone limit rules out AISI 4145 at normal service hardness, and a lower-carbon grade such as AISI 4130 is used instead.
What is the heat treatment for AISI 4145 forgings?
Forge at 1200–1230 °C finishing above 900 °C, then slow cool. Normalize at 870–900 °C, or anneal at 800–850 °C with furnace cooling for machining. Harden by austenitizing at 840–870 °C, holding one hour per 25 mm of section, and quenching in oil, polymer or agitated water by section size. Temper at 540–650 °C. Never temper between 250 °C and 400 °C.
What is the equivalent grade of AISI 4145?
SAE 4145 and UNS G41450 are the same material. JIS SCM445 and Chinese GB 45CrMo are close equivalents. There is no exact European equivalent: AISI 4145 sits between 42CrMo4 (1.7225) and 50CrMo4 (1.7228). Substitution should be checked against the actual heat analysis and the required hardenability, not against the grade name.
Which standards cover AISI 4145 drill collars?
API Spec 7-1 governs rotary drill-stem elements. Drill collars in AISI 4145H are full-length quenched and tempered to 285–341 HBW with a Charpy V-notch minimum of 40 ft·lb (54 J) at room temperature, measured 25 mm below the outside surface. Sizes run 3⅛″ to 11″ outside diameter in 30 and 31 ft lengths. API Spec 7G and the NS-1 and DS-1 inspection standards are commonly specified alongside.
Who supplies AISI 4145 forgings?
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, supplying AISI 4145 and 4145H forged rings, drill collars, shafts, flanges, discs, blocks and gear blanks from 20 kg to 30,000 kg per piece to customers worldwide. Contact sales@steelforgepieces.com or +86 189 2135 9659.
What certificates come with AISI 4145 forgings?
Every shipment carries an EN 10204 3.1 inspection certificate covering heat analysis, heat-treatment record, mechanical test results, hardness, NDT results and dimensions, traceable to the heat number. EN 10204 3.2 certificates witnessed by BV, SGS, TUV, Lloyd's Register, ABS, DNV or the customer's own inspector are available on request.
What is the minimum order and the lead time?
There is no fixed minimum quantity; single prototype forgings are accepted, though price per kilogram falls with quantity and with repeat orders from the same die setup. Typical lead time is 25 to 45 days from drawing approval, driven mainly by section size and the heat-treatment cycle. Quotations are issued within 24 hours of a complete enquiry.
Jiangyin Jiangnan Metal Co., Ltd.
An open-die forging factory in Jiangyin, Jiangsu, on the south bank of the Yangtze between Shanghai and Nanjing. We forge alloy steel, carbon steel, tool steel, stainless steel and nickel alloys into rings, bars, shafts, discs, flanges and custom shapes, and ship worldwide through the ports of Shanghai and Zhangjiagang.
Factory address
No.1 Chengxiqiao Road, Zhouzhuang Town Jiangyin City, Jiangsu Province China