AISI 6150, also written SAE 6150 or UNS G61500, is a medium-carbon chromium-vanadium alloy steel. It runs about 0.50% carbon, 1% chromium and at least 0.15% vanadium. The vanadium keeps the grain fine and holds fine carbides in place, so 6150 stays tough at hardness levels where a plain chromium steel would already be brittle. That is why it ends up in heavy-duty springs, torsion bars, gears, pinions and highly stressed shafts.
Jiangyin Jiangnan Metal Co., Ltd. forges AISI 6150 to drawing at its open-die shop at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Available forms include bars, hollow bars, seamless rolled rings, blocks, discs, gear shafts and flanges, all released with an EN 10204 3.1 certificate. Enquiries go to sales@steelforgepieces.com or +86-189-2135-9659.
AISI 6150 at a glance
- Grade family
- Chromium-vanadium (Cr-V) alloy steel, medium carbon, spring and gear grade
- US designations
- AISI 6150, SAE 6150, UNS G61500, ASTM A29/A29M grade 6150
- Closest European grade
- 50CrV4, material number 1.8159; 51CrV4 to EN 10083-3
- Nominal chemistry
- 0.50% C, 0.80 to 1.10% Cr, 0.15% V min, 0.70 to 0.90% Mn
- Density
- 7.85 g/cm³ (0.284 lb/in³)
- Forging range
- 1175 °C down to 870 °C (2150 to 1600 °F), slow cool after forging
- Hardening
- 845 to 885 °C (1550 to 1625 °F), oil quench; water quench for large simple sections
- Tempering
- 400 to 680 °C (750 to 1255 °F) depending on the strength required
- Typical service hardness
- 38 to 52 HRC as a spring or tool; 250 to 400 HB as a quenched and tempered shaft
- Weldability
- Poor. Avoid welding on heat-treated parts. Preheat and post-weld stress relief are mandatory if it cannot be avoided
- Forged forms available
- Round, square, flat and hex bars; hollow bars and sleeves; seamless rolled rings; slewing bearing rings; blocks, discs and plates; gear shafts, pinion shafts and spindles; flanges
- Certification
- EN 10204 3.1 mill test certificate; UT to ASTM A388 or SEP 1921 on request
Chemical composition of AISI 6150
The limits below follow SAE J404 for grade 6150. They apply to the ladle analysis. Product analysis carries the usual permissible variations of ASTM A29/A29M.
| Element | Symbol | Minimum % | Maximum % | Function in the steel |
|---|---|---|---|---|
| Carbon | C | 0.48 | 0.53 | Sets attainable hardness and strength |
| Silicon | Si | 0.15 | 0.35 | Deoxidiser; raises yield strength and temper resistance |
| Manganese | Mn | 0.70 | 0.90 | Improves hardenability and ties up sulphur |
| Chromium | Cr | 0.80 | 1.10 | Main hardenability element; forms wear-resistant carbides |
| Vanadium | V | 0.15 | n/a | Refines grain, pins grain boundaries, raises fatigue strength |
| Phosphorus | P | n/a | 0.035 | Residual, kept low to avoid temper embrittlement |
| Sulphur | S | n/a | 0.040 | Residual, kept low for transverse toughness |
| Iron | Fe | Balance | Base metal | |
Vanadium is what separates 6150 from the 5100 chromium series. At 0.15% and above it forms stable carbides that do not dissolve at austenitising temperature, so the prior-austenite grain stays fine through forging and hardening. Fine grain is the reason 6150 takes high hardness without the brittleness that plain chromium spring steels show.
International equivalents and cross-reference
AISI 6150 is specified worldwide under several designations. The grades below are commercially interchangeable for most work, but chemistry limits differ slightly between standards, so name the governing standard on the purchase order rather than the grade alone.
| Country / region | Standard | Designation | Material number |
|---|---|---|---|
| United States | SAE J404 / ASTM A29 | SAE 6150, AISI 6150 | UNS G61500 |
| Germany / EU | DIN 17222 / EN 10083-3 | 50CrV4, 51CrV4 | 1.8159 |
| United Kingdom | BS 970 | 735A50 | n/a |
| France | AFNOR NF A35-552 | 50CV4 | n/a |
| Japan | JIS G4801 | SUP10 | n/a |
| China | GB/T 1222 | 50CrVA | n/a |
| Russia | GOST 14959 | 50HFA | n/a |
| Italy | UNI 3545 | 50CrV4 | n/a |
| Sweden | SS 14 2230 | 2230 | n/a |
We forge every grade in this list from the same Cr-V family and certify to whichever standard the drawing calls out. If the print says 50CrV4 or 51CrV4 while the buyer's system says 6150, one heat can satisfy both provided the tighter limits are applied. Ask us to run that check before the ingot is picked.
Mechanical and physical properties
Quenched and tempered mechanical properties
Strength falls as section size grows, because a quench cools a thick core more slowly than a thin one. The values below are the acceptance limits for the 51CrV4 equivalent in EN 10083-3, quoted by ruling section. We work to these unless the drawing says otherwise.
| Ruling section | Yield strength Rp0.2 | Tensile strength Rm | Elongation A5 | Reduction of area Z |
|---|---|---|---|---|
| up to 16 mm | 900 MPa min | 1100 to 1300 MPa | 9 % min | 40 % min |
| 16 to 40 mm | 800 MPa min | 1000 to 1200 MPa | 10 % min | 45 % min |
| 40 to 100 mm | 700 MPa min | 900 to 1100 MPa | 11 % min | 50 % min |
| over 100 mm | By agreement. Properties are established on a test prolongation or sacrificial test block representing the ruling section. | |||
Acceptance values are agreed at order entry and reported on the EN 10204 3.1 certificate. On heavy open-die forgings, nominate both the test location (surface, mid-radius or centre) and the test orientation (longitudinal or tangential). A Cr-V steel shows a real property gradient through a thick section, and those two choices can move the reported figures a long way.
Properties in other supply conditions
| Condition | Typical hardness | Why it is ordered |
|---|---|---|
| As-forged | 280 to 360 HB | Lowest cost. Buyer heat treats after rough machining |
| Annealed | 197 to 229 HB | Best machinability. Standard for parts with heavy stock removal |
| Normalised | 255 to 302 HB | Uniform structure before final hardening. Refines a coarse forged grain |
| Quenched and tempered | 250 to 400 HB | Shafts, gears and pins delivered ready for finish machining |
| Hardened, low temper | 38 to 52 HRC | Springs, torsion bars, punches and chisels |
| As-quenched, thin section | 60 to 63 HRC | Reference maximum only. Never used untempered |
Physical properties
| Property | Value |
|---|---|
| Density | 7.85 g/cm³ (0.284 lb/in³) |
| Modulus of elasticity | about 205 GPa (29.7 × 10⁶ psi) |
| Thermal conductivity | about 42 W/m·K at 100 °C |
| Coefficient of thermal expansion | about 12.3 × 10⁻⁶ /K, 20 to 200 °C |
| Specific heat capacity | about 460 J/kg·K at 20 °C |
| Magnetic | Yes, ferromagnetic in all conditions |
| Corrosion resistance | None. 6150 is not a stainless steel and needs oiling, plating or paint |
Forging AISI 6150
AISI 6150 is forged from about 1175 °C down to a finishing temperature of roughly 870 °C (2150 °F down to 1600 °F). Working the steel below that finishing temperature invites cracking, so reheat rather than push the last blows into a cold billet.
Once the last blow is struck, the forging has to be slow-cooled. Bury it in lime or vermiculite, or put it straight back into a furnace held near the finishing temperature. Chromium-vanadium steel is air-hardening in heavy sections, and a forging left on the shop floor overnight can crack without ever seeing a quench tank.
We route every 6150 forging from the press into a slow-cool cycle, then normalise it before rough machining to break down the coarse as-forged grain. On rings and discs we work to a forging reduction ratio of at least 3:1, which keeps the grain flow following the contour of the part instead of being cut through by the tool. That is the practical reason a forged 6150 gear blank outlasts one machined from plate.
Heat treatment of AISI 6150
The cycles below are standard starting points. Soak times depend on section thickness, and any cycle should be proven on a test piece before it goes near a production forging.
| Operation | Temperature | Cooling | Purpose |
|---|---|---|---|
| Forging | 1175 to 870 °C 2150 to 1600 °F | Slow cool or furnace | Shape the part and close porosity |
| Normalising | about 900 °C 1650 °F | Still air | Refine the as-forged grain, even out the structure |
| Annealing | Austenitise 760 °C, isothermal hold 680 °C 1400 °F / 1250 °F | Furnace cool | Coarse lamellar pearlite to spheroidite for best machinability |
| Hardening | 845 to 885 °C 1550 to 1625 °F | Oil quench; water for large simple sections | Transform to martensite |
| Tempering | 400 to 680 °C 750 to 1255 °F | Air | Set the final strength and toughness balance |
| Stress relief | 550 to 650 °C, below the tempering temperature | Furnace cool to 300 °C | Remove machining and straightening stresses |
Tempering in practice: 400 to 500 °C gives spring and tool hardness around 45 to 52 HRC. 540 to 600 °C gives the high-strength shaft condition. 620 to 680 °C gives the toughest condition at the lowest strength. Avoid holding between 250 °C and 350 °C, where tempered martensite embrittlement can drop impact values with no visible change in hardness.
Machining, grinding and welding
Machining
Machine 6150 annealed, around 197 to 229 HB, wherever the design allows it. Rough machining at 350 HB and above works with carbide tooling, but tool life drops sharply and the residual stress released during cutting will bow a long shaft. The usual route for a gear shaft or spindle is: forge, normalise, rough machine leaving 3 to 6 mm of stock, quench and temper, stress relieve, then finish machine.
Grinding
Hardened 6150 above 45 HRC grinds well but burns easily. Use a soft open-structure wheel, flood the contact zone with coolant and take light finishing passes. Grinding cracks in Cr-V steel run across the grinding direction and are a common starting point for fatigue failure in spring and torsion-bar service.
Welding
AISI 6150 welds badly, and welding is not recommended on parts already quenched and tempered. Where it cannot be avoided, preheat to 300 to 350 °C, hold that interpass temperature, use a low-hydrogen process with matching or austenitic consumables, and stress relieve straight after welding at a temperature below the original tempering temperature. Do not let the part cool to room temperature between welding and stress relief.
AISI 6150 forged products we make
Every item below is forged to the customer's drawing rather than cut from stock. Open-die forging needs no dies, so there is no tooling charge and no minimum quantity. Single spares and one-off prototypes are quoted the same way as production batches.
- Forged barsRound, square, rectangular, flat and hex bars in AISI 6150, forged and then normalised, annealed or quenched and tempered.
- Forged shafts and spindlesGear shafts, pinion shafts, stepped shafts, spindles and axles, including long shafts with integral flanges.
- Hollow bars and sleevesForged hollow bars, sleeves, bushes, bushings, cylinders, hubs and housings, bored on the press to cut machining stock.
- Seamless rolled ringsRing-rolled AISI 6150 with continuous circumferential grain flow, in plain, stepped and profiled sections.
- Slewing bearing ringsInner and outer bearing races in 6150 for cranes, excavators and wind turbine yaw and pitch bearings.
- Blocks, discs and platesForged blocks, discs, disks and plates for gear blanks, die holders and tooling plates.
- Forged flangesWeld-neck, slip-on, blind and special-profile flanges forged from 6150 where spring or fatigue duty is required.
- Pipes, casings and shellsForged pipes, tubes, barrels, casings, cases, shells and cylinders in AISI 6150.
Typical single-piece range: forged weight 5 kg to 20 t, bar diameter 80 to 1200 mm, ring outside diameter 200 to 4000 mm. Send a drawing for anything outside those figures. Heavier and larger pieces are regularly placed within our forging group.
AISI 6150 compared with 5160, 9260 and 4140
Buyers usually weigh 6150 against three other grades. Pick 6150 when the part has to survive fatigue at high hardness. Pick 5160 when cost decides. Pick 9260 when spring yield is the only thing that matters. Pick 4140 when the section is heavy and moderate strength will do.
| Grade | Alloy type | Nominal C % | Key strength | Main limitation | Typical use |
|---|---|---|---|---|---|
| AISI 6150 | Cr-V | 0.50 | Fine grain, best fatigue life and toughness at high hardness | Higher alloy cost than 5160 | Heavy-duty springs, torsion bars, gears, spindles |
| AISI 5160 | Cr | 0.60 | Lowest cost of the spring grades, deep hardening | No vanadium, so grain coarsens more readily | Leaf springs, coil springs, blades |
| AISI 9260 | Si-Mn | 0.60 | Very high yield strength and elastic limit | Poor machinability, prone to decarburisation | Flat and coil springs, spring clips |
| AISI 4140 | Cr-Mo | 0.40 | Excellent hardenability in thick sections, tough and machinable | Lower attainable hardness and fatigue limit | General shafts, couplings, heavy forgings |
Comparable grades we also forge: AISI 4140, 42CrMo4, AISI 4340 and 34CrNiMo6.
Applications of AISI 6150
AISI 6150 is specified where a part has to combine fatigue strength, wear resistance and enough toughness to survive shock. It appears in forged components of medium and large cross section in automotive engineering, gearbox work and engine construction.
- Springs and torsion bars. Heavy coil springs, valve springs, leaf springs and vehicle torsion bars, normally hardened and tempered to 45 to 52 HRC.
- Gears and pinions. Intermediate gears, pinion shafts and gear blanks in gearboxes and final drives, where the vanadium-refined grain resists pitting.
- Engine and driveline forgings. Crankshafts, connecting rods, steering knuckles and spindles.
- Pump and machine shafts. Pump shafts, gear shafts and drive shafts carrying reversing loads.
- Hand tools and tooling. Punches, chisels, wrenches, sockets and mandrels.
- Rail and agricultural equipment. Suspension parts, tines, plough components and fasteners that take repeated impact.
How to order AISI 6150 forgings, and what to specify
- Send the drawing and the grade. Email the drawing, the grade (AISI 6150, SAE 6150, or the 50CrV4 / 51CrV4 equivalent) and the quantity to sales@steelforgepieces.com. A dimensioned sketch is enough if there is no formal print.
- State the delivery condition and testing. Forged, normalised, annealed, or quenched and tempered; the hardness or strength class; and any NDT such as ultrasonic testing to ASTM A388 or SEP 1921.
- Receive the quotation. We quote forged weight, machining allowance, lead time and packing, normally within 24 hours of receiving a drawing.
- Approve the forging and heat-treatment plan. Ingot or billet selection, forging reduction ratio, heat-treatment cycle and inspection hold points are confirmed before the press is booked.
- Inspection and shipment. Forgings are released against an EN 10204 3.1 mill test certificate covering chemistry, mechanical properties and NDT results, then shipped from Shanghai or Ningbo.
Worth putting on the enquiry: ruling section for the property test, test location and orientation, maximum acceptable decarburisation depth (critical on spring duty), grain size requirement, and whether the certificate has to be third-party endorsed.
Frequently asked questions about AISI 6150
What is AISI 6150 steel?
AISI 6150 is a medium-carbon chromium-vanadium alloy steel running about 0.50% carbon, 1% chromium and at least 0.15% vanadium. The vanadium keeps the grain fine and holds fine carbides in place, so the steel stays tough at hardness levels where a plain chromium grade would already be brittle. It is used for springs, gears, shafts and hand tools.
What is the chemical composition of AISI 6150?
Per SAE J404: 0.48 to 0.53% carbon, 0.15 to 0.35% silicon, 0.70 to 0.90% manganese, 0.80 to 1.10% chromium, 0.15% vanadium minimum, 0.035% phosphorus maximum and 0.040% sulphur maximum, balance iron.
What is the equivalent of AISI 6150?
AISI 6150 corresponds to SAE 6150 and UNS G61500 in the United States, 50CrV4 / 1.8159 and 51CrV4 in Germany and EN 10083-3, SUP10 in Japan, 50CrVA in China, 735A50 in the United Kingdom, 50CV4 in France and 50HFA in Russia. Chemistry limits vary slightly between the standards, so name the governing standard on the order rather than the grade alone.
At what temperature is AISI 6150 forged?
Between about 1175 °C and 870 °C (2150 to 1600 °F). Stop forging before the steel drops below the finishing temperature, and slow-cool or furnace-cool the piece afterwards. Chromium-vanadium steel is air-hardening in heavy sections, so an unprotected cool on the shop floor can crack a forging that never saw a quench tank.
How is AISI 6150 heat treated?
Normalise at about 900 °C and air cool. Anneal by austenitising at about 760 °C followed by an isothermal hold near 680 °C for best machinability. Harden from 845 to 885 °C with an oil quench for small or intricate sections and a water quench for large simple sections. Temper between 400 °C and 680 °C according to the strength and toughness required.
What is the difference between AISI 6150 and 5160?
Both are spring steels, but 6150 carries at least 0.15% vanadium and 5160 carries none. Vanadium keeps the grain fine through forging and austenitising, so 6150 holds better toughness and fatigue strength at the same hardness and copes better with heavy sections. 5160 has higher carbon at 0.56 to 0.64% and costs less, which keeps it common on leaf springs where the extra fatigue life is not needed.
What hardness can AISI 6150 reach?
Roughly 60 to 63 HRC as-quenched in thin sections, though it is never used untempered. After tempering it is normally applied at 38 to 52 HRC for springs and tools, and 250 to 400 HB for quenched and tempered shafts and gears. Core hardness falls as section size grows, so state the ruling section whenever you specify a hardness.
Is AISI 6150 weldable?
It welds badly, and welding is not recommended on parts already quenched and tempered. Where it cannot be avoided, preheat to 300 to 350 °C, use a low-hydrogen process with matching or austenitic consumables, and stress relieve straight after welding at a temperature below the original tempering temperature.
Who supplies AISI 6150 open-die forgings?
Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, supplies AISI 6150 / SAE 6150 forgings as bars, hollow bars and sleeves, seamless rolled rings, slewing bearing rings, blocks, discs, plates, gear shafts, pinion shafts, spindles and flanges. Enquiries go to sales@steelforgepieces.com or +86-189-2135-9659.
What is the minimum order quantity for AISI 6150 forgings?
One piece. Open-die forging needs no dies, so there is no tooling cost to amortise and single spares, prototypes and small batches are quoted on the same basis as production runs.
Cite this datasheet
Jiangyin Jiangnan Metal Co., Ltd. "AISI 6150 / SAE 6150 Forgings, 50CrV4 Chromium-Vanadium Steel Datasheet." steelforgepieces.com, updated 13 September 2026. https://www.steelforgepieces.com/Alloy-Steel/AISI-6150.html
Supplier: Jiangyin Jiangnan Metal Co., Ltd.
Jiangyin Jiangnan Metal Co., Ltd. runs an open-die forging shop in Jiangyin, Jiangsu Province, China. We forge AISI 6150 along with the rest of the alloy, carbon, tool and stainless range into bars, seamless rolled rings, discs, sleeves, shafts and flanges, to customer drawings, from one piece up, with EN 10204 3.1 mill test certificates and shipment from Shanghai or Ningbo.
Jiangyin Jiangnan Metal Co., Ltd.No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Telephone, WhatsApp and WeChat: +86-189-2135-9659
Email: sales@steelforgepieces.com
Related grades and forged products
Published 14 May 2018. Last reviewed 13 September 2026 by the technical sales team at Jiangyin Jiangnan Metal Co., Ltd. Property values on this page are indicative and meant for material selection. Acceptance values for a specific order are agreed at order entry and reported on the mill test certificate.