AISI 4150 Forgings (SAE 4150, UNS G41500, nearest 50CrMo4 / 1.7228)

What AISI 4150 forged products can you buy?

Jiangyin Jiangnan Metal produces AISI 4150 by three routes, chosen by geometry and order size. Open-die forging covers shafts, blocks, discs and heavy sections. Seamless ring rolling produces rings and gear blanks, and is almost always cheaper than machining a ring out of a solid disc. Upset forging handles short, large-section hubs and flanges. On a 0.50% carbon steel the forging route also determines the grain flow, and grain flow is what makes a forged gear or drill collar outlast a machined one.

Source: Jiangyin Jiangnan Metal Co., Ltd. open-die forging plant capability, Jiangyin, Jiangsu, China. Every form above can be supplied annealed, normalised, or quenched and tempered to a stated hardness, rough or finish machined to drawing, and certified to EN 10204 3.1 or 3.2. Send the finished drawing rather than a billet size: on a hardenable steel the forging route and the ruling section decide the achievable core properties.

What is AISI 4150, and why choose it over 4140?

The 41xx series is the workhorse family of chromium–molybdenum engineering steels. Every grade in it carries the same nominal 0.95% chromium and 0.20% molybdenum; the last two digits give the carbon content in hundredths of a percent. So 4130 is 0.30% carbon, 4140 is 0.40%, and 4150 is 0.50%.

Chromium and molybdenum do two jobs. They push the nose of the transformation curve to the right, so the steel can be quenched more slowly and still form martensite. That is hardenability, and it is why a 200 mm 4150 shaft can be hardened through where a plain carbon steel of the same carbon content could not. Molybdenum also suppresses temper embrittlement and holds strength at elevated temperature. Carbon works on a separate axis. It sets how hard the martensite can be, whatever depth it forms to.

The argument for 4150 over 4140 rests on that distinction.

• Maximum hardness. At 0.40% carbon, fully martensitic steel tops out near 55–57 HRC. At 0.50% carbon it reaches 58–60 HRC. If a drawing calls for 55 HRC on a wear surface, 4140 is at its ceiling and 4150 is comfortable.
• Tempered strength. At the same tempering temperature 4150 runs roughly 100–200 MPa stronger than 4140. To reach a given strength, 4150 can be tempered hotter, which leaves a more stable structure and lower residual stress.
• Wear resistance. More carbon means more carbide and a harder tempered martensite. This is why 4150 dominates in mill rolls, drill collars and die blocks.
• What you give up. Impact toughness at equal hardness is lower, the carbon equivalent rises to roughly 0.85–0.90 so welding needs real preheat, and the quench-cracking risk on section changes and sharp corners is materially higher.

What are the equivalents of AISI 4150?

Buyers meet this steel under half a dozen names. The designations below describe the same nominal 0.50C–1Cr–0.2Mo chemistry and we accept purchase orders under any of them. They are not, however, identical: the manganese ranges differ between the American and European grades, and manganese is a hardenability element. On a thin section the difference is invisible; on a 300 mm ruling section it is the difference between a hardened core and a soft one.

Cross-reference compiled by Jiangyin Jiangnan Metal Co., Ltd. from published national standards. Standards are cited by number only; always work to the revision in force at your contract date. A designation match is not by itself proof of equivalence. The product-form specification decides the test regime, not the chemistry.

What is the chemical composition of AISI 4150?

The composition below is the SAE J404 / ASTM A29 requirement for grade 4150, and it is what we buy raw material against unless a drawing calls for a tighter band. Carbon sets the attainable hardness. Chromium and molybdenum carry the hardenability and, in molybdenum's case, the resistance to temper embrittlement. Manganese contributes hardenability and ties up sulphur.

Source: SAE J404 and ASTM A29/A29M grade 4150, as forged by Jiangyin Jiangnan Metal Co., Ltd. Every heat is supplied with a ladle analysis on the mill certificate; product analysis can be added on request. Some published datasheets print silicon as 0.15–0.30% rather than 0.15–0.35%; both appear in circulation, so state which specification governs your order.

The H grade trades tighter chemistry for a guaranteed end-quench hardenability band to SAE J1268. For a heavy section where core hardness after quenching is on the drawing, specify 4150H and state the required Jominy band. For a small section where surface hardness governs, plain 4150 is normally sufficient and cheaper. Compiled by Jiangyin Jiangnan Metal Co., Ltd.

What are the physical properties of AISI 4150?

Compiled by Jiangyin Jiangnan Metal Co., Ltd. from published data for AISI 4150 and closely related 41xx grades. Transformation temperatures vary by a few degrees with the actual heat analysis and heating rate; where a heat-treatment procedure is being qualified, determine them by dilatometry on the actual heat rather than from a table.

What are the mechanical properties of AISI 4150?

There is no single set of mechanical properties for AISI 4150. The delivery condition sets the numbers, and there are three to order from: annealed, normalised, and quenched and tempered to a stated hardness or strength. Everything below is for a 25 mm test section; larger sections cool more slowly in the quench and will read lower, which is why the ruling section belongs on the enquiry.

Source: Jiangyin Jiangnan Metal Co., Ltd., AISI 4150 forging specification, compiled from published typical values for 25 mm sections. Rockwell C values below about 20 HRC are conversions outside the normal range and are given for comparison only. Annealed material is the condition to rough machine in; normalised material is the condition to buy if the part will be used as-forged without hardening.

How does AISI 4150 respond to tempering?

This is the table that actually gets used. Quench the part in oil from 830–860 °C and you have brittle martensite at 58–60 HRC that is unusable and, left overnight, liable to crack on its own. Tempering trades that hardness back for toughness, and the tempering temperature is the single control you have over the finished properties.

The colour bands below are the actual oxide tempering colours that form on a clean steel surface at each temperature. Before pyrometers they were how the heat treater read the temperature, and on a bright-machined part they still tell you at a glance roughly where a temper ran.

Table 7. Typical properties of AISI 4150 oil quenched from 830 °C and tempered, 25 mm section, one hour at temperature. Source: Jiangyin Jiangnan Metal Co., Ltd., compiled from published typical values for SAE 4150. These are typical results for screening, not design allowables, and not acceptance minima. Acceptance values are set by the specification on your order and are what appear on the certificate.

AISI 4150 compared with 4140, 4145, 4340 and 1045

Most enquiries come down to this comparison. AISI 4150 is chosen over 4140 when hardness or wear governs, and over 4340 when cost governs and the section is not very heavy. It loses on toughness, on weldability and on quench-cracking risk.

Comparison compiled by Jiangyin Jiangnan Metal Co., Ltd. Carbon equivalent calculated to the IIW formula at mid-range composition. All five grades are forged in this plant; see alloy steel grades for the full list.

Three questions that settle the choice

1. Is the hardness requirement above about 50 HRC? If yes, 4140 is at or past its practical ceiling and 4150 is the right answer.
2. Does the part take impact, or will it be welded? If yes, the extra carbon is working against you. Use 4140 or 42CrMo4 and get the hardness from induction hardening or nitriding instead.
3. Is the ruling section above roughly 150 mm and must the core be hard? Then hardenability, not carbon, is the limiting factor. Specify 4150H with a Jominy band, or move to 4340.

How is AISI 4150 forged and heat treated?

At 0.50% carbon with 1% chromium, this steel is hardenable enough to harden itself. A heavy forging left to cool in still air forms bainite and martensite in the skin while the core is still hot and contracting, and the resulting stresses crack parts. Most of the process rules below exist to manage that.

1. Verify the billet

   Confirm the heat analysis against SAE J404 / ASTM A29 grade 4150 and record the heat number. EAF + ladle furnace + vacuum degassing is our standard melt route; electroslag remelting is available where the drawing calls for it or where the part is ultrasonically critical.

2. Charge cold, heat slowly

   Charge below 400 °C and raise the temperature gradually. A cold 4150 billet pushed straight into a hot furnace develops a thermal gradient the material cannot accommodate.

3. Soak at 1,100–1,200 °C

   Roughly 30 minutes per 25 mm of ruling section, so the core reaches temperature and not just the surface. Do not exceed about 1,220 °C: at this carbon level the grain coarsens quickly and the coarse grain will still be there after quenching.

4. Forge, finishing above 900 °C

   Aim for a minimum 3:1 reduction ratio to break down the cast structure and develop grain flow. Reheat rather than continue deforming a cooling billet. Below about 900 °C forging loads climb steeply and surface cracking risk rises.

5. Cool slowly from the forging heat

   Cool in still air to about 400 °C, then cover, bury or furnace cool. This is the step most often skipped and it is the most common cause of cracked 4150 forgings arriving at the heat treatment shop.

6. Normalise at 860–900 °C

   Air cool. Refines the coarse as-forged grain and produces a uniform structure so the subsequent hardening responds predictably. Expect about 321 HB after normalising.

7. Anneal if rough machining follows

   Full anneal at 800–830 °C, furnace cool at 10–20 °C per hour to 600 °C, then air cool. Gives roughly 197 HB, the softest practical condition and the one to machine in.

8. Austenitise at 830–860 °C and oil quench

   Soak through, then quench in agitated oil. Water and polymer quenching are not recommended at this carbon level. The cracking risk on section changes outweighs the extra hardness. Radius every corner and avoid abrupt section changes at the design stage.

9. Temper immediately

   Temper as soon as the part reaches roughly 60 °C. Two hours per 25 mm of section, minimum two hours, at the temperature your hardness requires. Leaving quenched 4150 untempered overnight is how parts crack in the rack.

10. Test, examine and certify

    Tensile, impact and hardness testing, ultrasonic examination to ASTM A388 or EN 10228-3 and magnetic particle examination to ASTM E709 where the order calls for it. EN 10204 3.1 certification as standard, 3.2 with third-party witness.

Source: Jiangyin Jiangnan Metal Co., Ltd. heat-treatment practice for AISI 4150 open-die forgings, Jiangyin, Jiangsu, China. Furnaces are temperature-uniformity surveyed with chart recording; charts are supplied with the certificate. These are starting windows, not a qualified procedure. Qualify on coupons from the same heat, with thermocouples on the part, before releasing production parts.

Can AISI 4150 be nitrided or induction hardened?

Yes to both, and on many parts one of them is a better answer than through-hardening to high hardness.

Welding and machining AISI 4150

Welding

AISI 4150 is weldable but unforgiving. The carbon equivalent to the IIW formula is roughly 0.87 at mid-range composition, far above the 0.45 threshold at which preheat becomes mandatory. Weld metal and heat-affected zone both transform to untempered martensite on cooling, and with hydrogen present that martensite cracks.

• Weld in the annealed or normalised condition wherever the design allows.
• Preheat to 300–400 °C and maintain the interpass temperature. Do not let the part fall below preheat between passes.
• Use low-hydrogen consumables, dried and held in a quiver. Hydrogen is the variable most often ignored and most often responsible.
• Post-weld: either stress relieve at 600–680 °C, or re-temper below the original tempering temperature if the part is already quenched and tempered. Go straight from welding to the furnace without letting the part cool to room temperature.
• On a fully hardened part above 45 HRC, treat welding as a repair operation requiring a qualified procedure, not a shop-floor task.

Machining

Machinability is about 55% of the AISI 1212 free-machining reference in the annealed and cold-drawn condition. The practical window is 180–230 HB; below that the steel smears, above about 300 HB tool life falls away quickly.

• Rough machine annealed or normalised, leaving stock for heat-treatment distortion, then quench, temper and finish machine.
• Above 40 HRC, plan on carbide or CBN tooling, rigid setups, and finishing by grinding rather than turning.
• Deep holes and keyways are stress raisers in a quenched part. Where possible machine them before hardening, and radius every internal corner.
• Resulphurised variants give better chip control but reduce transverse ductility. Do not specify one for an impact-loaded forging.

How do AISI 4150 parts fail, and how do you prevent it?

What can Jiangyin Jiangnan Metal forge in AISI 4150?

AISI 4150 is one of our routine alloy steel grades. We hold billet in the common sizes and buy to specification for anything heavier, which is why lead times on this grade are short compared with the nickel and cobalt alloys.

Diameter range

100–6,000 mm

Length

to 12,000 mm

Single piece

10–15,000 kg

Rolled ring OD

200–6,000 mm

Ring wall, min

40 mm

Bar diameter

50–1,200 mm

Condition

Q&Tannealed or normalised also

Lead time

4–8 weekstypical for this grade

Jiangyin Jiangnan Metal Co., Ltd. employs approximately 460 people including 9 senior engineers and 32 intermediate engineers, at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. The envelope above is the plant capability across all grades. Send the drawing and we will confirm the size, weight and lead time for your specific part before quoting.

Which standards and certificates apply to AISI 4150 forgings?

Quality management is certified to ISO 9001:2015. Third-party witness certificates are issued through the inspection body you nominate: Lloyd's Register, DNV, Bureau Veritas, ABS, TÜV or SGS. Customers keep an unrestricted right to witness any production stage, including chemistry, forging, heat treatment and mechanical testing.

How do you specify an AISI 4150 forging order?

1. Name the grade and the product standard. Write AISI 4150 / UNS G41500 together with the product-form standard, for example ASTM A29 for bar or EN 10250-3 for an open-die forging. Chemistry alone does not define an acceptance regime.
2. State the delivery condition. Annealed, normalised, or quenched and tempered. If quenched and tempered, give the hardness or strength required, not just the words.
3. Give the hardness at a depth. "40–44 HRC at mid-radius" is a specification. "40 HRC" on its own means the surface, and on a heavy section the surface will pass while the core does not.
4. State the ruling section. It sets the soak times, the quench severity and whether 4150 or 4150H is needed. It is the single most useful number on the enquiry.
5. Specify 4150H if hardenability is critical. Name the required Jominy band to SAE J1268 and the distance at which it applies.
6. Define the test regime. Tensile and impact temperature and direction, test location, and whether tests come from a prolongation or a separately forged coupon. Above 50 mm section, say whether tests are longitudinal or transverse.
7. Define NDE and the acceptance class. "UT per EN 10228-3, quality class 3" or "UT per ASTM A388 with acceptance per the purchase order". An unqualified "ultrasonic test" is not a specification.
8. Cap the residuals if impact matters. Phosphorus 0.020% max and sulphur 0.015% max are worth specifying on impact-critical forgings, and cost very little.
9. Give quantity, date, Incoterm and destination. Quantity drives the melt and the machining setup, and both affect price and schedule.

Drawing callout you can copy

MATERIAL:      AISI 4150 / SAE 4150 / UNS G41500
               (nearest EN grade 50CrMo4 / 1.7228 - state which governs)
SPECIFICATION: ASTM A29/A29M grade 4150 (bar) or EN 10250-3 (open-die forging)
               SAE J1268 hardenability band if 4150H is required
MELT ROUTE:    EAF + LF + VD (state ESR if required)
FORGING:       Minimum 3:1 reduction ratio, finish above 900 deg C,
               cooled in still air to 400 deg C then covered
CONDITION:     Quenched and tempered. Austenitise 830-860 deg C, oil quench,
               temper ______ deg C, 2 h per 25 mm, minimum 2 h
HARDNESS:      ______ HRC at ______ mm depth / at mid-radius, per ASTM E18
CHEMISTRY:     Report all elements. P 0.020% max, S 0.015% max
TENSILE:       Per ASTM E8/E8M, ______ direction, from prolongation
IMPACT:        Charpy V per ASTM E23, ______ J average at ______ deg C
GRAIN SIZE:    ASTM E112, ______ or finer, reported per piece
NDE:           UT per EN 10228-3 quality class 3 (or ASTM A388)
               MT per ASTM E709 after final tempering
CERTIFICATE:   EN 10204 3.1 (3.2 with third-party witness if stated on the PO)
MARKING:       Heat number, specification, condition and drawing number,
               low-stress stamped or vibro-etched

Seven mistakes buyers make with AISI 4150

1. Ordering "4150, 50 HRC" with no depth and no section. Surface hardness on a 400 mm forging tells you nothing about the core. State the hardness, the depth and the ruling section together.
2. Assuming 50CrMo4 is an exact substitute. It permits manganese down to 0.50% where 4150 requires 0.75% minimum. On a heavy section that changes the core hardness.
3. Specifying 4150 for a welded fabrication. Carbon equivalent 0.87 means 300–400 °C preheat and mandatory post-weld heat treatment. If it must be welded, 4140 or 42CrMo4 will cost less overall.
4. Tempering in the 250–375 °C range for an impact-loaded part. Hardness looks right, toughness is in a trough, and no later treatment recovers it.
5. Water quenching to chase hardness. At 0.50% carbon this cracks parts. Oil quench and accept the hardenability limit, or move to 4150H or 4340.
6. Skipping the normalise after forging. As-forged grain is coarse and non-uniform, and the subsequent hardening will be equally non-uniform. Normalising costs one furnace cycle and prevents a scrapped part.
7. Buying to a billet size instead of a drawing. On a hardenable steel the forging route and the ruling section decide the achievable properties. Send the finished drawing and let the route be chosen for it.

Where is AISI 4150 used?

Two worked examples

Example 1: choosing between 4140 and 4150 for a ring gear

Given. A 1,200 mm outside diameter ring gear, 180 mm wall, teeth to be induction hardened to 55 HRC over a core at 280–320 HB, moderate shock loading from a mill drive.

Assessment. The 55 HRC tooth requirement is right at the ceiling of what 4140 will give after induction hardening, and the ceiling is where scatter turns into rejections. AISI 4150 reaches 58–60 HRC as quenched, so 55 HRC on the tooth flank is comfortable rather than marginal. The core requirement, 280–320 HB, is roughly 30–34 HRC and corresponds to a temper near 620 °C in 4150. That is above the temper-embrittlement range, so the ring must be cooled rapidly from the temper rather than furnace cooled.

Decision. Specify AISI 4150, seamless rolled ring, quenched and tempered to 280–320 HB at mid-wall, rapid cool from temper, teeth induction hardened to 55 HRC minimum with the case depth stated, magnetic particle examined after the final temper. Roll it as a ring rather than machine it from a disc. That saves cost, and in a ring gear the circumferential grain flow is a real service benefit rather than only a saving.

Example 2: why a rolled ring beats a machined disc

Given. A finished ring, 620 mm OD × 420 mm ID × 200 mm high, in AISI 4150.

Method. Net volume = π/4 × (0.620² − 0.420²) × 0.200 = 0.0327 m³. At 7,850 kg/m³ that is 257 kg finished. Rolled as a ring with 25% machining stock, the forging is about 321 kg. Machined instead from a solid forged disc of the same outside diameter and height, the input is 474 kg bare, or roughly 545 kg once stock is added to the diameter and the faces. Of that, 218 kg ends up as swarf.

Result. Ring rolling saves roughly a third of the purchased weight on this geometry, and rather more of the machining time. The saving grows as the wall gets thinner. At 480 mm bore instead of 420 mm it approaches half. Run both numbers through the weight calculator above with your own dimensions. Its defaults are set to this example, so the figures reproduce. This is also why we ask for the finished drawing rather than a billet size on every enquiry.

Glossary

References

1. SAE International, SAE J404: Chemical Compositions of SAE Alloy Steels. The source of the 4150 composition band.
2. SAE International, SAE J1268: Hardenability Bands for Alloy H Steels. Covers 4150H.
3. ASTM International, ASTM A29/A29M: General Requirements for Steel Bars, Carbon and Alloy, Hot-Wrought; and ASTM A322: Steel Bars, Alloy, Standard Grades.
4. ASTM International, ASTM A255: Determining Hardenability of Steel (Jominy end-quench test).
5. CEN, EN 10083-3: Steels for quenching and tempering — Alloy steels, covering 50CrMo4 / 1.7228; and EN 10250-3: Open-die steel forgings for general engineering purposes — Alloy special steels.
6. ASM International, ASM Handbook, Volume 1: Properties and Selection: Irons, Steels and High-Performance Alloys. Composition and property data for the 41xx series.
7. ASM International, ASM Handbook, Volume 4: Heat Treating. Tempering response, temper embrittlement and quench-cracking mechanisms in low-alloy steels.
8. ASM International, ASM Handbook, Volume 14A: Metalworking: Bulk Forming. Forging practice for medium-carbon low-alloy steels.
9. ASTM A388/A388M and EN 10228-3, ultrasonic examination of forgings; ASTM E709 magnetic particle examination; ASTM E112 grain size; ASTM E8/E8M and E23 tensile and impact testing; ASTM E10 and E18 hardness testing.
10. CEN, EN 10204: Metallic products — Types of inspection documents.

Standards are cited by number; always work to the revision in force at your contract date. Property values on this page are published typical figures for screening and are not design allowables. Test results on our certificates are independent and traceable to calibrated equipment.

About the manufacturer, and how to cite this page

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, with approximately 460 employees including 9 senior and 32 intermediate engineers. The plant runs 1 to 9 tonne open-die hammers, 4,500 and 5,000 tonne hydraulic presses and 3 m and 6 m seamless ring rolling lines, with in-house heat treatment, machining, mechanical testing and non-destructive examination. Alongside AISI 4150 we forge carbon, alloy and tool steels, the precipitation-hardening and duplex stainless families, and the nickel and cobalt high-temperature alloys. Quality management is certified to ISO 9001:2015; material is supplied with EN 10204 3.1 certification as standard and 3.2 with third-party witness on request.

Contact for technical questions or a quotation: Jiangyin Jiangnan Metal Co., Ltd., No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China · 0086-189-2135-9659 · sales@steelforgepieces.com · WhatsApp

Related grades and forged products

Chromium–molybdenum and alloy steels

• AISI 4140
• AISI 4140H
• AISI 4130
• 42CrMo4
• 42CrMoS4
• 42CrMo4V
• 1.7225
• 1.7227
• 1.7220
• 34CrMo4
• 34CrMoS4
• SCM440
• 42CD4
• 708M40
• 35KHM
• All alloy steel grades

Product forms we forge in AISI 4150

• Forged rings
• Forged discs
• Eccentric shafts
• Forged mill rolls
• Forged steel rolls
• All forged products
• Contact us