What is ASTM A291?
ASTM A291/A291M is the Standard Specification for Steel Forgings, Carbon and Alloy, for Pinions, Gears and Shafts for Reduction Gears. It applies to forgings that carry torque inside a gearbox, and it fixes the chemistry, the heat treatment condition and the mechanical properties those forgings have to meet after heat treatment.
Grade 1, Class A is normalized and tempered carbon steel. Grade 2 Class B, Grade 3 Class C, Grade 3A Class D, Grades 4 to 7 Classes E, F, G and H, Grade 8 Class I and Grade 9 Class J are liquid quenched and tempered alloy steels. The current edition is A291/A291M-19(2025), an active standard under ASTM Subcommittee A01.06 on Steel Forgings and Billets, printed in Volume 01.05 of the Annual Book of ASTM Standards under ICS code 77.140.85.
Test specimens are cut after the forging has been heat treated for mechanical properties. The figures on the certificate therefore belong to the part at its finished section, not to the steel as it was melted. A 900 mm bull gear blank and a 120 mm pinion in the same grade will not respond to the quench in the same way, which is why the standard is written around forgings rather than bar. It is common to see two suppliers offering 4140-type steel where only one of them can certify to A291.
The specification also says that all grades and classes are weldable under proper conditions, provided the welding procedure and inspection follow approved methods for the class of material used. Units are dual. SI and inch-pound values are treated separately and should not be mixed on a single order.
Grades and classes covered
A291 uses two designations for the same set of materials. Older drawings call out a grade number, newer ones the equivalent class letter. Putting both on the purchase order, for example ASTM A291 Grade 4 Class E, saves an email later.
| Grade | Class | Steel type | Heat treatment condition | Typical use in a gear train |
|---|---|---|---|---|
| Grade 1 | Class A | Carbon steel | Normalized and tempered | Low-duty gear blanks, slow-speed shafts, spacers |
| Grade 2 | Class B | Alloy steel | Liquid quenched and tempered | General gear blanks and shafts |
| Grade 3 | Class C | Alloy steel | Liquid quenched and tempered | Medium-duty gears, gear rims |
| Grade 3A | Class D | Alloy steel | Liquid quenched and tempered | Medium-duty gears with higher core strength |
| Grade 4 | Class E | Alloy steel (Ni-Cr-Mo type) | Liquid quenched and tempered | Bull gears, pinion shafts, impact-loaded drives |
| Grade 5 | Class F | Alloy steel (Ni-Cr-Mo type) | Liquid quenched and tempered | Heavy-section gears and shafts |
| Grade 6 | Class G | Alloy steel (Ni-Cr-Mo type) | Liquid quenched and tempered | High-torque pinions, marine reduction gears |
| Grade 7 | Class H | Alloy steel (Ni-Cr-Mo type) | Liquid quenched and tempered | Large through-hardened gears, mill drives |
| Grade 8 | Class I | Alloy steel (Ni-Cr-Mo-V type) | Liquid quenched and tempered | High-strength shafts in deep sections |
| Grade 9 | Class J | Alloy steel (Ni-Cr-Mo-V type) | Liquid quenched and tempered | Highest strength level in the specification |
Alloy content and strength level rise with the grade number. In practice the choice is driven by section size as much as by strength. A grade that reaches its properties in a 200 mm section can fall short in the core of a 700 mm gear blank, because hardenability runs out before tensile capability does. Tell us the finished section thickness and we will say which grades can certify at that size.
Chemical and mechanical requirements
A291 controls chemistry by heat and product analysis for carbon, manganese, phosphorus, sulfur, silicon, nickel, chromium, molybdenum, vanadium, copper and aluminium. Mechanical acceptance is by tensile strength, yield strength, elongation, reduction of area, Charpy V-notch impact energy and Brinell hardness, all measured on specimens taken after heat treatment for mechanical properties.
The numbers themselves sit in Table 1 and Table 2 of the standard, which ASTM International sells and holds the copyright on. We do not reprint them here. Ask for the grade you are working to and we will send a data sheet with the values we will guarantee at your section size. The document itself is available from the ASTM store.
| Requirement | Covered elements or properties | On our mill test certificate |
|---|---|---|
| Heat analysis | C, Mn, P, S, Si, Ni, Cr, Mo, V, Cu, Al | Full ladle analysis by spectrometer |
| Product analysis | Same elements, taken on the forging | On request or when specified |
| Tension test | Tensile strength, yield strength, elongation, reduction of area | Every heat-treatment lot |
| Impact test | Charpy V-notch absorbed energy | Set of three specimens, test temperature as ordered |
| Hardness | Brinell, HBW | Several positions per piece, each reported |
| Heat treatment record | Austenitising, quench medium, tempering temperature and soak | Furnace chart attached on request |
| Supplementary NDT | Ultrasonic, magnetic particle | ASTM A388 and ASTM A275, acceptance level as ordered |
Where test specimens are taken
On gear and pinion forgings the specimen location matters as much as the number it produces. Prolongations are left on the forging and heat treated attached to it, so the reported figures come from the part rather than a loose coupon. For heavy sections we take mid-radius and mid-thickness specimens when the drawing or the customer specification asks for core verification. Settle the location at enquiry stage. Changing it after the forging is made usually means starting again with new material.
Forged products supplied to ASTM A291
We are an open-die forging shop, so A291 material leaves here as a near-net forged shape rather than something cut out of bar stock. On gears and pinions that is worth having. An upset and ring-rolled blank keeps the grain flow running around the tooth root instead of across it.
| Forged shape | Size range | Single-piece weight | Typical part |
|---|---|---|---|
| Seamless rolled rings | 100 to 4000 mm OD | 20 kg to 20 t | Gear rims, bull gear blanks, ring gears |
| Gear and pinion blanks | 100 to 3000 mm OD | 20 kg to 25 t | Planet gears, pinions, spur and helical gear blanks |
| Shafts and stepped shafts | 80 to 1200 mm dia, to 12 m long | 30 kg to 30 t | Pinion shafts, gear shafts, input and idler shafts, splined shafts |
| Discs and plates | 200 to 3000 mm Ø | 20 kg to 25 t | Gear wheel blanks, end covers, flange plates |
| Blocks | To 2500 x 1500 x 800 mm | 50 kg to 25 t | Housings, gearbox bodies, die blocks |
| Hollow bars and sleeves | 150 to 2500 mm dia, wall from 40 mm | 30 kg to 20 t | Bushings, barrels, casings, cylinders, hubs |
| Forged bars | Round 80 to 1000 mm dia; square, flat and hex to drawing | 20 kg to 25 t | Shaft stock, pinion stock, machining blanks |
Grade 1 Class A is delivered normalized and tempered. Grades 2 to 9 are delivered liquid quenched and tempered. Forgings can go out black, rough machined to an agreed allowance, or finish machined to drawing including gear cutting through our partner shops. Above roughly 600 mm diameter we usually suggest rough machining before the final heat treatment, since it takes off the decarburised skin and lets the quench reach the section that has to meet properties.
How we make and test an A291 forging
This is the route an A291 order takes through the works.
- Steel making and ingot supply. Electric arc furnace steel with ladle refining and vacuum degassing on the alloy grades, keeping hydrogen and inclusion levels low enough for heavy sections.
- Open-die forging. Upsetting and drawing on hydraulic presses, with a minimum forging ratio agreed per part. On gear blanks that is typically 3:1 or better, so the centre of the ingot gets worked out.
- Ring rolling for rims and gear blanks above roughly 500 mm diameter, which gives circumferential grain flow.
- Preliminary heat treatment. Normalizing, or normalizing plus annealing, to refine grain and take out forging stress before machining.
- Rough machining to the agreed allowance, with prolongations left on for test specimens.
- Heat treatment for mechanical properties. Normalizing and tempering on Grade 1, or austenitising, liquid quenching and tempering on Grades 2 to 9, with charted furnace records.
- Testing. Tension, Charpy V-notch, Brinell hardness and chemical verification, followed by ultrasonic testing to ASTM A388 and magnetic particle examination to ASTM A275 where specified.
- Documentation and despatch. EN 10204 3.1 mill test certificate as standard, 3.2 with third-party inspection by SGS, BV, TUV or Lloyd's on request.
Where ASTM A291 forgings are used
A291 is a reduction gear specification. It turns up wherever a large speed reducer handles high torque and a broken gear or shaft costs real money: marine propulsion, mining and cement, steel rolling mills, wind and industrial gear units, and heavy off-highway equipment.
- Marine propulsion gearboxes. Main reduction gear wheels, pinions and quill shafts, often with class society survey.
- Mining and cement. Ball and SAG mill girth gear blanks, kiln drive pinions, crusher eccentric shafts.
- Steel plant drives. Rolling mill pinion stands, coiler and reeler drive shafts, mill gearbox bull gears.
- Wind and industrial gear units. Planet carriers, ring gear blanks, high-speed shafts.
- Heavy machinery. Winch and hoist drives, dredger gearboxes, sugar and paper mill reducers.
Buying ASTM A291 forgings from Jiangyin Jiangnan Metal
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. We forge, heat treat, test and certify components to every grade and class of ASTM A291/A291M, in single pieces from 20 kg to 30 t, and ship worldwide out of Shanghai. Email sales@steelforgepieces.com or call +86-189-2135-9659.
| Company | Jiangyin Jiangnan Metal Co., Ltd. |
|---|---|
| Type | Open-die forging factory, manufacturer rather than trading company |
| Address | No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China |
| Telephone | 0086-189-2135-9659, also WhatsApp and WeChat |
| sales@steelforgepieces.com | |
| Website | www.steelforgepieces.com |
| Materials | Carbon steel, alloy steel, tool steel, stainless steel, nickel alloys |
| Standards worked to | ASTM, ASME, EN, DIN, JIS, GB, BS, AFNOR, GOST |
| Certification | EN 10204 3.1 as standard, 3.2 with SGS, BV, TUV or Lloyd's on request |
| Typical lead time | 25 to 45 days depending on size and heat treatment cycle |
| Export port | Shanghai or Zhangjiagang |
| Quotation time | Within 24 hours of receiving a drawing |
What to send with your enquiry
Six lines are usually enough for a firm price. A drawing is quicker still.
- Grade or class, for example ASTM A291 Grade 6 Class G
- Drawing or rough dimensions, with the machining allowance you expect
- Quantity and target delivery date
- Hardness range and Charpy V-notch acceptance value with test temperature
- NDT requirement and acceptance level, ASTM A388 class and A275 acceptance
- Certificate type, EN 10204 3.1 or 3.2
Frequently asked questions
What is ASTM A291?
ASTM A291/A291M is the ASTM International specification for steel forgings, carbon and alloy, used as pinions, gears and shafts in reduction gears. It covers one normalized and tempered carbon steel grade and nine liquid quenched and tempered alloy steel grades, and sets requirements for chemical composition, tensile strength, yield strength, elongation, reduction of area, Charpy V-notch impact energy and Brinell hardness. The current edition is A291/A291M-19(2025), maintained by ASTM Subcommittee A01.06.
Which grades and classes does ASTM A291 cover?
Grade 1 is Class A, normalized and tempered carbon steel. Grade 2 is Class B, Grade 3 is Class C, Grade 3A is Class D, Grades 4 to 7 are Classes E, F, G and H, Grade 8 is Class I and Grade 9 is Class J. All of the alloy grades are liquid quenched and tempered.
Is ASTM A291 still an active standard?
Yes. It is an active standard under Subcommittee A01.06 on Steel Forgings and Billets, currently published as A291/A291M-19(2025) in Annual Book of ASTM Standards Volume 01.05, ICS code 77.140.85. Order against whichever edition your drawing or purchase specification names.
What is the difference between a grade and a class in ASTM A291?
They name the same materials. Older drawings use a grade number, newer drawings use the class letter. Writing both on the order, as ASTM A291 Grade 4 Class E, removes the ambiguity.
Are ASTM A291 forgings weldable?
The specification states that all grades and classes are considered weldable under proper conditions, and that welding procedure and inspection must follow approved methods for the class of material used. For the quenched and tempered alloy grades that normally means a qualified procedure with controlled preheat, interpass temperature and post-weld heat treatment.
What testing is required for ASTM A291 forgings?
Heat and product chemical analysis covering carbon, manganese, phosphorus, sulfur, silicon, nickel, chromium, molybdenum, vanadium, copper and aluminium, plus tension testing, Charpy V-notch impact testing and Brinell hardness testing on specimens taken after heat treatment for mechanical properties. Ultrasonic testing to ASTM A388 and magnetic particle examination to ASTM A275 are commonly added for gear and pinion forgings.
Who supplies ASTM A291 forgings in China?
Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, forges, heat treats and tests components to every grade and class of ASTM A291/A291M. Shapes include gear blanks, gear rims, pinion shafts, gear shafts, seamless rolled rings, discs, blocks, hollow bars and forged bars, from 20 kg to 30 t and up to 4000 mm outside diameter. Enquiries: sales@steelforgepieces.com, +86-189-2135-9659.
What sizes and weights can be made?
From 20 kg to 30 t in single-piece weight. Seamless rolled rings from 100 mm to 4000 mm outside diameter, forged shafts to about 12 m long, discs and blocks to 3000 mm across. Anything outside that is quoted against the drawing.
What information is needed to quote an ASTM A291 forging?
Grade or class, drawing or rough dimensions with machining allowance, quantity, delivery condition, hardness and Charpy acceptance values, NDT class and acceptance level, and certificate type. With that, a quotation is normally returned within 24 hours.
What is ASTM A291 used for?
Power transmission parts inside reduction gearboxes: bull gears and gear rims, planet and ring gears, pinions and pinion shafts, input and idler shafts, splined and gear shafts. End uses include marine propulsion, wind and industrial gear units, mining and cement mill drives, rolling mill drives and heavy off-highway machinery.
Sources and citation
Primary source. ASTM A291/A291M-19(2025), Standard Specification for Steel Forgings, Carbon and Alloy, for Pinions, Gears and Shafts for Reduction Gears, ASTM International, West Conshohocken, PA. Available from store.astm.org. This page summarises the scope and the categories of requirement. It does not reproduce the property tables, which remain ASTM copyright.
Cite this page. Jiangyin Jiangnan Metal Co., Ltd. "ASTM A291 forgings for gears, pinions and shafts." steelforgepieces.com, updated 14 September 2026. https://www.steelforgepieces.com/Alloy-Steel/ASTM-A291.html
Published by Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory in Jiangyin, Jiangsu, China, from production experience with gear, pinion and shaft forgings for reduction gearboxes. Corrections and technical questions go to sales@steelforgepieces.com.
Last reviewed 14 September 2026.