AISI 4820 Forgings Forged rings, seamless rolled rings, shafts, discs, flanges and gear blanks in nickel-molybdenum carburizing steel

AISI 4820 is a low-carbon nickel-molybdenum carburizing steel (UNS G48200) containing 0.18–0.23% carbon, 3.25–3.75% nickel and 0.20–0.30% molybdenum. No chromium is specified. Carburizing gives a wear-resistant case of 58–62 HRC over a tough core, so the grade is used for heavily loaded gears, pinions, shafts and bearing races. Jiangyin Jiangnan Metal Co., Ltd. produces AISI 4820 open-die forgings and seamless rolled rings at its factory in Jiangyin, Jiangsu, China.

What is AISI 4820 steel?

AISI 4820 belongs to the SAE 48xx series of nickel-molybdenum steels. Nickel at a nominal 3.5% raises hardenability and keeps the core tough at low service temperatures. Molybdenum suppresses temper embrittlement and helps heavy sections harden through. Carbon sits at 0.18–0.23%, which is too low for the steel to harden usefully on its own. The grade is designed to be carburized. Carbon diffuses into the surface during the carburizing cycle, and the finished part carries a hard case that resists pitting and abrasion over a ductile core that absorbs shock.

Buyers therefore order AISI 4820 as a blank in almost every case. The forging arrives annealed or normalized, the gear shop cuts teeth or machines the part, and carburizing and hardening follow afterwards. AISI 4820 turns up mainly in gear and bearing supply chains, and only rarely in pressure-retaining equipment.

AISI 4820 chemical composition

Table 1 gives the ladle composition range for AISI 4820. Jiangyin Jiangnan Metal melts the grade by electric arc furnace with ladle refining and vacuum degassing (EAF + LF + VD). The vacuum degassing stage keeps hydrogen low and improves internal soundness in heavy forgings.

AISI 4820 mechanical properties

Table 2 covers the annealed condition, which is how forged AISI 4820 blanks are normally delivered for machining. Properties after carburizing depend on the case depth and the hardening cycle, and are quoted separately.

Acceptance properties for a specific forging are agreed on the order. Fix the test location (surface, mid-radius or ¼ T), the orientation (longitudinal or tangential), and whether Charpy impact values at low temperature apply. State all three in the enquiry, because they change the heat-treatment route and the price.

Carburizing and heat treatment of AISI 4820

A typical route runs: normalize, rough machine, carburize at 900–930 °C to the required case depth, cool, reheat and oil quench, then temper at 150–200 °C. Nickel stabilizes austenite, so carburized 4820 holds more retained austenite than leaner grades. A sub-zero treatment before tempering is sometimes added where maximum case hardness or dimensional stability is required.

Case depth and hardness profile

The chart shows the shape of a typical hardness profile through a carburized AISI 4820 part with an effective case depth of about 1.2 mm. Effective case depth is conventionally measured to 550 HV (about 52 HRC).

What is AISI 4820 equivalent to?

AISI 4820 has no exact one-to-one international equivalent, because most European and Japanese carburizing grades of comparable strength also contain chromium. The first group in Table 4 covers the same steel under different US standards. The second group covers grades used for the same duty. Treat those as substitution candidates that need requalification.

AISI 4820 compared with the common alternatives

AISI 4820 forged products we manufacture

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory, so every AISI 4820 item is made to the customer's drawing or size list rather than from a fixed catalogue. Common forms include:

• Seamless rolled rings and forged rings for bearing races, slewing ring blanks and gear rims
• Forged discs and blanks for gears, pinions and couplings
• Forged shafts and spindles, straight, stepped, flanged or eccentric
• Round bars, hollow bars, sleeves and bushings
• Forged flanges, tube sheets and forged blocks
• Pinion shafts, drive shafts and rotor shafts for gearboxes

Because the steel is supplied for carburizing, forgings are normally delivered in the annealed or normalized condition with a machining allowance agreed on the drawing.

Size and weight range

Where AISI 4820 forgings are used

The grade justifies its alloy cost where a part carries high contact stress together with shock loading, and where the section is too heavy for a leaner steel to harden through.

• Power transmission: gears, pinions, gear rims, planetary carriers and gearbox shafts in mining, cement and steel-mill drives
• Bearings: large case-carburized bearing rings and races
• Oil and gas: drilling equipment shafts, mud pump components and downhole tool bodies
• Marine and shipbuilding: reduction gearing, thrust shafts and propulsion components
• Heavy machinery: crusher and mill pinions, rolling-mill drive components and press components
• Cold service: parts that need toughness at sub-zero temperatures, where the 3.5% nickel counts

How an AISI 4820 forging is produced

This is the standard production route used at the Zhouzhuang Town plant in Jiangyin. Each step produces a record that is traceable to the heat number stamped on the forging.

1. Melting and ingotSteel is melted by electric arc furnace, refined in the ladle furnace and vacuum degassed (EAF + LF + VD) to control hydrogen and inclusions.
2. Open-die forgingThe ingot or billet is heated to 1,100–1,200 °C and forged with a minimum forging ratio agreed on the order, typically 3:1 or higher, to close porosity and develop grain flow.
3. Ring rolling (for rings)Pierced blanks are rolled to finished ring dimensions, giving continuous circumferential grain flow that a cut-from-plate ring cannot match.
4. Heat treatmentAnnealing or normalizing, in a furnace with calibrated and recorded temperature charts, to deliver a machinable and dimensionally stable blank.
5. Rough machiningTurning or boring to the agreed machining allowance, so that testing is done on the delivered condition.
6. Testing and certificationChemical analysis, mechanical testing, ultrasonic inspection and issue of the mill test report before release.

Testing, inspection and certification

AISI 4820 forgings are released against the following, as specified on the order:

Frequently asked questions about AISI 4820

About the manufacturer

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China, supplying forged rings, seamless rolled rings, shafts, discs, flanges and bars in carbon steel, alloy steel, tool steel, stainless steel and nickel alloys. Forgings are made to customer drawings, heat treated in-house, ultrasonically tested and released with EN 10204 3.1 or 3.2 certification.

References and standards

• ASTM A29/A29M, General requirements for steel bars, carbon and alloy, hot-wrought (ASTM International)
• ASTM A322, Steel bars, alloy, standard grades
• ASTM A331, Steel bars, alloy, cold-finished
• ASTM A388/A388M, Ultrasonic examination of steel forgings
• SAE J404, Chemical compositions of SAE alloy steels (SAE International)
• EN 10204, Metallic products, types of inspection documents
• EN 10228-3, Non-destructive testing of steel forgings, ultrasonic testing of ferritic or martensitic steel forgings
• SEP 1921, Ultrasonic testing of forged steel bars and billets

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