How should the material for gear blank forgings be selected

In-depth Analysis of Core Elements in Forging
Material Selection

In the manufacturing of gear forgings, material selection should first be based on the application scenarios and characteristics of the product, and then a comprehensive balance of mechanical properties, process compatibility and economy should be made. The following are the six core elements widely recognized in the industrial circles of Europe and America:

Mechanical performance indicators

Tensile Strength: The key parameter that determines the carrying capacity of gears. For example, the tensile strength of SAE 4340 forgings after quenching and tempering treatment can reach 900-1100MPa, and they are suitable for heavy-duty gears of mining machinery.
Impact Toughness: In low-temperature environments (such as wind turbine gearboxes), it is necessary to ensure that the material still meets the Charpy V-notch impact energy of ≥27J at -40 ° C (reference ASTM A370).
Fatigue Limit: The failure threshold of gears under cyclic loads. The bending fatigue limit of carburized and quenched gears can be increased to 600-800MPa (EN 10084 standard).

The above environmental characteristics require the selection of materials and processes based on the working conditions and loads of the gear application scenarios!

Adaptability to heat treatment processes

Hardenability: The depth of material quenching is evaluated through the Jominy end quenching test. For example, EN 10083-1 34CrNiMo6 still maintains a hardness of HRC 45 or above at an end quenching distance of 50mm, and is suitable for the overall quenching of large-module gears.
Deformation control: For precision gears, low quenched deformation steel (such as SAE 8620H) should be selected. Combined with the isothermal quenching process, the dimensional tolerance can be controlled within ±0.05mm.

Environmental tolerance

High-temperature oxidation resistance: Aviation gears often adopt Inconel 718 forgings (AMS 5662 standard), which still maintain stable hardness at 650℃.
Corrosion resistance: For Marine gears, duplex stainless steel forgings (such as ASTM A182 F51) are recommended. The pitting equivalent (PREN) resistance is ≥35, and the salt spray test life exceeds 5000 hours.

Processing performance

Machinability: Sulfur-containing free-cutting steels (such as SAE 1144) can reduce tool wear, but the influence of sulfide inclusions on fatigue strength needs to be balanced.
Forging fluidity: For aluminum alloy forgings (such as AA 7075), the forging temperature needs to be controlled at 350-450℃ to avoid grain coarsening.

Cost and Supply Chain

Material utilization rate: Near-net-shape forging technology can reduce the weight of gear blank by 20%(WeForging precision forging ).
Alternative solution: Replace 4340 with SAE 4140 in non-critical parts, reducing the cost per ton by approximately $300. At the same time, 80% of the working conditions are met, but certain heat treatment processes need to be combined to improve the tensile and yield strength.

Regulations and Certification Requirements

Automotive industry: IATF 16949 certification mandating material traceability (full-process records from steelmaking furnace numbers to finished gears).
Energy industry: Wind power gears need to comply with the non-destructive testing (UT/MT) and residual stress control requirements in GL2010 or DNV-ST-0376 standards.

Ii. Comprehensive Comparison of Forging Material Standards in Europe and America

American standards (SAE/ASTM)

Standard Number	Typical Materials	Characteristics and Applicable Scenarios	Suggestions for Heat Treatment Process
SAE J404 1045	Carbon Steel	Low – cost general – purpose gears, suitable for low – load scenarios like agricultural machinery and conveyor belts.	Normalizing (HB 170 – 210) or quenching and tempering (HRC 28 – 32)
SAE J434 D – 4340	Nickel – Chromium – Molybdenum Alloy Steel	Preferred for heavy – duty gears, with a tensile strength of ≥930MPa, used in mining machinery and marine thrusters.	Oil quenching + tempering (HRC 35 – 40)
ASTM A668 Class D	Carbon Manganese Steel	An economical alternative to SAE 1045, suitable for mass production of medium and small module gears.	Normalizing + surface high – frequency quenching (HRC 50 – 55)

Case: Cascade Construction Machinery manufacturer uses ASTM A668 Class D forgings to manufacture the rotary gears of excavators. Through laser surface hardening, the hardness of the tooth surface reaches HRC 58, and the service life is increased by three times.

European Standards (EN/DIN/ISO)

Standard Number	Material	Typical Material Properties	Applicable Scenarios	Heat Treatment Process Suggestions
EN 10083 – 1 34CrNiMo6	Chromium – nickel – molybdenum alloy steel	Features excellent core toughness (KV≥60J)	Serves as mainstream materials for automotive gearboxes and aviation gears	Carburizing and quenching, with surface HRC reaching 60 – 64
EN 10250 – 4 42CrMo4	Chromium – molybdenum steel	Boasts a quenching penetration depth of ≥15mm (quenched in water at 850℃)	Used for wind power gearbox planetary gears and sun gears	Conditioning (HB 280 – 320) followed by nitriding
DIN 17210 20MnCr5	Low – carbon alloy steel	Offers low cost for carburized gears, with core hardness at HRC 30 – 35	Suitable for passenger car transmission gears	Gas carburizing with a layer depth of 0.6 – 1.0mm

Technical comparison

Fatigue resistance: The bending fatigue strength of EN 34CrNiMo6 after 10⁷ cycles is 12% higher than that of SAE 4340 (Data source: FZG Gear Test bench).
Cost efficiency: The material cost of DIN 20MnCr5 is 25% lower than that of EN 34CrNiMo6, making it suitable for the mass production of passenger car gears.

Special application standards

Aviation gears: AMS 6265 (carburized steel) requires grain size ≥ grade 5 and non-metallic inclusions ≤0.015%.
Medical device gears: ASTM F138 (316LVM stainless steel) must meet the requirements of biocompatibility and sterilization resistance (high-temperature and high-pressure steam circulation).

Iii. Cases of Failed Material Selection and Solutions

Case 1: Early pitting corrosion of wind power gears

Problem: A certain manufacturer used 25CrMo forgings to manufacture gears. After six months of operation, severe wear occurred on the tooth surface.

Analysis: The carbon content is too low, the overall hardness is relatively low, and the contact fatigue strength is lower than the design requirements.

Solution: Use EN 10250-4 42CrMo4 forgings instead. After two normalizing and tempering processes, the tooth surface hardness is increased to HRC 55, and the residual compressive stress is increased through shot peening.

Case 2: Excessive deformation of automotive gears during quenching

Problem: The ellipticity of the inner hole of the SAE 8620H gear after carburizing exceeds 0.1mm (requirement ≤0.05mm).
Analysis: Uneven quenching cooling rate leads to deformation.

Solution: Use graded quenching oil (fast oil → slow oil) and expansion sleeve fixtures to make the stress points at all angles relatively uniform, reducing the deformation to 0.03mm.

Iv. How to Obtain Customized Material Selection Support?

Youdaoplaceholder0 provides materials (metallographic and microstructure analysis of materials in the laboratory)- process design – performance testing – ultrasonic flaw detection one-stop service:

Material database: Covering over 200 standard grades from Europe and America, providing chemical composition analysis reports.
Process Simulation: Use QForm/Deform-3D to simulate the forging process and predict material flow and defects.
Rapid testing: Heat-treated samples are provided within 72 hours, supporting hardness/metallographic/fatigue testing.
Select alternative materials that can be used under different standards to reduce costs for mass production while ensuring quality.

How to Choose a powerful forging manufacturer?
Is there a reliable laboratory
Whether the forged products are long-term strategic partners for large-scale projects
A case is the best example of having a strong manufacturer, such as Weforging Hong Kong-Zhuhai-Macao Bridge

Weforging is a comprehensive manufacturing plant. If you have technical problems with forging, die, heat treatment machining, gear ring, etc, you can contact our technical team www.weforging.com