How To Manufacture High Quality 4140 Forged Steel?

Manufacturing high-quality 4140 forged steel requires strict adherence to key steps in material science and forging technology to ensure precise control of each link. Here is a step-by-step description:

1. 4140 Steel Raw Material Selection & Preparation

Composition control: Ensure that the chemical composition of the ingot or billet meets the ASTM A322 or AMS 6349 or ASTM A29 standards (such as: C 0.38-0.43%, Cr 0.8-1.1%, Mo 0.15-0.25%).
Purity: Reduce impurities (S, P content <0.025%) through vacuum degassing or electroslag remelting (ESR) to improve material homogeneity.
Billet surface treatment: Check the surface of the billet to eliminate external defects.

2. Heating Process For 4140 Steel

Heating temperature: uniform heating to 1100-1200°C (avoid overburning or insufficient temperature).
Furnace atmosphere: neutral or weakly reducing atmosphere (such as nitrogen protection) is used to prevent surface oxidation and decarburization.
Hot holding time: calculated according to the billet diameter (usually 1 hour/inch thickness), to ensure that the core surface temperature is consistent.

3. 4140 Steel Forging Process

Forging method: radial forging or rolling is used to ensure uniform deformation; free forging requires multi-directional forging to refine the grains.
Forging ratio: ≥3:1, optimize the grain structure through multiple upsetting and drawing.
Final forging temperature: controlled above 850-900°C to avoid cracks caused by low temperature forging.
Deformation rate: moderate to avoid internal defects caused by high-speed deformation.radial forging or rolling is used to ensure uniform deformation; free forging requires multi-directional forging to refine the grains.
Post-forging cooling: Use slow cooling (such as sand burying cooling or furnace cooling) to prevent martensite formation, or directly enter the heat treatment process.

5. Optimization of Heat Treatment of 4140 Steel

Normalizing treatment: heating to 870-900°C, air cooling, grain refinement and elimination of internal stress.
Quenching and tempering treatment :
– Quenching: 850-870°C oil quenching or water quenching (select medium according to size) to ensure complete austenitization.
– Tempering: 540-660°C insulation and air cooling, adjust to the target hardness (usually HRC 28-32).

6. Finishing & Processing

Straightening: hot or cold straightening to ensure the straightness of round steel (≤3mm/m).
Surface treatment: turning or grinding to remove oxide scale, roughness Ra≤3.2μm.
Non-destructive testing: ultrasonic testing (UT) to detect internal defects, magnetic particle testing (MT) to check surface cracks.

7. Quality Inspection & Certification

Mechanical properties: test tensile strength (≥850 MPa), yield strength (≥650 MPa), impact energy (≥25J).
Metallographic analysis: check grain size (ASTM 5-8), no banded structure or untempered martensite.
Dimension tolerance: meet AMS 6349 or customer requirements

Key Control Points & Common Problems

Overburn prevention: Heating temperature exceeding 1250°C will cause grain boundary melting, and the furnace temperature needs to be monitored in real time.
Crack control: If the final forging temperature is too low or the cooling is too fast, it is easy to crack, and process simulation optimization is required.
Hardness uniformity: Insufficient holding time during tempering will lead to uneven hardness, and the holding time needs to be extended.

Through the system control of the above steps, high-strength, high-toughness and precise-size 4140 forged round steel can be produced to meet high-demand application scenarios such as aerospace and automotive drive shafts.