4140 Precision Ground Shaft (ASTM A108)

Sometimes called chromoly due to its Chromium and Molybdenum content.

• Key Properties: Excellent combination of strength, toughness, and wear resistance.
• Alloys: Chromium and Molybdenum significantly increase its hardenability and allow it to maintain high strength even at elevated temperatures.

A precision ground shaft made from 4140 is typically sold in the Quenched & Tempered (QT) or Heat Treated (HT) condition.

• The heat treatment process of quenching and tempering optimizes the material's properties, providing a superior balance of high tensile strength (often around 110,000 to 160,000 PSI) and good ductility, making it much stronger than standard carbon steel.

The term "Precision Ground" refers to the highly accurate machining process used to finish the shaft's surface. This finish is also often referred to as Turned, Ground, and Polished (TG&P).

• Grinding: Abrasive wheels are used to remove material, resulting in exceptional dimensional accuracy. Typically, small diameters have tighter tolerances. Larger shafts typically require more liberal tolerances.
• Tight Tolerance: Essential for parts that must mate with high-precision components. Tolerances are always on the minus side of the nominal size.
• Straightness: The grinding process also significantly improves the straightness of the bar.
• Smooth Surface: A very smooth surface finish reduces friction and wear on mating parts.

Because of its balance of strength and precision, the 4140 Precision Ground Shaft is typically used in demanding, high-stress applications:

• Rotating Machinery: Spindles, axles, and precision shafts in machine tools.
• Automotive: High-performance axles, gears, and drive shafts.
• Heavy Equipment: Hydraulic piston rods, transmission components, and heavy-duty pins.
• Oil & Gas: Drill collars and high-pressure tools.