4140 Cold Drawn Flats, Squares, Rounds (ASTM A108)

The term 4140 Cold Drawn refers to a high-strength, low-alloy steel that has undergone a specific cold-working process to improve its dimensional accuracy and mechanical properties.

This material is a popular choice for high-stress components in manufacturing.

AISI 4140 is a medium carbon alloy steel. It is sometimes called Chromium-Molybdenum steel ("chromoly") due to its primary alloying elements.

• Key Alloying Elements
  • Carbon (C): 0.38%–0.43% (Provides high hardenability and strength.)
  • Chromium (Cr): 0.80%–1.10% (Enhances hardness, wear resistance, and corrosion resistance.)
  • Molybdenum (Mo): 0.15%–0.25% (Increases toughness and uniformity of hardness.)
• Key Properties: It is known for its high fatigue strength, excellent toughness, and good abrasion and impact resistance. It responds very well to heat treatment.
• Common Applications:Shafts, gears, axles, high-strength bolts, couplings, and other components requiring superior strength and durability.

Cold drawing is a metalworking process where a hot-rolled bar is pulled (or "drawn") through a die at room temperature (below the steel's recrystallization temperature).

This cold working process is done to achieve several improvements over the starting hot-rolled material:

1. Increased Strength: The drawing process cold-works the metal, which strain-hardens the steel and significantly increases its yield and tensile strength.
2. Superior Surface Finish: The bars have a smooth, bright, and clean finish, often eliminating the need for further surface preparation.
3. Enhanced Dimensional Accuracy: Cold drawing provides tighter size tolerances and better straightness, making the bars ideal for high-speed machining and precision parts.

Core Differences

1. Strength and Hardenability
   • 4140 is superior for strength. It contains chromium (Cr) and molybdenum (Mo), which are powerful alloying elements. In its quenched and tempered condition, 4140 can achieve tensile strengths more than double that of C1018.
   • Heat Treatment: This is the most significant difference.
   • C1018 cannot be hardened throughout due to its low carbon content. It is only suitable for case hardening (carburizing) to achieve a hard surface over a soft, tough core (e.g., for gears).
   • 4140 is a through-hardening steel, meaning it can be heat-treated (quenched and tempered) to achieve uniform high strength and hardness deep into its cross-section (e.g., for heavy-duty shafts).
2. Machinability and Weldability
   • C1018 is superior for ease of processing. Due to its low carbon content and relatively high manganese content, C1018 is one of the most free-machining carbon steels available, leading to lower machining costs and faster cycle times.
   • Weldability: C1018 is easily welded with minimal preparation. 4140 requires careful procedures, specifically pre-heating and post-weld stress relief or tempering. This helps avoid cracking and maintains adequate strength and ductility in the weld zone.