Steel Grade Comparison Chart: 1018 vs 4140 vs A36

Steel comes in hundreds of grades, each with specific properties for different applications. This guide compares the most common grades used in machining, fabrication, and general manufacturing, helping you select the right steel for your project.

Steel Numbering Systems

The SAE/AISI 4-digit system:

• 10xx: Plain carbon steel
• 11xx: Free-machining carbon steel (sulfur added)
• 41xx: Chromium-molybdenum steel
• 43xx: Nickel-chromium-molybdenum steel

The last two digits indicate carbon content (e.g., 1045 = 0.45% carbon).

Common Grades Compared

*Heat-treated strength varies with process.

1018: Low-Carbon Workhorse

• Carbon: 0.18% (low carbon)
• Strength: Low (64 ksi as-rolled)
• Machinability: Good
• Weldability: Excellent
• Best for: Shafts, pins, case-hardened parts, general fabrication
• Note: Can be case hardened for wear surfaces while core stays tough

1045: Medium-Carbon

• Carbon: 0.45% (medium carbon)
• Strength: Moderate (91 ksi as-rolled), higher heat-treated
• Machinability: Good
• Weldability: Fair (preheat often required)
• Best for: Gears, shafts, axles, bolts, parts needing through-hardening
• Note: Heat treatable to ~55 HRC surface, ~30 HRC core

4140: Chromoly All-Star

• Alloys: Chromium (~1%), Molybdenum (~0.2%)
• Strength: High (varies with heat treatment)
• Machinability: Good (especially annealed)
• Weldability: Fair (preheat and post-weld treatment needed)
• Best for: High-stress shafts, gears, couplings, machinery components
• Note: Available pre-hardened (HT) for convenience

4340: Maximum Strength

• Alloys: Nickel, chromium, molybdenum
• Strength: Very high (up to 280 ksi heat-treated)
• Machinability: Fair
• Weldability: Difficult
• Best for: Aircraft landing gear, high-stress shafts, critical applications
• Note: More expensive; use where 4140 won't suffice

A36: Structural Standard

• Type: Structural steel (not alloy designation)
• Strength: 36 ksi minimum yield
• Machinability: Fair
• Weldability: Excellent
• Best for: Structural shapes, plates, base plates, frames
• Note: Variable chemistry; not suitable for precision machining

12L14: Free-Machining Champion

• Additives: Lead, sulfur for chip breaking
• Strength: Moderate
• Machinability: Excellent (100% rating baseline)
• Weldability: Poor (lead contamination)
• Best for: Screw machine parts, bushings, fittings
• Note: Restricted in some regions due to lead content

Selection Guidelines

For Welded Fabrication

A36 or 1018. Low carbon means no preheat, no post-weld heat treatment, no cracking concerns.

For Heat-Treated Parts

1045 for moderate strength; 4140 for higher strength; 4340 for critical applications.

For Screw Machine Work

12L14 (or 1215/1117) for best machining. Choose based on required strength and lead restrictions.

For Case Hardening

8620 or 1018. Low core carbon allows carburizing for hard surface, tough core.

Common Mistakes

• Welding 4140 without preheat: Causes hydrogen cracking
• Assuming all "steel" is equal: Properties vary dramatically
• Specifying 4340 when 4140 works: Unnecessary cost and difficulty
• Ignoring the condition: Hot-rolled vs. cold-drawn vs. annealed matters

Start with 1018 for general work, step up to 1045 for through-hardening, 4140 for heavy-duty, and 4340 for critical applications. The right steel for the job balances strength, manufacturability, and cost.