Why Gear Failure Starts with Material Selection 

In gear engineering, failure is rarely caused by design alone. In most cases, it begins with incorrect material selection. 

• Gears operate under extreme conditions: 
• Continuous contact stress  
• Cyclic fatigue loading  
• Sliding wear and friction  

If the material does not provide the right balance of hardness and toughness, failures such as pitting, scuffing, and tooth breakage become inevitable. 

This is why case hardening steel for gears is the industry standard—delivering a hard outer surface with a tough internal core, essential for durability in demanding applications 

What is Case Hardening Steel? 

Case hardening steel is a low-carbon alloy steel that is heat-treated to achieve a hard wear-resistant surface and a tough core. 

Key Characteristics 

• Carbon content: 0.10–0.25%  
• Surface hardness after carburizing: up to 58–62 HRC  
• Core remains ductile and shock-resistant  

Why it is used in gears 

• Improves wear resistance  
• Enhances fatigue life  
• Prevents brittle failure under load  

Carburizing creates a hardened layer while maintaining a tough core, which is critical for components like gears and shafts 

Why Material Selection Matters in Gears 

Gear performance depends heavily on material properties, especially in high-load and high-cycle environments. 

Common Gear Failure Modes 

• Pitting → surface fatigue failure  
• Scuffing → poor lubrication and low hardness  
• Tooth breakage → insufficient core strength  

Engineering Insight 

Material must balance: 

• Surface hardness (wear resistance)  
• Core toughness (impact resistance)  
• Fatigue strength (long-term durability)  

Studies show that selecting the right steel can significantly improve wear resistance and fatigue life, with EN36 outperforming 8620 in demanding conditions 

EN36 vs 16MnCr5 vs 8620 – Material Overview 

These three are the most commonly used case hardening steels for gears across global industries. 

EN36 Steel (BS 970 / 655M13) 

EN36 is best for high-load gears due to its superior fatigue strength and deep case hardening capability. 

EN36 is a nickel-chromium alloy steel designed for high-stress and heavy-duty  applications. 

Key Features 

• High fatigue strength  
• Deep carburized case  
• Excellent wear resistance  

Typical Applications 

• Aerospace gears  
• Heavy-duty transmission systems  
• High-strength shafts  

EN36 offers superior performance in wear and fatigue compared to 8620, making it ideal for critical applications 

6MnCr5 Steel (EN 10084 / 1.7131) 

 16MnCr5 is best for cost-effective gear manufacturing with balanced performance. 

16MnCr5 is a chromium-manganese carburizing steel widely used in automotive and general engineering. 

Key Features 

• Good hardenability  
• Excellent machinability  
• Balanced wear and toughness  

Typical Applications 

• Automotive gearboxes  
• Industrial gears  
• Machine components  

It provides a strong wear-resistant surface with adequate core strength for standard applications 

8620 Steel (AISI / ASTM A29) 

 8620 is best for shock-loaded gears due to its excellent core toughness. 

8620 is a nickel-chromium-molybdenum steel designed for applications requiring impact resistance and durability. 

Key Features 

• High core toughness  
• Good fatigue resistance  
• Reliable carburizing response  

Typical Applications 

• Differential gears  
• Heavy-duty shafts  
• Oil & gas components  

Nickel and molybdenum improve toughness and impact resistance, making 8620 ideal for dynamic loading conditions 

Performance Comparison (Key Properties) 

Which Steel is Best for Gears? 

• EN36 is best for high-load and high-fatigue gear applications  
• 8620 is best for shock and impact loading  
• 16MnCr5 is best for cost-effective, high-volume production 

Quick Selection Guide 

Application-Based Selection Guide 

Heavy Load Gears 

Use EN36 
Reason: High fatigue strength and deeper case hardening 

Shock Load Applications 

Use 8620 
Reason: Superior core toughness prevents failure 

Automotive & Standard Gears 

Use 16MnCr5 
Reason: Cost-performance balance 

High Precision / Aerospace 

Use EN36 
Reason: Reliability under cyclic stress 

Chemical Composition 

Heat Treatment Performance 

Case hardening steels typically achieve a hard surface with a tough core after carburizing, which is essential for gear applications 

Advantages and Limitations 

Conclusion 

There is no single best steel—selection depends on application requirements. 

Final Recommendation 

• Choose EN36 for maximum performance and durability  
• Choose 8620 for shock and impact resistance  
• Choose 16MnCr5 for cost-efficient production  

If your application involves high load and fatigue → EN36 is the best choice 
If your priority is toughness → 8620 is preferred 
If your focus is cost → 16MnCr5 is ideal 

Need Help Selecting the Right Material? 

Choosing the wrong material leads to: 

• Premature failure  
• Increased downtime  
• Higher maintenance cost  

Contact Nifty Alloys for material selection support Get expert guidance tailored to your gear applications.