10.9 Grade – White zinc – Hexagon bolt

Grade 10.9 Performance Characteristics

Grade 10.9 fasteners represent a significant step up in performance. They are typically specified in applications where size constraints limit the use of larger bolts, necessitating a smaller bolt with higher strength. The material is heat-treated to achieve high hardness, making it critical to follow precise torque specifications during installation to avoid failure.

Mechanical Properties Specification

The "10.9" marking indicates specific metallurgical properties defined by ISO 898-1 standards:

Property	Value	Engineering Implication
Tensile Strength	1000 N/mm² (Min)	The absolute breaking point. Extremely resistant to snapping under tension.
Yield Strength	900 N/mm² (Min)	Calculated as 90% of tensile strength. Allows for very high pre-load clamping force.
Material Base	Low Carbon Alloy Steel	Contains alloy elements (like Boron or Manganese) for deep hardenability.

Quality Assurance

Given the critical nature of these bolts, material verification is often required. We can provide an EN 10204 3.1 Material Certificate upon request. Please note that third-party inspection services require an additional fee.

Critical Industrial Applications

Due to their high yield strength, Grade 10.9 bolts are essential in sectors involving high stress and vibration:

• Automotive Suspension: Control arms, struts, and brake calipers where failure is not an option.
• Heavy Trucking: Chassis assembly and wheel hubs.
• Construction Equipment: Hydraulic rams and pivot points on excavators and cranes.
• Wind Energy: Turbine nacelle assembly and blade root connections.

Frequently Asked Questions

What is Hydrogen Embrittlement?

High-strength bolts (Grade 10.9 and 12.9) are susceptible to hydrogen embrittlement during the zinc plating process (acid pickling). This can cause the bolt to crack unexpectedly under load. High-quality 10.9 zinc plated bolts undergo a "de-embrittlement baking" process immediately after plating to drive out the hydrogen and ensure safety.

Can I reuse Grade 10.9 bolts?

It depends on the application, but caution is advised. If a Grade 10.9 bolt has been torqued near its yield point, it may have undergone permanent deformation or fatigue. In critical safety applications (like automotive engines or suspension), it is standard practice to replace the bolts rather than reuse them.

Should I use washers with Grade 10.9 bolts?

Yes, but you must use hardened washers (typically HV 300). Using standard mild steel washers with a Grade 10.9 bolt is dangerous because the high clamping force will crush the soft washer, leading to a loss of preload and potentially loosening the joint.