Stainless Steel Fastener Material Selection Guide

Stainless steel fasteners are widely used in engineering and manufacturing sectors for their outstanding corrosion resistance and stable mechanical properties. However, various stainless steel grades have distinct characteristics and applicable scenarios. Below is a detailed guide for proper material selection.

Key Factors to Select Stainless Steel Material

Three core aspects shall be considered during material selection:

1. Environmental condition: For marine or chemical service environments, A4 series or B8M series are recommended.
2. Load requirement: Select the proper yield strength grade according to working load, such as A2-70, A2-80, A4-70, A4-80.
3. Project specification: Follow corresponding standards, e.g. ASTM F593 for North American projects.

A2 Series Stainless Steel

A2 series, also known as 304 stainless steel (1.4301), is the most common grade. It offers good corrosion resistance for general atmospheric environments. It is not suitable for seawater or high chloride environments.

• A2-50: Yield strength ≥500 MPa, for medium-load applications
• A2-70: Yield strength ≥700 MPa, cold-worked, widely used for higher-load conditions
• A2-80: Yield strength ≥800 MPa, high strength grade for heavy load requirements

✅ Application: General machinery, indoor equipment, outdoor projects without salt spray

A3 Series Stainless Steel

A3 series (302HQ /1.4310) is cold-work hardened austenitic stainless steel with excellent toughness. Its usage in standard bolts & nuts is far less common than A2/A4. It is mainly applied to precision lock parts and spring-type fasteners.

• A3-50: Yield strength ≥500 MPa, medium load
• A3-70: Yield strength ≥700 MPa, higher load

✅ Application: Precision self-locking nuts, spring fasteners (similar to your AMS5637 302 lock nut) ⚠️ Note: A3 is rarely used for standard hex bolts/nuts. Confirm drawing requirements before order.

A4 Series Stainless Steel

A4 series, also known as 316 stainless steel (1.4401) with molybdenum addition. Its chloride corrosion resistance is much better than A2, preferred for marine and chemical environments.

• A4-50: Yield strength ≥500 MPa, medium load in heavy corrosion environment
• A4-70: Yield strength ≥700 MPa, mainstream grade for high corrosion + higher load
• A4-80: Yield strength ≥800 MPa, for extreme corrosion & heavy load

✅ Application: Seawater, coastal salt spray, chemical fluid equipment, marine machinery

B8M Series Stainless Steel

B8M (ASTM A193 B8M) is 316 stainless steel for high temperature and heavy corrosion service. Matching nuts are normally A194 8M.

✅ Application: Pressure vessels, pipeline flanges, petrochemical high-temperature equipment

ASTM F593 Stainless Steel Series

ASTM F593 is the North American standard for stainless steel bolts and screws, including four popular grades:

• F593C: 304 stainless steel, general purpose (equivalent to A2)
• F593D: Reinforced cold-worked 304, high strength (equivalent to A2-80)
• F593G: 316 stainless steel, corrosion resistant (equivalent to A4)
• F593H: Reinforced 316, high strength (equivalent to A4-80)
• ✅ Application: North American engineering, construction, oil & gas and mechanical procurement

ASTM F593 VS DIN / ISO Fastener Standards

1. Region & Scope

• ASTM F593: Mainly adopted in North America (USA & Canada), widely used for construction, machinery and petrochemical industry.
• DIN / ISO: Popular in Europe, South America, Middle East and most global markets (your main DIN bolt & nut range).

2. Material Naming

• ASTM F593: Uses Grade C/D/G/H to define material and mechanical property.
• DIN & ISO: Marked as A2/A4 grades (A2-70, A4-80), with material number like 1.4301 /1.4401.

3. Marking & Certification

• ASTM F593: Mandatory grade marking on fastener body; material test reports often required for North American projects.
• DIN & ISO: Marking requirements also apply. EN10204 3.1 certificate is available, commonly requested by Egypt, Brazil customers.

Summary

This guide covers mainstream stainless steel grades for export fasteners. Customers can select material based on service environment, load and project standards. We can supply torque test reports, material certificates and samples for your evaluation.

If you have any questions, please feel free to contact our team.