AM 355 Stainless Steel (UNS S35500 / Alloy 355) | Alloy 355 / AMS 5547 / AMS 574

Physical characteristics of Alloy 355 (UNS S35500) at room temperature:

Alloy 355 maintains good mechanical properties at elevated temperatures, with the following key characteristics:

• Continuous Service Temperature: Up to 315°C (600°F) for structural applications
• Short-Term Service Temperature: Up to 427°C (800°F) for non-critical components
• Creep Resistance: Maintains 80% of room-temperature strength at 260°C (500°F) for 10,000 hours
• Oxidation Resistance: Resistant to scaling in air up to 538°C (1000°F) for intermittent exposure
• Strength Retention:
  • 200°C (392°F): ~95% of room temperature tensile strength
  • 300°C (572°F): ~85% of room temperature tensile strength
  • 400°C (752°F): ~70% of room temperature tensile strength

Note: Precipitation hardening treatments (H900/H950/H1000) optimize high-temperature performance; avoid prolonged exposure above 540°C (1000°F) to prevent carbide precipitation.

General Welding Characteristics

Alloy 355 is weldable with proper pre- and post-weld procedures, though its martensitic structure requires careful handling to avoid cracking and maintain mechanical properties:

Recommended Welding Methods

• GTAW (TIG): Most preferred method for high-quality welds (use ERNiCrMo-3 filler metal)
• GMAW (MIG): Suitable for production welding (use ER308L or ER316L filler metal)
• SMAW (Stick): For field welding (use E308L-16 or E316L-16 electrodes)
• PAW (Plasma Arc Welding): For precision thin-section welding

Critical Welding Procedures

1. Pre-Weld Preparation:
   • Clean all surfaces (remove oil, grease, oxides) within 25mm (1 inch) of weld joint
   • Preheat to 150-200°C (300-390°F) to reduce hydrogen cracking risk
2. Welding Parameters:
   • Maintain interpass temperature below 200°C (390°F)
   • Use low heat input (1.5-2.5 kJ/mm) to minimize grain growth
   • Travel speed: 100-150 mm/min (4-6 in/min)
3. Post-Weld Heat Treatment:
   • Stress relief: 620-675°C (1150-1250°F) for 1-2 hours, air cool
   • Re-hardening: Solution anneal at 1040°C (1900°F) + precipitation harden at 482°C (900°F)

Caution: Avoid oxy-fuel welding due to high carbon pickup risk; do not weld in the H900 condition (fully hardened state).

Machinability Rating

Alloy 355 has a machinability rating of 50-60% compared to AISI 1212 steel (100% baseline) when in the annealed condition:

Recommended Machining Practices

• Annealed Condition (softest state):
  • Brinell Hardness: 200-220 HB
  • Cutting speed: 60-90 m/min (200-300 ft/min) for turning/milling
  • Feed rate: 0.10-0.20 mm/rev (0.004-0.008 in/rev)
  • Depth of cut: 2-4 mm (0.08-0.16 in)
• Hardened Condition (H900):
  • Use carbide tools with positive rake angles
  • Cutting speed: 30-45 m/min (100-150 ft/min)
  • Use high-pressure coolant (emulsion type) to reduce tool wear

Fabrication Considerations

• Forming: Cold forming possible in annealed condition; warm forming (150-200°C) for complex shapes
• Grinding: Use aluminum oxide abrasives; avoid excessive heat build-up
• Polishing: Achieves 150-200 grit finish with standard stainless steel polishing techniques
• Heat Treatment After Fabrication: Stress relief at 620°C (1150°F) for 1 hour before final hardening

International equivalents and similar grades to Alloy 355 (UNS S35500):

Note: Always verify chemical composition and mechanical properties before substituting grades for critical applications.