Welding Technology for Stainless Steel and Nickel Alloys

I. Material Characteristics Comparison

1. ‌Stainless Steel Properties‌

   • Primary composition: Fe-Cr-Ni ternary system (e.g., 304, 316 series)
   • Key performance indicators:
     • Corrosion resistance: Forms stable passive film when Cr content ≥16%
     • Mechanical properties: Tensile strength ≥515MPa, elongation ≥40%
   • Typical applications: Chemical equipment, medical devices, food processing machinery

2. ‌Nickel-Based Alloy Properties‌

   • Composition characteristics: Ni content ≥50% with Mo, Cr, Nb strengthening elements
   • Outstanding properties:
     • High-temperature strength: Maintains ≥70% room temperature strength at 800°C
     • Corrosion resistance: Withstands strong corrosive media like concentrated sulfuric acid and hydrofluoric acid
   • Main application fields: Aircraft engine components, petrochemical reactors, nuclear power plant critical equipment

II. Welding Technical Challenges

1. ‌Metallurgical Incompatibility‌

   • Thermal expansion coefficient difference: Nickel alloys 15-20% lower than stainless steel
   • Phase transformation temperature range: 200-300°C difference
   • Conflicting oxidation characteristics: Coexistence of Cr₂O₃ protective film and porous NiO layer

2. ‌Process Control Difficulties‌

   • Hot cracking susceptibility: Ni-Al/Mg systems prone to liquation cracks in high-temperature zones
   • Element segregation tendency: Fe-Ni-Cr ternary system susceptible to dendritic segregation

III. Advanced Welding Techniques

1. ‌Transition Layer Welding Technology‌

   • Recommended filler metal: ERNiCrMo-3 (AWS A5.14 standard)
   • Process parameters:
     • Current type: DCEN (Direct Current Electrode Negative)
     • Heat input control: 8-12kJ/cm
     • Interpass temperature: ≤150°C

2. ‌High-Energy Beam Welding Processes‌

   Parameter	Electron Beam Welding	Laser Welding
   Vacuum (Pa)	10⁻³-10⁻⁴	Ambient/local shielding
   Penetration (mm)	≤50	≤12
   Distortion (%)	0.1-0.3	0.3-0.8

IV. Quality Control Essentials

1. ‌Pre-Weld Preparation‌

   • Groove treatment: Machining + electropolishing (Ra≤1.6μm)
   • Cleaning requirements: Ultrasonic acetone cleaning (15min) + alcohol degreasing

2. ‌Process Control‌

   • Shielding gas: Ar+2%H₂ mixture (dew point ≤-60°C)
   • Welding sequence: First weld nickel alloy transition layer, then stainless steel side

3. ‌Post-Weld Treatment‌

   • Heat treatment regime:
     • Solution treatment: 1100°C×1h/WQ
     • Stress relief annealing: 650°C×2h/AC
   • Inspection standards:
     • RT testing: Complies with ASME Section V Class B
     • Corrosion testing: Passes ASTM G28 Method A