GB/T 019Cr19Mo2NbTi Stainless Steel: High-Performance Austenitic Alloy for Elevated Temperature & Corrosive Environments

GB/T 019Cr19Mo2NbTi (commonly referenced as 1Cr19Mo2NbTi or Chinese equivalent to AISI 347/347H) is a stabilized austenitic stainless steel grade designed for superior intergranular corrosion resistance and high-temperature strength. Its chemical composition—featuring 19% chromium, 9-13% nickel, and stabilizing elements niobium (Nb) and titanium (Ti)—prevents chromium carbide precipitation during welding or prolonged exposure to 450-850°C. This grade is widely specified in petroleum refining, power generation, and chemical processing industries where thermal cycling and corrosive media are present. Below is a technical breakdown of its metallurgical properties, processing characteristics, and industrial applications.

1. Chemical Composition (GB/T 20878 & GB/T 1220 Standards)

2. Mechanical Properties (Annealed Condition)

• Tensile Strength (R_m): ≥ 520 MPa (GB/T 20878); higher in cold-worked or aged conditions.
• Yield Strength (R_p0.2): ≥ 205 MPa; retains strength at elevated temperatures (up to 600°C).
• Elongation (A): ≥ 40% (50mm gauge length); excellent ductility for forming complex shapes.
• Hardness (HB): ≤ 187; suitable for machining with carbide tools (avoid work hardening).
• Impact Toughness (AKV): ≥ 100 J at -20°C; maintains toughness in cryogenic and thermal cycling applications.
• Creep Resistance: Superior to 304/316 at 500-700°C due to Nb/Ti stabilization and Mo addition.

3. Manufacturing & Heat Treatment

1. Melting Practice: Electric arc furnace (EAF) + AOD (argon oxygen decarburization) or VOD (vacuum oxygen decarburization) to achieve ultra-low carbon and precise Nb/Ti ratios. Secondary refining ensures inclusion control (≤ 1.0 per ASTM E45 Method A).
2. Hot Working: Forged or rolled at 1150-1250°C; avoid temperatures below 900°C to prevent carbide precipitation. Water quenching post-hot working to retain austenite.
3. Cold Working: Readily formable via deep drawing, bending, or spinning. Intermediate annealing (1050-1100°C) required for heavy cold reduction (>30%) to restore ductility.
4. Solution Annealing: 1020-1120°C followed by rapid cooling (water or air) to dissolve NbC/TiC and homogenize microstructure. Critical for restoring corrosion resistance after welding.
5. Stabilization Treatment (Optional): 850-900°C for 2-4 hours (for welded components) to precipitate NbC and mitigate IGC risk in service.
6. Surface Finishing: Pickling (HNO₃ + HF) to remove oxide scale; passivation (HNO₃) to enhance Cr₂O₃ film. Common finishes: 2B (general), No.4 (architectural), BA (decorative).

4. Key Applications by Industry

5. Comparison with Related Grades

6. Selection Guidelines & Engineering Considerations

• Welding Procedures: Use ER347 or ER347H filler metal (AWS A5.9). Preheat not required for thin sections; maintain interpass temperature ≤ 150°C. Post-weld stabilization (850-900°C) recommended for thick sections (>6mm) in corrosive service.
• Corrosion Limitations: Avoid continuous use in halides (e.g., seawater) or strong oxidizing acids (e.g., concentrated nitric acid). For chloride pitting, consider 022Cr17Ni14Mo2 (316L) or super austenitics (e.g., 904L).
• High-Temperature Service: Maximum continuous service temperature: 750°C in air, 850°C in sulfur-free environments. Avoid thermal cycling in 450-850°C range to prevent sigma phase formation.
• Machinability: Use rigid setups, sharp tools (e.g., KC850 grade inserts), and slow speeds (60-90 m/min) to mitigate work hardening. Chip breakers recommended for turning operations.
• Quality Certification: Verify compliance with GB/T 24511 (pressure equipment), GB/T 4237 (hot-rolled plates), or ASME BPVC Section II for critical applications. Request PMI (positive material identification) for Nb/Ti content.