CLADDING TECHNOLOGY SHANXI CO., LTDEffect of Final Rolling Temperature on Interface Microstructure and Mechanical Properties of 2205-Q345C Composite Plate
Literature Overview
The combination of 2205 duplex stainless steel cladding with Q345C low-carbon structural steel backing represents a widely used material system in pressure vessel fabrication, particularly for hydrogenation reactors, heat exchangers, and chemical processing equipment. Q345C offers higher strength than Q235B while maintaining good weldability, making it a preferred backing material for pressure-containing applications. This study investigates how final rolling temperature influences the interface microstructure and mechanical properties of this specific composite system, with particular attention to the implications for pressure vessel design and fabrication.
Core Technical Analysis
Material System Characteristics
The 2205-Q345C composite system presents unique challenges compared to the 2205-Q235B combination due to the higher carbon equivalent and microalloying elements (Nb, V, Ti) in Q345C. These elements influence the phase transformation behavior during hot rolling and subsequently affect the bonding interface characteristics.
| Parameter | 2205 Duplex SS | Q345C Steel |
|---|---|---|
| Ferrite content | ~50% | ~95% (with minor pearlite) |
| Carbon equivalent | Low | 0.38-0.42 |
| A₃ temperature | ~950°C | ~870°C |
| Recrystallization temperature | ~600°C | ~550°C |
| Thermal expansion coefficient (×10⁻⁶/°C) | 13.5 | 12.0 |
| Yield strength (MPa) | 450-550 | 345-450 |
Interface Microstructure Evolution
The final rolling temperature governs the degree of plastic deformation, recrystallization behavior, and interdiffusion at the interface. The study reveals that Q345C exhibits different transformation behavior compared to Q235B, with the presence of microalloying elements retarding recrystallization and affecting intermetallic formation kinetics.
| Final Rolling Temperature | Interface Microstructure | Bond Quality | Key Observations |
|---|---|---|---|
| 900°C | Incomplete oxide removal, residual oxide films | Poor | Cold bonding, discontinuous interface |
| 950°C | Partial recrystallization, thin diffusion zone | Marginal | Q345C microalloying elements retard interface reaction |
| 1000°C | Full recrystallization, uniform diffusion layer | Good | Optimal balance of bond strength and ductility |
| 1050°C | Grain growth in Q345C, thicker intermetallic | Good to excellent | Higher bond strength but reduced ductility |
| 1100°C | Excessive intermetallic, brittle phases | Poor | Brittle fracture through interface |
Mechanical Performance Matrix
| Test Method | 900°C | 950°C | 1000°C | 1050°C | 1100°C |
|---|---|---|---|---|---|
| Peel strength (MPa) | 35 | 52 | 78 | 85 | 62 |
| Shear strength (MPa) | 155 | 215 | 310 | 335 | 260 |
| Impact energy - 2205 layer (J) | 28 | 35 | 45 | 42 | 30 |
| Impact energy - Q345C layer (J) | 32 | 38 | 42 | 38 | 28 |
| Interface hardness gradient (HV/μm) | 0.08 | 0.12 | 0.18 | 0.25 | 0.42 |
| Bond strength retention at -20°C (%) | 65 | 78 | 88 | 85 | 70 |
The optimal rolling temperature for 2205-Q345C composite plates is identified as 1000-1050°C, with 1020°C representing the ideal target for applications requiring both high bond strength and good low-temperature toughness. The slightly higher optimal temperature compared to 2205-Q235B composites is attributed to the higher recrystallization resistance of Q345C due to its microalloying elements.
Fracture Analysis
Fracture surface examination using SEM reveals distinct failure modes at different rolling temperatures:
- Below 950°C: Fracture occurs within the oxide films at the interface, showing clean separation with minimal material transfer. This indicates insufficient metallurgical bonding.
- 950-1050°C: Fracture initiates in the 2205 cladding layer and propagates through the material, indicating that the bond strength exceeds the strength of the cladding itself. This is the desired failure mode for structural applications.
- Above 1050°C: Fracture occurs within the brittle intermetallic layer, showing intergranular fracture characteristics with evidence of Fe₂CrO₄ and Fe₇Cr₇ phases.
Comparison with 2205-Q235B System
| Parameter | 2205-Q235B | 2205-Q345C | Practical Implication |
|---|---|---|---|
| Optimal rolling temperature | 980-1020°C | 1000-1050°C | Q345C requires higher temperature for equivalent bond quality |
| Maximum peel strength | 72 MPa | 85 MPa | Q345C backing provides higher achievable bond strength |
| Intermetallic formation rate | Moderate | Slower (due to microalloying) | More process tolerance for Q345C |
| Low-temperature toughness | Good | Excellent | Q345C suitable for cryogenic applications |
| Weldability of backing | Excellent | Good (requires preheat) | Q345C may require welding procedure qualification |
Pressure Vessel Design Considerations
For pressure vessel fabrication using 2205-Q345C composite plates, the following design considerations arise from the study findings:
- Welding procedure development: The Q345C backing requires preheating of 100-150°C for thick sections to prevent cold cracking. Welding consumables must bridge the composition gap between Q345C and 2205, typically using E309L or E310L for the first pass followed by E309L for subsequent passes.
- Post-weld heat treatment: For pressure vessel applications, PWHT at 600-650°C for 2 hours per 25 mm thickness is recommended to relieve welding residual stresses without significantly affecting the cladding interface.
- Inspection requirements: Per NB/T 47002 and ASME VIII Div.1, the composite plate must demonstrate: (a) peel strength exceeding 60 MPa, (b) no intermetallic layer exceeding 15 μm, (c) continuous wave pattern across the entire bonded surface.
- Hydrostatic testing: The composite pressure vessel should be hydrostatically tested at 1.25 times the design pressure, with particular attention to leak testing at composite welds where the thermal expansion mismatch between layers can create stress concentrations.
Study Insights
The comparison between 2205-Q235B and 2205-Q345C composite systems reveals that the choice of backing steel significantly influences the processing window and achievable quality. The Q345C backing, while requiring slightly higher rolling temperatures, offers superior bond strength potential and better low-temperature performance, making it the preferred choice for pressure vessels operating in demanding environments. However, the higher carbon equivalent of Q345C introduces additional considerations for subsequent welding operations, requiring careful welding procedure qualification and potentially limiting the maximum section thickness that can be practically welded. The study reinforces the principle that composite plate selection must consider not only the cladding material requirements but also the full fabrication sequence including welding, forming, and inspection.