CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Properties of 310 Stainless Steel Overlay on Q235 Carbon Steel
Literature Overview
This 2017 study by Liu Yang, Liu Aiguo, Zhang Xingpin, and Zhao Jing from the School of Materials Science and Engineering at Shenyang Ligong University investigates the microstructure and mechanical properties of 310 stainless steel overlay welds deposited on Q235 carbon steel substrate. The combination of 310 stainless steel (a high-temperature austenitic stainless steel) with Q235 (a common low-carbon structural steel) represents a challenging dissimilar metal welding scenario due to the significant differences in chemical composition, thermal properties, and metallurgical behavior between the two materials.
Technical Background
310 stainless steel (UNS S31008, equivalent to 06Cr25Ni20) contains approximately 25% chromium and 20% nickel, providing excellent resistance to oxidation and corrosion at elevated temperatures up to 1100°C. It is commonly used in furnace components, heat exchanger tubes, and high-temperature process equipment. Q235 steel is a widely used structural steel with approximately 0.14-0.22% carbon, serving as a cost-effective structural material. The combination of these two materials in a clad configuration offers the corrosion and heat resistance of 310 stainless steel with the structural strength and economic advantage of Q235 steel.
Material Properties Comparison
| Property | Q235 Steel | 310 Stainless Steel | Difference Factor |
|---|---|---|---|
| Carbon content (%) | 0.14-0.22 | 0.08 max | - |
| Chromium content (%) | 0.30 max | 24-26 | ~80x |
| Nickel content (%) | - | 19-21 | - |
| Thermal conductivity (W/m·K) | 50 | 26 | ~2x |
| Coefficient of thermal expansion (×10⁻⁶/K) | 12 | 18 | ~1.5x |
| Yield strength (MPa) | 235 | 205 | Similar |
| Dilution sensitivity | High | Low | - |
Welding Process and Parameters
The study examines submerged arc welding (SAW) as the primary process for depositing 310 stainless steel overlay on Q235 steel. The selection of SAW is based on its high deposition rate, deep penetration, and suitability for multi-layer overlay applications.
Optimal Process Parameters
| Parameter | Value | Justification |
|---|---|---|
| Welding current | 350-450 A | Adequate penetration without excessive dilution |
| Welding voltage | 32-36 V | Stable arc with appropriate heat input |
| Travel speed | 300-400 mm/min | Balanced cooling rate and deposition rate |
| Number of layers | 2-3 | First layer for bonding, subsequent layers for composition |
| Electrode | E310-16 (covered electrode) or equivalent | Low-hydrogen, designed for high-Cr Ni alloys |
| Flux | Basic flux with low sulfur and phosphorus | Minimizes impurity pickup |
| Preheat | 100-150°C | Reduce thermal gradient at interface |
Microstructural Analysis
Interface Zone
The interface between the Q235 base metal and the 310 stainless steel overlay is the most critical region from a metallurgical perspective. The study reveals:
- Dilution zone: The first weld layer exhibits significant dilution with carbon steel, resulting in a composition that is intermediate between 310 and Q235. This zone may contain mixed phases including ferrite, austenite, and carbides.
- Transition layer: As the overlay thickness increases, the composition approaches that of pure 310 stainless steel. The transition from mixed-phase to fully austenitic structure typically occurs within 1-2 mm from the interface.
- Bonding quality: The metallurgical bond at the interface is generally good, with no evidence of interfacial cracking or lack of fusion when proper welding parameters are used.
Overlay Microstructure
The fully austenitic 310 overlay layer exhibits the following characteristics:
- Grain structure: Predominantly equiaxed austenite grains with sizes of 20-50 μm in the upper layers
- Phase composition: Nearly 100% austenite (γ) in the upper overlay layers; minor δ-ferrite (1-3%) may be present near the interface due to dilution effects
- Carbide precipitation: Chromium carbides (Cr₂₃C₆, Cr₇C₃) may form at grain boundaries, particularly in the interface region where carbon content is higher
- Segregation: Slight segregation of chromium and nickel at grain boundaries due to the high alloy content
Mechanical Properties
| Property | Q235 Base | Interface Zone | Overlay Layer |
|---|---|---|---|
| Hardness (HV) | 180-200 | 250-320 | 180-220 |
| Tensile strength (MPa) | 375-500 | 450-550 | 520-600 |
| Elongation (%) | 26-31 | 15-20 | 35-45 |
| Impact energy (J, -20°C) | 47-60 | 25-35 | 80-120 |
The interface zone exhibits higher hardness due to carbide precipitation and the mixed-phase microstructure, while the overlay layer maintains the good toughness characteristics of 310 stainless steel.
Defect Analysis
| Defect Type | Cause | Detection | Prevention |
|---|---|---|---|
| Hot cracking | High sulfur and phosphorus content | RT or MT | Use low-S, low-P consumables; control preheat |
| Cold cracking | Hydrogen embrittlement in high-strength interface | Delayed cracking after cooling | Low-hydrogen consumables; post-weld baking |
| Excessive dilution | High heat input; insufficient layers | Spectroscopic analysis of first layer | Reduce heat input; add transition layer |
| Porosity | Flux contamination or gas entrapment | RT or UT | Proper flux storage; adequate shielding |
| Distortion | Thermal expansion mismatch | Dimensional inspection | Back-step welding; clamping fixtures |
Engineering Applications and Considerations
The Q235/310 stainless steel clad configuration finds applications in several industrial sectors:
- Furnace components: Structural elements that require high-temperature oxidation resistance (310 overlay) with structural support (Q235 base)
- Heat exchanger shells: Where the shell must resist high-temperature flue gases while maintaining structural integrity
- Chimney and stack liners: Combustion equipment requiring corrosion resistance at elevated temperatures
- Industrial waste incinerators: Equipment exposed to aggressive, high-temperature gas environments
Design Considerations
- The overlay thickness should be at least 3 mm to ensure a fully austenitic composition in the functional surface layer, with the first 1-2 mm serving as a transition zone.
- The Q235 base metal should be limited to thicknesses where the thermal mass does not cause excessive cooling rates at the interface. For thick base plates (>20 mm), additional preheat may be required.
- The clad configuration should be designed to minimize thermal cycling stresses, particularly at the interface where the coefficient of thermal expansion mismatch is greatest.
Study Insights
This research highlights the practical challenges and solutions associated with overlaying high-alloy austenitic stainless steel on low-alloy carbon steel. The key finding is that a multi-layer approach, with the first layer serving as a transition zone and subsequent layers achieving the target 310 composition, provides an effective strategy for managing dilution and ensuring proper overlay properties.
The study also underscores the importance of understanding the metallurgical behavior at the interface. The formation of carbides and the presence of mixed phases in the dilution zone can significantly affect the long-term performance of the clad component, particularly in cyclic thermal service. Engineers must carefully consider these factors when specifying the overlay thickness, welding parameters, and post-weld treatment for critical applications.
The practical value of this work lies in its demonstration that economically viable clad components can be produced using common structural steel as a base material, with the high-performance 310 stainless steel providing the necessary surface protection. This approach offers significant cost savings compared to using 310 stainless steel for the entire component, while maintaining the required performance characteristics.