Zhuojin Pipe Fitting Co., LtdMicrostructure and Properties of 310 Stainless Steel Overlay Welded on Q235 Steel Substrate
Literature Overview
This study by Liu Yang, Liu Aiguo, Zhang Xingpin, and Zhao Jing from Shenyang Ligong University, published in the Journal of Shenyang Ligong University (Vol. 36, No. 5, 2017, pp. 67-72), investigates the microstructure and mechanical properties of ER-310 (H12Cr26Ni21Si) austenitic stainless steel overlay welds deposited on Q235 carbon steel substrates using MIG welding. The research addresses a fundamental materials compatibility challenge: achieving durable, corrosion-resistant surface protection on carbon steel components without complete material replacement.
Technical Background
The combination of Q235 carbon steel substrate with 310 austenitic stainless steel overlay represents a classic dissimilar material joining challenge. The significant difference in thermal expansion coefficients, thermal conductivity, and metallurgical behavior between these materials creates unique challenges in achieving sound, durable overlay welds. This application is directly relevant to:
- Chemical processing equipment repair
- Pipeline components in corrosive service environments
- Heat exchanger tubesheets
- Storage tank internals
- Marine and offshore structural components
Optimized Process Parameters
The study systematically determined optimal welding parameters through experimental investigation:
| Parameter | Optimized Value | Purpose |
|---|---|---|
| Welding current | 208 A | Adequate penetration without excessive dilution |
| Welding voltage | 19.2 V | Stable arc with good wire feed |
| Oscillation width | 12 mm | Uniform coverage |
| Oscillation speed | 26 mm/s | Controlled deposit thickness |
| Travel speed | 5 mm/s | Sufficient heat input for fusion |
| Overlap ratio | 7 mm | Complete coverage without excessive buildup |
Parameter Optimization Rationale
The selected parameters balance several competing requirements:
- Adequate fusion: Current and voltage must provide sufficient heat to achieve complete metallurgical bonding with the Q235 substrate.
- Controlled dilution: Excessive heat input increases substrate dilution, reducing the Cr and Ni content of the overlay and compromising corrosion resistance.
- Uniform deposition: Oscillation parameters ensure consistent coverage across the weld width without cold lap or excessive buildup.
- Defect avoidance: The combination of parameters minimizes porosity, lack of fusion, and cracking risks.
Microstructural Analysis
The overlay weld microstructure consists of austenite dendrites with equiaxed grains, characteristic of the 310 stainless steel composition. The major alloying elements are:
| Element | Role | Effect |
|---|---|---|
| Ni | Austenite stabilizer | Maintains single-phase austenitic structure |
| Cr | Corrosion resistance | Forms protective Cr₂O₃ passive film |
| Fe | Base matrix | Dilution from substrate |
| Si | Deoxidizer | Improves fluidity and wetting |
The austenitic structure provides excellent resistance to both general and localized corrosion, while maintaining good ductility and thermal shock resistance. The absence of martensite or ferrite phases eliminates concerns about hydrogen-induced cracking and improves service reliability.
Performance Characteristics
Mechanical Properties
| Property | Overlay Weld | Q235 Substrate | Improvement |
|---|---|---|---|
| Hardness | Higher than substrate | Baseline | Significant |
| Corrosion resistance | Excellent | Poor | Dramatic |
| Ductility | Good (austenitic) | Moderate | Comparable |
| Thermal shock resistance | Excellent | Moderate | Significant |
Corrosion Performance
The 310 stainless steel overlay provides substantial improvement in corrosion resistance compared to the bare Q235 substrate. The high Cr (26%) and Ni (21%) content ensures:
- Complete passive film formation in oxidizing environments
- Resistance to intergranular corrosion
- Good performance in reducing acid environments
- Resistance to pitting and crevice corrosion in chloride-containing solutions
Engineering Practice Integration
This technology finds direct application in several pipeline and process equipment scenarios:
- Pipeline repair: Localized corrosion damage repair on carbon steel pipelines without complete section replacement.
- Chemical equipment: Upgrade of existing carbon steel equipment for service in corrosive media.
- Heat exchangers: Corrosion protection of tubesheets and channel covers in mixed-material assemblies.
- Storage tanks: Internal surface protection against corrosive product storage.
Quality Control Considerations
From a quality assurance perspective, the following inspections are essential:
- Visual examination: Surface quality, porosity, undercut assessment
- Magnetic particle testing: Cracking detection in the heat-affected zone
- Hardness testing: Verification of dilution level through hardness gradient measurement
- Corrosion testing: Immersion or electrochemical testing to verify corrosion performance
- Bond strength testing: Peel or shear testing of the overlay-substrate interface
Study Insights and Reflections
This research demonstrates that proper parameter selection can achieve excellent overlay weld quality even with significant substrate-overlay material mismatch. The MIG process with wire oscillation provides the flexibility needed to deposit uniform, defect-free layers on flat carbon steel surfaces.
The austenitic structure achieved through the 310 composition is particularly valuable for applications where thermal cycling is present. Unlike martensitic or ferritic overlays that may crack during thermal cycling, the austenitic structure accommodates expansion and contraction without cracking, making it suitable for service conditions involving temperature variation.
For engineers involved in equipment integrity management, this technology offers a cost-effective alternative to complete material replacement. The ability to extend the service life of carbon steel equipment through surface upgrading represents significant economic benefit, particularly for large-diameter vessels and piping systems where replacement costs are prohibitive.
The systematic parameter optimization approach presented in this study provides a practical framework that can be adapted to similar overlay welding applications across the process industry, establishing a foundation for standardized procedures in industrial repair operations.