Zhuojin Pipe Fitting Co., LtdMicrostructure and Properties of CMT Overlay Welding 310 Stainless Steel on Q235 Steel
Literature Overview
This paper by Liu Yang and Liu Aiguo from the School of Materials Science and Engineering at Shenyang Ligong University, published in Welding in 2017, investigates the microstructure, chemical composition, and mechanical properties of 310 stainless steel (H12Cr26Ni21Si) overlay welded onto Q235 carbon steel using the Cold Metal Transfer (CMT) welding process. The study provides detailed characterization of the overlay weld layer, including microstructure analysis, hardness measurement, and shear strength testing at the interface.
CMT Process Parameters and Weld Configuration
The CMT welding process was selected for this study due to its inherent advantages in low heat input, low spatter, and excellent weld appearance. The following table summarizes the welding parameters used in the study:
| Parameter | Value | Unit |
|---|---|---|
| Welding current | 108 | A |
| Welding voltage | 15.8 | V |
| Oscillation width | 12 | mm |
| Oscillation speed | 23 | mm/s |
| Travel speed | 2 | mm/s |
| Overlap amount | 7 | mm |
| Filler material | H12Cr26Ni21Si (310 stainless steel) | — |
| Base material | Q235 carbon steel | — |
The travel speed of 2 mm/s is notably low, which is characteristic of CMT welding where the cold metal transfer mechanism allows for controlled, low-energy deposition. The oscillation pattern with a width of 12 mm and speed of 23 mm/s ensures uniform coverage and a smooth weld surface, which is important for subsequent service performance.
Microstructure and Chemical Composition Analysis
The overlay weld layer microstructure consists of austenitic dendritic crystals and equiaxed crystals, which is consistent with the expected solidification behavior of 310 stainless steel. The dendritic structure forms at the fusion boundary where the cooling rate is highest, while the equiaxed crystals develop in the center of the weld deposit where the cooling rate is lower and the thermal gradient is reduced.
The chemical composition analysis confirmed that nickel, chromium, and iron are the primary elements in the overlay layer, with nickel and chromium providing the austenitic stabilization and corrosion resistance. The dilution from the Q235 base material introduces iron into the overlay, but the high nickel and chromium content of the 310 stainless steel filler material ensures that the overlay layer retains its austenitic character and corrosion resistance properties.
| Element | Expected in 310 SS | Overlay Layer (with dilution) | Effect of Dilution |
|---|---|---|---|
| Cr | 24-26% | Slightly reduced | Still above austenite stabilization threshold |
| Ni | 19-22% | Slightly reduced | Maintains austenitic structure |
| Fe | Balance | Increased | Dilution from Q235 base material |
| Si | Present | Present | Minor contribution to properties |
| C | Low | Low | Maintains solution strengthening |
Mechanical Properties and Interface Bond Strength
The hardness of the overlay layer is higher than that of the Q235 base material, which is expected given the alloying effects of chromium and nickel on solid solution strengthening. The austenitic structure of the overlay layer provides good ductility and toughness in addition to the increased hardness.
The most critical mechanical property for overlay welding applications is the bond strength between the overlay layer and the base material. The shear strength test at the overlay-base material interface yielded a value greater than 405 MPa. This is a significant result, as it indicates a strong metallurgical bond between the austenitic stainless steel overlay and the ferritic-pearlitic carbon steel base material.
| Property | Overlay Layer | Base Material (Q235) | Interface |
|---|---|---|---|
| Hardness | Higher than base | Lower | Gradient transition |
| Shear strength | N/A | N/A | > 405 MPa |
| Microstructure | Austenitic dendritic and equiaxed | Ferritic-pearlitic | Fusion boundary with dilution zone |
| Defect status | Dense, no defects | N/A | Clean interface |
Engineering Significance and Application Considerations
The CMT overlay welding of 310 stainless steel on Q235 steel has direct applications in the chemical, petrochemical, and food processing industries where corrosion-resistant linings are required on carbon steel equipment. The 310 stainless steel provides excellent resistance to oxidation and corrosion in high-temperature oxidizing environments, while the Q235 base material provides the structural strength and economic viability.
The shear strength exceeding 405 MPa is well above the typical minimum requirements for overlay weld bond strength, which are generally specified as 150-250 MPa in industry standards. This high bond strength provides excellent confidence in the long-term service performance of the overlay, particularly under cyclic loading or thermal cycling conditions.
The following table outlines typical applications where this overlay combination is suitable:
| Application | Service Environment | Key Requirement | Suitability |
|---|---|---|---|
| Chemical reactor lining | Corrosive chemical media | Corrosion resistance | High Ni-Cr content provides excellent resistance |
| Heat exchanger tube repair | High temperature oxidizing | Oxidation resistance | 310 SS excels above 800°C |
| Food processing equipment | Hygienic, corrosive | Cleanability and corrosion resistance | Smooth CMT weld surface facilitates cleaning |
| Flue gas ducting | High temperature, corrosive | Thermal and corrosion resistance | Combined high-temperature and corrosion resistance |
Study Insights and Process Recommendations
The successful application of CMT welding for stainless steel overlay on carbon steel demonstrates the process versatility of CMT technology. The low heat input characteristic of CMT minimizes dilution from the base material, which is critical for maintaining the corrosion resistance of the stainless steel overlay. The oscillation pattern produces a smooth, uniform weld surface that is important for both aesthetic and functional reasons in overlay applications.
From a process development perspective, the following recommendations emerge from this study:
- Maintain low travel speeds to ensure adequate deposition rate and overlay thickness while keeping heat input low.
- Use oscillation patterns to achieve uniform coverage and smooth weld surfaces.
- Ensure proper surface preparation of the base material to promote metallurgical bonding.
- Consider multi-pass welding for thicker overlay layers, with appropriate interpass temperature control.
- Perform hardness mapping and shear strength testing on production welds to verify overlay quality.
The study provides valuable data for engineers designing overlay welding processes for corrosion-resistant linings on carbon steel equipment. The combination of CMT process advantages and 310 stainless steel material properties creates a robust solution for challenging service environments, and the quantitative bond strength data provides the engineering confidence needed for production implementation.
This collection of five literature study notes covers a broad spectrum of overlay welding topics, ranging from numerical simulation of thermal and stress fields to fracture mechanics analysis, defect mechanism investigation, material development for industrial applications, and advanced welding process characterization. Together, they provide a comprehensive technical foundation for engineers working in the field of overlay welding, from fundamental research to practical process development and quality assurance. The common thread across all five studies is the importance of understanding the interaction between process parameters, material properties, and resulting performance, which remains the central challenge in overlay welding technology development and application.