Zhuojin Pipe Fitting Co., LtdMicrostructure and Properties of 310 Stainless Steel Surfacing on Q235 Steel Substrate
Literature Overview
The research by Liu Yang, Liu Aiguo, Zhang Xingpin, and Zhao Jing from Shenyang Ligong University, published in the Journal of Shenyang Ligong University (2017, Vol. 36, No. 5, pp. 67–72), investigates the microstructure and properties of 310 stainless steel (ER-310, H12Cr26Ni21Si) deposited on Q235 steel substrate using MIG (MIG/MAG) welding process. The study systematically evaluates welding parameters, microstructural evolution, chemical composition, microhardness distribution, and corrosion resistance of the resulting surfacing layer.
Optimal Welding Parameters
The research identifies the following optimal welding parameters for achieving a sound, defect-free stainless steel surfacing layer:
| Parameter | Optimal Value | Technical Rationale |
|---|---|---|
| Welding current | 208 A | Sufficient heat input for penetration and wetting |
| Welding voltage | 19.2 V | Stable arc length and arc force |
| Oscillation width | 12 mm | Adequate coverage of substrate surface |
| Oscillation speed | 26 mm/s | Uniform bead profile and deposition rate |
| Travel speed | 5 mm/s | Controlled heat input per unit length |
| Overlap ratio | 7 mm | Ensures complete coverage without excessive dilution |
These parameters represent a carefully balanced combination that achieves sufficient heat input for proper wetting and bonding while avoiding excessive substrate dilution that would compromise the corrosion resistance of the surfacing layer. The oscillation technique is particularly important for achieving uniform bead profiles and controlling the dilution rate across the width of the surfacing layer.
Microstructural Analysis
The surfacing layer microstructure consists of austenitic dendritic crystals and equiaxed grains, which is characteristic of high-nickel austenitic stainless steels solidifying from the liquid state. The dendritic structure forms in the upper portion of the weld bead where the solidification rate is lower, while equiaxed grains develop in regions of higher nucleation density, typically near the fusion boundary or in areas of thermal disturbance.
The chemical composition analysis confirms that Ni, Cr, and Fe are the principal elements constituting the surfacing layer. The high Ni content (approximately 21%) ensures complete austenite stabilization even at room temperature, while the elevated Cr content (approximately 26%) provides the necessary chromium for passive film formation and corrosion resistance. The silicon content serves as a deoxidizer during solidification and contributes to high-temperature oxidation resistance.
Corrosion Resistance and Mechanical Properties
The study demonstrates that the surfacing treatment significantly improves the corrosion resistance of the Q235 steel substrate. The austenitic microstructure with high Cr and Ni content provides excellent resistance to general corrosion, pitting corrosion, and intergranular corrosion in most aqueous environments. The microhardness of the surfacing layer exceeds that of the Q235 steel substrate, which is expected given the solid solution strengthening effects of Ni and Cr in austenitic stainless steel.
| Property | Q235 Steel Substrate | 310 Surfacing Layer | Improvement |
|---|---|---|---|
| Microstructure | Ferrite + Pearlite | Austenite (dendritic + equiaxed) | Phase transformation |
| Hardness | ~120 HV | >200 HV | Significant increase |
| Corrosion resistance | Poor | Excellent | Substantial improvement |
| Ni content | ~0% | ~21% | Alloy enrichment |
| Cr content | ~0.4% | ~26% | Passive film formation |
Standards and Specification Compliance
The ER-310 (H12Cr26Ni21Si) consumable conforms to multiple international standards for austenitic stainless steel welding consumables:
- AWS A5.4/A5.4M – Specification for stainless steel electrode and wire for gas shielded arc welding
- ISO 14341 – Specification for consumables for gas shielded arc welding
- GB/T 17493 – Chinese standard for austenitic stainless steel welding wire
- ASTM A269 – Specification for austenitic stainless steel pipe, bar, and shapes
The surfacing application should also be evaluated against the requirements of ASME B31.3 for process piping and ASME B31.4 for petroleum liquid pipelines, which specify acceptable welding procedures and material compatibility requirements for stainless steel overlays on carbon steel substrates.
Engineering Practice Considerations
The application of 310 stainless steel surfacing to Q235 steel components addresses a common engineering challenge: providing corrosion-resistant surfaces on economical carbon steel substrates without the cost of full stainless steel construction. This approach is particularly relevant for:
- Pipe fitting repair – Restoring corrosion-damaged carbon steel pipe fittings with stainless steel overlays
- Tank and vessel lining – Providing internal corrosion protection for process vessels
- Valve body hardfacing – Enhancing corrosion resistance of valve components in aggressive service environments
- Heat exchanger tube sheets – Providing corrosion-resistant surfaces where stainless steel tubes are welded to carbon steel headers
The dilution control is critical in this application, as excessive carbon steel dilution into the surfacing layer can reduce the Cr/Ni ratio below the threshold required for full austenite stabilization and adequate corrosion resistance. The optimal overlap ratio of 7 mm identified in this study helps ensure that each successive pass contains sufficient fresh alloy to maintain the required composition throughout the surfacing layer thickness.
Study Insights and Recommendations
This research provides a well-documented welding procedure specification for 310 stainless steel surfacing on Q235 steel, with clearly defined parameters that can be directly implemented in engineering practice. The combination of austenitic microstructure, high alloy content, and improved corrosion resistance makes this surfacing approach particularly suitable for applications where corrosion is the primary degradation mechanism. Engineers should note that while the surfacing layer provides excellent corrosion protection, the interface region between the surfacing layer and substrate requires careful evaluation for potential cracking under thermal cycling or mechanical loading conditions, as the thermal expansion mismatch between austenitic stainless steel and carbon steel can generate significant interface stresses.