Zhuojin Pipe Fitting Co., LtdMicrostructure and Properties of 310 Stainless Steel Overlay on Q235 Steel
Literature Overview
This paper by Liu Yang and colleagues, published in the Journal of Shenyang Ligong University (2017, Vol. 36, No. 5, pp. 67-72), investigates the microstructure and performance characteristics of ER-310 (H12Cr26Ni21Si) stainless steel overlay layers deposited on Q235 carbon steel substrates using MIG (Metal Inert Gas) welding. The study systematically evaluates welding parameters, microstructural evolution, hardness distribution, and corrosion resistance of the resulting overlay layers. This work addresses a common industrial requirement for corrosion-resistant surface protection on low-cost carbon steel components.
Welding Process Parameters
The study identifies optimal welding parameters through systematic experimentation:
| Parameter | Optimal Value | Technical Significance |
|---|---|---|
| Welding current | 208 A | Controls heat input and penetration depth |
| Welding voltage | 19.2 V | Determines arc stability and bead width |
| Oscillation width | 12 mm | Controls bead coverage and layer uniformity |
| Oscillation speed | 26 mm/s | Affects bead shape and porosity formation |
| Travel speed | 5 mm/s | Controls cooling rate and dilution |
| Overlap ratio | 7 mm | Ensures complete coverage and uniform thickness |
The use of oscillation (weaving) is particularly noteworthy for this application. The oscillation technique allows for wider bead coverage with a single pass, reducing the number of passes required and thereby minimizing total heat input. This is critical when overlaying austenitic stainless steel on carbon steel, as excessive heat input can lead to chromium carbide precipitation in the heat-affected zone and potential intergranular corrosion susceptibility.
Microstructural Analysis
The overlay layer microstructure consists of austenitic dendritic crystals and equiaxed grains. This mixed microstructure is characteristic of rapid solidification conditions in austenitic stainless steel welds. The dendritic primary phase forms during the initial solidification stage, while the equiaxed grains develop in regions of slower cooling or through solid-state transformation during cooling.
The elemental composition analysis reveals that Ni, Cr, and Fe are the primary constituents of the overlay layer, consistent with the ER-310 wire composition (12% Cr, 26% Ni, with Si additions). However, dilution from the Q235 substrate introduces additional Fe content and potentially reduces the Cr and Ni concentrations near the dilution zone. The degree of dilution directly affects the phase stability of the overlay layer, as austenite stability depends critically on the Cr/Ni ratio.
Hardness and Corrosion Performance
The overlay layer hardness exceeds that of the Q235 base metal, which is expected given the alloying effects of Cr and Ni in the austenitic microstructure. The hardness distribution across the overlay layer is not uniform—regions closer to the substrate interface show lower hardness due to higher dilution, while the top surface of the overlay layer approaches the hardness of fully austenitic stainless steel.
The corrosion resistance improvement is the primary functional benefit of this overlay application. The high Cr content (approximately 12% in the as-deposited layer) provides passive film formation capability, while the austenitic microstructure offers resistance to pitting and crevice corrosion. The improvement in surface corrosion resistance is particularly significant for applications involving chemical media, marine environments, or acidic process streams.
Engineering Application Context
From an engineering practice standpoint, this overlay technology has direct applications in the piping industry for:
- Corrosion-resistant linings on carbon steel pipe spools: Where full stainless steel piping would be prohibitively expensive, overlay welding provides a cost-effective corrosion barrier.
- Repair of localized corrosion damage: Selective overlay of damaged areas on existing piping systems.
- Transition joints: Creating corrosion-resistant zones at specific locations in piping systems, such as near pump discharge points or heat exchanger tube sheets.
The challenge lies in managing the dilution zone. When overlaying austenitic stainless steel on carbon steel, the dilution zone can develop a martensitic microstructure due to the interaction between the carbon from the base metal and the chromium from the overlay wire. This martensitic zone is susceptible to cracking and may have reduced corrosion resistance. Mitigation strategies include using multi-pass overlay with the first pass using a transition alloy (such as 309L), controlling inter-pass temperature, and applying post-weld heat treatment.
Study Insights and Implications
This research demonstrates that careful parameter optimization can produce high-quality overlay layers with excellent corrosion resistance on low-cost substrates. The systematic approach to parameter selection—evaluating current, voltage, oscillation parameters, and overlap ratio—provides a practical framework for process development in similar applications.
The finding that the overlay layer achieves a mixed dendritic-equiaxed microstructure is metallurgically significant. The equiaxed grain fraction contributes to improved ductility and crack resistance, while the dendritic structure provides adequate hardness. This microstructural balance is essential for overlay layers that must withstand both corrosion and mechanical loading in service.
A critical consideration not fully addressed in the paper is the long-term performance under thermal cycling conditions. Austenitic stainless steel overlays on carbon steel substrates are subject to thermal mismatch stresses during heating and cooling cycles. Over extended service life, these cyclic stresses can lead to fatigue cracking at the overlay-substrate interface, particularly if the dilution zone contains brittle martensite. For applications involving thermal cycling, additional engineering measures such as stress relief annealing or the use of ductile intermediate layers should be considered.