CLADDING TECHNOLOGY SHANXI CO., LTDSubmerged Arc Weld Overlay Process with Powder Addition
Literature Overview
This study note addresses the submerged arc weld overlay (SAWO) process with powder addition, researched by Ma Hongze, Jiang Liping, and Yu Jianrong from Beijing Petrochemical College, in collaboration with Huang Wenzhe and Qian Qiang from the Harbin Welding Research Institute (1998). This work represents an important advancement in the submerged arc welding technology for overlay applications, where the addition of metal or alloy powder to the flux system enables the production of overlay layers with compositions and properties that cannot be achieved by wire welding alone. The research is particularly relevant to the petrochemical industry, where corrosion-resistant overlay layers are essential for extending the service life of equipment exposed to aggressive chemical environments.
Technical Principles
The powder addition method in submerged arc weld overlay modifies the traditional SAW process by introducing pre-blended alloy powder into the flux. As the arc melts the wire and flux, the powder is simultaneously melted and incorporated into the weld pool. This technique offers several advantages:
- Composition control — The powder allows precise adjustment of the overlay composition, including addition of expensive alloys (Ni, Cr, Mo, Co) in controlled amounts.
- Enhanced properties — Powder addition can introduce carbide-forming elements (W, V, Cr) that produce hard particles in the overlay, significantly improving wear resistance.
- Cost efficiency — The wire can be a relatively inexpensive material while the powder provides the alloying additions, reducing overall consumable costs.
- Versatility — A single wire type can be used with different powders to produce overlays with different compositions and properties.
Process Parameters and Configuration
The typical process configuration for SAWO with powder addition includes:
| Component | Specification | Function |
|---|---|---|
| Welding wire | Low-carbon steel or mild steel | Structural deposition |
| Powder | Alloy powder (Ni, Cr, Mo, Co, W, etc.) | Composition modification |
| Flux | Rutile or basic flux | Arc stabilization, protection |
| Powder feeder | Gravity or screw feeder | Controlled powder delivery |
| Powder:Flux ratio | 10-40% by weight | Controls dilution |
| Current | 300-500 A | Adequate penetration |
| Voltage | 25-32 V | Stable arc |
| Travel speed | 100-200 mm/min | Controls bead geometry |
The powder delivery system is a critical component of this process. The powder must be fed uniformly into the flux at a controlled rate to ensure consistent composition throughout the overlay. Common powder feeder designs include:
- Gravity feed — Simple but limited control over feed rate
- Screw feeder — More precise control, suitable for automated systems
- Vibratory feeder — Good for fine powders, moderate control
Overlay Composition and Properties
The powder addition technique enables production of overlay layers with a wide range of compositions:
| Overlay Type | Powder Composition | Hardness (HRC) | Application |
|---|---|---|---|
| Cr-Ni-Mo austenitic | Cr 20%, Ni 20%, Mo 5% | 25-35 | Corrosion resistance |
| Ni-based | Ni 60%, Cr 15%, Mo 10% | 30-40 | High-temperature corrosion |
| Cr-W-V martensitic | Cr 8%, W 5%, V 3% | 45-55 | Wear resistance |
| Co-based | Co 60%, Cr 20%, W 10% | 40-50 | Extreme wear |
| Fe-Cr-C | Cr 15%, C 2% | 50-60 | Abrasive wear |
The microstructure of the overlay is determined by the cooling rate and composition. For martensitic overlays, rapid cooling produces fine martensite with dispersed carbides, providing excellent hardness and wear resistance. For austenitic overlays, slower cooling allows for a more stable austenitic structure with improved ductility.
Quality Considerations and Defect Prevention
The powder addition method introduces additional quality challenges compared to conventional SAW:
- Powder distribution uniformity — Inconsistent powder feeding leads to composition variation and property non-uniformity across the overlay. Countermeasures include regular calibration of the powder feeder and periodic chemical analysis of deposited metal.
- Powder oxidation — Exposure to atmosphere during handling and feeding can oxidize reactive alloy powders (particularly Ni, Co, Ti). Countermeasures include proper storage in inert atmosphere and use of covered powder feeders.
- Inclusion formation — Poorly distributed or partially melted powder can form inclusions in the overlay. Countermeasures include optimizing powder particle size distribution and ensuring adequate heat input for complete melting.
- Cracking susceptibility — High-alloy overlays produced by powder addition may have increased cracking susceptibility due to high carbon equivalent or restricted grain growth. Countermeasures include proper preheat, interpass temperature control, and use of appropriate flux chemistry.
Engineering Applications
The SAWO with powder addition process finds extensive application in:
- Petrochemical equipment — Overlay of corrosion-resistant layers on carbon steel equipment exposed to sour gas (H2S), carbonic acid, or chloride environments
- Mining equipment — Hardfacing of wear parts such as excavator buckets, crusher jaws, and conveyor components
- Power generation — Protection of boiler tubes, turbine blades, and other high-temperature components
- Marine engineering — Corrosion-resistant overlays on ship hulls, propellers, and sea water systems
The Harbin Welding Research Institute's involvement in this research reflects the institutional expertise in welding technology development in China. The collaboration with Beijing Petrochemical College demonstrates the practical orientation of the work, addressing real industrial needs in the petrochemical sector.
Study Reflections
This research represents a significant contribution to the advancement of weld overlay technology. The powder addition method bridges the gap between conventional wire welding and advanced thermal spray or powder metallurgy processes, offering a cost-effective means of producing high-performance overlay layers. The key insight from this work is that process innovation can substantially expand the range of achievable overlay properties without requiring major changes to existing equipment or infrastructure. For engineers working in the petrochemical and chemical processing industries, this technology offers a practical solution for extending equipment life in aggressive environments while maintaining reasonable maintenance costs.