While welding generally involves joining materials to each other, overlay welding is a welding method that applies welding characteristics as a surface treatment technology.
Purposes for which it is used include surface modification and shape restoration (repair). Coating (i.e. overlaying) only the surface of an item with a suitable metal makes it possible to improve performance more cheaply than by making the entire item out of an expensive metal.
Moreover, by repairing an item with a damaged (e.g. corroded or worn) surface using overlay welding, it is possible to use the item repeatedly. As overlay welding can produce thicker layers than thermal spraying or plating and because it creates a metallurgical bond between the base metal and the overlay, it can provide high durability and significant surface modification effects.
Shielded metal arc welding
The most common welding method.
Employs rods as weld material.
Core wire covered by coating material that adds special elements to weld metal.
Weld metal protected by slag created during welding.
Mainly used with ferrous materials.
CO2 welding
(carbon-dioxide-gas-shielded arc welding),
MAG welding
(Metal Active Gas welding)
As wire is used for the weld material, continuous welding is possible. For this reason, the technique is sometimes referred to as semi-automatic welding.
During welding, the shield gas (carbon dioxide gas or a mixture of argon and carbon dioxide gas) atmosphere protects from oxidation.
Weld materials include solid wire, metal-cored wire, and flux-cored wire.
Often used with ferrous materials.
MIG welding
(Metal Inert Gas welding),
TIG welding
(Tungsten Inert Gas welding)
Also referred to as inert gas welding.
During the welding process, the area to be welded is shielded by an inert gas (helium, argon).
MIG welding uses the same mechanism as semi-automatic welding.
TIG welding uses a tungsten electrode to generate an arc. The electrode is non-consumable, and the weld material is supplied externally (inserted into the arc) during welding.
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Often used with non-ferrous material also non-ferrous materials.
Submerged arc welding
Welding is performed when the arc is submerged in the flux.
Submerged arc welding comprises the union melt method, which uses wire as the weld material, and the band arc method, which uses hoops.
Like shielded metal arc welding and semi-automatic welding, special elements are added using flux, and the method is used for all types of alloy steel.
As welding uses a large current and employs thick-gage wires and hoops (steel bands) as weld materials, submerged arc welding is notable for its high efficiency.
PTA welding
(Plasma Transferred Arc welding)
This plasma arc method enable overlaying of hard complex carbide alloys, which have conventionally been difficult to weld.
Like TIG welding, an arc is generated from a non-consumable tungsten electrode and welding is performed with flux supplied externally into the arc.
A main feature of PTA welding is that the weld material is a powder. The method has the following benefits:
- (1) Material powders can be blended to create original flux for easy overlay welding
- (2) Allows welding of hard brittle materials such as complex carbide-metal alloys, which are difficult to shape into weld material forms like wire and rods
Example of weld metal microstructure
OSAKA FUJI Corporation deals with various general materials, but is mainly involved with welding the materials indicated below. We are also happy to be contacted regarding the welding of materials other than those indicated here. We handle everything from the welding test stage to commercialization.
Main weld materials handled by OFIC
| Fe-base alloys | Low-alloy steel High-alloy steel Stainless steel High-chromium cast iron |
|---|---|
| Ni-, Co-based alloys | Inconel alloy Monel alloy Hastelloy alloy Colmonoy alloy Ni-Cr alloy Stellite alloy Tribaloy alloy |
| Complex carbide alloy | Proprietary superhard alloys - Various carbides dispersed in a metal matrix - Materials designed to match required performance - Example carbides: WC, NbC, CrC, VC, etc. |
Selection of main weld materials handled by OFIC
| Material | Typical hardness of overlay (HV) |
Melting point (°C) |
Products used in | |
|---|---|---|---|---|
| Stellite alloy | No. 1 | 550 to 650 | 1265 | Valves, sleeves, bushes |
| No. 6 | 380 to 430 | 1290 | Valves, sleeves, bushes |
|
| Tribaloy alloy | T-400 | 500 to 580 | 1288 to 1338 | Petrochemical components |
| T-700 | 410 to 490 | 1243 to 1293 | Petrochemical components |
|
| T-800 | 550 to 620 | 1288 to 1352 | Petrochemical components |
|
| Material | Typical hardness of Carbide (HV) |
Melting point (°C) |
Products used in | |
|---|---|---|---|---|
| Complex carbide alloy (composite of various carbides in an Ni-base or Co-base alloy matrix) |
WC | 1800 | 2785 | Pump components, guide rollers, components for use in hot-dip baths |
| W2C | 3000 | 2795 | Pump components, guide rollers, components for use in hot-dip baths |
|
| NbC | 1950 | 3600 | Guide rollers, guide plates |
|
| Cr3C2 | 1350 | 1890 | Furnace interior components |
|
| VC | 3100 | 2850 | Hot work tools | |
Overlay welding Technology of Tribaloy
OSAKA FUJI Corporation's overlay welding business has a proven track record in a variety of weld materials like those indicated above. Of these materials, few companies have been able to successfully commercialize overlay welding applications to large components using the cobalt-base alloy, Tribaloy. The section describes our overlay welding applications using Tribaloy.
- Features
- Tribaloy combines the wear resistance of a superhard alloy with the corrosion resistance of Hastelloy C. OSAKA FUJI Corporation has established construction technology for large components like the one pictured using automatic overlaying (powder plasma welding). As welding is automated, we can construct products with stable quality.
- Successful Tribaloy overlay products
What sets us apart in the field of Tribaloy overlaying technology is our ability to process large components and perform dual-layer overlaying. The photos below show a product with an outer diameter of 320 mm to which a dual-layer weld overlay was applied.
Product with outer diameter of 320 mm coated with dual-layer overlay of Tribaloy T-800
Frequently asked questions related to our R&D(Welding).
- Can you perform overlay welding on a material that isn't listed on your website?
- Is it possible to export components for use in hot-dip baths and other overlaid products from Japan?
