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Hardfacing

TECH. INFO.

HARDFACING

Solid fillet welds are gaining more importance in modern engineering. They make it possible to renew the metallic parts economically in cases where corrosion, abrasion and other surface deformations occur. The renewing process also includes the renewal of parts worn by metal-metal friction (i.e. rolls, crane wheels, rails, shafts) as well as the parts exposed to mineral abrasion (i.e. engineering machines, screw conveyors, excavator buckets) with solid fillet weld.

The solid fillet welding is not only performed for renewal of the parts, but also commonly performed in manufacturing new parts and tools. In such a manufacturing process, the surfaces of the non-alloy or light-alloy steel materials used as the conveyor are coated with welding material that will result in a welding metal having the desired properties.

The main determinant in fillet welds is the abrasive conditions, which is whether the abrasion is caused by metals, minerals, corrosion, cavitation, erosion or high temperature. The welding material to be used is selected depending on these conditions. In addition, knowing the chemical composition of the base metal is very important to determine the pre-annealing and final-annealing temperatures.

The welding metal should have the properties suitable for the abrasive conditions prevalent at the workplace where the workpiece to be solid fillet welded is used. These properties are as follows:

1. Post-welding toughness
2. Toughness at high temperatures
3. Resistance to metal abrasion
4. Resistance to abrasion and milling phases
5. Impact resistance
6. Corrosionresistance
7. Resistance to scaling.

In some cases one or more of those abrasive conditions may exist and in such cases the welding metal should have all the necessary properties. Therefore the suitable welding metal must be selected consciously. Of course there is not a unique welding material having all these properties. However, it is possible to find and select the most suitable welding material that will be sufficiently successful for most cases.

Welding Materials

The solid fillet welding materials are classified acc. to DIN 8555 standard. The welding materials at this category are classified according to their alloy types and toughness levels. In addition to those the manufacturing method (i.e. GO = cast, GF = cored wire) as well as the properties of the welding metal (i.e. C = corrosion resistance, K = may be hardened with cold processes) are also mentioned in the said standard. The details of this standard the main properties of the welding materials are defined.

Solid Fillet Welding of Tools

Another interesting application area of the solid fillet welding is the renewal of solid tools such as blades, staple dies, cutting edges and deep drawing dies. "Gradually solidifying welding" is successful in this application area. The welding is performed at delayed transformation temperature between the perlite and bainite areas at TTT curve of the steel. So it is ensured that the hardenability of the steel is avoided. The welding temperatures are usually between 400C and 600C. "Intermittent welding method" is based on the fact that the austenitic transformation in these types of steels is delayed at specific temperatures.

Process order in solid fillet welding

a) Slowly heating the workpiece to the annealing temperature. At this temperature the structure is completely transformed into austenite.
b) Cooling down to the temperature at which the intermittent welding will be performed; this is the temperature point at which the austenitic transformation delay (relatively to the TTT curves) is most visible.
c) Performing the welding process at this temperature
d) Cooling down the workpiece at ambient conditions or in oil (to between 50C and 150C)
e) Tempering the workpiece at tempering temperature; in high-speed steels this temperature is between 550C and 570C.
f) Processing the welding area.

OERLIKON offers a wide range of suitable solutions and products for most of the abrasion issues such as coated electrodes, cored wire, solid wires for inert gas and submerged welding and submerged welding powders. The technical data of those products include the areas of application as well as all the technical properties.


At OERLIKON, we will be glad to provide you with the necessary technical support on your specific abrasion issues to resolve such issues with solid fillet welding.


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