Flux-cored Arc Welding Electrodes
The electrodes used for flux-cored arc welding provide the filler metal to the weld puddle and shielding for the arc. Shielding is required for sane electrode types. The purpose of the shielding gas is to provide protection from the atmosphere to the arc and molten weld puddle. The chemical composition of the electrode wire and flux core, in combination with the shielding gas, will determine the weld metal composition and mechanical properties of the weld. The electrodes for flux-cored arc welding consist of a metal shield surrounding a core of fluxing and/or alloying compounds as shown in figure 10-58. The cores of carbon steel and low alloy electrodes contain primarily fluxing compounds. Some of the low alloy steel electrode cores contain high amounts of alloying compounds with a low flux content. Most low alloy steel electrodes require gas shielding. The sheath comprises approximately 75 to 90 percent of the weight of the electrode. Self-shielded electrodes contain more fluxing compounds than gas shielded electrodes. The compounds contained in the electrode perform basically the same functions as the coating of a covered electrode used in shielded metal arc welding. These functions are:
2. To provide deoxidizers and scavengers which help purify and produce solid weld-metal.
3. To provide arc stabilizers which produce a smooth welding arc and keep spatter to a minimum.
4. To add alloying elements to the weld metal which will increase the strength and improve other properties in the weld metal.
5. To provide shielding gas. Gas shielded wires require an external supply of shielding gas to supplement that produced by the core of the electrode.
The classification system used for tubular wire electrodes was devised by the American Welding Society. Carbon and low alloy steels are classified on the basis of the following items:
- Mechanical properties of the weld metal.
- Welding position.
- Chemical composition of the weld metal.
- Type of welding current.
- Whether or not a CO2 shielding gas is used.
An example of a carbon steel flux-cored arc welding electrode classification is E70T-4, where:
1. The “E” indicates an electrode.
2. The second digit or “7” indicates the minimum tensile strength in units of 10,000 psi (69 MPa). Table 10-12, below, shows the mechanical property requirements for the various carbon steel electrodes.
3. The third digit or “0” indicates the welding positions. A “0” indicates flat and horizontal positions and a “1” indicates all positions.
4. The “T” stands for a tubular or flux cored wire classification.
5. The suffix “4” gives the performance and usability capabilities as shown in table 10-13. When a “G” classification is used, no specific performance and usability requirements are indicated. This classification is intended for electrodes not covered by another classification. The chemical composition requirements of the deposited weld metal for carbon steel electrodes are shown in table 10-14. Single pass electrodes do not have chemical composition requirements because checking the chemistry of undiluted weld metal does not give the true results of normal single pass weld chemistry.
The classification of low alloy steel flux-cored electrodes is similar to the classification of carbon steel flux-cored electrodes. An example of a low alloy steel classification is E81T1-NI2 where:
1. The “E” indicates electrode.
2. The second digit or “8” indicates the minimum tensile in strength in units of 10,000 psi (69 MPa). In this case it is 80,000 psi (552 MPa). The mechanical property requirements for low alloy steel electrodes are shown in table 10-15. Impact strength requirements are shown in table 10-16.
3. The third digit or “1” indicates the welding position capabilities of the electrode. A “1” indicates all positions and an “0” flat and horizontal position only.
4. The “T” indicates a tubular or flux-cored electrode used in flux cored arc welding.
5. The fifth digit or “1” describes the usability and performance characteristics of the electrode. These digits are the same as used in carbon steel electrode classification but only EXXT1-X, EXXT4-X, EXXT5-X and EXXT8-X are used with low alloy steel flux-cored electrode classifications.
6. The suffix or “Ni2” tells the chemical composition of the deposited weld metal as shown in table 10-17 below.
The classification system for stainless steel flux-cored electrodes is based on the chemical composition of the weld metal and the type of shielding to be employed during welding. An example of a stainless steel electrode classification is E308T-1 where:
1. The “E” indicates the electrode.
2. The digits between the “E” and the “T” indicates the chemical composition of the weld as shown in table 10-18 below.
3. The “T” designates a tubular or flux cored electrode wire.
4. The suffix of “1” indicates the type of shielding to be used as shown in table 10-19 below.