Meaning of E71T-1CH4 flux core wire, coating types and mode of metal transfer
Both the EXXT-1C (XX can be 60 or 70) and EXXT-1M electrodes have similar type slags and are designed for single and multiple pass welding using Direct Current Electrode Positive. EXXT-1C (XX can be 60 or 70) and EXXT-1M are characterized by a spray transfer, low spatter loss, flat to slightly convex bead contour, and a moderate volume of slag, which completely covers the weld bead. Electrodes of this classification have a rutile base slag and have the ability to produce high deposition rates.
The increase in manganese, silicon, or other alloys will increase the yield and tensile strengths and may affect impact properties.
Electrodes in the EXXT-1M group are classified with 75% to 80% argon/balance CO2 shielding gas. Increasing the amount of argon in the argon-CO2 mixture will reduce the manganese and silicon losses, along with losses of certain other elements such as chromium, that occur in the welding arc. The resulting increase of manganese, silicon, or other elements will increase the yield and tensile strengths and may affect impact properties.
Chemical and mechanical properties of E71T-1C and E71T-1M
The chemical and mechanical properties of E71T-1C and E71T-1M are given in below table.
FCAW Wire diameters and position limits
The larger diameters (usually 5/64 in [2.0 mm] and larger) wire of E71T-1C or E71T-1M are typically used for welding in the flat position and for welding fillet welds in the horizontal position. The smaller diameters (usually 1/16 in [1.6 mm] and smaller) are typically used for welding in all positions.
E71T-1C and E71T-1M Specification
E71T-1C or E71T-1M flux cored wire are supplied as per the SFA No.5.20 (Can be found in ASME Section IIC). The electrode classification system is given below:
- E: Refer Electrode
- Next digit (6 or 7 for example) mean electrode minimum tensile strength in Ksi multiplied by 10.
- Third digit refer to the welding position, 0 mean Flat & horizontal and 1 mean all positions.
- Fourth digit, T mean Tubular wire.
- Next digit after hyphen is the electrode usability characteristics. For example, in E71T-1C wire, 1 mean that wire can be used with DCEP. There can be 1 to 14 number or also can be written as G.
- Next digit either C or M. The letter “C” indicates that the electrode is classified using 100% CO2 shielding gas. The letter “M” indicates that the electrode is classified using 75%–80% Argon/balance CO2 shielding gas.
- H given at the end refer to the amount of diffusible hydrogen present in the weld deposit. It will be H4 or H8 or H16. For example, H4 mean 4 ml of Average Diffusible Hydrogen can present in maximum of mL/100g Deposited Metal.
A detailed overview in given in below figure.
A simple classification is given in below figure.
Toughness requirements for E71T-1C
Toughness requirements are not mandatory for the flux cored wires. These are optional and can be decided by the purchaser of the wire. If stated, The letter “J” when present in the electrode classification (E.g. E71T-1CJ) designates that the electrode meets the requirements for improved toughness and will deposit weld metal with Charpy V-Notch properties of at least 20 ft·lbf at –40°F [27J at –40°C] when the welds are made in a manner prescribed by this specification.
Welding Polarity for E71T-1C
The E71T-1C can be used only with DCEP polarity. Here, 1 at third digit, mean the electrode is meant for Direct Current Electrode Position polarity only.
Difference between E71T-1C and E71T-1M
The main difference E71T-1C and E71T-1M is the type of shielding gas used. Where C mean the shielding gas as pure CO2, M refer to the gas mixture of Argon and CO2 (usually 75%–80% Argon/balance CO2 shielding gas ).
Storage of Difference between E71T-1C and E71T-1M
The storage of E71T-1C and E71T-1M is very crucial. As these are cored wire which mean they have flux coating. These flux coating can absorb the moisture from the atmosphere easily and will result in welding porosity.
Thus storing them in a controlled atmosphere such as humidity controlled store room is mandatory. The storing temperature can be kept to ambient ( 20 to 30 Degree Celsius) and humidity of 30 to 55%.
Selection of current for E71T-1C and E71T-1M
The welding current shall be kept to controlled limit if welding for toughness application. As high heat input will going to reduce the weld toughness. The typical welding current for 1.2 mm E71T1-C wire in flat position is 120 to 300 ampere depending upon the material thickness and type of weld. For example, welding a fillet weld in 25 mm thickness, one can go upto 300 ampere but when welding a open root in groove weld, he will need only 100 to 130 ampere current only.